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毕业设计外文文献翻译
毕业设计(论文)外文资料翻译系别：专业：班级：姓名：学号：外文出处：附件： 1. 原文； 2. 译文2013年03月附件一：A Rapidly Deployable Manipulator SystemChristiaan J.J. Paredis, H. Benjamin Brown, Pradeep K. KhoslaAbstract:A rapidly deployable manipulator system combines the flexibility of reconfigurable modular hardware with modular programming tools, allowing the user to rapidly create a manipulator which is custom-tailored for a given task. This article describes two main aspects of such a system, namely, the Reconfigurable Modular Manipulator System (RMMS)hardware and the corresponding control software.1 IntroductionRobot manipulators can be easily reprogrammed to perform different tasks, yet the range of tasks that can be performed by a manipulator is limited by mechanicalstructure.Forexample, a manipulator well-suited for precise movement across the top of a table would probably no be capable of lifting heavy objects in the vertical direction. Therefore, to perform a given task,one needs to choose a manipulator with an appropriate mechanical structure.We propose the concept of a rapidly deployable manipulator system to address the above mentioned shortcomings of fixed configuration manipulators. As is illustrated in Figure 1, a rapidly deployable manipulator system consists of software and hardware that allow the user to rapidly build and program a manipulator which is customtailored for a given task.The central building block of a rapidly deployable system is a Reconfigurable Modular Manipulator System (RMMS). The RMMS utilizes a stock of interchangeable link and joint modules of various sizes and performance specifications. One such module is shown in Figure 2. By combining these general purpose modules, a wide range of special purpose manipulators can be assembled. Recently, there has been considerable interest in the idea of modular manipulators [2, 4, 5, 7, 9, 10, 14], for research applications as well as for industrial applications. However, most of these systems lack the property of reconfigurability, which is key to the concept of rapidly deployable systems. The RMMS is particularly easy toreconfigure thanks to its integrated quick-coupling connectors described in Section 3.Effective use of the RMMS requires, Task Based Design software. This software takes as input descriptions of the task and of the available manipulator modules; it generates as output a modular assembly configuration optimally suited to perform the given task. Several different approaches have been used successfully to solve simpli-fied instances of this complicated problem.A third important building block of a rapidly deployable manipulator system is a framework for the generation of control software. To reduce the complexity of softwaregeneration for real-time sensor-based control systems, a software paradigm called software assembly has been proposed in the Advanced Manipulators Laboratory at CMU.This paradigm combines the concept of reusable and reconfigurable software components, as is supported by the Chimera real-time operating system [15], with a graphical user interface and a visual programming language, implemented in OnikaA lthough the software assembly paradigm provides thesoftware infrastructure for rapidly programming manipulator systems, it does not solve the programming problem itself. Explicit programming of sensor-based manipulator systems is cumbersome due to the extensive amount of detail which must be specified for the robot to perform the task. The software synthesis problem for sensor-based robots can be simplified dramatically, by providing robust robotic skills, that is, encapsulated strategies for accomplishing common tasks in the robots task domain [11]. Such robotic skills can then be used at the task level planning stage without having to consider any of the low-level detailsAs an example of the use of a rapidly deployable system,consider a manipulator in a nuclear environment where it must inspect material and space for radioactive contamination, or assemble and repair equipment. In such an environment, widely varied kinematic (e.g., workspace) and dynamic (e.g., speed, payload) performance is required, and these requirements may not be known a priori. Instead of preparing a large set of different manipulators to accomplish these tasks—an expensive solution—one can use a rapidly deployable manipulator system. Consider the following scenario: as soon as a specific task is identified, the task based design software determinesthe task. This optimal configuration is thenassembled from the RMMS modules by a human or, in the future, possibly by anothermanipulator. The resulting manipulator is rapidly programmed by using the software assembly paradigm and our library of robotic skills. Finally,the manipulator is deployed to perform its task.Although such a scenario is still futuristic, the development of the reconfigurable modular manipulator system, described in this paper, is a major step forward towards our goal of a rapidly deployable manipulator system.Our approach could form the basis for the next generation of autonomous manipulators, in which the traditional notion of sensor-based autonomy is extended to configuration-based autonomy. Indeed, although a deployed system can have all the sensory and planning information it needs, it may still not be able to accomplish its task because the task is beyond the system’s physical capabilities. A rapidly deployable system, on the other hand, could adapt its physical capabilities based on task specifications and, with advanced sensing, control, and planning strategies, accomplish the task autonomously.2 Design of self-contained hardware modulesIn most industrial manipulators, the controller is a separate unit housing the sensor interfaces, power amplifiers, and control processors for all the joints of the manipulator.A large number of wires is necessary to connect this control unit with the sensors, actuators and brakes located in each of the joints of the manipulator. The large number of electrical connections and the non-extensible nature of such a system layout make it infeasible for modular manipulators. The solution we propose is to distribute the control hardware to each individual module of the manipulator. These modules then become self-contained units which include sensors, an actuator, a brake, a transmission, a sensor interface, a motor amplifier, and a communication interface, as is illustrated in Figure 3. As a result, only six wires are requiredfor power distribution and data communication.2.1 Mechanical designThe goal of the RMMS project is to have a wide variety of hardware modules available. So far, we have built four kinds of modules: the manipulator base, a link module, three pivot joint modules (one of which is shown in Figure 2), and one rotate joint module. The base module and the link module have no degrees-of-freedom; the joint modules have onedegree-of-freedom each. The mechanical design of the joint modules compactly fits aDC-motor, a fail-safe brake, a tachometer, a harmonic drive and a resolver.The pivot and rotate joint modules use different outside housings to provide the right-angle or in-line configuration respectively, but are identical internally. Figure 4 shows in cross-section the internal structure of a pivot joint. Each joint module includes a DC torque motor and 100:1 harmonic-drive speed reducer, and is rated at a maximum speed of 1.5rad/s and maximum torque of 270Nm. Each module has a mass of approximately 10.7kg. A single, compact, X-type bearing connects the two joint halves and provides the needed overturning rigidity. A hollow motor shaft passes through all the rotary components, and provides achannel for passage of cabling with minimal flexing.2.2 Electronic designThe custom-designed on-board electronics are also designed according to the principle of modularity. Each RMMS module contains a motherboard which provides the basic functionality and onto which daughtercards can be stacked to add module specific functionality.The motherboard consists of a Siemens 80C166 microcontroller, 64K of ROM, 64K of RAM, an SMC COM20020 universal local area network controller with an RS-485 driver, and an RS-232 driver. The function of the motherboard is to establish communication with the host interface via an RS-485 bus and to perform the lowlevel control of the module, as is explained in more detail in Section 4. The RS-232 serial bus driver allows for simple diagnostics and software prototyping.A stacking connector permits the addition of an indefinite number of daughtercards with various functions, such as sensor interfaces, motor controllers, RAM expansion etc. In our current implementation, only modules with actuators include a daughtercard. This card contains a 16 bit resolver to digital converter, a 12 bit A/D converter to interface with the tachometer, and a 12 bit D/A converter to control the motor amplifier; we have used an ofthe-shelf motor amplifier (Galil Motion Control model SSA-8/80) to drive the DC-motor. For modules with more than one degree-of-freedom, for instance a wrist module, more than one such daughtercard can be stacked onto the same motherboard.3 Integrated quick-coupling connectorsTo make a modular manipulator be reconfigurable, it is necessary that the modules can be easily connected with each other. We have developed a quick-coupling mechanism with which a secure mechanical connection between modules can be achieved by simply turning a ring handtight; no tools are required. As shown in Figure 5, keyed flanges provide precise registration of the two modules. Turning of the locking collar on the male end produces two distinct motions: first the fingers of the locking ring rotate (with the collar) about 22.5 degrees and capture the fingers on the flanges; second, the collar rotates relative to the locking ring, while a cam mechanism forces the fingers inward to securely grip the mating flanges. A ball- transfer mechanism between the collar and locking ring automatically produces this sequence of motions.At the same time the mechanical connection is made,pneumatic and electronic connections are also established. Inside the locking ring is a modular connector that has 30 male electrical pins plus a pneumatic coupler in the middle. These correspond to matching female components on the mating connector. Sets of pins are wired in parallel to carry the 72V-25A power for motors and brakes, and 48V–6A power for the electronics. Additional pins carry signals for two RS-485 serial communication busses and four video busses. A plastic guide collar plus six alignment pins prevent damage to the connector pins and assure proper alignment. The plastic block holding the female pins can rotate in the housing to accommodate the eight different possible connection orientations (8@45 degrees). The relative orientation is automatically registered by means of an infrared LED in the female connector and eight photodetectors in the male connector.4 ARMbus communication systemEach of the modules of the RMMS communicates with a VME-based host interface over a local area network called the ARMbus; each module is a node of the network. The communication is done in a serial fashion over an RS-485 bus which runs through the length of the manipulator. We use the ARCNET protocol [1] implemented on a dedicated IC (SMC COM20020). ARCNET is a deterministic token-passing network scheme which avoids network collisions and guarantees each node its time to access the network. Blocks ofinformation called packets may be sent from any node on the network to any one of the other nodes, or to all nodes simultaneously (broadcast). Each node may send one packet each time it gets the token. The maximum network throughput is 5Mb/s.The first node of the network resides on the host interface card, as is depicted in Figure 6. In addition to a VME address decoder, this card contains essentially the same hardware one can find on a module motherboard. The communication between the VME side of the card and the ARCNET side occurs through dual-port RAM.There are two kinds of data passed over the local area network. During the manipulator initialization phase, the modules connect to the network one by one, starting at the base and ending at the end-effector. On joining the network, each module sends a data-packet to the host interface containing its serial number and its relative orientation with respect to the previous module. This information allows us to automatically determine the current manipulator configuration.During the operation phase, the host interface communicates with each of the nodes at 400Hz. The data that is exchanged depends on the control mode—centralized or distributed. In centralized control mode, the torques for all the joints are computed on the VME-based real-time processing unit (RTPU), assembled into a data-packet by the microcontroller on the host interface card and broadcast over the ARMbus to all the nodes of the network. Each node extracts its torque value from the packet and replies by sending a data-packet containing the resolver and tachometer readings. In distributed control mode, on the other hand, the host computer broadcasts the desired joint values and feed-forward torques. Locally, in each module, the control loop can then be closed at a frequency much higher than 400Hz. The modules still send sensor readings back to the host interface to be used in the computation of the subsequent feed-forward torque.5 Modular and reconfigurable control softwareThe control software for the RMMS has been developed using the Chimera real-time operating system, which supports reconfigurable and reusable software components [15]. The software components used to control the RMMS are listed in Table 1. The trjjline, dls, and grav_comp components require the knowledge of certain configuration dependent parametersof the RMMS, such as the number of degrees-of-freedom, the Denavit-Hartenberg parameters etc. During the initialization phase, the RMMS interface establishes contact with each of the hardware modules to determine automatically which modules are being used and in which order and orientation they have been assembled. For each module, a data file with a parametric model is read. By combining this information for all the modules, kinematic and dynamic models of the entire manipulator are built.After the initialization, the rmms software component operates in a distributed control mode in which the microcontrollers of each of the RMMS modules perform PID control locally at 1900Hz. The communication between the modules and the host interface is at 400Hz, which can differ from the cycle frequency of the rmms software component. Since we use a triple buffer mechanism [16] for the communication through the dual-port RAM on the ARMbus host interface, no synchronization or handshaking is necessary.Because closed form inverse kinematics do not exist for all possible RMMS configurations, we use a damped least-squares kinematic controller to do the inverse kinematics computation numerically..6 Seamless integration of simulationTo assist the user in evaluating whether an RMMS con- figuration can successfully complete a given task, we have built a simulator. The simulator is based on the TeleGrip robot simulation software from Deneb Inc., and runs on an SGI Crimson which is connected with the real-time processing unit through a Bit3 VME-to-VME adaptor, as is shown in Figure 6.A graphical user interface allows the user to assemble simulated RMMS configurations very much like assembling the real hardware. Completed configurations can be tested and programmed using the TeleGrip functions for robot devices. The configurations can also be interfaced with the Chimera real-time softwarerunning on the same RTPUs used to control the actual hardware. As a result, it is possible to evaluate not only the movements of the manipulator but also the realtime CPU usage and load balancing. Figure 7 shows an RMMS simulation compared with the actual task execution.7 SummaryWe have developed a Reconfigurable Modular Manipulator System which currently consists of six hardware modules, with a total of four degrees-of-freedom. These modules can be assembled in a large number of different configurations to tailor the kinematic and dynamic properties of the manipulator to the task at hand. The control software for the RMMS automatically adapts to the assembly configuration by building kinematic and dynamic models of the manipulator; this is totally transparent to the user. To assist the user in evaluating whether a manipulator configuration is well suited for a given task, we have also built a simulator.AcknowledgmentThis research was funded in part by DOE under grant DE-F902-89ER14042, by Sandia National Laboratories under contract AL-3020, by the Department of Electrical and Computer Engineering, and by The Robotics Institute, Carnegie Mellon University.The authors would also like to thank Randy Casciola, Mark DeLouis, Eric Hoffman, and Jim Moody for their valuable contributions to the design of the RMMS system.附件二：可迅速布置的机械手系统作者：Christiaan J.J. Paredis, H. Benjamin Brown, Pradeep K. Khosla摘要：一个迅速可部署的机械手系统，可以使再组合的标准化的硬件的灵活性用标准化的编程工具结合，允许用户迅速建立为一项规定的任务来通常地控制机械手。
毕设外文原文及译文
北京联合大学毕业设计（论文）任务书题目：OFDM调制解调技术的设计与仿真实现专业：通信工程指导教师：张雪芬学院：信息学院学号：2011080331132班级：1101B姓名：徐嘉明一、外文原文Evolution Towards 5G Multi-tier Cellular WirelessNetworks:An Interference ManagementPerspectiveEkram Hossain, Mehdi Rasti, Hina Tabassum, and Amr AbdelnasserAbstract—The evolving fifth generation (5G) cellular wireless networks are envisioned to overcome the fundamental challenges of existing cellular networks, e.g., higher data rates, excellent end-to-end performance and user-coverage in hot-spots and crowded areas with lower latency, energy consumption and cost per information transfer. To address these challenges, 5G systems will adopt a multi-tier architecture consisting of macrocells, different types of licensed small cells, relays, and device-to-device (D2D) networks to serve users with different quality-of-service (QoS) requirements in a spectrum and energy-efficient manner. Starting with the visions and requirements of 5G multi-tier networks, this article outlines the challenges of interference management (e.g., power control, cell association) in these networks with shared spectrum access (i.e., when the different network tiers share the same licensed spectrum). It is argued that the existing interference management schemes will not be able to address the interference management problem in prioritized 5G multitier networks where users in different tiers have different priorities for channel access. In this context, a survey and qualitative comparison of the existing cell association and power control schemes is provided to demonstrate their limitations for interference management in 5G networks. Open challenges are highlighted and guidelines are provided to modify the existing schemes in order to overcome these limitations and make them suitable for the emerging 5G systems.Index Terms—5G cellular wireless, multi-tier networks, interference management, cell association, power control.I. INTRODUCTIONTo satisfy the ever-increasing demand for mobile broadband communications, the IMT-Advanced (IMT-A) standards have been ratified by the International Telecommunications Union (ITU) in November 2010 and the fourth generation (4G) wireless communication systems are currently being deployed worldwide. The standardization for LTE Rel-12, also known as LTE-B, is also ongoing and expected to be finalized in 2014. Nonetheless, existing wireless systems will not be able to deal with the thousand-fold increase in total mobile broadband data [1] contributed by new applications and services such as pervasive 3D multimedia, HDTV, VoIP, gaming, e-Health, and Car2x communication. In this context, the fifth generation (5G) wireless communication technologies are expected to attain 1000 times higher mobile data volume per unit area,10-100 times higher number of connecting devices and user data rate, 10 times longer battery life and 5 times reduced latency [2]. While for 4G networks the single-user average data rate is expected to be 1 Gbps, it is postulated that cell data rate of theorder of 10 Gbps will be a key attribute of 5G networks.5G wireless networks are expected to be a mixture of network tiers of different sizes, transmit powers, backhaul connections, different radio access technologies (RATs) that are accessed by an unprecedented numbers of smart and heterogeneous wireless devices. This architectural enhancement along with the advanced physical communications technology such as high-order spatial multiplexing multiple-input multiple-output (MIMO) communications will provide higher aggregate capacity for more simultaneous users, or higher level spectral efficiency, when compared to the 4G networks. Radio resource and interference management will be a key research challenge in multi-tier and heterogeneous 5G cellular networks. The traditional methods for radio resource and interference management (e.g., channel allocation, power control, cell association or load balancing) in single-tier networks (even some of those developed for two-tier networks) may not be efficient in this environment and a new look into the interference management problem will be required.First, the article outlines the visions and requirements of 5G cellular wireless systems. Major research challenges are then highlighted from the perspective of interference management when the different network tiers share the same radio spectrum. A comparative analysis of the existing approaches for distributed cell association and power control (CAPC) is then provided followed by a discussion on their limitations for5G multi-tier cellular networks. Finally, a number of suggestions are provided to modifythe existing CAPC schemes to overcome these limitations.II. VISIONS AND REQUIREMENTS FOR 5G MULTI-TIERCELLULAR NETWORKS5G mobile and wireless communication systems will require a mix of new system concepts to boost the spectral and energy efficiency. The visions and requirements for 5G wireless systems are outlined below.·Data rate and latency: For dense urban areas, 5G networks are envisioned to enable an experienced data rate of 300 Mbps and 60 Mbps in downlink and uplink, respectively, in 95% of locations and time [2]. The end-to- end latencies are expected to be in the order of 2 to 5 milliseconds. The detailed requirements for different scenarios are listed in [2].·Machine-type Communication (MTC) devices: The number of traditional human-centric wireless devices with Internet connectivity (e.g., smart phones, super-phones, tablets) may be outnumbered by MTC devices which can be used in vehicles, home appliances, surveillance devices, and sensors.·Millimeter-wave communication: To satisfy the exponential increase in traffic and the addition of different devices and services, additional spectrum beyond what was previously allocated to 4G standard is sought for. The use of millimeter-wave frequency bands (e.g., 28 GHz and 38 GHz bands) is a potential candidate to overcome the problem of scarce spectrum resources since it allows transmission at wider bandwidths than conventional 20 MHz channels for 4G systems.·Multiple RATs: 5G is not about replacing the existing technologies, but it is about enhancing and supporting them with new technologies [1]. In 5G systems, the existing RATs, including GSM (Global System for Mobile Communications), HSPA+ (Evolved High-Speed Packet Access), and LTE, will continue to evolve to provide a superior system performance. They will also be accompanied by some new technologies (e.g., beyondLTE-Advanced).·Base station (BS) densification: BS densification is an effective methodology to meet the requirements of 5G wireless networks. Specifically, in 5G networks, there will be deployments of a large number of low power nodes, relays, and device-to-device (D2D) communication links with much higher density than today’s macrocell networks.Fig. 1 shows such a multi-tier network with a macrocell overlaid by relays, picocells, femtocells, and D2D links. The adoption of multiple tiers in the cellular networkarchitecture will result in better performance in terms of capacity, coverage, spectral efficiency, and total power consumption, provided that the inter-tier and intratier interferences are well managed.·Prioritized spectrum access: The notions of both trafficbased and tier-based Prioriti -es will exist in 5G networks. Traffic-based priority arises from the different requirements of the users (e.g., reliability and latency requirements, energy constraints), whereas the tier-based priority is for users belonging to different network tiers. For example, with shared spectrum access among macrocells and femtocells in a two-tier network, femtocells create ―dead zones‖ around them in the downlink for macro users. Protection should, thus, be guaranteed for the macro users. Consequently, the macro and femtousers play the role of high-priority users (HPUEs) and lowpriority users (LPUEs), respectively. In the uplink direction, the macrocell users at the cell edge typically transmit with high powers which generates high uplink interference to nearby femtocells. Therefore, in this case, the user priorities should get reversed. Another example is a D2D transmission where different devices may opportunistically access the spectrum to establish a communication link between them provided that the interference introduced to the cellular users remains below a given threshold. In this case, the D2D users play the role of LPUEs whereas the cellular users play the role of HPUEs.·Network-assisted D2D communication: In the LTE Rel- 12 and beyond, focus will be on network controlled D2D communications, where the macrocell BS performs control signaling in terms of synchronization, beacon signal configuration and providing identity and security management [3]. This feature will extend in 5G networks to allow other nodes, rather than the macrocell BS, to have the control. For example, consider a D2D link at the cell edge and the direct link between the D2D transmitter UE to the macrocell is in deep fade, then the relay node can be responsible for the control signaling of the D2Dlink (i.e., relay-aided D2D communication).·Energy harvesting for energy-efficient communication: One of the main challenges in 5G wireless networks is to improve the energy efficiency of the battery-constrained wireless devices. To prolong the battery lifetime as well as to improve the energy efficiency, an appealing solution is to harvest energy from environmental energy sources (e.g., solar and wind energy). Also, energy can be harvested from ambient radio signals (i.e., RF energy harvesting) with reasonable efficiency over small distances. The havested energy could be used for D2D communication or communication within a small cell. Inthis context, simultaneous wireless information and power transfer (SWIPT) is a promising technology for 5G wireless networks. However, practical circuits for harvesting energy are not yet available since the conventional receiver architecture is designed for information transfer only and, thus, may not be optimal for SWIPT. This is due to the fact that both information and power transfer operate with different power sensitivities at the receiver (e.g., -10dBm and -60dBm for energy and information receivers, respectively) [4]. Also, due to the potentially low efficiency of energy harvesting from ambient radio signals, a combination of different energy harvesting technologies may be required for macrocell communication.III. INTERFERENCE MANAGEMENT CHALLENGES IN 5GMULTI-TIER NETWORKSThe key challenges for interference management in 5G multi-tier networks will arise due to the following reasons which affect the interference dynamics in the uplink and downlink of the network: (i) heterogeneity and dense deployment of wireless devices, (ii) coverage and traffic load imbalance due to varying transmit powers of different BSs in the downlink, (iii) public or private access restrictions in different tiers that lead to diverse interference levels, and (iv) the priorities in accessing channels of different frequencies and resource allocation strategies. Moreover, the introduction of carrier aggregation, cooperation among BSs (e.g., by using coordinated multi-point transmission (CoMP)) as well as direct communication among users (e.g., D2D communication) may further complicate the dynamics of the interference. The above factors translate into the following key challenges.·Designing optimized cell association and power control (CAPC) methods for multi-tier networks: Optimizing the cell associations and transmit powers of users in the uplink or the transmit powers of BSs in the downlink are classical techniques to simultaneously enhance the system performance in various aspects such as interference mitigation, throughput maximization, and reduction in power consumption. Typically, the former is needed to maximize spectral efficiency, whereas the latter is required to minimize the power (and hence minimize the interference to other links) while keeping theFig. 1. A multi-tier network composed of macrocells, picocells, femtocells, relays, and D2D links.Arrows indicate wireless links, whereas the dashed lines denote the backhaul connections. desired link quality. Since it is not efficient to connect to a congested BS despite its high achieved signal-to-interference ratio (SIR), cell association should also consider the status of each BS (load) and the channel state of each UE. The increase in the number of available BSs along with multi-point transmissions and carrier aggregation provide multiple degrees of freedom for resource allocation and cell-selection strategies. For power control, the priority of different tiers need also be maintained by incorporating the quality constraints of HPUEs. Unlike downlink, the transmission power in the uplink depends on the user’s batt ery power irrespective of the type of BS with which users are connected. The battery power does not vary significantly from user to user; therefore, the problems of coverage and traffic load imbalance may not exist in the uplink. This leads to considerable asymmetries between the uplink and downlink user association policies. Consequently, the optimal solutions for downlink CAPC problems may not be optimal for the uplink. It is therefore necessary to develop joint optimization frameworks that can provide near-optimal, if not optimal, solutions for both uplink and downlink. Moreover, to deal with this issue of asymmetry, separate uplink and downlink optimal solutions are also useful as far as mobile users can connect with two different BSs for uplink and downlink transmissions which is expected to be the case in 5G multi-tier cellular networks [3].·Designing efficient methods to support simultaneous association to multiple BSs: Compared to existing CAPC schemes in which each user can associate to a singleBS, simultaneous connectivity to several BSs could be possible in 5G multi-tier network. This would enhance the system throughput and reduce the outage ratio by effectively utilizing the available resources, particularly for cell edge users. Thus the existing CAPCschemes should be extended to efficiently support simultaneous association of a user to multiple BSs and determine under which conditions a given UE is associated to which BSs in the uplink and/or downlink.