高能搁浅双层底结构损伤特性和脱浅措施研究--英文译文分解

Research on Damage Characteristics of Double Bottom Structure in Ship Hard Grounding and measures for escaping from the shallow
Accidents of ship grounding will cause such disasters as ship hull damage, environmental pollution, lost lives and so on. Rese arching ship grounding is not only good for people’s secularity on sea and preventing marine pollution, but also can present foundation for ships in crowd water transport area in terms of standardizing velocity and operation rules. In this paper, internal mechanics of ship hard grounding is studied by numerical simulation method. Results of damage deformation, contact forces, and energy dissipation are analyzed. A new anti-grounding double bottom structure—YF is presented. The study shows that damage deformation is focused in the area where the structure and the rock contact. So the research on internal mechanics of hard grounding may mainly consider local ship structure; Existence of floors increases remarkably the ability of resisting grounding of bottom structure; in hard grounding process, the vertical penetration of rock into double bottom will decrease slightly because of vertical contact force; energy absorption ability of longitudinal girder can not perform and its resisting grounding effect will be negligible, when it is far from grounding area; Both energy absorption ability an d grounding force of YF double bottom structure are evidently higher than routine structure.
As the world's economic growth, water traffic is increasingly busy, accidents of ship grounding occur frequently. Usually, the grounding situation is not serious in the early. As time goes by, the situation becomes more complicate because of the change of the tide, the affection of wind and wave and other various factors, therefore, mastering the force and stability changes after the ship ran aground and choosing the correct measures from shallow is significant for taking off the shallow smoothly. The following have given the methods for calculating the force on the bottom and the position of the center, still the relationships between the supporting force, the depth at the supporting point and angle of transverse inclination according to hydrostatic principle when point or minor area gets stranded, analyzed with a case example, have given judge being able to take advantage of that tide taking off the shallow and several measures for escaping from the shallow. With the hope of giving relevant personnel correct guidance, the ship can escape from the shallow smoothly as soon as possible with the least loss.
1.Introduction
Ship grounding is a serious accident. It often results in such disastrous aftermaths as ship structure’s severe damage, spill of goods, environment pollution and personnel casualty. Researching
ship grounding is not on ly good for people’s secularity on sea and preventing ma rine pollution, but also helpful for understanding ship grounding as a non-linear dynamic response process under huge impact loads in very short time, and can present foundation for ships in crowd water transport area in term s of standardizing velocity and operation rules. Due to complexity of this problem and the restriction of research conditions, the research depth and width of ship grounding is extremely lesser than ship collision, the domestic research works of ship grounding is very lacking.
According to the kinds of ground, ship grounding mainly has two cases: stranding on relatively soft ground, which is called soft grounding; grounding on a rigid rock, which is called hard grounding. Generally, the research of ship grounding can be divided into two parts: external dynamics is related to ship’s rigid motion in six freedoms (surge, sway, heave, roll, pitch and yaw), all kinds of response forces acting on ship hull and energy dissipation of rigid motion; internal mechanics is about local damage, deformation and energy absorption of each component in the area where ship hull is contacted with the rock.
Most large tankers made recently have the structure hull damage in hard grounding is probably more severe of double bottom and shell, and ship than in soft grounding．Consequently, this paper is focused on researching the int ernal mechanics of large tanker’s double bottom structure.
2. Grounding model of double bottom structure
The double bottom structure researched in this paper is selected from parallel mid-hull of a 159000DW T oil tanker. The grounding model includes two parts of a double bottom structure and a rock. The rock is idealized to be conic and it adopts rigid material. The rock impacts the double bottom structure by the velocity of 10m/s. The double bottom structure adopts elastic—plastic material and some related data thereof are: material density 7800kg/m3 , plastic modulus 2.1 x 1011N/m2,Poisson ratio 0.3. yielding stress 2.35x108N／m2,maximum plastic failure strain 0.15. Nowadays, friction energy is still an uncertain variable in analysis of hard grounding, because it is related with many factors, such as the material of rock, shape, surface roughness and etc. This paper simplifies the calculation of friction. The static and dynamic coefficients are assumed to be 0.1.
3. Results of numerical simulation and analysis
MSC／DYTRAN, the commercial non—linear finite element analysis software of instantaneous
response, is used to simulate the internal mechanics of hard grounding. The calculation traces till the moment of t=2.694588s.
3.1 Motion
Fig. displays the initial and ending states of grounding simulation. Relative to double bottom structure, the rock turns in certain degree, which resembles longitudinal trim in practical grounding accidents. Fig. gives the displacement of rock in X, Y and Z directions. Comparing to X and Z, the displacement of Y direction is very small. The rock moves mainly in longitudinal and vertical orientations. The velocity of rock decreases from 10m/s to 8.7m/s as shown in Fig.4.
3.2 Damage deformation
The damage deformation of double bottom structure in hard grounding has evident local characteristics. The deformation is concentrated in the area contacted with the rock. Ship structure in other area has little deformation. Therefore，the research of internal mechanics of ship hard grounding may only consider local ship structure, and need not to analyze the total ship.
Serious tearing occurs in outer bottom plating and floors, as well as bending and membrane. Longitudinals encounter rupture, bending and twisting, and the phenomenon of lost stability is observed. Girders and inner bottom plating have slight deformation, such as bending in a small area and membrane respectively.
Fig. shows damage deformation process of the first floor (namely being contacted will the rock foremost). Before rock contacts it, the floor mainly endures outer extrusion of bottom plating. The load is in a plane and deformation is mostly crushing. When rock reaches it, the floor is cutting directly by the rock and has tearing and bending deformation. Otherwise, as shown in the figure, the size and shape of the deformation area floor accords well with the rock, which explains again the ship hull’s deformation in hard grounding has intensively local trait.
3.3 Contact force
As shown in Fig. before the rock contacts the first floor, the forces in X and Z directions increases along with spread of contacting area. The floor space of double bottom structure is 4.8m.Thus, it can be thought that the four extremum points of X and Z directions correspond respectively to the failure of four anterior floors. These four extrema of contact forces are degressive as a whole. In the process of hard grounding, the rock endures simultaneously horizontal and vertical resistance, and has vertical displacement. Its penetration to double bottom structure decreases gradually. That is the vertical
contact force may abate ship’s breakage due to rock by degrees. As a result of the 45。

