LS-dyna-常见问题汇总1.0.doc

LS-DYNA常见问题汇总1.0资料来源：网络和自己的总结 yuminhust2005Copyright of original English version owned by relative author. Chinese version owned by A/Kevin目录1.Consistent system of units 单位制度22.Mass Scaling 质量缩放33.Long run times 长分析时间84.Quasi-static 准静态105.Instability 计算不稳定136.Negative Volume 负体积167.Energy balance 能量平衡198.Hourglass control 沙漏控制269.Damping 阻尼3110.ASCII output for MPP via binout3611.Contact Overview 接触概述4012.Contact Soft 1 接触Soft=14413.LS-DYNA中夹层板(sandwich)的模拟4614. 怎样进行二次开发491.Consistent system of units 单位制度相信做仿真分析的人第一个需要明确的就是一致单位系统(Consistent Units)。计算机只认识0&1、只懂得玩数字，它才不管你用的数字的物理意义。而工程师自己负责单位制的统一，否则计算出来的结果没有意义，不幸的是大多数老师在教有限元数值计算时似乎没有提到这一点。见下面LS-DYNA FAQ中的定义：Definition of a consistent system of units (required for LS-DYNA):1 force unit = 1 mass unit * 1 acceleration unit1 力单位 1 质量单位 1 加速度单位1 acceleration unit = 1 length unit / (1 time unit)21 加速度单位 = 1 长度单位/1 时间单位的平方The following table provides examples of consistent systems of units.As points of reference, the mass density and Youngs Modulus of steel are provided in each system of units. “GRAVITY” is gravitational acceleration.MASSLENGTHTIMEFORCESTRESSENERGYDENSITYYOUNGsVelocity (56.3KMPH)GRAVITYkgmsNPaJoule7.83E+032.07E+1115.659.806kgcms1.e-02N7.83E-032.07E+091.56E+039.81E+02kgcmms1.e+04N7.83E-032.07E+031.569.81E-04kgcmus1.e+10N7.83E-032.07E-031.56E-039.81E-10kgmmmsKNGPaKN-mm7.83E-062.07E+0215.659.81E-03gmcmsdynedy/cm2erg7.83E+002.07E+121.56E+039.81E+02gmcmus1.e+07NMbar1.e7Ncm7.83E+002.07E+001.56E-039.81E-10gmmms1.e-06NPa7.83E-032.07E+111.56E+049.81E+03gmmmmsNMPaN-mm7.83E-032.07E+0515.659.81E-03tonmmsNMPaN-mm7.83E-092.07E+051.56E+049.81E+03lbfs2/ininslbfpsilbf-in7.33E-043.00E+076.16E+02386slugftslbfpsflbf-ft15.24.32E+0951.3332.17kgfs2/mmmmskgfkgf/mm2kgf-mm8.02E-107.00E+021.56E+04(Japan)kgmmsmN1000Pa7.83E-062.07E+089.81E+02gmcmms100000Pa7.83E+002.07E+062.Mass Scaling 质量缩放质量缩放指的是通过增加非物理的质量到结构上从而获得大的显式时间步的技术。在一个动态分析中，任何时候增加非物理的质量来增大时间步将会影响计算结果（因为F=ma）。有时候这种影响不明显，在这种情况下增加非物理的质量是无可非议的。比如额外的质量只增加到不是关键区域的很少的小单元上或者准静态的分析（速度很小，动能相对峰值内能非常小）。总的来说，是由分析者来判断质量缩放的影响。你可能有必要做另一个减小或消除了质量缩放的分析来估计质量增加对结果的灵敏度。你可以通过人工有选择的增加一个部件的材料密度来实现质量缩放。这种手动质量缩放的方法是独立于通过设置*Control_timestep卡DT2MS项来实现的自动质量缩放。当DT2MS设置为一个负值时，质量只是增加到时间步小于TSSFAC*|DT2MS|的单元上。通过增加这些单元的质量，它们的时间达到TSSFAC*|DT2MS|。有无数种TSSFAC和DT2MS的组合可以得到同样的乘积，因而有相同的时间步，但是对于每一种组合增加的质量将是不一样的。一般的趋势是TSSFAC越小，增加的质量越多。 作为回报，当TSSFAC减小时计算稳定性增加（就像在没有做质量缩放的求解中一样）。 如果TSSFAC缺省的值0.9会导致稳定性问题，可以试试0.8或者0.7。 如果你减小TSSFAC，你可以相应增加|DT2MS|，这样还是可以保证时间步乘积不变。为了确定什么时候和位置质量自动增加了，可以输出GLSTAT和MATSUM文件。这些文件允许你绘出完整的模型或者单独部件所增加的质量对时间的曲线。为了得到由壳单元组成的部件增加的质量云图，将*database_extent_binary卡的STSSZ项设置为3。 这样你可以用ls-prepost绘出每个单元的质量增加量的云图，具体方法是通过选择FcompMisctime step size。在*control_timestep中设置DT2MS正值和负值的不同之处如下：负值：初始时间步将不会小于TSSFAC*-DT2MS。质量只是增加到时间步小于TSSFAC*|DT2MS|的单元上。当质量缩放可接受时，推荐用这种方法。用这种方法时质量增量是有限的。过多的增加质量会导致计算任务终止。正值：初始时间将不会小于DT2MS。 单元质量会增加或者减小以保证每一个单元的时间步都一样。这种方法尽管不会因为过多增加质量而导致计算终止，但更难以作出合理的解释。*control_timestep卡中的参数MS1ST控制是否只是在初始化时增加一次质量（MS1ST=1）还是任何需要维持由DT2MS所指定的时间步时都增加质量（MS1ST=0)。你可以通过在*control_termination卡片中设置参数ENDMAS来控制当质量增加到初始质量一定比率时终止计算（只对自动质量缩放有效）可变形点焊梁的质量缩放*mat_spotweld卡的质量缩放参数DT只影响点焊单元。如果*control_timestep卡中没有指定质量缩放(DT2MS=0)，而且时间由可变形点焊控制，可以用参数DT来在初始化时增加惯量到点焊单元上来提高时间步达到DT指定的值。当DT不为0时，增加到可变形点焊梁元上的质量会输出到d3hsp文件里。MATSUM 中动量和动能不受增加到可变形点焊上的质量的影响。GSLTAT中DOES和总的KE受增加的质量的影响。考虑三种调用可变形点焊的质量缩放的情况：1.当DT2MS为负值*mat_spotweld卡DT0时，尽管在d3hsp文件中可变形点焊质量增量百分比不真实。