·Designing efficient methods for cooperation and coordination among multiple tiers: Cooperation and coordination among different tiers will be a key requirement to mitigate interference in 5G networks. Cooperation between the macrocell and small cells was proposed for LTE Rel-12 in the context of soft cell, where the UEs are allowed to have dual connectivity by simultaneously connecting to the macrocell and the small cell for uplink and downlink communications or vice versa [3]. As has been mentioned before in the context of asymmetry of transmission power in uplink and downlink, a UE may experience the highest downlink power transmission from the macrocell, whereas the highest uplink path gain may be from a nearby small cell. In this case, the UE can associate to the macrocell in the downlink and to the small cell in the uplink. CoMP schemes based on cooperation among BSs in different tiers (e.g., cooperation between macrocells and small cells) can be developed to mitigate interference in the network. Such schemes need to be adaptive and consider user locations as well as channel conditions to maximize the spectral and energy efficiency of the network. This cooperation however, requires tight integration of low power nodes into the network through the use of reliable, fast andlow latency backhaul connections which will be a major technical issue for upcoming multi-tier 5G networks. In the remaining of this article, we will focus on the review of existing power control and cell association strategies to demonstrate their limitations for interference management in 5G multi-tier prioritized cellular networks (i.e., where users in different tiers have different priorities depending on the location, application requirements and so on). Design guidelines will then be provided to overcome these limitations. Note that issues such as channel scheduling in frequency domain, timedomain interference coordination techniques (e.g., based on almost blank subframes), coordinated multi-point transmission, and spatial domain techniques (e.g., based on smart antenna techniques) are not considered in this article.IV. DISTRIBUTED CELL ASSOCIATION AND POWERCONTROL SCHEMES: CURRENT STATE OF THE ARTA. Distributed Cell Association SchemesThe state-of-the-art cell association schemes that are currently under investigation formulti-tier cellular networks are reviewed and their limitations are explained below.·Reference Signal Received Power (RSRP)-based scheme [5]: A user is associated with the BS whose signal is received with the largest average strength. A variant of RSRP, i.e., Reference Signal Received Quality (RSRQ) is also used for cell selection in LTE single-tier networks which is similar to the signal-to-interference (SIR)-based cell selection where a user selects a BS communicating with which gives the highest SIR. In single-tier networks with uniform traffic, such a criterion may maximize the network throughput. However, due to varying transmit powers of different BSs in the downlink of multi-tier networks, such cell association policies can create a huge traffic load imbalance. This phenomenon leads to overloading of high power tiers while leaving low power tiers underutilized.·Bias-based Cell Range Expansion (CRE) [6]: The idea of CRE has been emerged as a remedy to the problem of load imbalance in the downlink. It aims to increase the downlink coverage footprint of low power BSs by adding a positive bias to their signal strengths (i.e., RSRP or RSRQ). Such BSs are referred to as biased BSs. This biasing allows more users to associate with low power or biased BSs and thereby achieve a better cell load balancing. Nevertheless, such off-loaded users may experience unfavorable channel from the biased BSs and strong interference from the unbiased high-power BSs. The trade-off between cell load balancing and system throughput therefore strictly depends on the selected bias values which need to be optimized in order to maximize the system utility. In this context, a baseline approach in LTE-Advanced is to ―orthogonalize‖ the transmissions of the biased and unbiased BSs in time/frequency domain such that an interference-free zone is created.·Association based on Almost Blank Sub-frame (ABS) ratio [7]: The ABS technique uses time domain orthogonalization in which specific sub-frames are left blank by the unbiased BS and off-loaded users are scheduled within these sub-frames to avoid inter-tier interference. This improves the overall throughput of the off-loaded users by sacrificing the time sub-frames and throughput of the unbiased BS. The larger bias values result in higher degree of offloading and thus require more blank subframes to protect the offloaded users. Given a specific number of ABSs or the ratio of blank over total number of sub-frames (i.e., ABS ratio) that ensures the minimum throughput of the unbiased BSs, this criterion allows a user to select a cell with maximum ABS ratio and may even associate with the unbiased BS if ABS ratio decreases significantly. A qualitative comparison amongthese cell association schemes is given in Table I. The specific key terms used in Table I are defined as follows: channel-aware schemes depend on the knowledge of instantaneous channel and transmit power at the receiver. The interference-aware schemes depend on the knowledge of instantaneous interference at the receiver. The load-aware schemes depend on the traffic load information (e.g., number of users). The resource-aware schemes require the resource allocation information (i.e., the chance of getting a channel or the proportion of resources available in a cell). The priority-aware schemes require the information regarding the priority of different tiers and allow a protection to HPUEs. All of the above mentioned schemes are independent, distributed, and can be incorporated with any type of power control scheme. Although simple and tractable, the standard cell association schemes, i.e., RSRP, RSRQ, and CRE are unable to guarantee the optimum performance in multi-tier networks unless critical parameters, such as bias values, transmit power of the users in the uplink and BSs in the downlink, resource partitioning, etc. are optimized.B. Distributed Power Control SchemesFrom a user’s point of view, the objective of power control is to support a user with its minimum acceptable throughput, whereas from a system’s point of view it is t o maximize the aggregate throughput. In the former case, it is required to compensate for the near-far effect by allocating higher power levels to users with poor channels as compared to UEs with good channels. In the latter case, high power levels are allocated to users with best channels and very low (even zero) power levels are allocated to others. The aggregate transmit power, the outage ratio, and the aggregate throughput (i.e., the sum of achievable rates by the UEs) are the most important measures to compare the performance of different power control schemes. The outage ratio of a particular tier can be expressed as the ratio of the number of UEs supported by a tier with their minimum target SIRs and the total number of UEs in that tier. Numerous power control schemes have been proposed in the literature for single-tier cellular wireless networks. According to the corresponding objective functions and assumptions, the schemes can be classified into the following four types.·Target-SIR-tracking power control (TPC) [8]: In the TPC, each UE tracks its own predefined fixed target-SIR. The TPC enables the UEs to achieve their fixed target-TABLE IQUALITATIVE COMPARISON OF EXISTING CELL ASSOCIATION SCHEMESFOR MULTI-TIER NETWORKSSIRs at minimal aggregate transmit power, assuming thatthe target-SIRs are feasible. However, when the system is infeasible, all non-supported UEs (those who cannot obtain their target-SIRs) transmit at their maximum power, which causes unnecessary power consumption and interference to other users, and therefore, increases the number of non-supported UEs.·TPC with gradual removal (TPC-GR) [9], [10], and [11]:To decrease the outage ra -tio of the TPC in an infeasiblesystem, a number of TPC-GR algorithms were proposedin which non-supported users reduce their transmit power[10] or are gradually removed [9], [11].·Opportunistic power control (OPC) [12]: From the system’s point of view, OPC allocates high power levels to users with good channels (experiencing high path-gains and low interference levels) and very low power to users with poor channels. In this algorithm, a small difference in path-gains between two users may lead to a large difference in their actual throughputs [12]. OPC improves the system performance at the cost of reduced fairness among users.·Dynamic-SIR tracking power control (DTPC) [13]: When the target-SIR requirements for users are feasible, TPC causes users to exactly hit their fixed target-SIRs even if additional resources are still available that can otherwise be used to achieve higher SIRs (and thus better throughputs). Besides, the fixed-target-SIR assignment is suitable only for voice service for which reaching a SIR value higher than the given target value does not affect the service quality significantly. In contrast, for data services, a higher SIR results in a better throughput, which is desirable. The DTPC algorithm was proposed in [13] to address the problem of system throughput maximization subject to a given feasible lower bound for the achieved SIRs of all users in cellular networks. In DTPC, each user dynamically sets its target-SIR by using TPC and OPC in a selective manner. It was shown that when the minimum acceptable target-SIRs are feasible, the actual SIRs received by some users can be dynamically increased (to a value higher than their minimum acceptabletarget-SIRs) in a distributed manner so far as the required resources are available and the system remains feasible (meaning that reaching the minimum target-SIRs for the remaining users are guaranteed). This enhances the system throughput (at the cost of higher power consumption) as compared to TPC. The aforementioned state-of-the-art distributed power control schemes for satisfying various objectives in single-tier wireless cellular networks are unable to address the interference management problem in prioritized 5G multi-tier networks. This is due to the fact that they do not guarantee that the total interference caused by the LPUEs to the HPUEs remain within tolerable limits, which can lead to the SIR outage of some HPUEs. Thus there is a need to modify the existing schemes such that LPUEs track their objectives while limiting their transmit power to maintain a given interference threshold at HPUEs. A qualitative comparison among various state-of-the-art power control problems with different objectives and constraints and their corresponding existing distributed solutions are shown in Table II. This table also shows how these schemes can be modified and generalized for designing CAPC schemes for prioritized 5G multi-tier networks.C. Joint Cell Association and Power Control SchemesA very few work in the literature have considered the problem of distributed CAPC jointly (e.g., [14]) with guaranteed convergence. For single-tier networks, a distributed framework for uplink was developed [14], which performs cell selection based on the effective-interference (ratio of instantaneous interference to channel gain) at the BSs and minimizes the aggregate uplink transmit power while attaining users’ desire d SIR targets. Following this approach, a unified distributed algorithm was designed in [15] for two-tier networks. The cell association is based on the effective-interference metric and is integrated with a hybrid power control (HPC) scheme which is a combination of TPC and OPC power control algorithms.Although the above frameworks are distributed and optimal/ suboptimal with guaranteed convergence in conventional networks, they may not be directly compatible to the 5G multi-tier networks. The interference dynamics in multi-tier networks depends significantly on the channel access protocols (or scheduling), QoS requirements and priorities at different tiers. Thus, the existing CAPC optimization problems should be modified to include various types of cell selection methods (some examples are provided in Table I) and power control methods with different objectives and interference constraints (e.g., interference constraints for macro cell UEs, picocell UEs, or D2Dreceiver UEs). A qualitative comparison among the existing CAPC schemes along with the open research areas are highlighted in Table II. A discussion on how these open problems can be addressed is provided in the next section.V. DESIGN GUIDELINES FOR DISTRIBUTED CAPCSCHEMES IN 5G MULTI-TIER NETWORKSInterference management in 5G networks requires efficient distributed CAPC schemes such that each user can possibly connect simultaneously to multiple BSs (can be different for uplink and downlink), while achieving load balancing in different cells and guaranteeing interference protection for the HPUEs. In what follows, we provide a number of suggestions to modify the existing schemes.A. Prioritized Power ControlTo guarantee interference protection for HPUEs, a possible strategy is to modify the existing power control schemes listed in the first column of Table II such that the LPUEs limit their transmit power to keep the interference caused to the HPUEs below a predefined threshold, while tracking their own objectives. In other words, as long as the HPUEs are protected against existence of LPUEs, the LPUEs could employ an existing distributed power control algorithm to satisfy a predefined goal. This offers some fruitful direction for future research and investigation as stated in Table II. To address these open problems in a distributed manner, the existing schemes should be modified so that the LPUEs in addition to setting their transmit power for tracking their objectives, limit their transmit power to keep their interference on receivers of HPUEs below a given threshold. This could be implemented by sending a command from HPUEs to its nearby LPUEs (like a closed-loop power control command used to address the near-far problem), when the interference caused by the LPUEs to the HPUEs exceeds a given threshold. We refer to this type of power control as prioritized power control. Note that the notion of priority and thus the need of prioritized power control exists implicitly in different scenarios of 5G networks, as briefly discussed in Section II. Along this line, some modified power control optimization problems are formulated for 5G multi-tier networks in second column of Table II.To compare the performance of existing distributed power control algorithms, let us consider a prioritized multi-tier cellular wireless network where a high-priority tier consisting of 3×3 macro cells, each of which covers an area of 1000 m×1000 m, coexists with a low-priority tier consisting of n small-cells per each high-priority macro cell, each。
毕业设计论文外文文献翻译
毕业设计(论文）外文文献翻译院系：财务与会计学院年级专业：201＊级财务管理姓名:学号：132148*＊*附件: 财务风险管理【Abstract】Although financial risk has increased significantly in recent years risk and risk management are not contemporary issues。
The result of increasingly global markets is that risk may originate with events thousands of miles away that have nothing to do with the domestic market。
Information is available instantaneously which means that change and subsequent market reactions occur very quickly。
The economic climate and markets can be affected very quickly by changes in exchange rates interest rates and commodity prices。
Counterparties can rapidly become problematic。
As a result it is important to ensure financial risks are identified and managed appropriately. Preparation is a key component of risk management。
【Key Words】Financial risk，Risk management，YieldsI. Financial risks arising1.1What Is Risk1.1.1The concept of riskRisk provides the basis for opportunity. The terms risk and exposure have subtle differences in their meaning. Risk refers to the probability of loss while exposure is the possibility of loss although they are often used interchangeably。
毕设外文文献+翻译1
毕设外文文献+翻译1外文翻译外文原文CHANGING ROLES OF THE CLIENTS、ARCHITECTSAND CONTRACTORS THROUGH BIMAbstract:Purpose –This paper aims to present a general review of the practical implications of building information modelling (BIM) based on literature and case studies. It seeks to address the necessity for applying BIM and re-organising the processes and roles in hospital building projects. This type of project is complex due to complicated functional and technical requirements, decision making involving a large number of stakeholders, and long-term development processes.Design/methodology/approach–Through desk research and referring to the ongoing European research project InPro, the framework for integrated collaboration and the use of BIM are analysed.Findings –One of the main findings is the identification of the main factors for a successful collaboration using BIM, which can be recognised as “POWER”: product information sharing (P),organisational roles synergy (O), work processes coordination (W), environment for teamwork (E), and reference data consolidation (R).Originality/value –This paper contributes to the actual discussion in science and practice on the changing roles and processes that are required to develop and operate sustainable buildings with the support of integrated ICT frameworks and tools. It presents the state-of-the-art of European research projects and some of the first real cases of BIM application inhospital building projects.Keywords:Europe, Hospitals, The Netherlands, Construction works, Response flexibility, Project planningPaper type :General review1. IntroductionHospital building projects, are of key importance, and involve significant investment, and usually take a long-term development period. Hospital building projects are also very complex due to the complicated requirements regarding hygiene, safety, special equipments, and handling of a large amount of data. The building process is very dynamic and comprises iterative phases and intermediate changes. Many actors with shifting agendas, roles and responsibilities are actively involved, such as: the healthcare institutions, national and local governments, project developers, financial institutions, architects, contractors, advisors, facility managers, and equipment manufacturers and suppliers. Such building projects are very much influenced, by the healthcare policy, which changes rapidly in response to the medical, societal and technological developments, and varies greatly between countries (World Health Organization, 2000). In The Netherlands, for example, the way a building project in the healthcare sector is organised is undergoing a major reform due to a fundamental change in the Dutch health policy that was introduced in 2008.The rapidly changing context posts a need for a building with flexibility over its lifecycle. In order to incorporate life-cycle considerations in the building design, construction technique, and facility management strategy, a multidisciplinary collaboration is required. Despite the attempt for establishing integrated collaboration, healthcare building projects still facesserious problems in practice, such as: budget overrun, delay, and sub-optimal quality in terms of flexibility, end-user?s dissatisfaction, and energy inefficiency. It is evident that the lack of communication and coordination between the actors involved in the different phases of a building project is among the most important reasons behind these problems. The communication between different stakeholders becomes critical, as each stakeholder possesses different setof skills. As a result, the processes for extraction, interpretation, and communication of complex design information from drawings and documents are often time-consuming and difficult. Advanced visualisation technologies, like 4D planning have tremendous potential to increase the communication efficiency and interpretation ability of the project team members. However, their use as an effective communication tool is still limited and not fully explored. There are also other barriers in the information transfer and integration, for instance: many existing ICT systems do not support the openness of the data and structure that is prerequisite for an effective collaboration between different building actors or disciplines.Building information modelling (BIM) offers an integrated solution to the previously mentioned problems. Therefore, BIM is increasingly used as an ICT support in complex building projects. An effective multidisciplinary collaboration supported by an optimal use of BIM require changing roles of the clients, architects, and contractors; new contractual relationships; and re-organised collaborative processes. Unfortunately, there are still gaps in the practical knowledge on how to manage the building actors to collaborate effectively in their changing roles, and todevelop and utilise BIM as an optimal ICT support of the collaboration.This paper presents a general review of the practical implications of building information modelling (BIM) based on literature review and case studies. In the next sections, based on literature and recent findings from European research project InPro, the framework for integrated collaboration and the use of BIM are analysed. Subsequently, through the observation of two ongoing pilot projects in The Netherlands, the changing roles of clients, architects, and contractors through BIM application are investigated. In conclusion, the critical success factors as well as the main barriers of a successful integrated collaboration using BIM are identified.2. Changing roles through integrated collaboration and life-cycle design approachesA hospital building project involves various actors, roles, and knowledge domains. In The Netherlands, the changing roles of clients, architects, and contractors in hospital building projects are inevitable due the new healthcare policy. Previously under the Healthcare Institutions Act (WTZi), healthcare institutions were required to obtain both a license and a building permit for new construction projects and major renovations. The permit was issued by the Dutch Ministry of Health. The healthcare institutions were then eligible to receive financial support from the government. Since 2008, new legislation on the management of hospital building projects and real estate has come into force. In this new legislation, a permit for hospital building project under the WTZi is no longer obligatory, nor obtainable (Dutch Ministry of Health, Welfare and Sport, 2008). This change allows more freedom from the state-directed policy, and respectively,allocates more responsibilities to the healthcare organisations to deal with the financing and management of their real estate. The new policy implies that the healthcare institutions are fully responsible to man age and finance their building projects and real estate. The government?s support for the costs of healthcare facilities will no longer be given separately, but will be included in the fee for healthcare services. This means that healthcare institutions must earn back their investment on real estate through their services. This new policy intends to stimulate sustainable innovations in the design, procurement and management of healthcare buildings, which will contribute to effective and efficient primary healthcare services.The new strategy for building projects and real estate management endorses an integrated collaboration approach. In order to assure the sustainability during construction, use, and maintenance, the end-users, facility managers, contractors and specialist contractors need to be involved in the planning and design processes. The implications of the new strategy are reflected in the changing roles of the building actors and in the new procurement method.In the traditional procurement method, the design, and its details, are developed by the architect, and design engineers. Then, the client (the healthcare institution) sends an application to the Ministry of Healthto obtain an approval on the building permit and the financial support from the government. Following this, a contractor is selected through a tender process that emphasises the search for the lowest-price bidder. During the construction period, changes often take place due to constructability problems of the design and new requirements from the client.Because of the high level of technical complexity, and moreover, decision-making complexities, the whole process from initiation until delivery of a hospital building project can take up to ten years time. After the delivery, the healthcare institution is fully in charge of the operation of the facilities. Redesigns and changes also take place in the use phase to cope with new functions and developments in the medical world.The integrated procurement pictures a new contractual relationship between the parties involved in a building project. Instead of a relationship between the client and architect for design, and the client and contractor for construction, in an integrated procurement the client only holds a contractual relationship with the main party that is responsible for both design and construction. The traditional borders between tasks and occupational groups become blurred since architects, consulting firms, contractors, subcontractors, and suppliers all stand on the supply side in the building process while the client on the demand side. Such configuration puts the architect, engineer and contractor in a very different position that influences not only their roles, but also their responsibilities, tasks and communication with the client, the users, the team and other stakeholders.The transition from traditional to integrated procurement method requires a shift of mindset of the parties on both the demand and supply sides. It is essential for the client and contractor to have a fair and open collaboration in which both can optimally use their competencies. The effectiveness of integrated collaboration is also determined by the client?s capacity and strategy to organize innovative tendering procedures.A new challenge emerges in case of positioning an architect in a partnership with the contractor instead of with the client. In case of the architect enters a partnership with the contractor, an important issues is how to ensure the realisation of the architectural values as well as innovative engineering through an efficient construction process. In another case, the architect can stand at the client?s side in a strategic advisory role instead of being the designer. In this case, the architect?s responsibility is translating client?s requirements and wishes into the architectural values to be included in the design specification, and evaluating the contractor?s proposal against this. In any of this new role, the architect holds the responsibilities as stakeholder interest facilitator, custodian of customer value and custodian of design models.The transition from traditional to integrated procurement method also brings consequences in the payment schemes. In the traditional building process, the honorarium for the architect is usually based on a percentage of the project costs; this may simply mean that the more expensive the building is, the higher the honorarium will be. The engineer receives the honorarium based on the complexity of the design and the intensity of the assignment. A highly complex building, which takes a number of redesigns, is usually favourable for the engineers in terms of honorarium. A traditional contractor usually receives the commission based on the tender to construct the building at the lowest price by meeting the minimum specifications given by the client. Extra work due to modifications is charged separately to the client. After the delivery, the contractor is no longer responsible for the long-term use of the building. In the traditional procurement method, all risks are placed with theclient.In integrated procurement method, the payment is based on the achieved building performance; thus, the payment is non-adversarial. Since the architect, engineer and contractor have a wider responsibility on the quality of the design and the building, the payment is linked to a measurement system of the functional and technical performance of the building over a certain period of time. The honorarium becomes an incentive to achieve the optimal quality. If the building actors succeed to deliver a higher added-value thatexceed the minimum client?s requirements, they will receive a bonus in accordance to the client?s extra gain. The level of transparency is also improved. Open book accounting is an excellent instrument provided that the stakeholders agree on the information to be shared and to its level of detail (InPro, 2009).Next to the adoption of integrated procurement method, the new real estate strategy for hospital building projects addresses an innovative product development and life-cycle design approaches. A sustainable business case for the investment and exploitation of hospital buildings relies on dynamic life-cycle management that includes considerations and analysis of the market development over time next to the building life-cycle costs (investment/initial cost, operational cost, and logistic cost). Compared to the conventional life-cycle costing method, the dynamic life-cycle management encompasses a shift from focusing only on minimizing the costs to focusing on maximizing the total benefit that can be gained. One of the determining factors for a successful implementation of dynamic life-cycle management is the sustainable design of the building and building components, which means that the design carriessufficient flexibility to accommodate possible changes in the long term (Prins, 1992).Designing based on the principles of life-cycle management affects the role of the architect, as he needs to be well informed about the usage scenarios and related financial arrangements, the changing social and physical environments, and new technologies. Design needs to integrate people activities and business strategies over time. In this context, the architect is required to align the design strategies with the organisational, local and global policies on finance, business operations, health and safety, environment, etc.The combination of process and product innovation, and the changing roles of the building actors can be accommodated by integrated project delivery or IPD (AIA California Council, 2007). IPD is an approach that integrates people, systems, business structures and practices into a process that collaboratively harnesses the talents and insights of all participants to reduce waste and optimize efficiency through all phases of design, fabrication and construction. IPD principles can be applied to a variety of contractual arrangements. IPD teams will usually include members well beyond the basic triad of client, architect, and contractor. At a minimum, though, an Integrated Project should include a tight collaboration between the client, the architect, and the main contractor ultimately responsible for construction of the project, from the early design until the project handover. The key to a successful IPD is assembling a team that is committed to collaborative processes and is capable of working together effectively. IPD is built on collaboration. As a result, it can only be successful if the participants share and apply common values and goals.3. Changing roles through BIM applicationBuilding information model (BIM) comprises ICT frameworks and tools that can support