angle between the generatrix and the bottom of the ideal rock. The contact forces in X and Z directions have almost the same magnitude and trend. Comparing with X and Z forces, the contact force in Y direction is relatively small, but it cannot be ignored in the hard grounding analysis of double bottom structure. According to the figure of damage deformation in above paragraphs, outer bottom plating, floors and longitudinals are extruded laterally in different degrees, which is owing to the Y force.
3.4 Energy dissipation
Fig. is the distortional energy curve of double bottom structure. Energy dissipation in the grounding process is shown in Tab. Most dynamic energy of rock is changed into distortional energy of double bottom structure. Moreover，some is transform ed into friction energy between the rock and the double bottom structure. Local kinetic energy of double bottom structure, and hourglass energy that is inevitable in nonlinear finite element calculation with reduced integration. Both local energy and hourglass energy can be ignored, because they are much less than distortional energy ,and the difference is two orders of magnitude.
Outer bottom plating absorbs the most energy, Energy absorption capacity of inner bottom plating is not entirely brought into play. This is what we hope in practical grounding accidents, because the rupture of inner bottom plating will leads to catastrophic aftereffects of the ship and environment. 0n account of little initial penetration of rock to double bottom structure(vertex of rock is only 0.55m higher than inner bottom plating), and vertical displacement of rock, the contact area between the rock and inner bottom plating decreases and the rock has the trend of leaving inner bottom plating. In the numerical simulation of this paper, inner bottom plating does not rupture, but has certain plastic deformation and absorbs partial energy.
Longitudinals and floors are also main components of absorbing energy. Longitudinals existence enhances the longitudinal strength of bottom plating and the capacity of resisting the motion of rock. Moreover, such plastic deformation of longitudinals themselves as rupture, flexure and bending may absorb a considerable part of energy. Floors do not absorb as much energy as outer bottom plating and longitudinals. However, floors existence improves markedly the resistance of double bottom structure and strengthens the ability of structure’s resisting grounding (see the extremum points of contact forces in X and Z directions in Fig.)
Girders are strong components of ship bottom structure, but they absorb the least energy in the numerical simulation of this paper, because they are far from grounding area and do not contact the rock directly. As shown in Fig, most deformation of girders appears at their forepart (that is their free boundary). At the beginning, when the rock contacts double bottom structure, bending of big deflection occurs in outer bottom plating. Then girders receive lateral pressing of outer bottom plating
and have bending deformation. After rupture of outer bottom plating, the effect of outer bottom plating upon girders decreases evidently. Hence，most area of girders except the front does not deform clearly.
4. A new anti-grounding type of double bottom structure
This paper presents a new anti-grounding type of YF double bottom structure with Y floors, which is based on the design idea of increasing energy absorption and grounding force and control structure weight in an acceptable level.
4.1 The design ideas of YF double bottom structure
The energy absorption ability of transverse components (such as floors) is evidently higher than longitudinal components (such as girders), which are possibly far away from the grounding area. And the transverse structure can increase grounding force markedly. Consequently, making transverse components stronger is the main design idea of YF double bottom structure. Adding Y—floors to the original structure forms the new structure, and its section profile is shown in Fig. The reasons not to select conventional floors but Y-floors mostly are:
(1)In the same hard grounding condition, the deformation area of Y—floors is larger than conventional floors;
(2)The machining of Y—floor is relatively easy. A nd the new structure’s manufacture technology is not difficult.
4.2 Simulation research compared with the original structure
With the help of MSC／DYTRAN, this paper gets simulation results of YF double bottom structure at the instant of t=2.029259s,which is compared with the results of the original model.
As shown in Fig, the YF structure has higher grounding force than the original structure. The maximal force of cutting double bottom is 19949KN and 17346KN respectively. The YF structure’s maximal force is increased by approximately 15％. The mean force is 11200KN and 7500KN. The YF structure’s mean force is increased by approximately 49％. Obviously, Y-floors enhance the anti—grounding ability of double bottom structure and make it able to endure higher grounding loads.
On the Condition of the same kinetic energy of same rock, when the kinetic energy decreases to
about 60MJ, the displacement of rock of original model is about 27m, while the other rock in the YF model has only the displacement of 18m, see Fig. The YF structure’s damage length is evidently shorter that the original.