下面几个值是正确的：d3hsp中”added spotweld mass”; 第一个时间步之后的”added mass” & “percentage increase”; glstat和matsum中的”added mass”。2. 当DT2MS为负值且*mat_spotweld卡DT0时，可变形点焊质量增加不会包含在d3hsp、glstat、matsum文件中的”added mass”里。这非常容易令人误解。用户必须检查d3hsp文件的”added spotweld mass”。建议不要同时使用两种质量缩放标准，推荐使用第一种方法（即负的DT2MS&DT=0）。3. 如果DT2MS0且DT0，初始时间步将不考虑增加点焊的质量，但是之后每一个周期时间步都会增加10%，直到时间步达到正确的值（考虑点焊质量增加）。glstat & matsum不包含”added mass”的行。注意质量增加会引起能量比率增长。English Version：Mass-scaling refers to a technique whereby nonphysical mass is added to a structure in order to achieve a larger explicit timestep.Anytime you add nonphysical mass to increase the timestep in a dynamic analysis, you affect the results (think of F = ma). Sometimes the effect is insignificant and in those cases adding nonphysical mass is justifiable. Examples of such cases may include the addition of mass to just a few small elements in a noncritical area or quasi-static simulations where the velocity is low and the kinetic energy is very small relative to the peak internal energy. In the end, its up to the judgement of the analyst to gage the affect of mass scaling. You may have to reduce or eliminate mass scaling in a second run to gage the sensitivity of the results to the amount of mass added.One can employ mass scaling in a selective manner by artificially increasing material density of the parts you want to mass-scale. This manual form of mass scaling is done independently of the automatic mass scaling invoked with DT2MS in *control_timestep.When DT2MS is input as a negative value, mass is added only to those elements whose timestep would otherwise be less than TSSFAC * |DT2MS|. By adding mass to these elements, their timestep becomes equal to TSSFAC * |DT2MS|. An infinite number of combinations of TSSF and DT2MS will give the same product and thus the same timestep but the added mass will be different for each of those combinations. The trend is that the smaller the TSSF, the greater the added mass. In return, stability may improve as TSSF is reduced (just as in non-mass-scaled solutions). If stability is a problem with the default TSSF of 0.9, try 0.8 or 0.7. If you reduce TSSF, you can increase |DT2MS| proportionally so that the product/timestep is unchanged. To determine where and when mass is automatically added, write GLSTAT and MATSUM files. These files will allow you to plot added mass vs. time for the complete model and for individual parts, respectively. To produce fringe plots of added mass in parts comprised of shell elements (DT2MS negative), set STSSZ=3 in *database_extent_binary. You can then fringe the added mass (per element) using LS-POST by choosing Fcomp Misc time step size. (Here, the label “time step size” is really the element added mass.)The difference between using a positive or negative number for DT2MS in *control_timestep is as follows:Negative: Initial time step will not be less than TSSF * -DT2MS. Mass is added to only those elements whose timestep would otherwise be less than TSSF*abs(DT2MS). When mass scaling is appropriate, I recommend this method. The amount of mass that can be added using this method is limited. Excessive added mass will cause the job to terminate.Positive: Initial time step will not be less than DT2MS. Mass is added OR TAKEN AWAY from elements so that the timestep of every element is the same. This method is harder to rationalize although it is not