the integrated collaboration based on life-cycle design approach. BIM is a digital representation of physical and functional characteristics of a facility. As such it serves as a shared knowledge resource for information about a facility forming a reliable basis for decisions during its lifecycle from inception onward (National Institute of Building Sciences NIBS, 2007). BIM facilitates time and place independent collaborative working. A basic premise of BIM is collaboration by different stakeholders at different phases of the life cycle of a facility to insert, extract, update or modify information in the BIM to support and reflect the roles of that stakeholder. BIM in its ultimate form, as a shared digital representation founded on open standards for interoperability, can become a virtual information model to be handed from the design team to the contractor and subcontractors and then to the client.BIM is not the same as the earlier known computer aided design (CAD). BIM goes further than an application to generate digital (2D or 3D) drawings. BIM is an integrated model in which all process and product information is combined, stored, elaborated, and interactively distributed to all relevant building actors. As a central model for all involved actors throughout the project lifecycle, BIM develops andevolves as the project progresses. Using BIM, the proposed design and engineering solutions can be measured against the client?s requirements and expected building performance. The functionalities of BIM to support the design process extend to multidimensional (nD), including: three-dimensional visualisation and detailing, clash detection, material schedule, planning, costestimate, production and logistic information, and as-built documents. During the construction process, BIM can support the communication between the building site, the factory and the design office– which is crucial for an effective and efficient prefabrication and assembly processes as well as to prevent or solve problems related to unforeseen errors or modifications. When the building is in use, BIM can be used in combination with the intelligent building systems to provide and maintain up-to-date information of the building performance, including the life-cycle cost.To unleash the full potential of more efficient information exchange in the AEC/FM industry in collaborative working using BIM, both high quality open international standards and high quality implementations of these standards must be in place. The IFC open standard is generally agreed to be of high quality and is widely implemented in software. Unfortunately, the certification process allows poor quality implementations to be certified and essentially renders the certified software useless for any practical usage with IFC. IFC compliant BIM is actually used less than manual drafting for architects and contractors, and show about the same usage for engineers. A recent survey shows that CAD (as a closed-system) is still the major form of technique used in design work (over 60 per cent) while BIM is used in around 20 percent of projects for architects and in around 10 per cent of projects for engineers and contractors.The application of BIM to support an optimal cross-disciplinary and cross-phase collaboration opens a new dimension in the roles and relationships between the building actors. Several most relevant issues are: the new role of a model manager; the agreement on the access right and IntellectualProperty Right (IPR); the liability and payment arrangement according to the type of contract and in relation to the integrated procurement; and the use of open international standards.Collaborative working using BIM demands a new expert role of a model manager who possesses ICT as well as construction process know-how (InPro, 2009). The model manager deals with the system as well as with the actors. He provides and maintains technological solutions required for BIM functionalities, manages the information flow, and improves the ICT skills of the stakeholders. The model manager does not take decisions on design and engineering solutions, nor the organisational processes, but his roles in the chain of decision making are focused on:the development of BIM, the definition of the structure and detail level of the model, and the deployment of relevant BIM tools, such as for models checking, merging, and clash detections;the contribution to collaboration methods, especially decision making and communication protocols, task planning, and risk management;and the management of information, in terms of data flow and storage, identification of communication errors, and decision or process (re-)tracking.Regarding the legal and organisational issues, one of the actual questions is: “In what way does the intellectual property right (IPR) in collaborative working using BIM differ from the IPR in a traditional teamwork?”. In terms of combine d work, the IPR of each element is at tached to its creator. Although it seems to be a fully integrated design, BIM actually resulted from a combination of works/elements; for instance: the outline of the building design, is created by the architect, the design for theelectrical system, is created by the electrical contractor, etc. Thus, in case of BIM as a combined work, the IPR is similar to traditional teamwork. Working with BIM with authorship registration functionalities may actually make it easier to keep track of the IPR.How does collaborative working, using BIM, effect the contractual relationship? On the one hand,collaborative working using BIM does not necessarily change the liability position in the contract nor does it obligate an alliance contract. The General Principles of BIM A ddendum confirms: …This does not effectuate or require a restructuring of contractual relationships or shifting of risks between or among the Project Participants other than as specifically required per the Protocol Addendum and its Attachments? (ConsensusDOCS, 2008). On the other hand, changes in terms of payment schemes can be anticipated. Collaborative processes using BIM will lead to the shifting of activities from to the early design phase. Much, if not all, activities in the detailed engineering and specification phase will be done in the earlier phases. It means that significant payment for the engineering phase, which may count up to 40 per cent of the design cost, can no longer be expected. As engineering work is done concurrently with the design, a new proportion of the payment in the early design phase is necessary.4. Review of ongoing hospital building projects using BIMIn The Netherlands, the changing roles in hospital building projects are part of the strategy, which aims at achieving a sustainable real estate in response to the changing healthcare policy. Referring to literature and previous research, the main factors that influence the success of the changing roles can be concluded as: the implementation of an integrated procurementmethod and a life-cycle design approach for a sustainable collaborative process; the agreement on the BIM structure and the intellectual rights; and the integration of the role of a model manager. The preceding sections have discussed the conceptual thinking on how to deal with these factors effectively. This current section observes two actual projects and compares the actual practice with the conceptual view respectively.The main issues, which are observed in the case studies, are: the selected procurement method and the roles of the involved parties within this method;the implementation of the life-cycle design approach;the type, structure, and functionalities of BIM used in the project;the openness in data sharing and transfer of the model, and the intended use of BIM in the future; and the roles and tasks of the model manager.The pilot experience of hospital building projects using BIM in the Netherlands can be observed at University Medical Centre St Radboud (further referred as UMC) and Maxima Medical Centre (further referred as MMC). At UMC, the new building project for the Faculty of Dentistry in the city of Nijmegen has been dedicated as a BIM pilot project. At MMC, BIM is used in designing new buildings for Medical Simulation and Mother-and-Child Centre in the city of Veldhoven.The first case is a project at the University Medical Centre (UMC) St Radboud. UMC is more than just a hospital. UMC combines medical services, education and research. More than 8500 staff and 3000 students work at UMC. As a part of the innovative real estate strategy, UMC has considered to use BIM for its building projects. The new development of the Faculty ofDentistry and the surrounding buildings on the Kapittelweg in Nijmegen has been chosen as a pilot project to gather practical knowledge and experience on collaborative processes with BIM support.The main ambition to be achieved through the use of BIM in the building projects at UMC can be summarised as follows: using 3D visualisation to enhance the coordination and communication among the building actors, and the user participation in design;integrating the architectural design with structural analysis, energy analysis, cost estimation, and planning;interactively evaluating the design solutions against the programme of requirements and specifications;reducing redesign/remake costs through clash detection during the design process; andoptimising the management of the facility through the registration of medical installations andequipments, fixed and flexible furniture, product and output specifications, and operational data.The second case is a project at the Maxima Medical Centre (MMC). MMC is a large hospital resulted from a merger between the Diaconessenhuis in Eindhoven and St Joseph Hospital in Veldhoven. Annually the 3,400 staff of MMC provides medical services to more than 450,000 visitors and patients. A large-scaled extension project of the hospital in Veldhoven is a part of its real estate strategy. A medical simulation centre and a women-and-children medical centre are among the most important new facilities within this extension project. The design has been developed using 3D modelling with several functionalities of BIM.The findings from both cases and the analysis are as follows.Both UMC and MMC opted for a traditional procurement method in which the client directly contracted an architect, a structural engineer, and a mechanical, electrical and plumbing (MEP) consultant in the design team. Once the design and detailed specifications are finished, a tender procedure will follow to select a contractor. Despite the choice for this traditional method, many attempts have been made for a closer and more effective multidisciplinary collaboration. UMC dedicated a relatively long preparation phase with the architect, structural engineer and MEP consultant before the design commenced. This preparation phase was aimed at creating a common vision on the optimal way for collaboration using BIM as an ICT support. Some results of this preparation phase are: a document that defines the common ambition for the project and the collaborative working process and a semi-formal agreement that states the commitment of the building actors for collaboration. Other than UMC, MMC selected an architecture firm with an in-house engineering department. Thus, the collaboration between the architect and structural engineer can take place within the same firm using the same software application.Regarding the life-cycle design approach, the main attention is given on life-cycle costs, maintenance needs, and facility management. Using BIM, both hospitals intend to get a much better insight in these aspects over the life-cycle period. The life-cycle sustainability criteria are included in the assignments for the design teams. Multidisciplinary designers and engineers are asked to collaborate more closely and to interact with the end-users to address life-cycle requirements. However, ensuring the building actors to engage in an integrated collaboration to generate sustainable design solutions that meet the life-cycle。
毕业设计外文文献翻译(原文+译文)
Environmental problems caused by Istanbul subway excavation and suggestionsfor remediation伊斯坦布尔地铁开挖引起的环境问题及补救建议Ibrahim Ocak Abstract：Many environmental problems caused by subway excavations have inevitably become an important point in city life. These problems can be categorized as transporting and stocking of excavated material, traffic jams, noise, vibrations, piles of dust mud and lack of supplies. Although these problems cause many difficulties,the most pressing for a big city like Istanbul is excava tion,since other listed difficulties result from it. Moreover, these problems are environmentally and regionally restricted to the period over which construction projects are underway and disappear when construction is finished. Currently, in Istanbul, there are nine subway construction projects in operation, covering approximately 73 km in length; over 200 km to be constructed in the near future. The amount of material excavated from ongoing construction projects covers approximately 12 million m3. In this study, problems—primarily, the problem with excavation waste(EW)—caused by subway excavation are analyzed and suggestions for remediation are offered.摘要：许多地铁开挖引起的环境问题不可避免地成为城市生活的重要部分。
(完整版)本科生_毕业设计说明书外文文献及翻译_
Computer networking summarizeNetworking can be defined as the linking of people, resources and ideas. Networking occurs via casual encounters, meetings, telephone conversation, and the printed words. Now the computer networking provide beings with new networking capabilities. Computer network are important for services because service tasks are information intensive. During the is transmitted between clients, coworkers, management, funding sources, and policy makers. Tools with rapidly speed up communication will dramatically affect services.Computer network growing explosively. Two decades ago, few people essential part of our infrastructure. Networking is used in every aspect of business, including advertising, production, shipping, planning, bulling, and accounting. Consequently, most corporations in on-line libraries around the world. Federal, state, and local government offices use networks, as do military organizations. In short, computer networks are everywhere.The growth in networking economic impact as well. An entire industry jobs for people with more networking expertise. Companies need workers to plan, acquire, install, operate, and manage the addition computer programming is no longer restricted to individual computers; programmers are expected to design and implement application software that can communicate with software on other computers.Computer networks link computers by communication lines and software protocols, allowing data to be exchanged rapidly and reliably. Traditionally, they split between wide area networks (WANs) and local area networks (LANs). A WAN is a network connected over long-distance telephone lines, and a LAN is a localized network usually in one building or a group of buildings close together. The distinction, computers. Today networks carry e-mail, provide access to public databases, and are beginning to be used for distributed systems. Networks also allow users in one locality to share expensive resources, such as printers and disk-systems.Distributed computer systems are built using networked computers that cooperate to perform tasks. In this environment, each part of the networked system does what it is best at. The of a personal computer or workstation provides a good user interface. The mainframe, on the other the results to the users. In a distributed environment, a user might use in a special language (e. g. Structured Query Language-SQL), to the mainframe, which then parrrses the query, returning the user only the data requested. The user might then use the data. By passing back the user’s PC only the specific information requested, network traffic is reduced. If the whole file were transmitted, the PC would then of one network to access the resources on a different type of network. For example, a gateway could be used to connect a local area network of personal computers to a mainframe computer network. For example, if a company this example, using a bridge makes more sense than joining all thepersonal computers together in one large network because the individual departments only occasionally need to access information on the other network.Computer networking technology can be divided into four major aspects.The first is the data transmission. It explains that at the lowest level electrical signals traveling across wires are used to carry information, and shows be encoded using electrical signals.The second focuses on packet transmission. It explains why computer network use packets, and shows . LANs and WANs discussed above are two basic network.The third covers internetworking—the important idea that allows system, and TCPIP, the protocol technology used in global internet.The fourth explains networking applications. It focuses on , and programs provide services such as electronic mail and Web browsing.Continued growth of the global Internet is one of most interesting and exciting phenomena in networking. A decade ago, the Internet was a research project that involved a few dozen sites. Today, the Internet into a production communication system that reaches millions of people in almost all countries on all continents around the world. In the United States, the Internet connects most corporations, colleges and universities, as well as federal, state, and local government offices. It will soon reach most elementary,junior, and senior addition, many private residences can reach the Internet through a dialup telephone connection. Evidence of the Internet’s impact on society can be seen in advertisements, in magazines and on television, which often contain a reference to an Internet Web site that provide additional information about the advertiser’s products and services.A large organization with diverse networking requirements needs multiple physical networks. More important, if the organization chooses the type network that is best for each task, the organization will network can only communicate with other computers attached to same network. The problem became evident in the 1970s as large organizations began to acquire multiple networks. Each network in the organizations formed an island. In many early installations, each computer attached to a single network and employees employees was given access to multiple svreens and keyboards, and the employee was forced to move form one computer to another to send a massage across the appropriate network. Users are neither satisfied nor productive when they must use a separate computer. Consequently, most modern computer communication syetem allow communication between any two computers analogous to the way a telephone system provides communication between any two telephones. Known as universal service, the concept is a fundamental part of networking. With universal service, a user on any computer in any part of an organization can send messages or data to any other users. Furthermore, a user does not need to change computer systems whenchanging tasks—all information is available to all computers. As a result, users are more productive.The basic component used to commect organization to choose network technologies appropriate for each need, and to use routers to connect all networks into a single internet.The goal of internetworking is universal service across an internet, routers must agree to forward information from a source on one network to a specified destination on another. The task is complex because frame formats and addressing schemes used by underlying networks can differ. As s resulrt, protocol software is needed on computers and routers make universal service possible. Internet protocols overcome differences in frame formats and physical addresses to make communication pissible among networks that use different technologies.In general, internet software provides the appeatrance of a single, seamless communication system to which many computers attach. The syetem offers universal service :each computer is assigned an address, and any computer can send a packet to any other computer. Furthermore, internet protocol software —neither users nor application programs are a ware of the underlying physical networks or the routers that connect them.We say that an internet is a virtual network system because the communication system is an abstraction. That is, although a combination of of a uniform network syetem, no such network exists.Research on internetworking modern networking. In fact,internet techmology . Most large organizations already use internetworking as primary computer communication mechanism. Smaller organizations and individuals are beginning to do so as well. More inportant, the TCPIP technology computers in schools, commercial organications, government, military sites and individuals in almost all countries around the world.电脑网络简述网络可被定义为人、资源和思想的联接。
土木工程专业毕业设计外文文献翻译2篇
土木工程专业毕业设计外文文献翻译2篇XXXXXXXXX学院学士学位毕业设计（论文）英语翻译课题名称英语翻译学号学生专业、年级所在院系指导教师选题时间Fundamental Assumptions for Reinforced ConcreteBehaviorThe chief task of the structural engineer is the design of structures. Design is the determination of the general shape and all specific dimensions of a particular structure so that it will perform the function for which it is created and will safely withstand the influences that will act on it throughout useful life. These influences are primarily the loads and other forces to which it will be subjected, as well as other detrimental agents, such as temperature fluctuations, foundation settlements, and corrosive influences, Structural mechanics is one of the main tools in this process of design. As here understood, it is the body of scientific knowledge that permits one to predict with a good degree of certainly how a structure of give shape and dimensions will behave when acted upon by known forces or other mechanical influences. The chief items of behavior that are of practical interest are (1) the strength of the structure, i. e. , that magnitude of loads of a give distribution which will cause the structure to fail, and (2) the deformations, such as deflections and extent of cracking, that the structure will undergo when loaded underservice condition.The fundamental propositions on which the mechanics of reinforced concrete is based are as follows:1.The internal forces, such as bending moments, shear forces, and normal andshear stresses, at any section of a member are in equilibrium with the effect of the external loads at that section. This proposition is not an assumption but a fact, because any body or any portion thereof can be at rest only if all forces acting on it are in equilibrium.2.The strain in an embedded reinforcing bar is the same as that of thesurrounding concrete. Expressed differently, it is assumed that perfect bonding exists between concrete and steel at the interface, so that no slip can occur between the two materials. Hence, as the one deforms, so must the other. With modern deformed bars, a high degree of mechanical interlocking is provided in addition to the natural surface adhesion, so this assumption is very close to correct.3.Cross sections that were plane prior to loading continue to be plan in themember under load. Accurate measurements have shown that when a reinforced concrete member is loaded close to failure, this assumption is not absolutely accurate. However, the deviations are usually minor.4.In view of the fact the tensile strength of concrete is only a small fraction ofits compressive strength; the concrete in that part of a member which is in tension is usually cracked. While these cracks, in well-designed members, are generally so sorrow as to behardly visible, they evidently render the cracked concrete incapable of resisting tension stress whatever. This assumption is evidently a simplification of the actual situation because, in fact, concrete prior to cracking, as well as the concrete located between cracks, does resist tension stresses of small magnitude. Later in discussions of the resistance of reinforced concrete beams to shear, it will become apparent that under certain conditions this particular assumption is dispensed with and advantage is taken of the modest tensile strength that concrete can develop.5.The theory is based on the actual stress-strain relation ships and strengthproperties of the two constituent materials or some reasonable equivalent simplifications thereof. The fact that novelistic behavior is reflected in modern theory, that concrete is assumed to be ineffective in tension, and that the joint action of the two materials is taken into consideration results in analytical methods which are considerably more complex and also more challenging, than those that are adequate for members made of a single, substantially elastic material.These five assumptions permit one to predict by calculation the performance of reinforced concrete members only for some simple situations. Actually, the joint action of two materials as dissimilar and complicated as concrete and steel is so complex that it has not yet lent itself to purely analytical treatment. For this reason, methods of design and analysis, while using these assumptions, are very largely based on the results of extensive and continuing experimental research. They are modified and improved as additional test evidence becomes available.钢筋混凝土的基本假设作为结构工程师的主要任务是结构设计。
软件工程专业毕业设计外文文献翻译
软件工程专业毕业设计外文文献翻译1000字本文将就软件工程专业毕业设计的外文文献进行翻译，能够为相关考生提供一定的参考。
外文文献1: Software Engineering Practices in Industry: A Case StudyAbstractThis paper reports a case study of software engineering practices in industry. The study was conducted with a large US software development company that produces software for aerospace and medical applications. The study investigated the company’s software development process, practices, and techniques that lead to the production of quality software. The software engineering practices were identified through a survey questionnaire and a series of interviews with the company’s software development managers, software engineers, and testers. The research found that the company has a well-defined software development process, which is based on the Capability Maturity Model Integration (CMMI). The company follows a set of software engineering practices that ensure quality, reliability, and maintainability of the software products. The findings of this study provide a valuable insight into the software engineering practices used in industry and can be used to guide software engineering education and practice in academia.IntroductionSoftware engineering is the discipline of designing, developing, testing, and maintaining software products. There are a number of software engineering practices that are used in industry to ensure that software products are of high quality, reliable, and maintainable. These practices include software development processes, software configuration management, software testing, requirements engineering, and project management. Software engineeringpractices have evolved over the years as a result of the growth of the software industry and the increasing demands for high-quality software products. The software industry has developed a number of software development models, such as the Capability Maturity Model Integration (CMMI), which provides a framework for software development organizations to improve their software development processes and practices.This paper reports a case study of software engineering practices in industry. The study was conducted with a large US software development company that produces software for aerospace and medical applications. The objective of the study was to identify the software engineering practices used by the company and to investigate how these practices contribute to the production of quality software.Research MethodologyThe case study was conducted with a large US software development company that produces software for aerospace and medical applications. The study was conducted over a period of six months, during which a survey questionnaire was administered to the company’s software development managers, software engineers, and testers. In addition, a series of interviews were conducted with the company’s software development managers, software engineers, and testers to gain a deeper understanding of the software engineering practices used by the company. The survey questionnaire and the interview questions were designed to investigate the software engineering practices used by the company in relation to software development processes, software configuration management, software testing, requirements engineering, and project management.FindingsThe research found that the company has a well-defined software development process, which is based on the Capability Maturity Model Integration (CMMI). The company’s software development process consists of five levels of maturity, starting with an ad hoc process (Level 1) and progressing to a fully defined and optimized process (Level 5). The company has achieved Level 3 maturity in its software development process. The company follows a set of software engineering practices that ensure quality, reliability, and maintainability of the software products. The software engineering practices used by the company include:Software Configuration Management (SCM): The company uses SCM tools to manage software code, documentation, and other artifacts. The company follows a branching and merging strategy to manage changes to the software code.Software Testing: The company has adopted a formal testing approach that includes unit testing, integration testing, system testing, and acceptance testing. The testing process is automated where possible, and the company uses a range of testing tools.Requirements Engineering: The company has a well-defined requirements engineering process, which includes requirements capture, analysis, specification, and validation. The company uses a range of tools, including use case modeling, to capture and analyze requirements.Project Management: The company has a well-defined project management process that includes project planning, scheduling, monitoring, and control. The company uses a range of tools to support project management, including project management software, which is used to track project progress.ConclusionThis paper has reported a case study of software engineering practices in industry. The study was conducted with a large US software development company that produces software for aerospace and medical applications. The study investigated the company’s software development process,practices, and techniques that lead to the production of quality software. The research found that the company has a well-defined software development process, which is based on the Capability Maturity Model Integration (CMMI). The company uses a set of software engineering practices that ensure quality, reliability, and maintainability of the software products. The findings of this study provide a valuable insight into the software engineering practices used in industry and can be used to guide software engineering education and practice in academia.外文文献2: Agile Software Development: Principles, Patterns, and PracticesAbstractAgile software development is a set of values, principles, and practices for developing software. The Agile Manifesto represents the values and principles of the agile approach. The manifesto emphasizes the importance of individuals and interactions, working software, customer collaboration, and responding to change. Agile software development practices include iterative development, test-driven development, continuous integration, and frequent releases. This paper presents an overview of agile software development, including its principles, patterns, and practices. The paper also discusses the benefits and challenges of agile software development.IntroductionAgile software development is a set of values, principles, and practices for developing software. Agile software development is based on the Agile Manifesto, which represents the values and principles of the agile approach. The manifesto emphasizes the importance of individuals and interactions, working software, customer collaboration, and responding to change. Agile software development practices include iterative development, test-driven development, continuous integration, and frequent releases.Agile Software Development PrinciplesAgile software development is based on a set of principles. These principles are:Customer satisfaction through early and continuous delivery of useful software.Welcome changing requirements, even late in development. Agile processes harness change for the customer's competitive advantage.Deliver working software frequently, with a preference for the shorter timescale.Collaboration between the business stakeholders and developers throughout the project.Build projects around motivated individuals. Give them the environment and support they need, and trust them to get the job done.The most efficient and effective method of conveying information to and within a development team is face-to-face conversation.Working software is the primary measure of progress.Agile processes promote sustainable development. The sponsors, developers, and users should be able to maintain a constant pace indefinitely.Continuous attention to technical excellence and good design enhances agility.Simplicity – the art of maximizing the amount of work not done – is essential.The best architectures, requirements, and designs emerge from self-organizing teams.Agile Software Development PatternsAgile software development patterns are reusable solutions to common software development problems. The following are some typical agile software development patterns:The Single Responsibility Principle (SRP)The Open/Closed Principle (OCP)The Liskov Substitution Principle (LSP)The Dependency Inversion Principle (DIP)The Interface Segregation Principle (ISP)The Model-View-Controller (MVC) PatternThe Observer PatternThe Strategy PatternThe Factory Method PatternAgile Software Development PracticesAgile software development practices are a set ofactivities and techniques used in agile software development. The following are some typical agile software development practices:Iterative DevelopmentTest-Driven Development (TDD)Continuous IntegrationRefactoringPair ProgrammingAgile Software Development Benefits and ChallengesAgile software development has many benefits, including:Increased customer satisfactionIncreased qualityIncreased productivityIncreased flexibilityIncreased visibilityReduced riskAgile software development also has some challenges, including:Requires discipline and trainingRequires an experienced teamRequires good communicationRequires a supportive management cultureConclusionAgile software development is a set of values, principles, and practices for developing software. Agile software development is based on the Agile Manifesto, which represents the values and principles of the agile approach. Agile software development practices include iterative development, test-driven development, continuous integration, and frequent releases. Agile software development has many benefits, including increased customer satisfaction, increased quality, increased productivity, increased flexibility, increased visibility, and reduced risk. Agile software development also has some challenges, including the requirement for discipline and training, the requirement for an experienced team, the requirement for good communication, and the requirement for a supportive management culture.。