Tab. accounts for the energy dissipation of the YF structure and the original, when penetration of rock is 19.176m. Noticeably, the distortional energy of YF is 35.495MJ more than the original’s, while total energy absorption is 43.1 20MJ more than the original’s,for friction mechanism absorbs approximately 7.630MJ. Since the steel flats in the middle of Y—floors increase contact area between the double bottom and the rock, the effect of friction is more distinct, and more kinetic energy of rock turns into friction energy. The distortional energy of Y—floors is 46.240MJ, while the total energy loss is 1 94.560MJ. Evidently, Y—floors absorb a considerable quantity of energy. Mass of YF is 252.9447t, which is equal to the original structure. Energy absorption of YF in unit mass is 0.7692MJ／t, while the original’s is 0.5987, so YF is 28.5％more than the original in this key item.
5 work to be done before taking off the shallow
After the ship ran aground, we shall take all feasible measures as far as possible to minimize the damage to the ship and environment because of the stranded ship. Concrete steps: (1) investigate and judge the situation after the ship ran aground; (2) Temporarily fix of the ship ran aground.
5.1 investigate and judge the situation after the ship ran aground
In the sailing of the ship, no matter what contributed to the reasons for departure from the ship course, to make the ship in the danger of being stranded or running aground, emergency measures should be taken to reduce the extent of damaged hull and the prevention of expansion to the environment. For example, when there are shallow reefs in front of the ship, she should be promptly reversed, or to reduce the ship dragged anchor of Momentum, when in front of isolated reef, avoid hunting in time with the rudder, not to stern to be aground to preserve the ship mobility as far as possible.
When the ship has been stranded, she should be stopped immediately, measures to be done in the way according to the emergency grounding. It is forbidden to reverse without knowing the situation clearly, thereby increasing the losses.
(1) Continuous measuring the water level of double bottom, bilge holes and fore and aft peak tank. Clearly know the damage extent, location and the speed of incoming water.
(2) Continuous bathymetric surveys and sediment around the ship to determine the direction from the shallow, further determine the grounding location. Soundings should be alongside the vessel like the radiation, while under observation in mind, high tide and time of high, low ebb. Conducted the sampling to estimate the shallow and the friction of the grasp of the anchor as much as possible when do the submarine sounding.
(3) To identify whether main engineer and auxiliary engineers are normal, whether the rudder and propeller are damaged.
(4) Whether the transfer of goods, record the draughts of both two sides of fore, middle and aft, write down time, high tide and time of high and low tide in order to calculate the loss of displacement.
(5) Accurately locate and record the direction and ran aground at the bow to the stranded. Large-scale should be targeted on the charts. Re-test at a certain time.
(6) Make the best of weather and tidal conditions, the person assigned to observe hearings. The preparation of high tide table, a clear upsurge in the trend of the time and direction, size, on time and make records.
The good division should be made for the above investigation, record at the same time, and strive to correct. Investigation and the measures taken should try to report to ship owners and their agents as soon as possible in order to obtain advice and assistance in the matter and recorded in the logbook.
5.2 Temporarily fix of the ship ran aground
After the ship ran aground, if we do not take measures to temporarily fix the ship hull, the damage will expand because of the influence of tide gauges, the trend of the wind and waves, to bring greater difficulties to salvage, even the ship be completely destroyed or simply no way to do salvage. There are basically two ways to temporarily fixed the ship ran aground: by anchoring and filling water.
5.2.1 Fix by anchoring
When the bow grounded in the shoal or reef, the ship can be easily abeam if not fix its stern, resulting in the hull to the shore. The ship may be in danger of squatting or even broking to sinking If any possible surge. The way which the salvage boat takes proper measures to fix grounding ship by anchoring according to the influence of ambinent force the up and down of sea bottom and the grounding situation is called fixing by anchoring. The method is very significant to prevent being abeam and re-grounded, but not so good to prevent squatting.
The method to arrange anchors should be based on actual need, when the hull is vertical to shoreline, the ship ran aground with both vessels in both lines into the direction of 45 degrees on the anchor, after the end of the necessary configuration is required from the anchor fixed hull and
beneficial to both the shallow target. When the ship is parallel with the shoreline the focus should be considered to withstand the impact of the tide and swell. Not only to be 45 degrees in both directions but also to be in force may be great position (Against flow direction, the direction of welcome to surge) supported by re-anchoring of long-chains, so that the hull fixed to play a major role.
5.2.2 Fixing by filling water