subject to termination from excessive added mass.The parameter MS1ST in *control_timestep controls whether mass is added only once during initialization (MS1ST=1) or anytime as necessary to maintain the desired timestep specified via DT2MS (MS1ST=0).You can use ENDMAS in *control_termination to stop the calculation after a certain amount of mass has been added (active for automatic mass scaling only)._Mass-scaling of deformable spotweld beams:The mass-scaling parameter in *mat_spotweld (DT) affects only the spotwelds. If no mass-scaling is invoked in *control_timestep (DT2MS=0.) AND the timestep is controlled by the deformable spotwelds, DT can be used to add inertia to the spotwelds during intialization in order to increase the timestep to a value of DT. When DT is nonzero, mass added to spotweld beams is reported to d3hsp. MATSUM momentum and KE does NOT factor in added mass to def. spotwelds. GLSTAT DOES factor in added mass to total KE (spotweld.beam.type9.mscale.initvel.k)Consider 3 cases of invoking mass-scaling in a model with deformable spotwelds:1.Although “percentage mass increase” under “Deformable Spotwelds:” in d3hsp is bogus when DT2MS is neg. and DT in *mat_spotweld = 0, the following are correct:“added spotweld mass” in d3hsp“added mass” and “percentage increase” in d3hsp AFTER the first time step“added mass” in glstat and matsum2. Added spotweld mass controlled by DT in *mat_spotweld is NOT INCLUDED in “added mass” given in d3hsp, glstat, or matsum when DT2MS is neg. and DT in *mat_spotweld is nonzero. This can be quite misleading. User must check for “added spotweld mass” in d3hsp. Recommended: Do not invoke both mass-scaling criteria. Neg. DT2MS with DT=0 (case 1 above) is preferred.3. If DT is nonzero and DT2MS=0, the initial timestep will NOT consider added spotweld mass but the time step will increase by 10% each cycle until the correct timestep (considering added spotweld mass) is achieved. Glstat and matsum contain no “added mass” line item.The above can be illustrated using /j5000a_2/jday/test/weld/spotweld.beam.type9.mscale.k._Note that added mass may cause the energy ratio to rise. (See /j5000a_2/jday/test/erode/taylor.mat3.noerode.mscale.k)3.Long run times 长分析时间当用显式时间积分时，对于仿真非常小的部件而分析时间又要相当长时没有好的方法。质量缩放(mass-scaling)增加了需要确认非物理质量的增加不会显著影响计算结果的负担。当使用时间缩放(time-scaling)时也有同样的问题。时间缩放(time-scaling)是指为了减小需要的时间步数，通过增加加载速率而缩短仿真时间。要确认时间步不是仅由很少的小单元或者刚度大单元控制，可以通过在d3hsp文件中搜索”smallest”来显示100个最小的时间步单元。如果只有很少的几个单元控制时间步，可以把那些单元及邻近区域重新remesh或者把它们变成刚体。可是仅运行必要长的时间是很明显的。这意味着在一个跌落分析的情况时，给跌落物体一个初速度，把它放在离地面一个非常小的距离。冲击之后，仅运行足够得到需要的结果的时间。值得注意的是对于一个长时间的仿真，如果时间步数超过了50万步，最好使用双精度版本的LS-DYNA求解器，使截断误差的影响最小化。运行双精度版本要增加30%的时间。对于长时间的分析，自动显式/隐式转换可能是一个选择。使用这种方法，用户可以指定在一个时间段内使用隐式积分。隐式积分的优点是时间步不由单元尺寸控制，所以可以得到大的时间步。当然，隐式计算也非常点用cpu时间。而且，目前并不是所有的LS-DYNA的功能和材料都在隐式分析中实现(大部分已经实现)。下面的FEA information newsletter里讨论了显式/隐式转换(/pages/pdfnews/3feadec.pdf)。