本科毕业设计外文文献及译文
本科毕业设计外文文献及译文文献、资料题目：Structural Design of ReinforcedConcrete Sloping Roof文献、资料来源：网络文献、资料发表（出版）日期：2007.1院（部）：xxx专业：xxx班级：xxx姓名：xxx学号：2007011287指导教师：xxx翻译日期：xxx外文文献：Structural Design of Reinforced Concrete Sloping Roof Abstract: This paper point out common mistakes and problems in actual engineering design according immediately poured reinforced concrete sloping roof especially common residential structure.It brings out layout and design concept use folded plate and arch shell structure in order to reduction or elimination beam and column Layout to reduce costs and expand use function for user of garret . The paper also discussed the need to open the roof holes, windows, and with other design with complex forms . The corresponding simple approximate calculation method and the structure treatment also described in this paper.Keywords : sloping roof;folded plate; along plane load;vertical plane load1. IntroductionIn recent years, reinforced concrete slope of the roof has been very common seen, the correct method of it’s design need establish urgently It’s target is to abolish or reduce the roof beams and columns, to obtain big room and make the roof plate "clean ". This not only benefits tructure specialty itself but also to the design of the building professionals to develop new field, and ultimately to allow users, property developers benefited,and so it has far-reaching significance.In the common practice engineering practice, a designer in the calculation of the mechanical model often referred sloping roof as vertical sloping roof under the projection plane Beam, or take level ridge, ramps ridge contour as a framework and increase unnecessary beam and tilt column . In fact ,the stress is similar between General square planar housing, double slope, multi-slope roof and arch, shell.Ping and oblique ridge are folded plate like “A”, whether layout beams and columns, its ridge line of the deformation pattern is different from the framework fundamentally. All these method will make the difference between calculation results and real internal structure force. During the construction process, housing backbone, plate bias department template has complex shapes, multi-angle bars overlap, installation and casting is very difficult. These projects are common in construction and is a typical superfluous. Some scholars use the elastic shell theory to analyze folded plate roof、internal force and deformation, reveals the vertical loads law of surrounding the base is neither level rise nor the vertical displacement whichto some extent reflects the humps and shell’s features .But assume that boundary conditions which is very different from general engineering actual situation and covered the eaves of a vertical cross-settlement and bottom edge under the fundamental characteristics of rally, so it is not for general engineering design .2. Outlines of MethodsFor most frequently span, the way to cancel the backbone of housing, didn’t add axillary often. But in the periphery under the eaves to the framework need established grid-beam or beams over windows. For long rectangular planar multi-room, multi-column, building professionals in a horizontal layout of the partition wall between each pair of columns and the direction set deep into the same thickness width have possession of a gathering of the rafah beam profiles . Pull beam above has a two-slope roof plate affixed sloping beams expect smaller span. For residential, if it has no needs according construction professional, we will be able to achieve within the household no ceiling beams exposed, see figure 1. Similar lattice theory, this approach emphasizes the use of axial force component effect, But is different with the truss because it’s load distribution along the bar not only single but also along the axis of the plate. Generally each plate has force characteristics of folded plate, for bear gravity at the roof, wind, earthquake loads, caused the plate along with the internal force components, each plate is equivalent to strengthen the thin flange beams .Among vertical bearing , it is thin-walled beams anti-edge horizontal component to balance Wang thrust formed by arch shell effect. When plates bear the the vertical component load, each plate is equivalent to a solid edge embedded multilateral bearing plates .The design feature of this method is establish and perfect the sloping roof of the arch, folded plate system Consciously, at top of the roof, using a minimal level of rafah balance beam ramp at the level of thrust.It’s calculation methods can be divided into hand algorithm and computer paper, this paper focus on the hand algorithm.Hand algorithm take the single-slope plate of sloping roof plate as slider , through approximate overall analysis, Simplified boundary conditions of determine plate,solving load effect along level and vertical plane, Internal forces of various linear superposition under the condition of assumption of normal straight, testing stability and integrated reinforcement. The method pursuit of operational, use general engineer familiar calculation steps to address more complex issues.This method is suitable for the framework structure, little modifications also apply to masonry structure or Frame-wall structure. General arch structure have good anti-seismic performance, if designed properly, the sloping roof will also do so. In this paper the pseudo-static is used to analysis earthquake effects.3. Analysis and Design for Along Plane Effect of LoadsFirst regard to cross profile of figure 1,we analysis equal width rectangular parts of long trapezoidal panels 1、2. as for approximate calculation,it is take plane loads along plane as a constant just like four rectangular plate can be simplified to one-way slab,we take along to long unit width narrow structure as analysis object ,take hinged arch model shown in figure 2.图2a图3a图2b图3b图2c图3cIn Figure 2 the right supports vertical linkage representatives roof beams supporting role, ramps connecting rod on behalf of the board itself thin beam reaction effect which is virtual and approximate equivalent. We would like to calculate two anti-bearing.Because the total pressure of physical project through two plate roof beams and transfer to the ends column, So Anti two numerical difference can be seen as two plates bear along with the plane load and roof beams bear the vertical load pressure. Two Anti power link expressions in Various conditions were given as follows, because the model take units width,so the results is line averageload distribution except it has Focus quality in house.They are bouth represent by N , English leftover subscript s, b, represent the plane along the roof panels and vertical role in the roof beam, g, w, e,represent gravity, air pressure and the level of earthquake separately. d, c, represent distribution of concentrated load or effect separately, In the formula h is thicness of every plate,g is gravitation acceleration, a is roof for the horizontal seismic acceleration value formula, Wk represent the standard value Pressure.m with number footnotesrepresent every numbered ramp the quality distribution per unit area ,m with english footnotes represent quality of per location.as to two symmetrical slopes, the formula can be moreconcise.Figure 2a represent situation of vertical gravity load ,these formulas as follows:()()'''111100110cos cos 38cos cos cos cos L AL L m L AL N l h l h l m ωαβμααββ-=++ ()()()()'10000000101'100000cos cos 2cos cos 8sin cos 8sin cos cos 8sin cos cos cos l l l l l h m m s h N l l h h l h l μαβωααηαβωμβββαββααβ++-=--++ ()()()()101101110100001012111cos 2cos cos 2L L L L L L L m LL L L mLL L L L L L N h B hL hL LIμξβαβ⎡⎤⎛⎫⎛⎫⎛⎫--+-+--+⎢⎥ ⎪ ⎪ ⎪⎝⎭⎝⎭⎝⎭⎣⎦=++()()()()()001001110011200101021000110111121cos sin 2sin 2sin cos cos A L h L m LL L L mL L m a L L L L h h L m l m N L L L Ah L L k B h L h L δδββββαβ⎛⎫⎛⎫⎡⎤⎛⎫-+-+--+ ⎪ ⎪ ⎪⎢⎥+⎝⎭⎝⎭⎝⎭⎣⎦=+---++Figure 2b represent situation of bear wind load, these formulas as follows:()()222211122111cos cos cos 8cos cos cos cos wkL h L L S li N a L h h b ωαωββαβα-=++ ()()()()22222001111222212110cos cos cos 11cos cos cos cos sin 5cos sin cos cos sin cos k K L h l w L w w h w h m L N l l AL h L a h L αωαβαβλαβααββββαββ⎡⎤-⎡⎤+⎢⎥=+++-+⎢⎥++⎢⎥⎣⎦⎣⎦Figure 2c represent situation of role of level earthquake, these formulas as follows:()()2222210011022001sin cos sin cos 3sin cos cos cos cos cos a a L h l L L N L h l hl αμβαωαβωβδαβαβδβ+=--+ ()()()()222221011120322222102101sin cos sin cos sin sin sin 3cos 2ln cos 5ln cos cos cos cos a l h m l m L m m m N n s l l l g h l h l δβααβαββββαβαβαβ++=++++ ()()()0010011012110121000111sin cos 2cos 2cos cos cos a a L L m L L L n L L L L L nh L N L l h l h l ββαβαβ⎡⎤⎛⎫⎛⎫-+-+⎢⎥ ⎪ ⎪⎝⎭⎝⎭⎢⎥=+⎢⎥+⎢⎥⎢⎥⎣⎦ ()00000201sin 2cos a a L m L L L h L l θβα⎡⎤⎛⎫-+-⎢⎥ ⎪⎝⎭⎣⎦+()()()2000010121001sin sin cos sin cos sin cos cos 2sin cos a e L m L L L h L m m N l l h βααβαββαβββ⎡⎤⎛⎫-+-⎢⎥ ⎪+⎝⎭⎣⎦=-+()()()001001001221111221001sin 1sin cos 2cos 2cos cos cos sin a a L L L L L L m L L L L L h L h l L h l h ωαββαβαββ⎡⎤⎛⎫⎛⎫-+-+⎢⎥ ⎪ ⎪⎝⎭⎝⎭⎢⎥-+⎢⎥+⎢⎥⎢⎥⎣⎦ When vertical seismic calculation required by Seismic Design ParametersIt’s calculate formula generally similar as formula 1 to 4 which only need take gravity g as vertical seismic acceleration a. Above formulas apply to right bearings in figure 2 and also to left when exchange data of two plate.As end triangle of Multi-slope roof ,for simplify and approximate calculation need, we assume two lines distribution load only produced by roof board of several load, effect.now II-II cross-section from figure is took to analysis Long trapezoidal plate two’s end triangle, assuming the structure symmetry approximately, take half of structure to establish model (figure 3). Because linked with the end triangular plate-3 plane has great lateral stiffness ,therefore assume the model leftist stronghold along the central component around which can not be shifted direction. Central Plate vertical stiffness small, in general gravity load of roughly symmetric midpoint only next movement happened possible, Therefore, the model used parallel two-link connection. Wind loading, and the general role of the earthquake in two slope was roughly antisymmetric,so plate model in the central use fixed hinge bearings which allow rotation and transtlateral force to plate 3near the plate beam. Under plate two triangular area is eaves of vertical beams and plates itself along with plane load distribution is functionshown in Figure 1 take the variable x as an argument,assume the distance from position of section II to end part is x 0s so the slope level length is y 0=x 0L 2/L 3,formula 11 to 14 is the value of Vertical triangle of gravity along the x direction arbitrary location of the two load distribution ,where h 3 is Slitting vertical thickness of plate 3.()22001cos 212cos e a a mkxL h x N L sh v l x ββ⎡⎤=-⎢⎥+-⎢⎥⎣⎦ ()211121001sin cos 212cos m kvL h x N l xh x L V βββ⎡⎤=+⎢⎥+-⎢⎥⎣⎦()22000002221100max 1123cos L La h L L L L N VL h h l a V L L αγβ⎡⎤⎛⎫=---⎢⎥ ⎪+-⎢⎥⎝⎭⎣⎦ ()22201000112222201001ln 23cos a L L h l L L L n V s xl h v h L x x l L ββ⎡⎤⎛⎫=+-⎢⎥ ⎪+-⎢⎥⎝⎭⎣⎦As wind load and earthquake effect, sketch could use approximate figure 3b 、3c and use method of structural mechanics to solve But the process is cumbersome and reasonable extent is limited .the wind and earthquake effect is not important compare with the load effect. Moreover, the triangle area is small As approximate calculation, such direct-use rectangular plate slope calculation is more convenient and not obvious waste. The method of solve two load distribution of plate three is same as the solution of Long trapezoidal plate area just make the change of x and y 、L 2 and L 3 in figure 1.The actual profile is part III-III shown in figure 1 A BC 图4a 图4b BDFigure 4 is vertical launch plan and bear load portfolio value of roof ramp shown in Figure 1 to analysis inclined plate and the internal forces of the anti-bearing column . in the figure hypotenuse is oblique roof equal to strengthen frame, Similar wind ramp truss rod and the next edge portfolio, could form the dark truss system ,while long rectangular plate can be seen as part of thin-walled beams, which could also be seen as truss. Therefore, we called roof boarding the plane formed a "thin-walled beam-truss" system, in concrete theory, between the truss and the beam have no natural divide . it’s no need h and count accurate internal forces and bearing force to such a joint system, Because on the one hand span more, big bending stiffness structure sensitive to the bearing uneven subsidence and have to stay safe reserves; on the other hand it has high cross-section, by increasing reinforced to increase capacity on the cost impact is not significant. Specific algorithm is: Single-ramp calculate by simple cradle, Multi-Span ramp’s bending moment, shear, and supporting anti-edge use the calculate value by the possiblemaximum numerical control methods, Moment is calculate by simple cradle two sides of supports middle Shear, negative moment and support force calculate according to bearing this continuous, two-hinged, about two span take the largest one. Pin-Pin bearing shear force that is supported by the inter-simple calculate according to simple cradle. But in this method the location of the various internal force’s safety level is uneven expansion, appropriate adjustment should be made is late calculation. No mater f the triangular or rectangular part of plate, Thin-plane bending rebar can get by method of moment right boards from the bottom point for the moment distance which assigned to the eaves or roof. The author believe it has no necessary control number of reinforcement according to smallest beams reinforced rate. On the rim of triangle equivalent to ramp strut can shear entirety. when consider the end is weak can properly reinforced its roof beam below the reinforcement. If shear required stirrup in the rectangular part of thin-walled, should superposition to the beam, generally it’s no need to intentionally imaginary abdominal strengthening reinforcement at rod position.4. Calculation and Design of Pull Beam and Roof BeamsBy column in figure 1 marked calculated value of supporting force and their level of vertical component, horizontal component of the total force multiplied by the cosine of angle. Take column A as example, the first footnotes in R A2 is column number, the first footnotes represent the force generated by the panel two. Their horizontal component balanced by triangle three under the eaves of beams. horizontal component of intermediate support reaction is balanced by the two-level pull beam in deep direction. Then pull beam and above the sloping beams constitutes steel Arch. Because of the existence of antisymmetric load, bilateral role in the anti-power-level components may be inconsistent and pull beam should take the average lag. consider the support impact of uneven settlement, the level pull beam design should take bigger value.Roof beams general under four internal forces: First of the above is levels Rally, The second is axial force generated when oblique roofing in the flange plate plane bending. The third is the vertical load to bear as the roof slab edge beams under bending moment, shear ,like board supported by multi-faceted, Actual force is smaller than bear calculated by one-way plate N b,Fourth is the effect of lateral framework of internal forces .it should linear superposition ,Composite Reinforced, in the situation of weight Load, span and the small dip,checking computations should be took for tension beams cracking, appropriate intensify the section, with fine steel, including the side beams of steel beams rafah terminal should take two meander anchorage,just like letter L With ng as 10d long bends, meander 135 degrees angle and put pull beam intersection with the vertical reinforcement column touting the Meander overcast horn.This paper take model in figure 1 as example, ignore tigers window , 4 sloping roof are 35 o angle, the length of roof slab dimensions are shown in figure 4. Plate unit area quality is 350 kg/m2,Overhaul live load is 0.50 kN/m2, Pressure standard of windward side is 0.21 kN/m2, Leeward face is -0.45 kN/m2, Design value of roof horizontal seismic acceleration is 0.1g, Calculate the bearing capacity limit by standardizing, Considered separately with and without seismic load effect of the combination basic design value,we use combination of without earthquake force through compare，Load calculation and analysis results of every position shown in table 1:Roof triangular plate3 the long trapezoidal plate2D～A B=800m A～B L=11.00m B B～C L=12.00mSymbol Units Formula D Span A FormulaA SpanB B Span CSurface load Seismic loadwithoutpermanentstandardN kN/m (11) 0-18.62 18.6218.62-0 (2) 0-18.62 18.6218.6218.6218.62 18.62-0No seismic loadstandard oflivingN kN/m (11) 0-2.66 2.66 2.66-0 (2) 0-2.66 2.66 2.66 2.66 2.66 2.66-0Seismic gravityload arepresentativeN kN/m (11) 0-19.95 19.9519.95-0 (2) 0-19.95 19.9519.9519.9519.95 19.95-0valueWind Load N kN/m (6) Parallel with the wind at theplate(6) 0-0.76 0.76 0.76 0.76 0.76 0.76-0Earthquake level role N kN/m (8) Earthquake direction parallelwith the board and notconsidered(8) 0-2.09 2.09 2.09 2.09 2.09 2.09-0Momen t Moment designvalueM kN﹒m 151.36429.25-510.84-510.84510.84Axial force N kN 34.4497.67116.24116.24116.24Shear V kN 56.76 56.76 156.09 212.85212.85170.28Anti vertical edge R kN 56.76 56.76 156.09 212.85425.70212.85170.28Anti level of R kN 46.50 46.50 127.86 174.35 348.71174.35139.49Vertical and horizontal beams pull beam Rally kN A～B 46.50 A～D 127.86 348.71Column C and beamdirection betweencolumns139.495. Analysis and Design for Roof of the Vertical Loads Under Sloping RoofSlabs as a Multilateral Support PlateFolded plate structure has character of “unified of borad and frame”: General intersection of each pair of ramps are for mutual support, both sides of the transition line’ plate can be counted dogleg small rotation and transmission, distribution Moment.Under load control which is the role of gravity the two sloping geometry load roughly symmetrical occasions, there is no corner at symmetry capital turning point, Approximate seen as the plate embedded solid edge.if take out a distance by plate of eaves, plate of inside ridge also formation to negative moment,and longroof slabs in the plate sloping beams department and neighbor plate linked together, these all can be approximated as embedded-plate edge to process.For antisymmetric load like horizontal seismic load,the Ping roof should be treated as shear,but it is not control load usually. Plate final design moment value is the status of various unfavorable combination of linear superposition, from the cross-sectional direction plate reinforced by the columns, Reference, balance the require of concrete deep beams of tectonic, upper plate for Moment of negative reinforcement should be reinforced at all or an entire cross-leader, as they also serve as a deep beam distribution lumbar tendons or stirrup. plate in the bottom vertical with reinforcement eaves, Negative reinforcement in accordance with their respective calcualte requirements,and it is different after superposition stirrups requirementBoth sides of "stirrup" in this situation cann’t linked at awnings edge follow shape “U”, can be bent to shape "L" follow upper and down direction,legnth of packs could equal to thickness of plate.It should enhenced at the node of ramp at the intersection appropriately. It recommended that use swagger tectonic shown as in Figure 5 considing simple structure without axillary at the situation of Cloudy angle without pull. To ensure all reinforced Installing accuracy, Few of the rhombus with the supports and rebar stirrups could be added to formed positioning Skeleton at strengthening reinforced department in the figure, Let two later installed sloping steel plate tie to its lashing,designers should use a three-dimensional geometric method to accurately calculate the diamond stirrups limb edge length and Forming a swagger construction plans6. Calculating and processing of open window and hole in sloping roof Assume the plate in figure 6 has a big hole whose wideth is b ,height is h0 ,assuming that tung center along with the plane bending moment, shear, respectively are M and V through overall calculation, use vierendeel calculation method get about middle cave:1XO MM T τ= 2NR MM T τ=3113312h V V h h =+ 0X O N R M M M V h --= Where I 1、I 2 、I respectively represent upper and down plate limb’s Section moment of inertia anddouble limbs section moment of inertia.while Edge Moment by hole is:1113I M V b M α=+ 2212I M V b M μ=+ not very big by the hole, close to the neutral axis in most cases overall, under the no-hole designof the reinforced the opening hole after the plane can meet the demands by calculation,under theno-hole design of the reinforced the opening hole after the plane can meet the demands bycalculation.General tiger window’s form prominent roof Facade which a hole had opened up and the otherfaces a concrete slab closed.when analysis of vertical slab roof slab surface loads ,compare withwithout windows and roof slabs hole window sheet increased load. profiles of window’s foldedplate form make it reduce the bending stiffness compare with without hole roof board, But withthe profile hole edge which parallel to the vertical plate is a partial increase in bending stiffness.In the absence of the vertical plate window subordinate legislation should have upturns beam toincrease stiffness of the surrounding caves near.in this way i can temporarily ignore the platestiffness variation acording to the actual load, size and boundary conditions by entities plate tocalculate psitive and negative moment and further processing nodes.it should point out thattheRoof ramp layout hole edge ideal location is near the plate-bending line, especially in theopen side of the window because it was cut down byvertical transmission line of the moment. If the roof slab roof beams department no outward roofthen the actual plate-bending force on the line near the roof beam reversed also true, Because ofthis architects should strive for when determine oosition of tiger position take appropriatecare.When pin tung far away from line-bending window wall and roofing in the intersection mustbear folded plate and transmission moment, but compare with plate without hole its capacity isweaken surely,and it’s node turn into weak parts. To fill thy judgment and calculation errorstwo panels can be double reinforcement. When the hole is less than line-bending scope shouldincrease negative reinforcement around to keep overall security plate bearing capacity. To ensuresteel plate in place accuratly,also should use positioning stirrups and longitudinal reinforcement constitute skeleton similar as figure 5. Hoop end within vertical bars should be strengthen steel and end cave corner should be harvested more than one anchor length to make sure that bottom of the cave 4 tensile stress concentration.7. Stabilize Roof SlopeIn China's V-shaped folded plate structure design norms,the method prevent both sides of the flanges at local instability is limit its generous ratio,This requirement come from the use of isotropic plate buckling theory analysis. In research the flanges outside instability in critical state, the boundary conditions of winglets suppose as freedom outside, fixed interior, pre - and post-hinged on both sides,the situation plates subjected to the bending stress to solve width and height ratio corresponding with the critical pressure compressive stress. When the grade of concreteIs C30,the limit of width and height(b/t)ratio is 47, take 35 as stress non-normative value. Concrete elastic modulus and strength levels is not a linear relationship if use high-strength concrete other study should be taken. In the actual slope roof only a long row to the middle plate bearing plate outside may receive pressure. And here is just the pouringplate affixed roof sloping beams and horizontal pull beam cast together.Have no possible of rollover and foreign rising displacement. norms limited of folded plate span is 21m. roof below and the vertical column spacing generally much smaller it. And the board which into one with roof beams changed boundary conditions of plate, anti-great instability role also very big. For other locations ramp vertical compression edge May also set up the appropriate plate edge beams all these method will receive beyond the norms of redundant safety. Taking into account the plate shear plane, while the vertical direction of the load caused the exit plane effects, Therefore, the grasp of security of caution should cautious. This paper proposed ramp thickness not less than to the short span of 1 / 35 which also conform to design experience of generally confined SLABS, Concrete should graded between C25 and C35 while Steel should I or class II.puter Calculation Method of Local Sloping Roof Structure andOverall ICC of Overall StructureAny calculate software with inclined plate shell modules and the modules bar structural finite element can calculation of competent sloping roof. Shell element of each node have 3 membrane freedom and three panels freedom and can analysis the plane board and internal forces Of out-of-plane effects. However, the current prevalence of certain spatial structure finite element computer program which although have shell model but some are not inclined plate, some not right at the same plane, the stress state and foreign integrated reinforcement are not perfect. With structures becoming more diverse, complex and ramp space problems often encountered. Such software should expand its pre - and post-processing functions for conversion of shell element stiffness matrix and loading vector in the direction of freedom and further analysis of ramp space, the space of concrete against stress integrated reinforcement. In a fundamental sense manual method and the finite element method are interchangeable but the result may be very different. As long as layout roof component as this concept,then use the software to calculate can fast, precise, to achieve this goal of this paper.From the eaves to the roof elevation areas, the whole roof of anti-lateral stiffness lower than mutation, quality small than lower,this could not easy to simulate in calculation of whole housing. At the top construction of the seismic as higher-mode response which is also whiplash effect, the earthquake-lateral force may be abnormal and have effect on under layers. Therefore, in the partial hand count roof occasions when take ICC analysis to the overall structure, it proposed roof layer use model of tilt rod ramp support to reduce effect on the overall results distortion.If use software with function of space ramp handling and sloping roof modeling with shell element,all will be wrapped from top to bottom. Top results can be directly used and the distortion of the overall impact would cease to exist.10. Conclusion1）Concrete ramps, side beams in different directions superposition of internal forces, reinforced and ramp stability, the hole limits all to be do in-depth study related this research. Similar typical problems are top floor of structural transformation layer and box-type base box side wall all their research results can be used to adopt.It’s a important method do observation on project; finite element analysis ICC will be more economical, practical and popular. Currently existing completed sloping roof no matter the subjective designers use what kind of assumptions。