When there are no suitable anchors, chains, ropes or even if there are such items but it is difficult to move, we can take measures to fix the hull by filling water into the cargo holds, which is called fixing by filling water. This is a positive approach of the fixing hull in shallow can not escape in a short period of time, and the ship ran aground on the storm may be sufficient to lead to the collapse of the ship and cargo when the enormous losses suffered.
So called fixing by filling water includes not only the water tank, but also the use of ballast tank, including the use of the cargo holds. For the merchant ship, under normal circumstances, it meets the requirement with two cabins filling water , and it also need to further increase irrigation module when bad weather, which needs to make the right choice as per the goods installation, quantity and variety .
However, we must be very careful when use the method of filling water, to fill the holds means the loss of buoyancy, to be sure to take in water after the weather conditions of the ship floating such as the circumstances allowed to use.
6 Measures for taking off the shallow
Generally speaking, the ways for taking off the shallow can be divided into two parts, self-reliance from shallow and taking off by help.
6.1 Taking off the shallow by itself
Basic operations should be completed as follows for self-reliance from shallow:
(1) After the ship ran aground in water damage, plugging leaks, all finished, and have good drainage and strengthening support work.
(2) Moving heavy objects (oil, water and goods) has revised the ship ran aground in the trim and Wang dumping and, if necessary, to be set to split the work or are abandoned.
(3) Along the direction of shallow ready to be used from shallow scheduled to throw the anchor position and be able to complete the reel, wire rope, such as the anchor chain of guitar so that the package be able to drag all the appliances in place.
(4) To main and auxiliary steering gear, anchors of the full inspection, full and ready to do a good job in car steering and to be able to use shallow anchor preparation.
(5) General upsurge in one hour before moving cars and activities with steering the boat, started to be able to Anchorage and to be able to cope with car steering, in the height of the shallow.
6.2 Taking off by help
If The ship ran aground seriously, such as the broken hole is bigger, the speed of incoming water is faster and it lost buoyance, or damage to main engineer, steering gear and propeller, or the force required to take off the shallow is too big to be provided, in efforts to rescue themselves at the same time, Did not hesitate to request foreign aid, so that the ship early from shallow.
The information and material provided to salvage boat:
(1) The principal of ships, including the main headquarters of home-scale hydro static map of the original DWT and a few, while Bian mechanical aspects of the deck, such as mechanical power.
(2) Of cargo and be able to receipt of the subdivision map, water and the number of sites, such as carrying dangerous goods should set out the number of accommodation and attention to issues and help to advance .
(3) The course speed before ran aground, the bow and ran aground time.
(4) Before and after the grounding of the draft and changes, and ran aground after it was adopted emergency measures, including the tidal measuring vessel position and sounding data.
Operations from shallow in the use of anchors, cables and other appliances:
(1) Anchors, cables and other appliances, parking, should be of high strength and can
withstand the powerful tensions, they get greater weight and diameter than the anchors,
cables, chains, valves on the deck of a grounded ship.
(2) The arrangement of anchors should be in accordance with the principle that the
grounding ship can escape from the shallow best. However, the common requirement
is that it should be towards the deep water and against wind and flow. As to the choices
that the anchors should be fastened to the bow or he stern, we should consider the use of
the anchors, it is the general requirement that to protect propeller and rudder.
(3) It is often difficult to take off the shallow because of surge and swell, but also given the
opportunity to create the chance to escape from shallow. keep the tension of the state of
maintaining a chain or cable in the process to take off , once the current surge changes
in the approach of the ship surging, it issue a strong and sustained power, which is
extremely favorable to take off the shallow.
7. Conclusions
(1) Damage deformation is concentrated in the area where structure is contacted with the rock. The research of internal mechanics in hard grounding may only consider local ship hull structure.
(2) Floors existence remarkably enhances capacity of ship bottom structure’s resisting grounding.
(3) Due to vertical contact force, the penetration of rock to double bottom will decrease appreciably in the process of hard grounding.
(4) Girders can not exert themselves on absorbing energy, and their performance of resisting grounding will be very poor, if they are far from grounding area.
(5) According to simulation analysis and comparative research, both energy absorption ability and grounding force of YF double bottom structure are evidently higher than routine structure.
高能搁浅双层底结构损伤特性和脱浅措施研究
船舶搁浅事故会引起船体破损、环境污染和人员伤亡等严重后果。