See also: mass_scaling, quasistaticEnglish Version：When youre using explicit time integration, there is no magic cure for long run times associated with simulating very small geometries over relatively long periods of time. Mass-scaling carries a burden of having to confirm that the addition of nonphysical mass does not significantly affect the results (see attached file “mass_scaling”). A similar burden exists when time-scaling is employed. Time-scaling is a technique where the loading rate is increased and thus the simulation time is shortened in order to reduce the required number of timesteps.Make sure that your timestep is not being controlled by only a few small or stiff elements by searching in the d3hsp file for the string “smallest”. If there are only a few controlling elements, you can remesh in the vicinity of those elements or perhaps make them rigid.Though its rather obvious, run only as long as is necessary. This means in the case of a drop simulation, assigning an initial velocity to the dropped object and placing it a very small distance from the landing surface. After impact, run only long enough to get the results you need.Be aware that for lengthy simulations where the number of timesteps goes above half a million or so, youd be well advised to use a double precision executable of LS-DYNA to minimize error due to roundoff. Running double precision carries with it a cpu penalty of around 30%.Automatic explicit/implicit switching may be an option. Using this technique, the user can specify time windows in which implicit time integration is used as opposed to explicit time integration. An advantage of implicit time integration is that timesteps are not tied to element size and can thus be much larger. Of course, an implicit timestep is also much more expensive in terms of cpu. Further, not all LS-DYNA features and materials are implemented for implicit analysis at this time (though most are). Explicit/implicit switching is discussed in the following archived FEA Information newsletter/pages/pdfnews/3feadec.pdfSee also: mass_scaling, quasistatic.4.Quasi-static 准静态动态松驰(Dynamic relaxation)并不是有意为一般的准静态(quasi-static)分析设置的。它适合于当预载只产生小的弹情况应变的施加预载，或者初始化系统到一个预定义的几何形状1。但对其它更多情况并不适合。你可以通过做一个常规的显示仿真来模拟准静态分析，通过按需要调用时间/质量缩放(time-scaling,mass-scaling)来在可接受的时间内得到结果，但这种方法是需要技巧地。你必须监测系统动能按希望的使惯性效应最小化。基本上动能相对内能应该保持在一个较小的值。时间缩放是指加载比在准静态实验里更快，以减少总的仿真时间。关于质量缩放更多内容可以看”mass_scaling”一节。或者你可以尝试用LS-DYNA运行一个隐式静力分析。可以看用户手册里的卡片*control_implicit_”和Appendix M。See also: gravity.txt, readme.preload, mass_scaling, long_run_times, implicit.general, quick_initialization.Note1：初始化到预定义的几何1. 从第一次分析的最终状态输出一个节点位移文件。（这一部分未按原文翻译）注意d3plot文件里不包含节点转动信息，因此转动输出为0。这对初始化壳和梁单元会是个问题。LS-Prepost有一个选项是输出节点位移，在Output-Nodal Displacements里。但是这个输出是i8,3e16格式的，但需要的是i8,3e15，所以要注意修改一下。如果你做了一个正常的动态松驰分析来得到初始状态，一个预定义位移和转动的drdisp.sif文件在DR阶段结束时会自动创建。2. 在第二次分析时，快速的初始化到第一步输出的预定义的几何。你需要设置卡片*control_dynamic_relaxation里的参数IDRFLG=2，而且在命令行里指定”m=filename”(其中filename指第一步创建的文件)。这样在瞬态分析之前，LS-DYNA会自动做一个100步的预分析来使节点根据文件filename指定的数据移动到指定值。English Version:Dynamic relaxation is not intended for general quasistatic analysis. Its ok for applying preload when the preload produces only small elastic strains or for initializing a system to a prescribed geometry1 but its not good for much else.You can do a quasi-static analysis by running a regular explicit simulation, invoking time- and/or mass-scaling as necessary to crank out the results in a reasonable timeframe, but this approach can be tricky. You have to keep an eye on the kinetic energy in the system as you want to minimize the inertial effects. Basically, the kinetic energy should remain small relative to the internal energy. (By time-scaling, I mean applying the load more quickly than in the quasi-static experiment in order to reduce the simulation time.) See the file “mass_scaling” for more on mass-scaling.Or, you