毕业设计文献翻译英文原文
Tooth contact analysis of a misaligned isostaticplanetary gear trainDaniele VecchiatoVia G.Garibaldi,24,33050Castions di Strada,UD,ItalyReceived 3May 2005;received in revised form 26August 2005;accepted 5October 2005Available online 1December 2005AbstractAn isostatic planetary gear train is considered.This mechanism is capable of self-regulation for compensation of var-ious errors of alignment.Localization of bearing contact and application of tooth contact analysis (TCA)are provided.Trajectory of the floating member and function of transmission errors are obtained for several errors of alignment.Ó2005Elsevier Ltd.All rights reserved.Keywords:Isostatic planetary gear train;Floating sun;TCA;Localization of bearing contact1.IntroductionPlanetary gear trains have attracted the attention of designers for the possibility of efficient and quiet trans-formation of rotation as well as the transmission of large torques with gears of relatively small dimensions.This advantage is subordinated to the application of several planet gears for sharing of the total torque.How-ever,experimental evidence and theoretical analysis have proven that the distribution of the load among the planets is generally not uniform.Improvement of load distribution is one of the main goals of design of planetary gear trains and it is a topic of broad literature.Load distribution in planetary trains has been determined experimentally in the works [1–3].Effect of tol-erances of manufacture and assembly have been considered.Static and dynamic models have been considered for conceptual presentation of the problem of non-uniform load distribution,[4–6].The researchers agree that one of the main factors affecting the load distribution is the number of planet gears,that is usually limited to five (rarely to six).It was shown that the load distribution may be improved due to elastic deformations.An original approach has been proposed for regulation of installment of planet gears on the carrier for improvement of the load distribution not requiring large elastic deformations [7].The approach is based on modification of geometry of planet gears and regulation of installment performed during the process of assembly.0094-114X/$-see front matter Ó2005Elsevier Ltd.All rights reserved.doi:10.1016/j.mechmachtheory.2005.10.001E-mail address:daniele@Mechanism and Machine Theory 41(2006)617–631andMachine TheoryAnother approach is based on design of a planetary gear train that allows self-regulation of position of the mating members during the process of rotation.This may be achieved by removing of some constraints of the gear train,designed as a mechanical system of rigid bodies with floating members.This concept is the basic principle of design of the so-called isostatic planetary gear train.Such a train is designed as a multi-body system formed by several planet gears being in mesh with mating gears simultaneously.The concept of an isostatic planetary gear train with three planets has been considered conceptually,on the basis of the balance between the parameters of motion of the bodies and the provided constraints including,as a constrain,the angular position of the input link.The case of a floating (unconstrained)sun gear has been considered in work [2],wherein the trajectory of the sun gear has been measured.In works [4,8]it has been proven that at high speed of rotation,due to dynamics of the loaded gear drive and frictions,the load distribution between the planets is not an uniform one.The contents of the paper cover:(i)Analysis of structure of an isostatic planetary gear train for various cases.(ii)Avoidance of edge contact in meshing by localization of tangency of tooth surfaces and by providingdouble crowning (see Section 3).(iii)Analytical analysis of conditions of meshing of tooth surfaces of a misaligned planetary gear train.Theanalysis is computerized by application of developed TCA (tooth contact analysis)computer program (see Section 4).(iv)Proof that the self-regulation of position of links of train exists indeed,and determination of trajectoriesand transmission errors resulted from applied errors of alignment.The contents of the paper cover a planetary gear train with three planets,but developed ideas are presented for a general case.Numerical examples for illustration of developed theory are provided.2.Structure of an isostatic gear trainThe analysis of the structure of a planetary gear train (Fig.1)is based on the balance between the possible degrees of freedom of movable links and the constraints beingprovided.618 D.Vecchiato /Mechanism and Machine Theory 41(2006)617–631Henceforth we will consider that all members of the mechanism perform planar motions identified by three parameters(degrees of freedom):the lateral position of the axis of rotation,and the angular position of the member of the planetary gear train.The planetary gear is formed by three bodies(ring and sun gears,and the carrier)and N p planet gears.The total number of degrees of freedom is determined as N f=9+3N p.In order to design an isostatic planetary gear train,the number of constraints N c has to be equal to the number of degrees of freedom N f of the links.Initially,assume that(i)the angular position of the input shaft is given(one constraint),(ii)the ring gear is fully constrained(three constraints),(iii)each planet gear is pinned on the carrier(two constraints for each planet gear),and(iv)each planet gear is in tangency simultaneously with the sun and ring gears(two constraints per planet).These conditions provide a total of N c=4+4N p constraints.Under these conditions,taking N f=N c,the planetary gear becomes isostatic for N p=5planet gears.Axes of the sun gear and the carrier are free.Continuing the analysis,we may assume that one axis of the two(suppose the carrier)isfixed.Then,twoadditional constraints are provided and N0c ¼6þ4N p.Taking N0c¼N f,we willfind that the train may beprovided with N p=3planets.In the case wherein also the remaining axis isfixed,we obtain an isostatic gear train with one planetary gearonly.The result is obtained taking N00c ¼8þ4N p¼N f,that yields N p=1.The most common configuration of a planetary train is the following one:N p=3,the axis of the carrier isfixed,and the axis of the sun gear is free(it mayfloat).Although the following discussions are referred to this specific case,the ideas of the structure of an isostatic train are general and may be applied to various cases.3.Localization of contactApplication of spur and helical gears in planetary gear trains is common in design.Tooth surfaces of such gears contact each other along a contact line under the condition the gear train is an aligned one.However,it has been found that these gears are very sensitive to misalignment[9].Therefore,the geometry of the gears has to be modified as an additional requirement of the design of this train.Henceforth,we will consider two cases of localization of the contact:(i)obtained by profile crowning,(ii) by double crowning.Profile crowning.Profile crowning may be interpreted as follows:(i)Consider two helicoids that provide rotation between parallel axes.The theoretical gear ratio m12may berepresented as[10]m12¼xð1Þxð2Þ¼p2p1¼N2N1ð1Þwhere x(i)is the angular velocity,p(i)is the screw parameter,and N i is the tooth number.(ii)The gear ratio m12does not depend on the shapes of the cross-section profiles.For instance,one of the profiles may be an involute one,and the mating profile may be a circular one.The original idea of Novi-kov–Wildhaber gears is based on application of circular arc profiles for the pinion and the gear,but the ratio of curvatures of tooth surfaces allows to reduce the contact stresses.(iii)The possibility of variation of cross-section profiles is the essence of profile crowning.(iv)The profile crowned helical gears are in point contact(the tooth contact is localized)and such gears are not sensitive to the change of center distance.The main disadvantage of profile-crowned gears is the sensitivity of the gear drive to the change of the crossing angle.This misalignment is accompanied with edge contact and the function of transmission errors is a discontinuous linear one.Such shape of function of transmission errors is the source of vibration due to the jump of the function at the beginning of the cycle of meshing.This is the reason why our design of isostatic planetary gear trains is based on the double-crowning approach.D.Vecchiato/Mechanism and Machine Theory41(2006)617–631619Double crowning.Double crowing may be provided in the process of manufacturing of one of the pair of mating tooth ually,double crowning is provided for the pinion,wherein it is generated by a disk or by a worm.In the case of generation by a disk (generation by form)double crowning is performed by variation of plunging of the disk.The plunging is performed by variation of the shortest distance between the generating disk.The magnitude of plunging corresponds to a parabolic function that relates the plunge and the displace-ment of the disk along the axis of the pinion [11].Double crowning of the pinion by a grinding worm may be accomplished by a modified roll of feed motion instead of the plunging motion [12].The advantages of double crowing are:(i)the avoidance of edge-contact,and (ii)the development of a pre-designed parabolic function that absorbs linear function of transmission errors caused by misalignment.Absorption of linear functions of transmission errors allows to reduce the noise of the gear drive.Fig.2illus-trates the paths of contact and the predesigned parabolic function of a gear drive with helical gears designed with application of double crowning.4.Simulation of contactSimulation of contact of gear drives may be performed by the well-known approach of TCA (tooth contact analysis)[10].Such an approach is based on continuous tangency of a pair of surfaces that may perform simple motions,usually rotation,about one axis.The surfaces represent the tooth surfaces of the pinion and the gear.Extension of this approach is necessary for simulation of planetary gear trains.The extensions will cover the cases wherein:(i)more than one pair of surfaces are in meshing,and (ii)some of the surfaces perform planetary motion.This section includes a brief introduction on TCA,and extension to the case of a planetary train formed by only one planet.A planetary gear train with a single planet corresponds to a subtrain of a more complicated train that may include several planets.Considerations on the subtrain will be applied for solution of a more complicated mechanism.4.1.Tooth contact analysis of a gear drive formed by two gearsA gear drive formed by gears 1and 2(pinion and gear)is considered.Respective tooth surfaces R 1and R 2perform rotation about pinion and gear axis.Angles of rotation are /1and /2.Family of surfaces R 1and R2620 D.Vecchiato /Mechanism and Machine Theory 41(2006)617–631are described in a reference system rigid with the gearbox,thefixed reference system S f,as rð1Þf ðu1;h1;/1Þandrð2Þf ðu2;h2;/2Þ,respectively.Here(u i,h i)are the surface parameters,and/i is the angle of rotation(i=1,2).Assuming surface-to-surface tangency,the well-known algorithm of TCA is represented as follows[10]:rð1Þf ðu1;h1;/1ÞÀrð2Þfðu2;h2;/2Þ¼0ð2ÞNð1Þf Áo rð2Þfo u2¼0ð3ÞNð1Þf Áo rð2Þfo h2¼0ð4ÞHere,vector equation(2)corresponds to three scalar equations and enforces coincidence of surfaces at a point. Scalar equations(3)and(4)require that the normal of R1(indicated as Nð1Þf)will be perpendicular to thetangent plane of surface R2,defined by tangent vectors o rð2Þf2and o rð2Þf2.In other words,vectors of normals tosurfaces R1and R2are collinear.Systems(2)–(4)corresponds tofive equations in six unknowns.One parameter,say/1,may be chosen as the input one.If conditions of the theorem of implicit function system existence are verified[10],the following functions exist locally½u1ð/1Þ;h1ð/1Þ;u2ð/1Þ;h2ð/1Þ;/2ð/1Þ 2C1ð5ÞConsidering the position vectors of contacting surfaces R1and R2,and functions(5),we may represent the paths of contact on R1and R2by functions of/1;the transmission function of the misaligned gear drive is derived from/2(/1).Henceforth,we will refer to the system formed by thefive scalar equations(2)–(4)as TCA12ðu1;h1;/1;u2;h2;/2Þ¼0ð6Þ4.2.Extension of TCA to a planetary gear subtrain with one planetDevelopment of TCA even for a simple gear train with two gears[13,14]was an important step forward for improvement of misaligned gear drives.Extension of TCA for a planetary gear train has required development of new ideas:(i)temporary appli-cation of imaginary gear train with an extended number of carriers(instead of one carrier existing in reality), and(ii)consequent application of additional parameters in TCA.An isostatic planetary gear train provided with a single planet is considered initially.The centers of the sun gear and the carrier arefixed,and the ring gear is fully constrained.The family of tooth surfaces may be represented as follows:(i)Sun gear tooth surface R1performs rotation about sun gear axis,and is represented infixed referencesystem S f conventionally asrð1Þfðu1;h1;/1Þð7Þwhere u1and h1are the surface parameters,and/1is the angle of rotation of the sun gear.(ii)Ring gear tooth surface R3isfixed,and is represented by vector functionrð3Þfðu3;h3Þð8Þ(iii)The planet gear perform complex rotation:(i)about its axis with parameter/2,and(ii)with the carrier, about the axis of the mechanism,with parameter/c.Two distinct surfaces have to be considered:surface R2,1being in mesh with R1,and surface R2,3being in mesh with R3.The position vectors of the surfaces are represented asD.Vecchiato/Mechanism and Machine Theory41(2006)617–631621r ð2;1Þf ðu 2;1;h 2;1;/2;/c Þð9Þr ð2;3Þfðu 2;3;h 2;3;/2;/c Þð10ÞTangency between sun and planet gears.Following notations introduced in Eq.(6),tangency between sun and planet gears (surfaces R 1and R 2,1,respectively)may be represented by the following equation:TCA 12ðu 1;h 1;/1;u 2;1;h 2;1;/2;/c Þ¼0ð11ÞSystem (11)represents five equations in seven unknowns,in agreement with the fact that this portion of the mechanism has two degrees of freedom.Tangency between planet and ring ing the same notations,tangency between surfaces R 2,3and R 3may be represented asTCA 23ðu 2;3;h 2;3;/2;/c ;u 3;h 3Þ¼0ð12ÞSystem equations (12)represents five equations in six unknowns;two unknowns,/2and /c ,appeared already in Eq.(11).Then,if Eqs.(11)and (12)are considered simultaneously,a system of 10equations in 11unknowns is obtainedTCA 12ðu 1;h 1;/1;u 2;1;h 2;1;/2;/c Þ¼0TCA 23ðu 2;3;h 2;3;/2;/c ;u 3;h 3Þ¼0ð13ÞUnder the conditions of the theorem of implicit function system existence,we may choose an independent var-iable and determine 10implicit functions,of this variable only,that satisfy Eq.(13).It is logical to choose as an independent variable the parameter /1or /c ,if the mechanism is a reducer or a multiplier,respectively.Choosing /1as independent parameter and following the requirement to the respective JacobianD ðTCA 12;TCA 23ÞD ðu 1;h 1;u 2;1;h 2;1;/2;/c ;u 2;3;h 2;3;u 3;h 3Þ¼0ð14Þwe obtain the solutions for TCA byfunctions622 D.Vecchiato /Mechanism and Machine Theory 41(2006)617–631/cð/1Þ;/2ð/1Þ;u1ð/1Þ; (15)For the purpose of simplification of notations,we designate as TCA13the system of Eq.(13).4.3.Extension to planetary gear train with three planetsAn isostatic planetary gear train formed by three planets is considered,Fig.3.Such a mechanism has twoadditional unknowns that represent the center position of the sun gear by D Eð1Þx and D Eð1Þy.We may consider two approaches for formulation and solution of such a problem:(i)by direct formulation, (ii)by augmenting the number of unknowns.Direct formulation.We may represent the equations of tangency of the three subtrains as follows:TCAð1Þ13ðD Eð1Þx;D Eð1Þy;/1;/c;...Þ¼0TCAð2Þ13ðD Eð1Þx;D Eð1Þy;/1;/c;...Þ¼0TCAð3Þ13ðD Eð1Þx;D Eð1Þy;/1;/c;...Þ¼08>><>>:ð16ÞHere,the lower dots represent the omitted unknowns u,h,etc.for respective surfaces.System(16)represent15 equations in16unknowns.Choosing/1as an input parameter,and following the theorem of implicit functionsystem existence,we may determine functions D Eð1Þx ð/1Þ,D Eð1Þyð/1Þ,/c(/1)etc.Augmented formulation.Newton–Raphson method is applied for numerical solution of non-linear equa-tions,[15].Numerical solution of the direct formulation is difficult due to the large number of unknowns an the non-linearity of equations.We propose to simplify the problem by augmenting the number of unknowns.For this purpose,three newunknowns/ðiÞc (i=1,2,3)are considered.Previously applied unknown/c is not required anymore,thereforethe problem now has18unknowns,instead of16.The new unknowns correspond to the angular position of the imaginary additional carriers applied for the set of respective subtrains.System of Eq.(16)is represented now asTCAð1Þ13ðD Eð1Þx;D Eð1Þy;/1;/ð1Þc;...Þ¼0TCAð2Þ13ðD Eð1Þx;D Eð1Þy;/1;/ð2Þc;...Þ¼0TCAð3Þ13ðD Eð1Þx;D Eð1Þy;/1;/ð3Þc;...Þ¼08>><>>:ð17ÞIn addition,the following two scalar equations have to be observed/ð1Þc À/ð2Þc¼0/ð2Þc À/ð3Þc¼0(ð18ÞEq.(18)requires that the imaginary additional carriers of each subtrains will have the same angular position/ð1Þc ¼/ð2Þc¼/ð3Þc¼/c.Table1Gear data for the numerical exampleDesign parameter Sun Planet RingNumber of teeth z6543151Module m[mm]4Pressure angle a[deg]20°Face width b[mm]40Addendum of the tool h a0[mm] 1.25mAddendum of the gear h a[mm]mProfile shift coefficient x0Tool parabola coefficient a p[mmÀ1]0 1.25·10À30 Longitudinal parabola coeff.a l[mmÀ1]062.5·10À60D.Vecchiato/Mechanism and Machine Theory41(2006)617–631623Simultaneous consideration of Eqs.(17)and(18)yields a system of17equations in18unknowns.Choosing an input parameter,the solution becomes possible.However,direct way of solution is still difficult.The advantage of this formulation consists in splitting system(17)in three independent sets offive equations.Each set may be used for determination of the respective implicit functions such as/ð1Þc ðD Eð1Þx;D Eð1Þy;/1Þð19Þ/ð2Þc ðD Eð1Þx;D Eð1Þy;/1Þð20Þ/ð3Þc ðD Eð1Þx;D Eð1Þy;/1Þð21ÞThen,functions(19)–(21)may be applied in Eq.(18)obtaining a system of two equations in two unknowns, provided that/1may be used indeed as the input parameter.Summarizing,the augmented method requires solution of a system of two equations in two unknowns.The two equations are defined implicitly,by solving three independent systems offive equations infive unknowns each.Therefore,the maximum number of unknowns to be solved simultaneously in this approach isfive, compared to15of the direct approach.4.4.Determination of backlash of neighboring tooth surfacesThe determination of backlash of tooth surfaces neighboring to the contacting ones is the key for the detection of the change of meshing from one pair of teeth to the next one.Analysis of backlash is performed after each step of computation of TCA.Angular positions/ðiÞc and/ðiÞ2are adopted from solution of system of Eq.(18).624 D.Vecchiato/Mechanism and Machine Theory41(2006)617–631Two values of backlash have to be determined for each subtrain:s ps between the toothflanks of the planet and the sun gear,and s pr between the toothflanks of planet and ring gear.Determination of s ps is accomplished by the solution of the following systems offive equations infive unknownsrð2Þf Àrð1Þf¼nð1Þfs psnð1Þf Áo rð2Þf2¼0nð1Þf Áo rð2Þfo h2¼08>>><>>>:ð22ÞHere nð1Þf is the outward unit normal to the sun toothflank surface.Similarly may be performed determination of s pr.If s ps or s pr are negative,the corresponding teeth surfaces are intersecting,and they should be considered for TCA instead of the current ones.5.Numerical exampleAn isostatic planetary gear train with three planets is considered,see Fig.3.The gear data that defines the train is represented in Table1.A special computer program for TCA of this planetary train has been developed based on the ideas presented in Section4.Five cases of errors are considered in the performed analysis:D.Vecchiato/Mechanism and Machine Theory41(2006)617–631625626 D.Vecchiato/Mechanism and Machine Theory41(2006)617–631(1)Ideal gear train,without error of manufacturing and assembly.(2)Error of indexing of the carrier D E t.(3)Error of center position of the carrier.(4)Error of run-out(eccentricity)of the sun gear.(5)Error of run-out of a planetary gear.For each case,two results of simulation are provided:(i)wherein the planet gears are involute gears,and(ii) double crowned gears.Case1:Ideal gear train.Consideration of this simple case is directed to test the correctness of the developed computer program.Application of involute helical gears shows that the center of the sun gear remainsfixed,even if not constrained,see Fig.4(a).No transmission errors are detected,see Fig.4(b).Application of double crowned gears is interesting.Gears have been designed with a transmission error of 800of amplitude.Fig.5(a)shows that the center position of the sun performs a complicated trajectory similar to a vibration about the theoretical center position.Amplitude of vibration is very small,about1.5l m.As a result of this vibration,errors of transmission are self-compensated,and the mechanism has no errors of trans-mission due to parabolic modification of profile,see Fig.5(b).This effect has been found in all considered cases.However,it has to be noticed that these results correspond to a quasi-static train formed by rigid bodies.Case2:Error of indexing of the carrier.Error of indexing of the carrier is of main concern of investigation while considering the load distribution.Results of performed investigation for the case of involute gears are represented in Fig.6(a)and(b).Results of investigation confirmed that simultaneous tangency of all planets is achieved.Fig.6(a)shows the trajectory of the sun for a full revolution of the carrier.The trajectory is exactly a cir-cular one.The sun gear performs therefore a planetary motion formed by:(i)rotation about its axis withangular velocity of the sun gears,and(ii)rotation about the mechanism axis with the angular velocity of the carrier.The position of the sun gear appearfixed if it is considered in the carrier reference system.The carrier lags with respect to its theoretical position at about6.400,constant.Constant errors of transmis-sion are not the source of noise and torsional vibrations.Geometrical interpretation of case2.The geometrical interpretation of the effect of an error of indexing of the carrier represents a good illustration for understanding of kinematics of an isostatic planetary gear train (see Fig.7).(i)Initially,it is considered that the center of the sun gear coincides with the axis of the mechanism.Axesp iÀp i,i=1,2,3represent the lines of action of the contacts between the sun and planet gears.The tri-angle that is formed by these lines is circumscribed by the base circle of the sun gear.Assuming that errorD E t is small,we may consider that the triangle is equilateral.(ii)Error D Eð1Þt causes a small backlash between sun gear1and planet2(1).The amount of backlash, measured across line p1Àp1,is approximately s=2D E t cos a,where a=20°is the pressure angle of the gears.Assuming D E t=20l m,we obtain s=37.6l m.(iii)This backlash has to be compensated by relative motion of the sun gear and the mechanism.Since the sun is in tangency with planet gears2(2)and2(3),the motion will cause a small rotation centered at point 023,defined by intersection of pressure lines p2Àp2and p3Àp3.The angle of rotation of the sun gear is D/1¼s=O23H,or D/1=s/(3r b1),where r b1is the base circle of the sun gear,and O23H¼3r b1.Substituting the numbers,we obtain D/1=103l rad=21.200.The resulting angular error,measured on the carrier,will be D/c=D/1m c1=21.2Æ0.301=6.3800.This value corresponds to the increase of lag of the carrier from the condition of an ideal train(case(1)), to the condition wherein error of indexing is applied.These values are in perfect agreement with the results obtained from the numerical simulation,for both cases of involute and double crowned gears.(iv)The magnitude of displacement of the center of the sun gear is obtained as D E1¼D/1ÁO23O1.Since O23O1¼2r b1,we obtain after substitution D E1=2s/3.Substituting the numbers,we obtain D E1=25l m,that corresponds to the radius of circle of Fig.6, thereby confirming the results.Case3:Error of center position of the carrier.This example confirms that errors of center position of the carrier are of no concern for this planetary gear drive.The error is absorbed by automatic relocation of the center of the sun gear,see Fig.8(a)for involute gears.No errors of transmission are observed,see Fig.8(b).Case4:Error of run-out(eccentricity)of the sun gear.Performed analysis shows that an error of run-out of the sun gear is compensated by the gear drive.The center of the sun gear performs a circular trajectory,see Fig.9(a).This circular motion is repeated for each revolution of the sun gear,and the circle radius corre-sponds to the eccentricity error.Therefore,the self-performed regulation is able to cancel the effect of the eccentricity,providing an‘‘error’’which is equal and opposite to it.Also in this case,there are no errors of transmission,see Fig.9(b).Case5:Error of run-out(eccentricity)of a planet gear.The error of run-out of the planet gear2(i),i=1, represents an interesting case.The motion of the planet gear relative to the carrier has to be considered.This motion is a rotation,and the angular velocity is(x p)rel=(x1Àx c)N1/N2=1.057x1.Therefore,the effect of error of eccentricity is periodic with1/1.057=0.9463revolutions of the sun gear.Fig.10(a)shows the center position of the sun gear for rotation of the sun gear of0.9463of a revolution. The described trajectory belongs to the family of hypotrochoids,and is a‘‘rose’’with afinite number of petals [16].Transmission errors are not constant(Fig.10(b)),but are of a periodic(harmonic)shape.The period is one revolution of the planet,with respect to the carrier.。
毕业设计论文翻译（译文+原文）
Hacking tricks toward security on network environments Tzer-Shyong Chen1, Fuh-Gwo Jeng 2, and Yu-Chia Liu 11 Department of Information Management, Tunghai University, Taiwan2 Department of Applied Mathematics, National Chiayi University, TaiwanE-Mail:****************.edu.twAbstractMounting popularity of the Internet has led to the birth of Instant Messaging, an up-and-coming form of Internet communication. Instant Messaging is very popular with businesses and individuals since it has instant communication ability. As a result, Internet security has become a pressing and important topic for discussion. Therefore, in recent years, a lot of attention has been drawn towards Internet security and the various attacks carried out by hackers over the Internet. People today often handle affairs via the Internet. For instance, instead of the conventional letter, they communicate with others by e-mails; they chat with friends through an instant messenger; find information by browsing websites instead of going to the library; perform e-commerce transactions through the Internet, etc. Although the convenience of the Internet makes our life easier, it is also a threat to Internet security. For instance, a business email intercepted during its transmission may let slip business confidentiality; file transfers via instant messengers may also be intercepted, and then implanted with backdoor malwares; conversations via instant messengers could be eavesdropped. Furthermore, ID and password theft may lose us money when using Internet bank service. Attackers on the Internet use hacking tricks to damage systems while users are connected to the Internet. These threats along with possible careless disclosure of business information make Instant Messaging a very unsafe method of communication for businesses. The paper divides hacking tricks into three categories: (1) Trojan programs that share files via instant messenger. (2) Phishing or fraud via e-mails. (3) Fake Websites. Keywords:Hacking tricks, Trojan programs, Phishing, Firewall, Intrusion detection system.1. IntroductionIncreasingly more people are using instant messengers such as MSN Messenger, Yahoo! Messenger, ICQ, etc as the media of communication. These instant messengers transmit alphanumeric message as well as permit file sharing. During transfer, a file may be intercepted by a hacker and implanted with backdoor malware. Moreover, the e-mails users receive every day may include Spam, advertisements, and fraudulent mail intended to trick uninformed users. Fake websites too are prevalent. Websites which we often visit could be counterfeited by imitating the interface and the URL of the original, tricking users. The paper classifies hacking tricks into three categories which are explained in the following sections.2. Hacking TricksThe paper divides hacking tricks into three categories: (1) Trojan programs that share files via instant messenger. (2) Phishing (3) Fake Websites.2.1 Trojan programs that share files via instant messengerInstant messaging allows file-sharing on a computer [9]. All present popular instant messengers have file sharing abilities, or allow users to have the above functionality by installing patches or plug-ins; this is also a major threat to present information security. These communication softwares also makeit difficult for existing hack prevention methods to prevent and control information security. Therefore, we shall discuss how to control the flow of instant messages and how to identify dangerous user behavior.Hackers use instant communication capability to plant Trojan program into an unsuspected program; the planted program is a kind of remotely controlled hacking tool that can conceal itself and is unauthorized. The Trojan program is unknowingly executed, controlling the infected computer; it can read, delete, move and execute any file on the computer. The advantages of a hacker replacing remotely installed backdoor Trojan programs [1] with instant messengers to access files are:When the victim gets online, the hacker will be informed. Thus, a hacker can track and access the infected computer, and incessantly steal user information.A hacker need not open a new port to perform transmissions; he can perform his operations through the already opened instant messenger port.Even if a computer uses dynamic IP addresses, its screen name doesn’t change.Certain Trojan programs are designed especially for instant messengers. These Trojans can change group settings and share all files on the hard disk of the infected computer. They can also destroy or modify data, causing data disarray. This kind of program allows a hacker access to all files on an infected computer, and thus poses a great threat to users. The Trojan program takes up a large amount of the resources of the computer causing it to become very slow and often crashes without a reason.Trojan programs that access a user computer through an instant messenger are probably harder to detect than classic Trojan horse programs. Although classic Trojan intrudes a computer by opening a listening or outgoing port which is used to connect toa remote computer, a desktop firewall can effectively block such Trojans. Alternatively, since it is very difficult for the server’s firewall to spot intrusion by controlling an instant messenger’s flow, it is extremely susceptible to intrusion.Present Trojan programs have already successfully implemented instant messengers. Some Trojan programs are Backdoor Trojan, AIMVision, and Backdoor. Sparta.C. Backdoor Trojans use ICQ pager to send messages to its writer. AIMVision