研究船舶搁浅，不仅有利于海上生命安全、防止海洋污染，还可为船体结构的抗冲击设计及规范航运繁忙区域中船舶的航速、操作规程提供一定的依据。

本文用数值仿真法研究了船舶高能搁浅中的内部力学问题，分析了典型双层底结构的损伤变形、受力和能量耗散等结果，提出了一种新式的抗搁浅YF双层底结构，并与原结构进行了比较。

研究表明，损伤变形集中于结构与礁石相接触的区域，高能搁浅内部力学问题的研究可以主要考虑局部的船体结构；肋板的存在显著增加了船底结构的抗搁浅能力；高能搁浅过程中。

由于垂直方向的接触力，礁石对双层底的垂向贯入量会略有减小；当纵桁远离搁浅区域时，它的吸能能力无法发挥，抗搁浅作用很弱；YF双层底结构比原结构具有更大的吸能能力和抗搁浅力。

随着世界经济的增长，水上交通日益繁忙，船舶的搁浅事故时有发生。

通常，船舶搁浅初期搁浅情况并不严重；随着时间的推移，潮水的变化、风浪的作用以及其它各种因素的影响，搁浅情况变得尤为复杂。

因此，掌握搁浅后船舶的受力及稳性变化，选择正确的脱浅措施对船舶的顺利脱浅意义重大。

根据船舶静力学原理，提出了船舶单点或小面积搁浅时的底部受力及其受力中心位置的计算方法以及支承力、支承点的水深同横倾角的关系，且案例分析；并给出了能否乘潮脱浅的判断方法以及几点脱浅措施；以期给相关人员正确指导，使搁浅船舶尽早顺利脱浅，将损失降到最小。

1 结构研究介绍
船舶搁浅是一种严重的事故.其结果往往是在这种灾难性的后遗症，例如船体结构的严重破坏，溢出的商品，对环境的污染和人员伤亡。

研究船舶搁浅不仅是对海上和防止海洋污染良好的为人民的观念，而且还有助于了解船舶搁浅作为一个非线性动态响应的过程下，巨大的冲击载荷在很短的时间内，并能在目前的基础船只在人群水运的地区来说，船舶的
速度和规范的运作规则。