can try an implicit, static analysis using LS-DYNA. See the commands *control_implicit_ and Appendix M in the Users Manual. There are examples of implicit analysis on our “user” ftp site in the ls-dyna/example directory. See also: gravity.txt, readme.preload, mass_scaling, long_run_times, implicit.general, quick_initialization. Note 1* Initializing to a prescribed geometry *1. Write a file of nodal displacements from the final state of your first run. To get this data in the necessary format, use LS-TAURUS as follows:ls-taurus g=d3plot executes 1000 goes to final state deform write a file as described above t Nodal Displacements but the output is i8,3e16 rather than the required i8,3e15 and hence thesuggested use of LS-TAURUS. LS-TAURUS is not available for Windows PCs. Its free and available for Unix and Linux workstations.If you do a regular dynamic relaxation run to get to the initialized state, a file of prescribed displacements and rotations will automatically be written at the conclusion of the DR phase (drdisp.sif).Bug #2020 reported on 9/22/2004 that rigid body nodes do not get initialized according to data in “m=pres_geom_file”. Additional example in /home/jday/test/cantilever/solid/typ2sol_dr_nrb.k (creates drdisp.sif) and typ2sol_presgeom_nrb.k (m=drdisp.sif run). Nodes 11,22,33,44 are not initialized to whats in drdisp.sif 2. In your second run, quickly initialize to the prescribed geometry written in step 1. You need to set:IDRFLG=2 in *control_dynamic_relaxation and include “m=filename” on the execution line where “filename” is the file created in step 1. Before the transient run begins, LS-DYNA will automatically run a precusor analysis of 100 timesteps wherein the nodse are displaced according to the data in “filename”.5.Instability 计算不稳定一些表示计算不稳定的消息如：“out-of-range velocities” 速度超出范围 “negative volume in brick element” 体单元负体积“termination due to mass increase” 因质量增加而终止用来克服显式求解中的不稳定的方法如下：首先(也是最重要的)是使用可获得的最新的LS-DYNA版本。最新的执行块可以从上下载(注：前提是你有访问权限)。联系LSTC获得user帐号的密码。最新的BETA版执行块可以在/outgoing/ls971上找到(不需要密码，但lstc公司对ftp访问有IP限制)。其次是增加d3plot的输出频率到可以显示出不稳定的出现过程。这可以提供导致不稳定性发生的线索。其它的不些解决数值不稳定性的技巧：* 试着用双精度LS-DYNA版本运行一次* 试着减小时间步(timestep)缩放系数(即使使用了质量缩放mass-scaling)* 单元类型和/或沙漏(hourglass)控制。对出现不稳定的减缩体和壳单元，试着用沙漏控制type 4 和沙漏系数0.05。或者试着用类型16的壳单元，沙漏控制type 8。如果壳响应主要是弹性，设置BWC=1 和 PROJ=1 (仅对B-T壳)。避免使用type=2体单元。对体单元部件，在厚度方向最少用两个体单元。* 接触。设置接触的bucket sorts之间周期数为0，这样会使用缺省的分类间隔。如果参与接触的两个部件的相对速度异常的大，可能需要减小bucket sort的间隔(比如减小到5,2甚至1)。如果仿真过程中有明显的接触穿透出现，转换到使用*contact_automatic_surface_to_surface或者*contact_automatic_single_surface，并设置SOFT=1。 确保几何考虑了壳单元的厚度。如果壳非常薄，比如小于1mm，放大或者设置接触厚度到一个更加合理的值。* 避免冗余的接触定义，也就是说不要对同样的两个部件定义多于一个的接触对。* 查找出现不稳定的部件的材料定义中的错误(比如误输入，不一致的单位系统等)* 关掉所有的*damping这些技巧是一些通用的方法，可能并不适合于所有的情况。See also: negative_volume_in_brick_element.tips，shooting-nodesEnglish Version:Some messages that indicate an instability has occurred:“out-of-range velocities”“negative volume in brick element”“termination due to mass increase”Approaches to combating instability of an explicit solution:First and foremost, use the latest version/revision of LS-DYNA available. The latest production executables can be downloaded from . Contact LSTC for the password to this “user” ftp account. More recent BETA executables are found in /outgoing/ls971 (no password required).The next step is to write plot states frequently enough to see the evolu