复习仿真与虚拟现实

什么是系统仿真和分类？

A simulation is

The imitation of the operation of a real-world process or system over time.

A technique, whereby a model of a system, is run in compressed time, to

perform experimentation for analyzing system performance.

根据模型的种类分类

•物理仿真：按照真实系统的物理性质构造系统的物理模型，并在物理模型上进行试验的过程。优点：直观、形象；

•缺点：模型改变困难，试验限制多，投资大

•数学仿真：对实际系统进行抽象，并将其特性用数学关系加以描述而得到系统的数学模型，对数学模型进行试验的过程称为数学仿真。也称为计算机仿真。

•优点：方便、灵活、经济

•缺点：数学模型不易建立，受限于系统建模技术。

•半实物仿真：将数学模型与物理模型甚至实物联合起来进行试验。简单的建模，复杂的作实物模型，然后联合起来做试验。

仿真分类

•根据仿真计算机类型分类：

•模拟计算机仿真（50-60年代）

•数字计算机仿真（计算机仿真指数字计算机仿真）数学模型用计算机程序加以实现，•数字模拟混合仿真（60-70年代，数字计算机仿真技术不成熟）数字计算机和模拟计算机用数模和模数转换装置交换信息

仿真分类

•根据仿真时钟与实际时钟的比例关系分类：

•实时仿真、仿真时钟与实际时钟完全一致，仿真速度=运行速度，

•条件：系统中存在物理模型或实物时。如训练仿真器

•亚实时仿真、慢于实际时钟

•条件：对仿真速度要求不苛刻时。如离线仿真。

•超实时仿真：快于实际时钟如：交通系统的仿真。

仿真分类

根据仿真的设备

•逻辑仿真：只用计算机软硬件

•含实物仿真

•人在回路中的仿真

•根据系统模型的特性分类：连续系统仿真、离散时间系统仿真

二、研究步骤？

Steps in a simulation study (cont.)

•1. Problem formulation.

–Every study should begin with a statement of the problem.

•2. Setting of objectives and overall project plan.

•3. Model conceptualization.

•4. Data collection.

•5. Model translation.

–Since most real-world systems result in models that require a great deal of information storage and computation, the model must be entered into a computer-recognizable format. We use the term “program”

Steps in a simulation study (cont.)

•6. Verified?

–Verification pertains to the computer program prepared for the simulation model. Is the computer program performing properly?

•7. Validated?

–Validation is the determination that a model is an accurate representation of the real system. •8. Experimental design.

•9. Production runs and analysis.

–Production runs, and their subsequent analysis, are used to estimate measures of performance for the system designs that are being simulated.

Steps in a simulation study (cont.)

•10. More Runs?

–Based on the analysis of runs that have been completed, the analyst determines if additional runs are needed and what design those additional experiments should follow.

•11. Documentation and reporting.

–Two types of documentation: program and progress. Program documentation is necessary for numerous reasons.

–Project reports give a chronology of work done and decisions made.

•12. Implementation.

三、什么是好的模型？

•Good models should be

––Appropriate representation of the system (depending on purpose of investigation)

–– As small as possible without impeding appropriateness

–– Reusable for similar systems, as a part in other systems

–– Parameterizable

–– Amenable to appropriate investigation method

•In acceptable time, with acceptable effort, with desired accuracy

•Method also depends on desired results

四、仿真系统的状态、事件记录、FEL表、事件列表？

System state

● A collection of variables that contain all the information necessary to

describe the system at any time.

Event notice

● A record of an event to occur at the current or some future time, along with

any associated data necessary to execute the event; at a minimum, the

record includes the event type and the event time.

Event list

● A list of event notices for future events, ordered by time of occurrence; also

known as the future event list (FEL).

五、随机数及其特点和评价指标？

什么是随机数：Random numbers ----numbers from a continuous uniform distribution between 0 and 1。

特点：

Uniformity

If the interval (0, 1) is divided into n classes, or subintervals of equal length, the

expected number of observations in each interval is N/n, where N is the total

number of observations

Independence

The probability of observing a value in a particular interval is independent of the

previous values drawn.

Each random number Ri is an independent sample drawn from a continuous

uniform distribution between 0 and 1

评价标准：

六、典型的虚拟现实系统（三种以上）简介？

•桌面系统

•沉浸式系统

•分布式系统