由于复杂，这个问题和限制的研究条件，研究的深度和广度船舶搁浅是非常较船舶碰撞，国内的研究工程，船舶搁浅是非常缺乏。

根据搁浅底质的不同，船舶搁浅主要有两种情况：搁浅在比较软的地面，这是所谓的软搁浅；搁浅在比较坚硬的岩石，这是所谓的硬搁浅。

一般地，研究船舶搁浅可分为两部分组成：外部动力是有关船舶的刚体运动在6个自由度（纵荡，横荡，垂荡，横摇，纵摇和偏荡），各种反作用里对船体产生作用，船体和耗能刚性。

内部力学是关于局部损伤，变形和能量吸收各组分在该地区的地方船体是接触与岩石。

最近制造的多数大型油轮在硬搁浅的时候极有可能比双底和硬壳船软搁浅要更严重，本文的重点是研究内部机械的大型油轮的双层底结构。

2 双层底结构的搁浅模式
本文对双层底结构的研究是由选定的平行中船体一艘159000总载重吨油轮.搁浅模型包括两部分，一个双层底结构和岩石.岩石是理想化的要圆锥曲线和它采用刚性材料。

岩石影响双层底结构，由速度10m/s.双层底结构采用弹塑性材料及一些相关的数据有：材料密度7800kg/m3 ，塑胶模量2.1 x 1011n/m2，泊松比0.3.拉伸应力2.35x108n/m2，最大塑性失效应变0.15。

当今世界，摩擦耗能仍是一个不确定的变数分析的硬搁浅，因为它是与许多因素，如材料的岩石，形状，表面粗糙度等。

本文简化计算因素.静态和动态系数均假定为0.1 。

3数值模拟与分析结果
MSC／DYTRAN ，商业非线形有限元分析软件的瞬态响应，是用来模拟硬搁浅的内部力学计算的轨迹直到时刻为2.694588s。

3.1动态
显示搁浅模拟的初始状态和结束状态。

相对双层底结构，岩石在一定程度上会翻转，这类似于在实际搁浅事故中的纵倾。

让移动的岩石在X ，Y和Z 方向.相对与到X和Z ，位移Y方向是非常小。

岩石的举动，主要是在纵向和垂直方向。

岩石的速度跌幅从10m/s 到8.7m/s。

3.2 破损变形
双层底结构的损坏变形，在硬搁浅具有明显的局部特征。

变形集中在与岩石的接触地区。

船体结构在其他地区只有很少变形。

因此，对船舶硬搁浅的内部机制的研究只考虑搁浅点的船体结构，不需要分析总的船舶。

严重撕裂弯曲和膜发生在外底部的列板及底板。

纵向结构遇到破裂，弯曲和扭曲，以及出现失去了稳性的现象。

梁和内底列板有轻微变形，如小范围内的弯曲和膜。

表明损伤变形的过程中第一底板（即最先接触岩石的底板）。

在岩石接触它之前，底板主要受底部列板的挤压.负荷是在一个平面上和变形的大多是碎裂。

当岩石达到它，底板直接被岩石切割，并已撕裂和弯曲变形。

否则，如数字显示。

变形区的大小和形状由底板决定，这点再次解释在硬搁浅的情况下船体的变形在密集地方。

3.3接触力
显示所得，在岩石接触第一底板之前，随着接触面积的蔓延力量在X和Z方向增加。

双层底结构底板面空间是4.8m。

这样，可以认为，在X和Z方向的四极值点分别对应以前四块垮掉的底板。

这四个极值的接触力是作为一个整体在递减的。

在硬搁浅的过程中，岩石同时给出横向和纵向的垂直反作用力，且提供垂直的排水量.其对双层底结构的渗透逐渐减小。

这是垂直接触力可消减船舶的破损，由于岩石角度。

结果夹角母线和底部的理想礁石的角度是45度。

在x和z方向的接触力有几乎相同规模和大小，与X和Z 方向上的作用力相比，在Y方向的接触力是相对较小，但在硬搁浅分析双层底结构时它不能被忽略.
根据上述各段损伤变形的数据，由于的Y方向上的作用力，外列板，底板和纵向结构在不同程度上受到侧向挤压。