steals AIM related information stored in the Windows registry, enabling a hacker to setup an AIM user id. Backdoor. Sparta.C uses ICQ to communicate with its writer and opens a port on an infected host and send its IP Address to the hacker, and at the same time attempts to terminate the antivirus program or firewall of the host.2.1.1 Hijacking and ImpersonationThere are various ways through which a hacker can impersonate other users [7]. The most commonly used method is eavesdropping on unsuspecting users to retrieve user accounts, passwords and other user related information.The theft of user account number and related information is a very serious problem in any instant messenger. For instance, a hacker after stealing a user’s information impersonate the user; the user’s contacts not knowing that the user’s account has been hacked believe that the person they’re talking to is the user, and are persuaded to execute certain programs or reveal confidential information. Hence, theft of user identity not only endangers a user but also surrounding users. Guarding against Internet security problems is presently the focus of future research; because without good protection, a computer can be easily attacked, causing major losses.Hackers wishing to obtain user accounts may do so with the help of Trojans designed to steal passwords. If an instant messenger client stores his/her password on his/her computer, then a hacker can send a Trojan program to the unsuspecting user. When the user executes the program, the program shall search for the user’s password and send it to the hacker. There are several ways through which a Trojan program can send messages back to the hacker. The methods include instant messenger, IRC, e-mails, etc.Current four most popular instant messengers are AIM, Yahoo! Messenger, ICQ, and MSN Messenger, none of which encrypts its flow. Therefore, a hackercan use a man-in-the-middle attack to hijack a connection, then impersonate the hijacked user and participate in a chat-session. Although difficult, a hacker can use the man-in-the-middle attack to hijack the connection entirely. For example, a user may receive an offline message that resembles that sent by the server, but this message could have been sent by the hacker. All at once, the user could also get disconnected to the server. Furthermore, hackers may also use a Denial of Service (DoS) tool or other unrelated exploits to break the user’s connection. However, the server keeps the connection open, and does not know that the user has been disconnected; thus allowing the hacker to impersonate the user. Moreover, since the data flow is unencrypted and unauthenticated, a hacker can use man-in-the-middle attacks that are similar to that of ARP fraud to achieve its purpose.2.1.2 Denial of Service (DoS)There are many ways through which a hacker can launch a denial of service (DoS) attack [2] on an instant messenger user. A Partial DoS attack will cause a user end to hang, or use up a large portion of CPU resources causing the system to become unstable.Another commonly seen attack is the flooding of messages to a particular user. Most instant messengers allow the blocking of a particular user to prevent flood attacks. However, a hacker can use tools that allow him to log in using several different identities at the same time, or automatically create a large number of new user ids, thus enabling a flood attack. Once a flood attack begins, even if the user realizes that his/her computer has been infected, the computer will not be able to respond. Thus, the problem cannot be solved by putting a hacker’s user id on the ignore list of your instant messenger.A DoS attack on an instant messenger client is only a common hacking tool. The difficulty of taking precautions against it could turn this hacking tool into dangerous DoS type attacks. Moreover, some hacking tools do not just cause an instant messenger client to hang, but also cause the user end to consume large amount of CPU time, causing the computer to crash.2.1.3 Information DisclosureRetrieving system information through instant messenger users is currently the most commonly used hacking tool [4]. It can effortlessly collect user network information like, current IP, port, etc. IP address retriever is an example. IP address retrievers can be used to many purposes; for instance, a Trojan when integrated with an IP address retriever allows a hacker to receive all information related to the infected computer’s IP address as soon as the infected computer connects to the internet. Therefore, even if the user uses a dynamic IP address, hackers can still retrieve the IP address.IP address retrievers and other similar tools can also be used by hackers to send data and Trojans to unsuspecting users. Hackers may also persuade unsuspecting users to execute files through social engineering or other unrelated exploits. These files when executed search for information on the user’s computer and sends them back to the hacker through the instant messenger network.Different Trojan programs were designed for different instant messaging clients. For example, with a user accounts and password stealing Trojans a hacker can have full control of the account once the user logs out. The hacker can thus perform various tasks like changing the password and sending the Trojan program to all of the user’s contacts.Moreover, Trojans is not the only way through which a hacker can cause information disclosure. Since data sent through instant messengers are unencrypted, hackers can sniff and monitor entire instant messaging transmissions. Suppose an employee of an enterprise sends confidential information of the enterprise through the instant messenger; a hacker monitoring the instant messaging session can retrieve the data sent by the enterprise employee. Thus, we must face up to the severity of the problem.2.2 PhishingThe word “Phishing” first appeared in 1996. It is a variant of ‘fishing’, and formed by replacing the ‘f’ in ‘fishing’ with ‘ph’ from phone. It means tricking users of their money through e-mails.Based on the statistics of the Internet Crime Complaint Center, loss due to internet scam was as high as $1.256 million USD in 2004. The Internet Crime Complaint Center has listed the above Nigerian internet scam as one of the ten major internet scams.Based on the latest report of Anti-Phishing Working Group (APWG) [8], there has been a 28% growth of Phishing scams in the past 4 months, mostly in the US and in Asia. Through social engineering and Trojans, it is very difficult for a common user to detect the infection.To avoid exploitation of your compassion, the following should be noted:(1)When you need to enter confidentialinformation, first make sure that theinformation is entered via an entirely secureand official webpage. There are two ways todetermine the security of the webpage:a.The address displayed on the browserbegins with https://, and not http://. Payattention to if the letter ‘s’ exists.b.There is a security lock sign on the lowerright corner of the webpage, and whenyour mouse points to the sign, a securitycertification sign shall appear.(2)Consider installing a browser security softwarelike SpoofStick which can detect fake websites.(3)If you suspect the received e-mail is a Phishinge-mail, do not open attachments attached to theemail. Opening an unknown attachment couldinstall malicious programs onto your computer.(4)Do not click on links attached to your emails. Itis always safer to visit the website through theofficial link or to first confirm the authenticityof the link. Never follow or click on suspiciouslinks in an e-mail. It is advisable to enter theURL at the address bar of the web browser,and not follow the given link.Generally speaking, Phishing [3] [5] is a method that exploits people’s sympathy in the form of aid-seeking e-mails; the e-mail act as bait. These e-mails usually request their readers to visit a link that seemingly links to some charitable organization’s website; but in truth links the readers to a website that will install a Trojan program into the reader’s computer. Therefore, users should not forward unauthenticated charity mails, or click on unfamiliar links in an e-mail. Sometimes, the link could be a very familiar link or an often frequented website, but still, it would be safer if you’d type in the address yourself so as to avoid being linked to a fraudulent website. Phisher deludes people by using similar e-mails mailed by well-known enterprises or banks; these e-mails often asks users to provide personal information, or result in losing their personal rights; they usually contain a counterfeit URL which links to a website where the users can fillin the required information. People are often trapped by phishing due to inattentionBesides, you must also be careful when using a search engine to search for donations and charitable organizations.2.3 Fake WebsitesFake bank websites stealing account numbers and passwords have become increasingly common with the growth of online financial transactions. Hence, when using online banking, we should take precautions like using a secure encrypted customer’s certificate, surf the net following the correct procedure, etc.There are countless kinds of phishing baits, for instance, messages that say data expired, data invalid, please update data, or identity verification intended to steal account ID and matching password. This typeof online scam is difficult for users to identify. As scam methods become finer, e-mails and forged websites created by the impostor resemble their original, and tremendous losses arise from the illegal transactions.The following are methods commonly used by fake websites. First, the scammers create a similar website homepage; then they send out e-mails withenticing messages to attract visitors. They may also use fake links to link internet surfers to their website. Next, the fake website tricks the visitors into entering their personal information, credit card information or online banking account number and passwords. After obtaining a user’s information, the scammers can use the information to drain the bank accounts, shop online or create fake credit cards and other similar crimes. Usually, there will be a quick search option on these fake websites, luring users to enter their account number and password. When a user enters their account number and password, the website will respond with a message stating that the server is under maintenance. Hence, we must observe the following when using online banking:(1)Observe the correct procedure for entering abanking website. Do not use links resultingfrom searches or links on other websites.(2)Online banking certifications are currently themost effective security safeguard measure. (3)Do not easily trust e-mails, phone calls, andshort messages, etc. that asks for your accountnumber and passwords.Phishers often impost a well-known enterprise while sending their e-mails, by changing the sender’s e-mail address to that of the well known enterprise, in order to gain people’s trust. The ‘From’ column of an e-mail is set by the mail software and can be easily changed by the web administrator. Then, the Phisher creates a fake information input website, and send out e-mails containing a link to this fake website to lure e-mail recipients into visiting his fake website.Most Phishers create imitations of well known enterprises websites to lure users into using their fake websites. Even so, a user can easily notice that the URL of the website they’re entering has no relation to the intended enterprise. Hence, Phishers may use different methods to impersonate enterprises and other people. A commonly used method is hiding the URL. This can easily be done with the help of JavaScript.Another way is to exploit the loopholes in an internet browser, for instance, displaying a fake URL in the browser’s address bar. The security loophole causing the address bar of a browser to display a fake URL is a commonly used trick and has often been used in the past. For example, an e-mail in HTML format may hold the URL of a website of a well-known enterprise, but in reality, the link connects to a fake website.The key to successfully use a URL similar to that of the intended website is to trick the visual senses. For example, the sender’s address could be disguised as that of Nikkei BP, and the link set to http://www.nikeibp.co.jp/ which has one k less than the correct URL which is http://www.nikkeibp.co.jp/. The two URLs look very similar, and the difference barely noticeable. Hence people are easily tricked into clicking the link.Besides the above, there are many more scams that exploit the trickery of visual senses. Therefore, you should not easily trust the given sender’s name and a website’s appearance. Never click on unfamiliar and suspicious URLs on a webpage. Also, never enter personal information into a website without careful scrutiny.3. ConclusionsBusiness strategy is the most effective form of defense and also the easiest to carry out. Therefore, they should be the first line of defense, and not last. First, determine if instant messaging is essential in the business; then weigh its pros and cons. Rules and norms must be set on user ends if it is decided that the business cannot do without instant messaging functionality. The end server should be able to support functions like centralized logging and encryption. If not, then strict rules must be drawn, and carried out by the users. Especially, business discussions must not be done over an instant messenger.The paper categorized hacking tricks into three categories: (1) Trojan programs that share files via instant messenger. (2) Phishing (3) Fake Websites. Hacking tricks when successfully carried out could cause considerable loss and damage to users. The first category of hacking tricks can be divided into three types: (1) Hijacking and Impersonation; (2) Denial of Service; (3) Information Disclosure.Acknowledgement:This work was supported by the National Science Council, Taiwan, under contract No. NSC 95-2221-E-029-024.References[1] B. Schneier, “The trojan horse race,”Communications of ACM, Vol. 42, 1999, pp.128.[2] C. L. Schuba, “Analysis of a denial of serviceattack on TCP,” IEEE Security and PrivacyConference, 1997, pp. 208-223.[3] E. Schultz, “Phishing is becoming moresophisticated,” Computer and Security, Vol.24(3), 2005, pp. 184-185.[4]G. Miklau, D. Suciu, “A formal analysis ofinformation disclosure in data exchange,”International Conference on Management ofData, 2004, pp. 575-586.[5]J. Hoyle, “'Phishing' for trouble,” Journal ofthe American Detal Association, Vol. 134(9),2003, pp. 1182-1182.[6]J. Scambray, S. McClure, G. Kurtz, Hackingexposed: network security secrets and solutions,McGraw-Hill, 2001.[7]T. Tsuji and A. Shimizu, “An impersonationattack on one-time password authenticationprotocol OSPA,” to appear in IEICE Trans.Commun, Vol. E86-B, No.7, 2003.[8]Anti-Phishing Working Group,.[9]/region/tw/enterprise/article/icq_threat.html.有关网络环境安全的黑客技术摘要：现在人们往往通过互联网处理事务。
毕业设计外文翻译例文
大连科技学院毕业设计(论文)外文翻译学生姓名专业班级指导教师职称所在单位教研室主任完成日期 2016年4月15日Translation EquivalenceDespite the fact that the world is becoming a global village, translation remains a major way for languages and cultures to interact and influence each other. And name translation, especially government name translation, occupies a quite significant place in international exchange.Translation is the communication of the meaning of a source-language text by means of an equivalent target-language text. While interpreting—the facilitating of oral or sign-language communication between users of different languages—antedates writing, translation began only after the appearance of written literature. There exist partial translations of the Sumerian Epic of Gilgamesh (ca. 2000 BCE) into Southwest Asian languages of the second millennium BCE. Translators always risk inappropriate spill-over of source-language idiom and usage into the target-language translation. On the other hand, spill-overs have imported useful source-language calques and loanwords that have enriched the target languages. Indeed, translators have helped substantially to shape the languages into which they have translated. Due to the demands of business documentation consequent to the Industrial Revolution that began in the mid-18th century, some translation specialties have become formalized, with dedicated schools and professional associations. Because of the laboriousness of translation, since the 1940s engineers have sought to automate translation (machine translation) or to mechanically aid the human translator (computer-assisted translation). The rise of the Internet has fostered a world-wide market for translation services and has facilitated language localizationIt is generally accepted that translation, not as a separate entity, blooms into flower under such circumstances like culture, societal functions, politics and power relations. Nowadays, the field of translation studies is immersed with abundantly diversified translation standards, with no exception that some of them are presented by renowned figures and are rather authoritative. In the translation practice, however, how should we select the so-called translation standards to serve as our guidelines in the translation process and how should we adopt the translation standards to evaluate a translation product?In the macro - context of flourish of linguistic theories, theorists in the translation circle, keep to the golden law of the principle of equivalence. The theory of Translation Equivalence is the central issue in western translation theories. And the presentation of this theory gives great impetus to the development and improvement of translation theory. It‟s not diffi cult for us to discover that it is the theory of Translation Equivalence that serves as guidelines in government name translation in China. Name translation, as defined, is the replacement of thename in the source language by an equivalent name or other words in the target language. Translating Chinese government names into English, similarly, is replacing the Chinese government name with an equivalent in English.Metaphorically speaking, translation is often described as a moving trajectory going from A to B along a path or a container to carry something across from A to B. This view is commonly held by both translation practitioners and theorists in the West. In this view, they do not expect that this trajectory or something will change its identity as it moves or as it is carried. In China, to translate is also understood by many people normally as “to translate the whole text sentence by sentence and paragraph by paragraph, without any omission, addition, or other changes. In both views, the source text and the target text must be “the same”. This helps explain the etymological source for the term “translation equivalence”. It is in essence a word which describes the relationship between the ST and the TT.Equivalence means the state or fact or property of being equivalent. It is widely used in several scientific fields such as chemistry and mathematics. Therefore, it comes to have a strong scientific meaning that is rather absolute and concise. Influenced by this, translation equivalence also comes to have an absolute denotation though it was first applied in translation study as a general word. From a linguistic point of view, it can be divided into three sub-types, i.e., formal equivalence, semantic equivalence, and pragmatic equivalence. In actual translation, it frequently happens that they cannot be obtained at the same time, thus forming a kind of relative translation equivalence in terms of quality. In terms of quantity, sometimes the ST and TT are not equivalent too. Absolute translation equivalence both in quality and quantity, even though obtainable, is limited to a few cases.The following is a brief discussion of translation equivalence study conducted by three influential western scholars, Eugene Nida, Andrew Chesterman and Peter Newmark. It‟s expected that their studies can instruct GNT study in China and provide translators with insightful methods.Nida‟s definition of translation is: “Translation consists in reproducing in the receptor language the closest natural equivalent of the source language message, first in terms of meaning and secondly in terms of style.” It i s a replacement of textual material in one language〔SL〕by equivalent textual material in another language（TL）. The translator must strive for equivalence rather than identity. In a sense, this is just another way of emphasizing the reproducing of the message rather than the conservation of the form of the utterance. The message in the receptor language should match as closely as possible the different elements in the source language to reproduce as literally and meaningfully as possible the form and content of the original. Translation equivalence is an empirical phenomenon discovered bycomparing SL and TL texts and it‟s a useful operational concept like the term “unit of translati on”.Nida argues that there are two different types of equivalence, namely formal equivalence and dynamic equivalence. Formal correspondence focuses attention on the message itself, in both form and content, whereas dynamic equivalence is based upon “the principle of equivalent effect”.Formal correspondence consists of a TL item which represents the closest equivalent of a ST word or phrase. Nida and Taber make it clear that there are not always formal equivalents between language pairs. Therefore, formal equivalents should be used wherever possible if the translation aims at achieving formal rather than dynamic equivalence. The use of formal equivalents might at times have serious implications in the TT since the translation will not be easily understood by the target readership. According to Nida and Taber, formal correspondence distorts the grammatical and stylistic patterns of the receptor language, and hence distorts the message, so as to cause the receptor to misunderstand or to labor unduly hard.Dyn amic equivalence is based on what Nida calls “the principle of equivalent effect” where the relationship between receptor and message should be substantially the same as that which existed between the original receptors and the message. The message has to be modified to the receptor‟s linguistic needs and cultural expectation and aims at complete naturalness of expression. Naturalness is a key requirement for Nida. He defines the goal of dynamic equivalence as seeking the closest natural equivalent to the SL message. This receptor-oriented approach considers adaptations of grammar, of lexicon and of cultural references to be essential in order to achieve naturalness; the TL should not show interference from the SL, and the …foreignness …of the ST setting is minimized.Nida is in favor of the application of dynamic equivalence, as a more effective translation procedure. Thus, the product of the translation process, that is the text in the TL, must have the same impact on the different readers it was addressing. Only in Nida and Taber's edition is it clearly stated that dynamic equivalence in translation is far more than mere correct communication of information.As Andrew Chesterman points out in his recent book Memes of Translation, equivalence is one of the five element of translation theory, standing shoulder to shoulder with source-target, untranslatability, free-vs-literal, All-writing-is-translating in importance. Pragmatically speaking, observed Chesterman, “the only true examples of equivalence (i.e., absolute equivalence) are those in which an ST item X is invariably translated into a given TL as Y, and vice versa. Typical examples would be words denoting numbers (with the exceptionof contexts in which they have culture-bound connotations, such as “magic” or “unlucky”), certain technical terms (oxygen, molecule) and the like. From this point of view, the only true test of equivalence would be invariable back-translation. This, of course, is unlikely to occur except in the case of a small set of lexical items, or perhaps simple isolated syntactic structure”.Peter Newmark. Departing from Nida‟s receptor-oriented line, Newmark argues that the success of equivalent effect is “illusory “and that the conflict of loyalties and the gap between emphasis on source and target language will always remain as the overriding problem in translation theory and practice. He suggests narrowing the gap by replacing the old terms with those of semantic and communicative translation. The former attempts to render, as closely as the semantic and syntactic structures of the second language allow, the exact contextual meaning of the original, while the latter “attempts to produce on its readers an effect as close as possible to that obtained on the readers of the original.” Newmark‟s description of communicative translation resembles Nida‟s dynamic equivalence in the effect it is trying to create on the TT reader, while semantic translation has similarities to Nida‟s formal equivalence.Meanwhile, Newmark points out that only by combining both semantic and communicative translation can we achieve the goal of keeping the …spirit‟ of the original. Semantic translation requires the translator retain the aesthetic value of the original, trying his best to keep the linguistic feature and characteristic style of the author. According to semantic translation, the translator should always retain the semantic and syntactic structures of the original. Deletion and abridgement lead to distortion of the author‟s intention and his writing style.翻译对等尽管全世界正在渐渐成为一个地球村，但翻译仍然是语言和和文化之间的交流互动和相互影响的主要方式之一。
毕业设计外文文献翻译
毕业设计外文文献翻译Graduation design of foreign literature translation 700 words Title: The Impact of Artificial Intelligence on the Job Market Abstract:With the rapid development of artificial intelligence (AI), concerns arise about its impact on the job market. This paper explores the potential effects of AI on various industries, including healthcare, manufacturing, and transportation, and the implications for employment. The findings suggest that while AI has the potential to automate repetitive tasks and increase productivity, it may also lead to job displacement and a shift in job requirements. The paper concludes with a discussion on the importance of upskilling and retraining for workers to adapt to the changing job market.1. IntroductionArtificial intelligence (AI) refers to the development of computer systems that can perform tasks that typically require human intelligence. AI has made significant advancements in recent years, with applications in various industries, such as healthcare, manufacturing, and transportation. As AI technology continues to evolve, concerns arise about its impact on the job market. This paper aims to explore the potential effects of AI on employment and discuss the implications for workers.2. Potential Effects of AI on the Job Market2.1 Automation of Repetitive TasksOne of the major impacts of AI on the job market is the automation of repetitive tasks. AI systems can perform tasks faster and moreaccurately than humans, particularly in industries that involve routine and predictable tasks, such as manufacturing and data entry. This automation has the potential to increase productivity and efficiency, but also poses a risk to jobs that can be easily replicated by AI.2.2 Job DisplacementAnother potential effect of AI on the job market is job displacement. As AI systems become more sophisticated and capable of performing complex tasks, there is a possibility that workers may be replaced by machines. This is particularly evident in industries such as transportation, where autonomous vehicles may replace human drivers, and customer service, where chatbots can handle customer inquiries. While job displacement may lead to short-term unemployment, it also creates opportunities for new jobs in industries related to AI.2.3 Shifting Job RequirementsWith the introduction of AI, job requirements are expected to shift. While AI may automate certain tasks, it also creates a demand for workers with the knowledge and skills to develop and maintain AI systems. This shift in job requirements may require workers to adapt and learn new skills to remain competitive in the job market.3. Implications for EmploymentThe impact of AI on employment is complex and multifaceted. On one hand, AI has the potential to increase productivity, create new jobs, and improve overall economic growth. On the other hand, it may lead to job displacement and a shift in job requirements. To mitigate the negative effects of AI on employment, it is essentialfor workers to upskill and retrain themselves to meet the changing demands of the job market.4. ConclusionIn conclusion, the rapid development of AI has significant implications for the job market. While AI has the potential to automate repetitive tasks and increase productivity, it may also lead to job displacement and a shift in job requirements. To adapt to the changing job market, workers should focus on upskilling and continuous learning to remain competitive. Overall, the impact of AI on employment will depend on how it is integrated into various industries and how workers and policymakers respond to these changes.。
_毕业设计外文文献及翻译_
_毕业设计外文文献及翻译_Graduation Thesis Foreign Literature Review and Chinese Translation1. Title: "The Impact of Artificial Intelligence on Society"Abstract:人工智能对社会的影响摘要：人工智能技术的快速发展引发了关于其对社会影响的讨论。
本文探讨了人工智能正在重塑不同行业（包括医疗保健、交通运输和教育）的各种方式。
还讨论了AI实施的潜在益处和挑战，以及伦理考量。
总体而言，本文旨在提供对人工智能对社会影响的全面概述。
2. Title: "The Future of Work: Automation and Job Displacement"Abstract:With the rise of automation technologies, there is growing concern about the potential displacement of workers in various industries. This paper examines the trends in automation and its impact on jobs, as well as the implications for workforce development and retraining programs. The ethical and social implications of automation are also discussed, along with potential strategies for mitigating job displacement effects.工作的未来：自动化和失业摘要：随着自动化技术的兴起，人们越来越担心各行业工人可能被替代的问题。
1.毕设外文翻译(原版)
IEEE TRANSACTIONS ON AUTOMATIC CONTROL, VOL. AC-19, NO.
5,
OCTOBER
1974
