How to deal with ""Program terminated -time step too small"" error message? "
""Time step too small"" is shown when the current time step is less than 10% of the initial time step. You can always decrease the minimum time step to continue the calculation. After loading your problem, go to the Controls panel and select Timestep Options. Change the Minimum Time Step to a very small number, or zero. Zero Minimum Time Step means that the minimum time step size is calculated automatically by the code. The variables affecting the time step are the smallest cell size, gap size, velocity, and sound speed. For Lagrangian type parts, you need to examine the geometry of the parts to see if there are distorted cells. For Eulerian type parts, you need to examine the velocity and sound speed of the parts to see if there are abnormal velocity or sound speeds. If Lagrange-Lagrange interaction is involved in the calculation, you need to check the gap size and gap type. If internal gap is used, the time step is usually calculated from the gap size because it is the smallest. The internal gap size decreases with the decreasing cell length and thus causes the smaller time step size. So the best type of gap is EXTERNAL GAP. Change the gap type to EXTERNAL and run the model again. For Euler calculations, following the instructions help you to prevent a small timestep: 1. Use Internal Energy Transport. This is set in the Controls panel under Transport, by selecting internal for the ALE/Euler Energy option. The default in AUTODYN is Total Energy Transport. In Euler calculations of shaped charges or detonation of explosives where the detonation products escape into a void at high speed, a better result will be achieved using internal energy transport as this provides a more accurate determination of the internal energy in a cell, which in turn is used in the explosive equation of state. 2. Use large relative density cutoffs 1.0E-4 instead of default 1.0E-6. This is set for each material and can be changed in the Material panel by selecting the relevant material from the list and pressing the Modify button. The escaping detonation products are typically at very low density. It is useful to limit the diffusion of extremely small masses which can causes very small time step by increasing this cutoff value. 3. Use a Maximum velocity cutoff of ~10,000 m/sec. Very small masses of explosive escaping into Void can sometimes achieve unrealistic velocities which results in verysmall time step This should be limited by setting the Maximum velocity cutoff in the Controls panel under Global Cutoffs."
当前时间步长小于初始时间步长的10％时，将显示“时间步长太小”。您始终可以减少最短时间步长以继续计算。加载问题后，转到“控制”面板，然后选择“时间步选项”。将“最小时间步长”更改为非常小的数字，或者为零。最小时间步长为零表示最小时间步长由代码自动计算。影响时间步长的变量是最小的像元大小，间隙大小，速度和声速。对于拉格朗日类型的零件，您需要检查零件的几何形状以查看是否存在扭曲的单元。对于欧拉型零件，您需要检查零件的速度和声速，以查看是否存在异常的速度或声速。如果计算中涉及拉格朗日-拉格朗日相互作用，则需要检查间隙大小和间隙类型。如果使用内部间隙，则时间步长通常根据间隙大小来计算，因为它是最小的。内部间隙尺寸随着单元长度的减小而减小，从而导致较小的时间步长。因此，最好的间隙类型是EXTERNAL GAP。将间隙类型更改为EXTERNAL，然后再次运行模型。对于Euler计算，请按照说明进行操作以帮助您避免浪费时间：1.使用内部能量传输。通过在ALE / Euler Energy选项中选择internal，可以在“控制”面板中的“运输”下进行设置。AUTODYN中的默认值为总能量传输。在欧拉计算爆炸物的定型装药或爆炸时，爆炸产物以高速逃逸到空隙中，使用内部能量传输将获得更好的结果，因为这可以更准确地确定单元中的内部能量，进而将其用于爆炸状态方程中。2.使用较大的相对密度极限1.0E-4代替默认的1.0E-6。这是为每种物料设置的，可以通过从列表中选择相关物料并按“修改”按钮在“物料”面板中进行更改。逃逸的爆炸产物通常处于非常低的密度。限制极小质量的扩散非常有用，这可以通过增加该截止值来导致非常小的时间步长。3.使用〜10,000 m / sec的最大速度截止。
另外几种建议：
- in analysis setting -->maximum energy error = a big number 1e6 and time step safety factor = 0.5