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。

When you’re 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.

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。

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.

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。

Though it’s 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.

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。