3.4能量耗散
双底结构扭曲的能量曲线，在搁浅的过程中表现为能量耗散。

绝大多数的岩石的动态能量转变为双层底结构扭曲变形的能量。

再者，有些转化到岩石和双层底之间的摩擦耗能。

双层底结构的局部动能，沙漏的能量是无可避免的在非线性有限元计算减少了一体化。

局部能量和沙漏能可以被忽略，因为他们是远低于变形能量，和变形能量是不同的两个数量级。

外底部列板吸收绝大多数的能量。

内底列板对能量的吸收也不是完全不起作用。

这正是我们在实际的搁浅事故中所期望的，因为内底列板的破裂将导致灾难性的船舶损伤和环境污染。

考虑到岩石对双层底结构初期渗透性不大（岩石顶部只有0.55米高于内底列板），和岩石的垂直位移，岩石和内底列板之间的接触面减小，岩石有离开内底列板的趋势。

本文在数值模拟，内底列板不破裂，但具有一定的塑性变形和吸收了部分能量。

纵向结构和底板的是吸收能量的主要组成部分。

纵向结构的存在增强了底部列板的总纵强度和抵御礁石动量的能力。

此外，纵向结构的塑性变形例如破裂，扭曲和弯曲可吸收相当一部分能量。

底板吸收的能量外底列板及纵向结构的多。

虽然如此，底板的存在显着改善双层底结构的阻力，并加强结构的抗搁浅能力（见极值的接触点，力量在X和Z方向）。

梁是船舶底部结构的强组成部分，但在本文数值模拟它们吸收最少的能量，因为他们是远离接地面并且不直接接触岩石。

正如显示，梁的绝大多数变形出现在它们的前端（这是他们的自由边界）。

在开始时，当岩石接触双层底结构时，弯曲的大挠度发生在外底列板。

然后梁受到外底列板的侧向挤压并且有弯曲变形。

在外底列板破裂以后，外底列板对梁的作用明显减小。

因此，梁的大部分地区除前面变形不明显。

4双层底结构新的抗搁浅类型
本文提出了一种新的抗搁浅类型的使用Y底板的YF双层底结构，这是基于增加能量吸收和搁浅作用力和控制结构重量在可接受的水平设计理念。

4.1 YF双层底结构的设计理念
横向组件（如底板）的吸收能量的能力明显高于纵向组件（如大梁），这是因为纵向组件可能远离搁浅地。

并且横向结构可以明显增加搁浅力。

结果是，YF双层底结构的设计理念主要是制造更牢固的横向结构。

在原来的结构形式上增加 Y底板新结构，其资料表明，不选择传统的底板选择但Y型底板的理由大多是：
（ 1 ）在相同的硬搁浅情况下，Y型底板的变形区的大于常规底板；
（ 2 ）加工Y型底板相对比较容易，新结构的制造技术并不难。

4.2 与原结构仿真研究相比
在MSC／DYTRAN 的帮助下，本文得到了在瞬时2.029259s YF双层底结构的模拟结果，这是与原来的模型比较的结果。

显示表明， YF结构比原来的结构具有更强的抗搁浅力，切割双层底最大的力量分别是19949kn和17346kn。

YF结构的最大力量是增加了大约15 ％。

平均作用力是11200kn 和7500kn。

YF结构的平均力是增加了大约49 ％。

显然， Y型地板加强了双层底结构抗搁浅的能力，使它能够承受较高的搁浅负荷。

在相同的岩石相同动能的条件下，当动能降至约60MJ时，原来模型的岩石唯一是大约27米，而在YF模型下其他岩石，只位移18米，YF结构的损害比原来的很明显的少。

当岩石的渗透率是19.176m时，考虑YF结构和原有的结构的耗能。

值得注意的是，YF 结构的变形的能量是35.495MJ,比原来的更多，而总的能量吸收比原来的结构多43.120MJ 以上，摩擦的机制吸收了大约7.630MJ。

因为Y 底板结构船中处的钢板增大了双层底和礁石的接触面积，摩擦的影响更加明显，更多的岩石动能转化为摩擦耗能。

Y型底板的变形能量是46.240MJ，而总的能量损失是194.560MJ.很明显的，Y型地板吸收了相当数量的能。