H. P. Geering, “ O p t k l control theory for nonscalar-valued [22] L. A. Zadeh, “Optimality and non-scalar-valued performance performance criteria, Ph.D. dissertation, Dept. Elec. Eng., criteria,” I E E E Trans. Automat. Contr. (Corresp.), vol. AC-8, Mass. Inst. Technol., Cambridge, Aug. 1971 (available in the pp. 59-60, 1963. form of Microfiche Nr. AD 731213, NTIS, U. S. Dept. of Comm.). theory for H. P. Geering and M. Athans,“Optimalcontrol non-scalar-valued performance criteria,” in Proc. 5th Ann. Princeton Conf. Information Sciences and Systems, Princeton, N.J., Mar. 1971. H. Halkin, “On the necessary condition for optimal control of non-linear systems,” J . Analyse Mathhatique, vol. 12, pp. IHans P. Geering (S’7&M’71) was bornon 82, 1964. June 7, 1942. H e received the degree of H. Halkin, “Topological aspects of optimal control of dynamicalpolysystems,” Contrib. Differential Equations, vol. 3, pp. Diplomierter Elektroingenieur from the Eid377-385. 1964. genoesische Technische Hochschulein Zurich, E. B. Lee and L. Markus, Foundations of Optimal Control Switzerland, in 1966, and the M.S. and Ph.D. Theory. New York: Wiley, 1967. degrees from the Massachusetts Institute of L. W.-Neustadt, “A general theory of extremals,” J . Comput. Technology, Cambridge,in 1969 and 1971, Sci. Syst., V O ~ .3, pp. 57-92, 1969. respectively. C. Olech, “Existence theorems for optimal problems with vecIn 1967 and 1968, he worked with Sprecher tor valued cost function,” Center of Dynamical Systems, & Schuh AG in Suhr, Switzerland, and Brown University, Providence, R.I., Tech. Rep. 67-6, 1967. Oerlikon-Buehrle AG in Zurich, Switzerland, K. Ritter, “Optimization theory in linear spaces-Part I,” Math. Annul., vol. 182, pp. 189-206, 1969. From September, 1968 to August, 1971 he was a Research Assistant , “Optimization theory in linear spaces-Part 11,” Math. in the M.I.T. Electronic Systems Laboratory and a Teaching AsAnnal., vol. 183, pp. 169-180, 1969. sistant in the Department of Electrical Engineering at M.I.T. He is , “Optimization theory in linear spaces-Part 111,”Math. presently with Oerlikon-Buehrle AG. His research interests are in Annul., vol. 184, pp. 133-154, 1970. estimation and control theory. R.. T. ltockafellar, Con.vexAnalysis. Princeton, N.J.: Princeton Dr. Geel.ing is a member of Schweizerische Gesellschaft fur AutoUniv. Press, 1970. E. Tse. “On the oDtimal control of linear svstems with in- matik (IFAC) and Schweizerischer Elektrotechnischer Verein. completeinformati&,” Ph.D. dissertation, U*ep. Elec. Eng., Mass. Inst. Technol., Cambridge, Nov., 1969. [20] B. Z. Vulikh, Introduction to the Theory of Partially Ordered Spaces. Groningen, The Netherlands: Wolters-Noordhoff Sc., 1967. [21] H. S. Witsenhausen, “Minimax control of uncertain system,” Electronic Systems Lab., Mass. Inst. Technol., Cambridge, Michael Athans (S’58-M%-SM’69-F’73) for a photograph and Rep. ESGIt-269, 1966. biography see page 30 of February the issue of TRANSACTIONS. this
毕业设计文献翻译
毕业设计文献翻译篇一：毕业设计外文文献翻译毕业设计文文献翻译专业学生姓名班级学号指导教师优集学院外外文资料名称： Knowledge-Based Engineeri- -ng Design Methodology外文资料出处： Int.J.Engng Ed.Vol.16.No.1 附件： 1.外文资料翻译译文基于知识工程设计方法D. E. CALKINS1. 背景复杂系统的发展需要很多工程和管理方面的知识、决策，它要满足很多竞争性的要求。
设计被认为是决定产品最终形态、成本、可靠性、市场接受程度的首要因素。
高级别的工程设计和分析过程特别重要，因为大多数的生命周期成本和整体系统的质量都在这个阶段。
产品成本的压缩最可能发生在产品设计的最初阶段。
整个生命周期阶段大约百分之七十的成本花费在概念设计阶段结束时，缩短设计周期的关键是缩短概念设计阶段，这样同时也减少了工程的重新设计工作量。
工程权衡过程中采用良好的估计和非正式的启发进行概念设计。
传统CAD工具对概念设计阶段的支持非常有限。
有必要，进行涉及多个学科的交流合作来快速进行设计分析。
最后，必须能够管理大量的特定领域的知识。
解决方案是在概念设计阶段包含进更过资源，通过消除重新设计来缩短整个产品的时间。
所有这些因素都主张采取综合设计工具和环境，以在早期的综合设计阶段提供帮助。
这种集成设计工具能够使由不同学科的工程师、设计者在面对复杂的需求和约束时能够对设计意图达成共识。
那个设计工具可以让设计团队研究在更高级别上的更多配置细节。
问题就是架构一个设计工具，以满足所有这些要求。
2. 虚拟原型模型现在需要是一种代表产品设计为得到一将允许一产品的早发展和评价的真实事实上原型的过程的方式。
虚拟样机将取代传统的物理样机，并允许设计工程师，研究“假设”的情况，同时反复更新他们的设计。
真正的虚拟原型，不仅代表形状和形式，即几何形状，它也代表如重量，材料，性能和制造工艺的非几何属性。
本科毕业设计外文文献及译文1
本科毕业设计外文文献及译文文献、资料题目：Transit Route Network Design Problem:Review文献、资料来源：网络文献、资料发表（出版）日期：2007.1院（部）：xxx专业：xxx班级：xxx姓名：xxx学号：xxx指导教师：xxx翻译日期：xxx外文文献：Transit Route Network Design Problem:Review Abstract:Efficient design of public transportation networks has attracted much interest in the transport literature and practice,with manymodels and approaches for formulating the associated transit route network design problem _TRNDP_having been developed.The presentpaper systematically presents and reviews research on the TRNDP based on the three distinctive parts of the TRNDP setup:designobjectives,operating environment parameters and solution approach.IntroductionPublic transportation is largely considered as a viable option for sustainable transportation in urban areas,offering advantages such as mobility enhancement,traffic congestion and air pollution reduction,and energy conservation while still preserving social equity considerations. Nevertheless,in the past decades,factors such as socioeconomic growth,the need for personalized mobility,the increase in private vehicle ownership and urban sprawl have led to a shift towards private vehicles and a decrease in public transportation’s share in daily commuting (Sinha2003;TRB2001;EMTA2004;ECMT2002;Pucher et al.2007).Efforts for encouraging public transportation use focuses on improving provided services such as line capacity,service frequency,coverage,reliability,comfort and service quality which are among the most important parameters for an efficient public transportation system(Sinha2003;Vuchic2004.) In this context,planning and designing a cost and service efficientpublic transportation network is necessary for improving its competitiveness and market share. The problem that formally describes the design of such a public transportation network is referred to as the transit route network design problem(TRNDP);it focuses on the optimization of a number of objectives representing the efficiency of public transportation networks under operational and resource constraints such as the number and length of public transportation routes, allowable service frequencies,and number of available buses(Chakroborty2003;Fan and Machemehl2006a,b).The practical importance of designing public transportation networks has attractedconsiderable interest in the research community which has developed a variety of approaches and modelsfor the TRNDP including different levels of design detail and complexity as well as interesting algorithmic innovations.In thispaper we offer a structured review of approaches for the TRNDP;researchers will obtain a basis for evaluating existing research and identifying future research paths for further improving TRNDP models.Moreover,practitioners will acquire a detailed presentation of both the process and potential tools for automating the design of public transportation networks,their characteristics,capabilities,and strengths.Design of Public Transportation NetworksNetwork design is an important part of the public transportation operational planning process_Ceder2001_.It includes the design of route layouts and the determination of associated operational characteristics such as frequencies,rolling stock types,and so on As noted by Ceder and Wilson_1986_,network design elements are part of the overall operational planning process for public transportation networks;the process includes five steps:_1_design of routes;_2_ setting frequencies;_3_developing timetables;_4_scheduling buses;and_5_scheduling drivers. Route layout design is guided by passenger flows:routes are established to provide direct or indirect connection between locations and areas that generate and attract demand for transit travel, such as residential and activity related centers_Levinson1992_.For example,passenger flows between a central business district_CBD_and suburbs dictate the design of radial routes while demand for trips between different neighborhoods may lead to the selection of a circular route connecting them.Anticipated service coverage,transfers,desirable route shapes,and available resources usually determine the structure of the route network.Route shapes areusually constrained by their length and directness_route directness implies that route shapes are as straight as possible between connected points_,the usage of given roads,and the overlapping with other transit routes.The desirable outcome is a set of routesconnecting locations within a service area,conforming to given design criteria.For each route, frequencies and bus types are the operational characteristics typically determined through design. Calculations are based on expected passenger volumes along routes that are estimated empirically or by applying transit assignmenttechniques,under frequency requirement constraints_minimum and maximum allowedfrequencies guaranteeing safety and tolerable waiting times,respectively_,desired load factors, fleet size,and availability.These steps as well as the overall design.process have been largely based upon practical guidelines,the expert judgment of transit planners,and operators experience_Baaj and Mahmassani1991_.Two handbooks by Black _1995_and Vuchic_2004_outline frameworks to be followed by planners when designing a public transportation network that include:_1_establishing the objectives for the network;_2_ defining the operational environment of the network_road structure,demand patterns,and characteristics_;_3_developing;and_4_evaluating alternative public transportation networks.Despite the extensive use of practical guidelines and experience for designing transit networks,researchers have argued that empirical rules may not be sufficient for designing an efficient transit network and improvements may lead to better quality and more efficient services. For example,Fan and Machemehl_2004_noted that researchers and practitioners have been realizing that systematic and integrated approaches are essential for designing economically and operationally efficient transit networks.A systematic design process implies clear and consistent steps and associated techniques for designing a public transportation network,which is the scope of the TRNDP.TRNDP:OverviewResearch has extensively examined the TRNDP since the late1960s.In1979,Newell discussed previous research on the optimal design of bus routes and Hasselström_1981_ analyzed relevant studies and identified the major features of the TRNDP as demand characteristics,objective functions,constraints,passengerbehavior,solution techniques,and computational time for solving the problem.An extensive review of existing work on transit network design was provided by Chua_1984_who reported five types of transit system planning:_1_manual;_2_marketanalysis;_3_systems analysis;_4_systems analysis with interactive graphics;and_5_ mathematical optimization approach.Axhausemm and Smith_1984_analyzed existing heuristic algorithms for formulating the TRNDP in Europe,tested them,anddiscussed their potential implementation in the United States.Ceder and Wilson_1986_reportedprior work on the TRNDP and distinguished studies into those that deal with idealized networks and to those that focus on actual routes,suggesting that the main features of the TRNDP include demand characteristics,objectivesand constraints,and solution methods.At the same period,Van Nes et al._1988_grouped TRNDP models into six categories:_1_ analytical models for relating parameters of the public transportation system;_2_models determining the links to be used for public transportation route construction;_3_models determining routes only;_4_models assigning frequencies to a set of routes;_5_two-stage models for constructing routes and then assigning frequencies;and_6_models for simultaneously determining routes and frequencies.Spacovic et al._1994_and Spacovic and Schonfeld_1994_proposed a matrix organization and classified each study according to design parameters examined,objectives anticipated,network geometry,and demand characteristics. Ceder and Israeli_1997_suggested broad categorizations for TRNDP models into passenger flow simulation and mathematical programming models.Russo_1998_adopted the same categorization and noted that mathematical programming models guarantee optimal transit network design but sacrifice the level of detail in passenger representation and design parameters, while simulation models address passenger behavior but use heuristic procedures obtaining a TRNDP solution.Ceder_2001_enhanced his earlier categorization by classifying TRNDP models into simulation,ideal network,and mathematical programming models.Finally,in a recent series of studies,Fan and Machemehl_2004,2006a,b_divided TRNDP approaches into practical approaches,analytical optimization models for idealized conditions,and metaheuristic procedures for practical problems.The TRNDP is an optimization problem where objectives are defined,its constraints are determined,and a methodology is selected and validated for obtaining an optimal solution.The TRNDP is described by the objectives of the public transportation network service to be achieved, the operational characteristics and environment under which the network will operate,and the methodological approach for obtaining the optimal network design.Based on this description of the TRNDP,we propose a three-layer structure for organizing TRNDP approaches_Objectives, Parameters,and Methodology_.Each layer includes one or more items that characterize each study.The“Objectives”layer incorporates the goals set when designing a public transportation system such as the minimization of the costs of the system or the maximization of the quality of services provided.The“Parameters”layer describes the operating environment and includes both the design variables expected to be derived for the transit network_route layouts,frequencies_as well as environmental and operational parameters affecting and constraining that network_for example,allowable frequencies,desired load factors,fleet availability,demand characteristics and patterns,and so on_.Finally,the“Methodology”layer covers the logical–mathematical framework and algorithmic tools necessary to formulate and solve the TRNDP.The proposed structure follows the basic concepts toward setting up a TRNDP:deciding upon the objectives, selecting the transit network items and characteristics to be designed,setting the necessary constraints for the operating environment,and formulating and solving the problem. TRNDP:ObjectivesPublic transportation serves a very important social role while attempting to do this at the lowest possible operating cost.Objectives for designing daily operations of a public transportation system should encompass both angles.The literature suggests that most studies actually focus on both the service and economic efficiency when designing such a system. Practical goals for the TRNDP can be briefly summarized as follows_Fielding1987;van Oudheudsen et al.1987;Black1995_:_1_user benefit maximization;_2_operator cost minimization;_3_total welfare maximization;_4_capacity maximization;_5_energy conservation—protection of the environment;and_6_individual parameter optimization.Mandl_1980_indicated that public transportation systems have different objectives to meet. He commented,“even a single objective problem is difficult to attack”_p.401_.Often,these objectives are controversial since cutbacks in operating costs may require reductions in the quality of services.Van Nes and Bovy_2000_pointed out that selected objectives influence the attractiveness and performance of a public transportation network.According to Ceder and Wilson_1986_,minimization of generalized cost or time or maximization of consumer surplus were the most common objectives selected when developing transit network design models. Berechman_1993_agreed that maximization of total welfare is the most suitable objective for designing a public transportation system while Van Nes and Bovy_2000_argued that the minimization of total user and system costs seem the most suit able and less complicatedobjective_compared to total welfare_,while profit maximization leads to nonattractive public transportation networks.As can be seen in Table1,most studies seek to optimize total welfare,which incorporates benefits to the user and to the er benefits may include travel,access and waiting cost minimization,minimization of transfers,and maximization of coverage,while benefits for the system are maximum utilization and quality of service,minimization of operating costs, maximization of profits,and minimization of the fleet size used.Most commonly,total welfare is represented by the minimization of user and system costs.Some studies address specific objectives from the user,theoperator,or the environmental perspective.Passenger convenience,the number of transfers, profit and capacity maximization,travel time minimization,and fuel consumption minimization are such objectives.These studies either attempt to simplify the complex objective functions needed to setup the TRNDP_Newell1979;Baaj and Mahmassani1991;Chakroborty and Dwivedi2002_,or investigate specific aspects of the problem,such as objectives_Delle Site and Fillipi2001_,and the solution methodology_Zhao and Zeng2006;Yu and Yang2006_.Total welfare is,in a sense,a compromise between objectives.Moreover,as reported by some researchers such as Baaj and Mahmassani_1991_,Bielli et al._2002_,Chackroborty and Dwivedi_2002_,and Chakroborty_2003_,transit network design is inherently a multiobjective problem.Multiobjective models for solving the TRNDP have been based on the calculation of indicators representing different objectives for the problem at hand,both from the user and operator perspectives,such as travel and waiting times_user_,and capacity and operating costs _operator_.In their multiobjective model for the TRNDP,Baaj and Majmassani_1991_relied on the planner’s judgment and experience for selecting the optimal public transportation network,based on a set of indicators.In contrast,Bielli et al._2002_and Chakroborty and Dwivedi_2002_,combined indicators into an overall,weighted sum value, which served as the criterion for determining the optimaltransit network.TRNDP:ParametersThere are multiple characteristics and design attributes to consider for a realistic representation of a public transportation network.These form the parameters for the TRNDP.Part of these parameters is the problem set of decision variables that define its layout and operational characteristics_frequencies,vehicle size,etc._.Another set of design parameters represent the operating environment_network structure,demand characters,and patterns_, operational strategies and rules,and available resources for the public transportation network. These form the constraints needed to formulate the TRNDP and are,a-priori fixed,decided upon or assumed.Decision VariablesMost common decision variables for the TRNDP are the routes and frequencies of the public transportation network_Table1_.Simplified early studies derived optimal route spacing between predetermined parallel or radial routes,along with optimal frequencies per route_Holroyd1967; Byrne and Vuchic1972;Byrne1975,1976;Kocur and Hendrickson1982;Vaughan1986_,while later models dealt with the development of optimal route layouts and frequency determination. Other studies,additionally,considered fares_Kocur and Hendrickson1982;Morlok and Viton 1984;Chang and Schonfeld1991;Chien and Spacovic2001_,zones_Tsao and Schonfeld1983; Chang and Schonfeld1993a_,stop locations_Black1979;Spacovic and Schonfeld1994; Spacovic et al.1994;Van Nes2003;Yu and Yang2006_and bus types_Delle Site and Filippi 2001_.Network StructureSome early studies focused on the design of systems in simplified radial_Byrne1975;Black 1979;Vaughan1986_,or rectangular grid road networks_Hurdle1973;Byrne and Vuchic1972; Tsao and Schonfeld1984_.However,most approaches since the1980s were either applied to realistic,irregular grid networks or the network structure was of no importance for the proposed model and therefore not specified at all.Demand PatternsDemand patterns describe the nature of the flows of passengers expected to be accommodated by the public transportation network and therefore dictate its structure.For example,transit trips from a number of origins_for example,stops in a neighborhood_to a single destination_such as a bus terminal in the CBD of a city_and vice-versa,are characterized as many-to-one_or one-tomany_transit demand patterns.These patterns are typically encountered in public transportation systems connecting CBDs with suburbs and imply a structure of radial orparallel routes ending at a single point;models for patterns of that type have been proposed by Byrne and Vuchic_1972_,Salzborn_1972_,Byrne_1975,1976_,Kocur and Hendrickson _1982_,Morlok and Viton_1984_,Chang and Schonfeld_1991,1993a_,Spacovic and Schonfeld_1994_,Spacovic et al._1994_,Van Nes_2003_,and Chien et al._2003_.On the other hand,many-to-many demand patterns correspond to flows between multiple origins and destinations within an urban area,suggesting that the public transportation network is expected to connect various points in an area.Demand CharacteristicsDemand can be characterized either as“fixed”_or“inelastic”_or“elastic”;the later meaning that demand is affected by the performance and services provided by the public transportation network.Lee and Vuchic_2005_distinguished between two types of elastic demand:_1_demand per mode affected by transportation services,with total demand for travel kept constant;and_2_total demand for travel varying as a result of the performance of the transportation system and its modes.Fan and Machemehl_2006b_noted that the complexity of the TRNDP has led researchers intoassuming fixed demand,despite its inherent elastic nature.However,since the early1980s, studies included aspects of elastic demand in modeling the TRNDP_Hasselstrom1981;Kocur and Hendrickson1982_.Van Nes et al._1988_applied a simultaneous distribution-modal split model based on transit deterrence for estimatingdemand for public transportation.In a series of studies,Chang and Schonfeld_1991,1993a,b_ and Spacovic et al._1994_estimated demand as a direct function of travel times and fares with respect to their elasticities,while Chien and Spacovic2001_,followed the same approach assuming that demand is additionally affected by headways,route spacing and fares.Finally, studies by Leblanc_1988_,Imam_1998_,Cipriani et al._2005_,Lee and Vuchic_2005_;and Fan and Machemehl_2006a_based demand estimation on mode choice models for estimating transit demand as a function of total demand for travel.中文译文：公交路线网络设计问题：回顾摘要：公共交通网络的有效设计让交通理论与实践成为众人关注的焦点，随之发展出了很多规划相关公交路线网络设计问题（TRNDP）的模型与方法。
毕业设计外文翻译英文翻译英文原稿
Harmonic source identification and current separationin distribution systemsYong Zhao a，b，Jianhua Li a，Daozhi Xia a,*a Department of Electrical Engineering Xi’an Jiaotong University, 28 West Xianning Road, Xi’an, Shaanxi 710049, Chinab Fujian Electric Power Dispatch and Telecommunication Center, 264 Wusi Road, Fuzhou, Fujian, 350003, China AbstractTo effectively diminish harmonic distortions, the locations of harmonic sources have to be identified and their currents have to be separated from that absorbed by conventional linear loads connected to the same CCP. In this paper, based on the intrinsic difference between linear and nonlinear loads in their V –I characteristics and by utilizing a new simplified harmonic source model, a new principle for harmonic source identification and harmonic current separation is proposed. By using this method, not only the existence of harmonic source can be determined, but also the contributions of the harmonic source and the linear loads to harmonic voltage distortion can be distinguished. The detailed procedure based on least squares approximation is given. The effectiveness of the approach is illustrated by test results on a composite load.2004 Elsevier Ltd. All rights reserved.Keywords: Distribution system; Harmonic source identification; Harmonic current separation; Least squares approximation1. IntroductionHarmonic distortion has experienced a continuous increase in distribution systems owing to the growing use of nonlinear loads. Many studies have shown that harmonics may cause serious effects on power systems, communication systems, and various apparatus [1–3]. Harmonic voltages at each point on a distribution network are not only determined by the harmonic currents produced by harmonic sources (nonlinear loads), but also related to all linear loads (harmonic current sinks) as well as the structure and parameters of the network. To effectively evaluate and diminish the harmonic distortion in power systems, the locations of harmonic sources have to be identified and the responsibility of the distortion caused by related individual customers has to be separated.As to harmonic source identification, most commonly the negative harmonic power is considered as an essential evidence of existing harmonic source [4–7]. Several approaches aiming at evaluating the contribution of an individual customer can also be found in the literatures. Schemes based on power factor measurement to penalize the customer’s harmonic currents are discussed in Ref. [8]. However, it would be unfair to use economical penalization if we could not distinguish whether the measured harmonic current is from nonlinear load or from linear load.In fact, the intrinsic difference between linear and nonlinear loads lies in their V –I characteristics. Harmonic currents of a linear load are i n linear proportion to its supplyharmonic voltages of the same order 次, whereas the harmonic currents of a nonlinear load are complex nonlinear functions of its supply fundamental 基波and harmonic voltage components of all orders. To successfully identify and isolate harmonic source in an individual customer or several customers connected at same point in the network, the V –I characteristics should be involved and measurement of voltages and currents under several different supply conditions should be carried out.As the existing approaches based on measurements of voltage and current spectrum or harmonic power at a certain instant cannot reflect the V –I characteristics, they may not provide reliable information about the existence and contribution of harmonic sources, which has been substantiated by theoretical analysis or experimental researches [9,10].In this paper, to approximate the nonlinear characteristics and to facilitate the work in harmonic source identification and harmonic current separation, a new simplified harmonic source model is proposed. Then based on the difference between linear and nonlinear loads in their V –I characteristics, and by utilizing the harmonic source model, a new principle for harmonic source identification and harmonic current separation is presented. By using the method, not only the existence of harmonic source can be determined, but also the contributions of the harmonic sources and the linear loads can be separated. Detailed procedure of harmonic source identification and harmonic current separation based on least squares approximation is presented. Finally, test results on a composite load containing linear and nonlinear loads are given to illustrate the effectiveness of the approach.2. New principle for harmonic source identification and current separationConsider a composite load to be studied in a distribution system, which may represent an individual consumer or a group of customers supplied by a common feeder 支路in the system. To identify whether it contains any harmonic source and to separate the harmonic currents generated by the harmonic sources from that absorbed by conventional linear loads in the measured total harmonic currents of the composite load, the following assumptions are made.(a) The supply voltage and the load currents are both periodical waveforms withperiod T; so that they can be expressed by Fourier series as1()s i n (2)h h h v t ht T πθ∞==+ (1)1()sin(2)h h h i t ht πφ∞==+The fundamental frequency and harmonic components can further be presented bycorresponding phasorshr hi h h hr hi h hV jV V I jI I θφ+=∠+=∠ , 1,2,3,...,h n = (2)(b) During the period of identification, the composite load is stationary, i.e. both its composition and circuit parameters of all individual loads keep unchanged.Under the above assumptions, the relationship between the total harmonic currents of the harmonic sources(denoted by subscript N) in the composite load and the supply voltage, i.e. the V –I characteristics, can be described by the following nonlinear equation ()()()N i t f v t = (3)and can also be represented in terms of phasors as()()122122,,,...,,,,,,...,,Nhr r i nr ni Nh Nhi r inr ni I V V V V V I I V V V V V ⎡⎤=⎢⎥⎣⎦ 2,3,...,h n = (4)Note that in Eq. (4), the initial time (reference time) of the voltage waveform has been properly selected such that the phase angle u1 becomes 0 and 10i V =, 11r V V =in Eq. (2)for simplicity.The V –I characteristics of the linear part (denote by subscript L) of the composite load can be represented by its equivalent harmonic admittance Lh Lh Lh Y G jB =+, and the total harmonic currents absorbed by the linear part can be described as,Lhr LhLh hr Lh Lhi LhLh hi I G B V I I B G V -⎡⎤⎡⎤⎡⎤==⎢⎥⎢⎥⎢⎥⎣⎦⎣⎦⎣⎦2,3,...,h n = (5)From Eqs. (4) and (5), the whole harmonic currents absorbed by the composite load can be expressed as()()122122,,,...,,,,,,...,,hr Lhr Nhr r i nr ni h hi Lhi Nhi r inr ni I I I V V V V V I I I I V V V V V ⎡⎤⎡⎤⎡⎤==-⎢⎥⎢⎥⎢⎥⎣⎦⎣⎦⎣⎦ 2,3,...,h n = (6)As the V –I characteristics of harmonic source are nonlinear, Eq. (6) can neither be directly used for harmonic source identification nor for harmonic current separation. To facilitate the work in practice, simplified methods should be involved. The common practice in harmonic studies is to represent nonlinear loads by means of current harmonic sources or equivalent Norton models [11,12]. However, these models are not of enough precision and new simplified model is needed.From the engineering point of view, the variations of hr V and hi V ; ordinarily fall into^3% bound of the rated bus voltage, while the change of V1 is usually less than ^5%. Within such a range of supply voltages, the following simplified linear relation is used in this paper to approximate the harmonic source characteristics, Eq. (4)112222112322,ho h h r r h i i hnr nr hni ni Nh ho h h r r h i i hnr nr hni ni a a V a V a V a V a V I b b V b V b V b V b V ++++++⎡⎤=⎢⎥++++++⎣⎦2,3,...,h n = (7)这个地方不知道是不是原文写错？23h r r b V 其他的都是2The precision and superiority of this simplified model will be illustrated in Section 4 by test results on several kinds of typical harmonic sources.The total harmonic current (Eq. (6)) then becomes112222112222,2,3,...,Lh Lh hr ho h h r r h i i hnr nr hni ni h Lh Lh hi ho h h r r h i i hnr nr hni ni G B V a a V a V a V a V a V I B G V b b V b V b V b V b V h n-++++++⎡⎤⎡⎤⎡⎤=-⎢⎥⎢⎥⎢⎥++++++⎣⎦⎣⎦⎣⎦= (8)It can be seen from the above equations that the harmonic currents of the harmonic sources (nonlinear loads) and the linear loads differ from each other intrinsically in their V –I characteristics. The harmonic current component drawn by the linear loads is uniquely determined by the harmonic voltage component with same order in the supply voltage. On the other hand, the harmonic current component of the nonlinear loads contains not only a term caused by the same order harmonic voltage but also a constant term and the terms caused by fundamental and harmonic voltages of all other orders. This property will be used for identifying the existence of harmonic source sin composite load.As the test results shown in Section 4 demonstrate that the summation of the constant term and the component related to fundamental frequency voltage in the harmonic current of nonlinear loads is dominant whereas other components are negligible, further approximation for Eq. (7) can be made as follows.Let112'012()()nh h hkr kr hki ki k k h Nhnh h hkr kr hki kik k h a a V a V a V I b b V b V b V =≠=≠⎡⎤+++⎢⎥⎢⎥=⎢⎥⎢⎥+++⎢⎥⎢⎥⎣⎦∑∑ hhr hhi hr Nhhhr hhi hi a a V I b b V ⎡⎤⎡⎤''=⎢⎥⎢⎥⎣⎦⎣⎦hhrhhihr Lh Lh Nh hhrhhi hi a a V I I I b b V ''⎡⎤⎡⎤'''=-=⎢⎥⎢⎥''⎣⎦⎣⎦,2,3,...,hhr hhiLh Lh hhrhhi hhr hhi Lh Lh hhr hhi a a G B a a h n b b B G b b ''-⎡⎤⎡⎤⎡⎤=-=⎢⎥⎢⎥⎢⎥''⎣⎦⎣⎦⎣⎦The total harmonic current of the composite load becomes112012(),()2,3,...,nh h hkr kr hki ki k k hhhrhhi hr h Lh NhLhNh n hhrhhi hi h h hkr kr hki kik k h a a V a V a V a a V I I I I I b b V b b V b V b V h n=≠=≠⎡⎤+++⎢⎥⎢⎥''⎡⎤⎡⎤''=-=-=-⎢⎥⎢⎥⎢⎥''⎣⎦⎣⎦⎢⎥+++⎢⎥⎢⎥⎣⎦=∑∑ (9)By neglecting ''Nh I in the harmonic current of nonlinear load and adding it to the harmonic current of linear load, 'Nh I can then be deemed as harmonic current of thenonlinear load while ''Lh I can be taken as harmonic current of the linear load. ''Nh I =0 means the composite load contains no harmonic sources, while ''0NhI ≠signify that harmonic sources may exist in this composite load. As the neglected term ''Nh I is not dominant, it is obviousthat this simplification does not make significant error on the total harmonic current of nonlinear load. However, it makes the possibility or the harmonic source identification and current separation.3. Identification procedureIn order to identify the existence of harmonic sources in a composite load, the parameters in Eq. (9) should be determined primarily, i.e.[]0122hr h h h rh i hhr hhihnr hni C a a a a a a a a ''= []0122hi h h h rh i hhrhhihnr hni C b b b b b b b b ''=For this purpose, measurement of different supply voltages and corresponding harmoniccurrents of the composite load should be repeatedly performed several times in some short period while keeping the composite load stationary. The change of supply voltage can for example be obtained by switching in or out some shunt capacitors, disconnecting a parallel transformer or changing the tap position of transformers with OLTC. Then, the least squares approach can be used to estimate the parameters by the measured voltages and currents. The identification procedure will be explained as follows.(1) Perform the test for m （2m n ≥）times to get measured fundamental frequency andharmonic voltage and current phasors ()()k k h h V θ∠,()()k k hh I φ∠,()1,2,,,1,2,,k m h n == .(2) For 1,2,,k n = ，transfer the phasors corresponding to zero fundamental voltage phase angle ()1(0)k θ=and change them into orthogonal components, i.e.()()11kkr V V = ()10ki V =()()()()()()()()()()11cos sin kkkkk kkkhr h h hihhV V h V V h θθθθ=-=-()()()()()()()()()()11cos sin k kkkk kkkhrhhhihhI I h I I h φθφθ=-=-,2,3,...,h n =(3)Let()()()()()()()()1221Tk k k k k k k k r i hr hi nr ni VV V V V V V V ⎡⎤=⎣⎦ ,()1,2,,k m = ()()()12Tm X V V V ⎡⎤=⎣⎦ ()()()12T m hr hr hr hrW I I I ⎡⎤=⎣⎦()()()12Tm hi hi hihi W I I I ⎡⎤=⎣⎦ Minimize ()()()211hr mk hr k I C V=-∑ and ()()()211him k hi k IC V=-∑, and determine the parametershr C and hi C by least squares approach as [13]:()()11T T hr hr T T hi hiC X X X W C X X X W --== (10)(4) By using Eq. (9), calculate I0Lh; I0Nh with the obtained Chr and Chi; then the existence of harmonic source is identified and the harmonic current is separated.It can be seen that in the course of model construction, harmonic source identification and harmonic current separation, m times changing of supply system operating condition and measuring of harmonic voltage and currents are needed. More accurate the model, more manipulations are necessary.To compromise the needed times of the switching operations and the accuracy of the results, the proposed model for the nonlinear load (Eq. (7)) and the composite load (Eq. (9)) can be further simplified by only considering the dominant terms in Eq. (7), i.e.01111,Nhr h h hhr hhi hr Nh Nhi ho h hhrhhi hi I a a V a a V I I b b V b b V +⎡⎤⎡⎤⎡⎤⎡⎤==+⎢⎥⎢⎥⎢⎥⎢⎥+⎣⎦⎣⎦⎣⎦⎣⎦2,3,,h n = (11) 01111h h Nh ho h a a V I b b V +⎡⎤'=⎢⎥+⎣⎦01111,hr hhrhhi hr h h h LhNh hi hhr hhihi ho h I a a V a a V I I I I b b V b b V ''+⎡⎤⎡⎤⎡⎤⎡⎤''==-=-⎢⎥⎢⎥⎢⎥⎢⎥''+⎣⎦⎣⎦⎣⎦⎣⎦2,3,,h n = (12) In this case, part equations in the previous procedure should be changed as follows[]01hr h h hhrhhi C a a a a ''= []01hi h h hhrhhiC b b b b ''= ()()()1Tk k k hr hi V V V ⎡⎤=⎣⎦ Similarly, 'Nh I and 'Lh I can still be taken as the harmonic current caused by thenonlinear load and the linear load, respectively.4. Experimental validation4.1. Model accuracyTo demonstrate the validity of the proposed harmonic source models, simulations are performed on the following three kind of typical nonlinear loads: a three-phase six-pulse rectifier, a single-phase capacitor-filtered rectifier and an acarc furnace under stationary operating condition.Diagrams of the three-phase six-pulse rectifier and the single-phase capacitor-filtered rectifier are shown in Figs. 1 and 2 [14,15], respectively, the V –I characteristic of the arc furnace is simplified as shown in Fig. 3 [16].The harmonic currents used in the simulation test are precisely calculated from their mathematical model. As to the supply voltage, VekT1 is assumed to be uniformly distributed between 0.95 and 1.05, VekThr and VekThi ek 1; 2;…;m T are uniformly distributed between20.03 and 0.03 with base voltage 10 kV and base power 1 MVFig. 1. Diagram of three-phase six-pulse rectifier.Fig. 2. Diagram of single-phase capacitor-filtered rectifierFig. 3. Approximate V –I characteristics of arc furnace.Three different models including the harmonic current source (constant current) model, the Norton model and the proposed simplified model are simulated and estimated by the least squares approach for comparison.For the three-phase six-pulse rectifier with fundamental currentI=1.7621; the1 parameters in the simplified model for fifth and seventh harmonic currents are listed in Table 1.To compare the accuracy of the three different models, the mean and standard deviations of the errors on Ihr; Ihi and Ih between estimated value and the simulated actual value are calculated for each model. The error comparison of the three models on the three-phase six-pulse rectifier is shown in Table 2, where mhr; mhi and mha denote the mean, and shr; shi and sha represent the standard deviations. Note that I1 and _Ih in Table 2are the current values caused by rated pure sinusoidal supply voltage.Error comparisons on the single-phase capacitor-filtered rectifier and the arc furnace load are listed in Table 3 and 4, respectively.It can be seen from the above test results that the accuracy of the proposed model is different for different nonlinear loads, while for a certain load, the accuracy will decrease as the harmonic order increase. However, the proposed model is always more accurate than other two models.It can also be seen from Table 1 that the componenta50 t a51V1 and b50 t b51V1 are around 20:0074 t0:3939 0:3865 and 0:0263 t 0:0623 0:0886 while the componenta55V5r and b55V5i will not exceed 0:2676 ￡0:03 0:008 and 0:9675 ￡0:003 0:029; respectively. The result shows that the fifth harmonic current caused by the summation of constant term and the fundamental voltage is about 10 times of that caused by harmonic voltage with same order, so that the formal is dominant in the harmonic current for the three-phase six-pulse rectifier. The same situation exists for other harmonic orders and other nonlinear loads.4.2. Effectiveness of harmonic source identification and current separationTo show the effectiveness of the proposed harmonic source identification method, simulations are performed on a composite load containing linear load (30%) and nonlinear loads with three-phase six-pulse rectifier (30%),single-phase capacitor-filtered rectifier (20%) and ac arc furnace load (20%).For simplicity, only the errors of third order harmonic current of the linear and nonlinear loads are listed in Table 5, where IN3 denotes the third order harmonic current corresponding to rated pure sinusoidal supply voltage; mN3r ;mN3i;mN3a and mL3r ;mL3i;mL3a are error means of IN3r ; IN3i; IN3 and IL3r ; IL3i; IL3 between the simulated actual value and the estimated value;sN3r ;sN3i;sN3a and sL3r ;sL3i;sL3a are standard deviations.Table 2Table 3It can be seen from Table 5 that the current errors of linear load are less than that of nonlinear loads. This is because the errors of nonlinear load currents are due to both the model error and neglecting the components related to harmonic voltages of the same order, whereas only the later components introduce errors to the linear load currents. Moreover, it can be found that more precise the composite load model is, less error is introduced. However, even by using the very simple model (12), the existence of harmonic sources can be correctly identified and the harmonic current of linear and nonlinear loads can be effectively separated. Table 4Error comparison on the arc furnaceTable 55. ConclusionsIn this paper, from an engineering point of view, firstly anew linear model is presented for representing harmonic sources. On the basis of the intrinsic difference between linear and nonlinear loads in their V –I characteristics, and by using the proposed harmonic source model, a new concise principle for identifying harmonic sources and separating harmonic source currents from that of linear loads is proposed. The detailed modeling and identification procedure is also developed based on the least squares approximation approach. Test results on several kinds of typical harmonic sources reveal that the simplified model is of sufficient precision, and is superior to other existing models. The effectiveness of the harmonic source identification approach is illustrated using a composite nonlinear load.AcknowledgementsThe authors wish to acknowledge the financial support by the National Natural Science Foundation of China for this project, under the Research Program Grant No.59737140. 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Application of algorithms and artificial intelligence approach for locating multiple harmonics in distribution systems. IEE Proc.—Gener. Transm. Distrib 1999;146(3):325–9.[8] Mceachern A, Grady WM, Moncerief WA, Heydt GT, McgranaghanM. Revenue and harmonics: an evaluation of someproposed rate structures. IEEE Trans Power Deliv 1995;10(1):474–82.[9] Xu W. Power direction method cannot be used for harmonic sourcedetection. Power Engineering Society Summer Meeting, IEEE; 2000.p. 873–6.[10] Sasdelli R, Peretto L. A VI-based measurement system for sharing the customer and supply responsibility for harmonic distortion. IEEETrans Instrum Meas 1998;47(5):1335–40.[11] Arrillaga J, Bradley DA, Bodger PS. Power system harmonics. NewYork: Wiley; 1985.[12] Thunberg E, Soder L. A Norton approach to distribution networkmodeling for harmonic studies. IEEE Trans Power Deliv 1999;14(1):272–7.[13] Giordano AA, Hsu FM. Least squares estimation with applications todigital signal processing. 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毕业设计(论文)外文文献原文及译文
毕业设计（论文）外文文献原文及译文Chapter 11. Cipher Techniques11.1 ProblemsThe use of a cipher without consideration of the environment in which it is to be used may not provide the security that the user expects. Three examples will make this point clear.11.1.1 Precomputing the Possible MessagesSimmons discusses the use of a "forward search" to decipher messages enciphered for confidentiality using a public key cryptosystem [923]. His approach is to focus on the entropy (uncertainty) in the message. To use an example from Section 10.1(page 246), Cathy knows that Alice will send one of two messages—BUY or SELL—to Bob. The uncertainty is which one Alice will send. So Cathy enciphers both messages with Bob's public key. When Alice sends the message, Bob intercepts it and compares the ciphertext with the two he computed. From this, he knows which message Alice sent.Simmons' point is that if the plaintext corresponding to intercepted ciphertext is drawn from a (relatively) small set of possible plaintexts, the cryptanalyst can encipher the set of possible plaintexts and simply search that set for the intercepted ciphertext. Simmons demonstrates that the size of the set of possible plaintexts may not be obvious. As an example, he uses digitized sound. The initial calculations suggest that the number of possible plaintexts for each block is 232. Using forward search on such a set is clearly impractical, but after some analysis of the redundancy in human speech, Simmons reduces the number of potential plaintexts to about 100,000. This number is small enough so that forward searches become a threat.This attack is similar to attacks to derive the cryptographic key of symmetric ciphers based on chosen plaintext (see, for example, Hellman's time-memory tradeoff attack [465]). However, Simmons' attack is for public key cryptosystems and does not reveal the private key. It only reveals the plaintext message.11.1.2 Misordered BlocksDenning [269] points out that in certain cases, parts of a ciphertext message can be deleted, replayed, or reordered.11.1.3 Statistical RegularitiesThe independence of parts of ciphertext can give information relating to the structure of the enciphered message, even if the message itself is unintelligible. The regularity arises because each part is enciphered separately, so the same plaintext always produces the same ciphertext. This type of encipherment is called code book mode, because each part is effectively looked up in a list of plaintext-ciphertext pairs.11.1.4 SummaryDespite the use of sophisticated cryptosystems and random keys, cipher systems may provide inadequate security if not used carefully. The protocols directing how these cipher systems are used, and the ancillary information that the protocols add to messages and sessions, overcome these problems. This emphasizes that ciphers and codes are not enough. The methods, or protocols, for their use also affect the security of systems.11.2 Stream and Block CiphersSome ciphers divide a message into a sequence of parts, or blocks, and encipher each block with the same key.Definition 11–1. Let E be an encipherment algorithm, and let Ek(b) bethe encipherment of message b with key k. Let a message m = b1b2…, whereeach biis of a fixed length. Then a block cipher is a cipher for whichE k (m) = Ek(b1)Ek(b2) ….Other ciphers use a nonrepeating stream of key elements to encipher characters of a message.Definition 11–2. Let E be an encipherment algorithm, and let Ek(b) bethe encipherment of message b with key k. Let a message m = b1b2…, whereeach bi is of a fixed length, and let k = k1k2…. Then a stream cipheris a cipher for which Ek (m) = Ek1(b1)Ek2(b2) ….If the key stream k of a stream cipher repeats itself, it is a periodic cipher.11.2.1 Stream CiphersThe one-time pad is a cipher that can be proven secure (see Section 9.2.2.2, "One-Time Pad"). Bit-oriented ciphers implement the one-time pad by exclusive-oring each bit of the key with one bit of the message. For example, if the message is 00101 and the key is 10010, the ciphertext is01||00||10||01||10 or 10111. But how can one generate a random, infinitely long key?11.2.1.1 Synchronous Stream CiphersTo simulate a random, infinitely long key, synchronous stream ciphers generate bits from a source other than the message itself. The simplest such cipher extracts bits from a register to use as the key. The contents of the register change on the basis of the current contents of the register.Definition 11–3. An n-stage linear feedback shift register (LFSR)consists of an n-bit register r = r0…rn–1and an n-bit tap sequence t =t 0…tn–1. To obtain a key bit, ris used, the register is shifted one bitto the right, and the new bit r0t0⊕…⊕r n–1t n–1 is inserted.The LFSR method is an attempt to simulate a one-time pad by generating a long key sequence from a little information. As with any such attempt, if the key is shorter than the message, breaking part of the ciphertext gives the cryptanalyst information about other parts of the ciphertext. For an LFSR, a known plaintext attack can reveal parts of the key sequence. If the known plaintext is of length 2n, the tap sequence for an n-stage LFSR can be determined completely.Nonlinear feedback shift registers do not use tap sequences; instead, the new bit is any function of the current register bits.Definition 11–4. An n-stage nonlinear feedback shift register (NLFSR)consists of an n-bit register r = r0…rn–1. Whenever a key bit is required,ris used, the register is shifted one bit to the right, and the new bitis set to f(r0…rn–1), where f is any function of n inputs.NLFSRs are not common because there is no body of theory about how to build NLFSRs with long periods. By contrast, it is known how to design n-stage LFSRs with a period of 2n– 1, and that period is maximal.A second technique for eliminating linearity is called output feedback mode. Let E be an encipherment function. Define k as a cryptographic key,(r) and define r as a register. To obtain a bit for the key, compute Ekand put that value into the register. The rightmost bit of the result is exclusive-or'ed with one bit of the message. The process is repeated until the message is enciphered. The key k and the initial value in r are the keys for this method. This method differs from the NLFSR in that the register is never shifted. It is repeatedly enciphered.A variant of output feedback mode is called the counter method. Instead of using a register r, simply use a counter that is incremented for every encipherment. The initial value of the counter replaces r as part of the key. This method enables one to generate the ith bit of the key without generating the bits 0…i – 1. If the initial counter value is i, set. In output feedback mode, one must generate all the register to i + ithe preceding key bits.11.2.1.2 Self-Synchronous Stream CiphersSelf-synchronous ciphers obtain the key from the message itself. The simplest self-synchronous cipher is called an autokey cipher and uses the message itself for the key.The problem with this cipher is the selection of the key. Unlike a one-time pad, any statistical regularities in the plaintext show up in the key. For example, the last two letters of the ciphertext associated with the plaintext word THE are always AL, because H is enciphered with the key letter T and E is enciphered with the key letter H. Furthermore, if theanalyst can guess any letter of the plaintext, she can determine all successive plaintext letters.An alternative is to use the ciphertext as the key stream. A good cipher will produce pseudorandom ciphertext, which approximates a randomone-time pad better than a message with nonrandom characteristics (such as a meaningful English sentence).This type of autokey cipher is weak, because plaintext can be deduced from the ciphertext. For example, consider the first two characters of the ciphertext, QX. The X is the ciphertext resulting from enciphering some letter with the key Q. Deciphering, the unknown letter is H. Continuing in this fashion, the analyst can reconstruct all of the plaintext except for the first letter.A variant of the autokey method, cipher feedback mode, uses a shift register. Let E be an encipherment function. Define k as a cryptographic(r). The key and r as a register. To obtain a bit for the key, compute Ek rightmost bit of the result is exclusive-or'ed with one bit of the message, and the other bits of the result are discarded. The resulting ciphertext is fed back into the leftmost bit of the register, which is right shifted one bit. (See Figure 11-1.)Figure 11-1. Diagram of cipher feedback mode. The register r is enciphered with key k and algorithm E. The rightmost bit of the result is exclusive-or'ed with one bit of the plaintext m i to produce the ciphertext bit c i. The register r is right shifted one bit, and c i is fed back into the leftmost bit of r.Cipher feedback mode has a self-healing property. If a bit is corrupted in transmission of the ciphertext, the next n bits will be deciphered incorrectly. But after n uncorrupted bits have been received, the shift register will be reinitialized to the value used for encipherment and the ciphertext will decipher properly from that point on.As in the counter method, one can decipher parts of messages enciphered in cipher feedback mode without deciphering the entire message. Let the shift register contain n bits. The analyst obtains the previous n bits of ciphertext. This is the value in the shift register before the bit under consideration was enciphered. The decipherment can then continue from that bit on.11.2.2 Block CiphersBlock ciphers encipher and decipher multiple bits at once, rather than one bit at a time. For this reason, software implementations of block ciphers run faster than software implementations of stream ciphers. Errors in transmitting one block generally do not affect other blocks, but as each block is enciphered independently, using the same key, identical plaintext blocks produce identical ciphertext blocks. This allows the analyst to search for data by determining what the encipherment of a specific plaintext block is. For example, if the word INCOME is enciphered as one block, all occurrences of the word produce the same ciphertext.To prevent this type of attack, some information related to the block's position is inserted into the plaintext block before it is enciphered. The information can be bits from the preceding ciphertext block [343] or a sequence number [561]. The disadvantage is that the effective block size is reduced, because fewer message bits are present in a block.Cipher block chaining does not require the extra information to occupy bit spaces, so every bit in the block is part of the message. Before a plaintext block is enciphered, that block is exclusive-or'ed with the preceding ciphertext block. In addition to the key, this technique requires an initialization vector with which to exclusive-or the initial plaintext block. Taking Ekto be the encipherment algorithm with key k, and I to be the initialization vector, the cipher block chaining technique isc 0 = Ek(m⊕I)c i = Ek(mi⊕ci–1) for i > 011.2.2.1 Multiple EncryptionOther approaches involve multiple encryption. Using two keys k and k' toencipher a message as c = Ek' (Ek(m)) looks attractive because it has aneffective key length of 2n, whereas the keys to E are of length n. However, Merkle and Hellman [700] have shown that this encryption technique can be broken using 2n+1encryptions, rather than the expected 22n(see Exercise 3).Using three encipherments improves the strength of the cipher. There are several ways to do this. Tuchman [1006] suggested using two keys k and k':c = Ek (Dk'(Ek(m)))This mode, called Encrypt-Decrypt-Encrypt (EDE) mode, collapses to a single encipherment when k = k'. The DES in EDE mode is widely used in the financial community and is a standard (ANSI X9.17 and ISO 8732). It is not vulnerable to the attack outlined earlier. However, it is vulnerable to a chosen plaintext and a known plaintext attack. If b is the block size in bits, and n is the key length, the chosen plaintext attacktakes O(2n) time, O(2n) space, and requires 2n chosen plaintexts. The known plaintext attack requires p known plaintexts, and takes O(2n+b/p) time and O(p) memory.A second version of triple encipherment is the triple encryption mode [700]. In this mode, three keys are used in a chain of encipherments.c = Ek (Ek'(Ek''(m)))The best attack against this scheme is similar to the attack on double encipherment, but requires O(22n) time and O(2n) memory. If the key length is 56 bits, this attack is computationally infeasible.11.3 Networks and CryptographyBefore we discuss Internet protocols, a review of the relevant properties of networks is in order. The ISO/OSI model [990] provides an abstract representation of networks suitable for our purposes. Recall that the ISO/OSI model is composed of a series of layers (see Figure 11-2). Each host, conceptually, has a principal at each layer that communicates with a peer on other hosts. These principals communicate with principals at the same layer on other hosts. Layer 1, 2, and 3 principals interact only with similar principals at neighboring (directly connected) hosts. Principals at layers 4, 5, 6, and 7 interact only with similar principals at the other end of the communication. (For convenience, "host" refers to the appropriate principal in the following discussion.)Figure 11-2. The ISO/OSI model. The dashed arrows indicate peer-to-peer communication. For example, the transport layers are communicating with each other. The solid arrows indicate the actual flow of bits. For example, the transport layer invokes network layer routines on the local host, which invoke data link layer routines, which put the bits onto the network. The physical layer passes the bits to the next "hop," or host, on the path. When the message reaches the destination, it is passed up to the appropriatelevel.Each host in the network is connected to some set of other hosts. They exchange messages with those hosts. If host nob wants to send a message to host windsor, nob determines which of its immediate neighbors is closest to windsor (using an appropriate routing protocol) and forwards the message to it. That host, baton, determines which of its neighbors is closest to windsor and forwards the message to it. This process continues until a host, sunapee, receives the message and determines that windsor is an immediate neighbor. The message is forwarded to windsor, its endpoint.Definition 11–5. Let hosts C0, …, Cnbe such that Ciand Ci+1are directlyconnected, for 0 i < n. A communications protocol that has C0 and Cnasits endpoints is called an end-to-end protocol. A communications protocolthat has Cj and Cj+1as its endpoints is called a link protocol.The difference between an end-to-end protocol and a link protocol is that the intermediate hosts play no part in an end-to-end protocol other than forwarding messages. On the other hand, a link protocol describes how each pair of intermediate hosts processes each message.The protocols involved can be cryptographic protocols. If the cryptographic processing is done only at the source and at the destination, the protocol is an end-to-end protocol. If cryptographic processing occurs at each host along the path from source to destination, the protocolis a link protocol. When encryption is used with either protocol, we use the terms end-to-end encryption and link encryption, respectively.In link encryption, each host shares a cryptographic key with its neighbor. (If public key cryptography is used, each host has its neighbor's public key. Link encryption based on public keys is rare.) The keys may be set on a per-host basis or a per-host-pair basis. Consider a network with four hosts called windsor, stripe, facer, and seaview. Each host is directly connected to the other three. With keys distributed on a per-host basis, each host has its own key, making four keys in all. Each host has the keys for the other three neighbors, as well as its own. All hosts use the same key to communicate with windsor. With keys distributed on a per-host-pair basis, each host has one key per possible connection, making six keys in all. Unlike the per-host situation, in the per-host-pair case, each host uses a different key to communicate with windsor. The message is deciphered at each intermediate host, reenciphered for the next hop, and forwarded. Attackers monitoring the network medium will not be able to read the messages, but attackers at the intermediate hosts will be able to do so.In end-to-end encryption, each host shares a cryptographic key with each destination. (Again, if the encryption is based on public key cryptography, each host has—or can obtain—the public key of each destination.) As with link encryption, the keys may be selected on a per-host or per-host-pair basis. The sending host enciphers the message and forwards it to the first intermediate host. The intermediate host forwards it to the next host, and the process continues until the message reaches its destination. The destination host then deciphers it. The message is enciphered throughout its journey. Neither attackers monitoring the network nor attackers on the intermediate hosts can read the message. However, attackers can read the routing information used to forward the message.These differences affect a form of cryptanalysis known as traffic analysis.A cryptanalyst can sometimes deduce information not from the content ofthe message but from the sender and recipient. For example, during the Allied invasion of Normandy in World War II, the Germans deduced which vessels were the command ships by observing which ships were sending and receiving the most signals. The content of the signals was not relevant; their source and destination were. Similar deductions can reveal information in the electronic world.第十一章密码技术11．1问题在没有考虑加密所要运行的环境时，加密的使用可能不能提供用户所期待的安全。
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High power matrix converter for wind power generation applications高功率矩阵交换器在风力发电中的应用摘要：矩阵变换器在风力发电系统的应用中有很多优点。
矩阵变换器是紧凑和高效的，因为它将电流直接从交流发电机转换到交流电网中而不需要经过发电中间直流总线，但是传统的背靠背转换系统需要在直流母线中装设许多电解电容器，并且这些电容器体型笨重，寿命时间短。
矩阵变换器同时具有驾驭和再生电流的能力，能在电网中保持较低的谐波电流，此外，它还可以向电网提供无功功率，这对于风电场在电网故障期间和之后保持电力系统稳定具有非常重要的意义。
本文介绍了高功率矩阵转换器在风力发电中的应用，并描述了它的主要技术特点和优势。
而且利用永磁发电机进行的实验结果表明，高功率矩阵转换器在风力发电应用中具有良好的可行性。
关键词：交流-交流转换器低电压穿越矩阵转换器风力发电系统图1风力发电机组传动系统中矩阵变换器的基本概念一引言矩阵转换器是一种直接的从交流到交流的电力转换拓扑结构1）主电路的MXC 由输入滤波器和9个双向开关组成2）它是完全可再生的，并且具有控制输入正弦电流功率因数的能力。
3）MXC的一个很大的优势是它无需安装既笨重寿命时间又短的直流母线电容器[1]-[4]。
MXC比传统的电压源背靠别转换系统更加高效和紧凑。
图1中的双向开关通常由两对反向的IGBT二极管构成[5]- [6]。
通过一种独特的PWM控制方法，MXC可以同时控制输出电压和具有较低谐波的输入电流[7] - [9]。
图2低压矩阵换流器的主电路图2所示的拓扑结构是MXC的一种典型的配置，但它更适合于额定功率小于几百千瓦，额定电压在690伏以下的系统，因为其它电流增加和电压评级的限制。
因此，基于MXC的基本拓扑结构的模块化的矩阵转换器已经得到了开发[3]。
它为那些需要具有再生能力能力的高功率驱动器的市场提供了一个极具吸引力的解决方案，比如纸复卷机，大功率水泵，钢厂以及风力发电系统。
它体积小巧，并且其输入和输出的波形具有较低的谐波。
本文解释了高功率矩阵转换器的基本模块化概念，然后在实验结果的基础上阐述了其在风力发电系统中的应用。
图3单相矩阵变换器功率单元的配置二矩阵变换器的拓扑结构在风力发电系统中的应用A.矩阵变换器的模块化概念在转换器的设计中功率和额定电压的灵活性对于满足不同客户的要求是很重要的。
适用于风力发电机组传动系统的矩阵变换器采用了模块化设计的概念，使得它为满足功率和额定电压的各种需求提供快速和最佳的解决方案时具有很大的灵活性。
风力发电系统电压有望随着系统额定功率的增加逐步从标准电压690V 增加到中压级别，电压升高的的优点压在于它可以降低发电机和电源转换器之间电力传输的损耗，并能减少体积和机舱的重量，降低成本[10]。
模块化驱动器的一个基本模块是单相输出矩阵转换器（SPMC），如图3-4所示。
级联H桥电压源逆变器拓扑和使用高压电源开关的三电平逆变器在中压驱动器中得到了广泛的应用[11]- [16]。
但背靠背转换器-逆变器系统应当用于需要再生的功率流的设备中。
图3中所示的电池单元由6双向开关和交流电容器组成。
基本上，此电路是一个三相输入单相输出的矩阵转换器，简化如图4所示。
它根据参考的三相输出电压生成单相输出电压，这一点类似于VSI的H-桥。
输入电流功率因数通过根据输入电压波形调整每个开关的传导比来控制[8] - [9]。
图4简化的单相矩阵变换器的电路a 高额定电流驱动器的配置b 中额定电压驱动的配置图5 矩阵变换器的高功率应用的模块化概念SPMC单元可以根据驱动器的额定电压和电流实现并联或串联。
在图5(a)中，动力电池的输入电压是690伏，单相额定输出电压为635 V、，两个单元并联用来增加额定电流，输出电压可以设计成线电压1千伏总共5千伏的形式。
图6.线式3.3千伏输出电压中压矩阵转换器。
在图5(b)，每个单元的额定输出电压是635V，并且三个单元以串联形式连接。
相电压为1905V，线电压变为3.3千伏，共有13级输出。
因此，它非常接近于图6所示1700V级用于电力单元的IGBT的正弦波。
IGBT的额定电流由SPMC 单元的额定电流确定。
B.高功率矩阵变换器的配置图7显示了3.3千伏中等电压等级矩阵转换器的整体配置，其中包括一个多绕组变压器，电压从3300V逐步下降到690V，次级绕组的相位在+20，0和-20度之间切换以改善输入电流谐波。
它与广为人知的18脉冲整流器的原理是一样的[13] - [14]。
移相也有利于消除输出电压波形中的输入电压纹波。
它与逆变器拓扑相比还对相对较低的输出电压进行了补偿[3]。
标准的低电压MXC要求利用LC滤波器以减少在电网中的PWM谐波，但在模块化的MXC拓扑中，利用变压器的泄漏电感可以消除这一影响。
为了获得平稳的输出电压变化，功率单元的PWM时序相互之间被转换了120度。
对于6.6千伏线电压驱动器，6个功率单元采用串联的方式进行连接。
图7。
风力发电机组传动系统矩阵变换器的示意图三矩阵变换器系统的主要特点由于没有用寿命相对较短的直流母线电容器，高功率MXC在可靠性、大小和效率上都有优势；同时较高的可靠性也减少维修费用；使用功率单元的模块化设计的MXC非常紧凑，维修和服务起来也很方便；个别小模块可以快速更换，因此它还减少了停机时间。
图8.风力涡轮机系统（1.5 MVA）矩阵转换器的外部视图。
图8显示了在风力发电的应用中矩阵变换器的外部视图。
它包括一个控制器面板，多绕组变压器面板和一个主电路板。
功率单元堆放在主电路板上。
标准的产品配置包括适用于1千伏电压等级的2兆瓦，3兆伏驱动器和适用于3千伏电压等级的2兆瓦3兆瓦驱动器。
可能输出的额定功率范围从200千瓦到6兆瓦，电压等级为从690 V至6.6千伏。
图9.实验四象限运行3.3KV，800KVA矩阵转换器图9显示了3.3千伏，800千伏安矩阵变换器在四个象限的速度，扭矩，功率和输入/输出电流，这些是风力发电机组传动系统的基本特征量，实验使用的是600千瓦，1200转的异步电动机。
该图显示从驾驭到再生的平稳过渡，在加速和减速过程中扭矩和电机电流得到了很好的控制，电机的转速与速度参考值也得到了较好的温和。
包括多输出变压器的3.3千伏系统整体效率约98％，而典型的背靠背逆变器系统的效率只有97％左右。
图10.国贸代码：在电网电压模式的极限曲线连接。
四矩阵变换器的低电压穿越由于在全球范围内风力发电对电力系统的影响越来越大，低电压穿越能力对于大型风电场在电网中能否可靠运行起到非常重要的影响[17] - [21]。
突然低电压条件下，风力发电系统必须在一个给定的持续时间内保持连接到电网，并在故障排除过程中和排除后通过提供无功功率对维持系统稳定性做出贡献。
图10显示在国贸电网代码中描述的低电压穿越的条件[22]。
在限制电压曲线之上绝不能从电网断开。
风力发电系统必须提供无功电流（容性或感性）在图11所示的电压下降和电压上升的时段。
矩阵变换器的电网侧的电流控制类似于一个电流源整流器[23][26]。
图11.国贸代码：事件在电网电压支持的原则故障（无功功率的需求）。
电网侧的无功电流是由以下变量控制：- 发电机侧电流幅值- 发电机侧的功率因数- 电网侧功率因数。
矩阵电流的电网侧电流幅值依赖于发电机侧的有功电流分量，因为无功电流分量在循环发电机侧，不影响电网侧。
在低压电力故障期间，电网侧无功电流可以通过调整输入功率因数和输出电压参考波形来控制。
图12.基于标准IEC61400 - 21（2008）的低压穿越图13断路器开关的低电压穿越序列测试的实验装置通过测试。
图12显示了基于标准IEC61400 - 21（2008）的低压穿越测试的实验装置[24]，用简单的分压器电路模拟电网电压骤降。
矩阵转换器的输入电压是由两个电感Z1和Z2的阻抗比决定的。
图13显示了交换机的切换序列。
在正常情况下S1闭合，S2断开。
当S1断开，S2闭合时电压发生骤降。
图14显示了用1440V，100千伏图14低压穿越测试结果安矩阵转换器和一个400V级永磁发电机所做的小规模低电压穿越测试的结果。
当开关S2闭合时，输入电压下降到几乎为零，由于电网电压低于正常水平，矩阵转换开始向电网提供无功电流。
在真正的风电场，无功电流命令是根据TSO 的要求计算的[25]。
但是，在测试中，补偿水平是按电网的百分比压降提前确定的。
在测试中，无功电流参考100％。
伴随着发电机的转矩降低，电网侧的无功电流减小到零。
电网故障被清除后，无功电流减小到零而有功电流返回到以前的正常水平。
图15显示了在电压骤降50％的情况下低压穿越的测试结果。
无功电流补偿级别设置为100％。
由于输入电压的下降和电网侧位移角的增加，最大输出电压降低[26] - [27]，发电机转矩控制能力是有限的。
当电网电压非常低，电网电压的相位角控制可转换为更好的无功电流控制。
图14和15表明发生低压穿越故障时矩阵转换器的无功电流补偿是可能的。
图15 在电压骤降50％的情况下低压穿越的测试结果五结论本文介绍了高功率矩阵变换器技术在了风力发电中的应用。
使用单相MXC单元的模块化的设计理念应用到高功率驱动器中，模块化为额定功率和额定电压的确定提供了极大的灵活性。
高功率矩阵转换器相对于传统的背靠背转换器逆变器系统在效率，尺寸和可靠性方面都有一定的优势。
四象限速度扭矩操作表明了矩阵转换器的基本性能，而低电压穿越测试的结果则证明了矩阵变换器在风力发电应用中的可行性。