MBD for ANSYS模型调试技巧

使用MBD for ANSYS时，经常需要调试模型，下面分享一些调试技巧：

• Expression    出现概率:中等       

表达式   Check if there is any radical change of a value.

检查是否有值的突变。     The radical change of a force or motion can cause numerical instability. For example, using a Step function or an IF function which causes a rapid change of a value, or using a stiffness which is too big, can cause simulation failure or poor performance.

In this case, the function or parameters either need to be adjusted to avoid the radical change of the value or use a smaller Maximum Time Step in the Parameter tab of the Dynamic/Kinematics Analysis dialog box.

力或运动的突变可能引起数值不稳定性。例如，使用一个Step函数或一个IF函数，或使用一个太大的刚度值，可导致仿真失效或不良表现。这种情况下，函数或参数需要被调整以避免值的突变或在动态/运动学分析对话框的Parameter选项卡中使用较小的最大时间步。

• Expression    出现概率:中等       

表达式   Use a Step Function rather than an IF function.

使用一个Step函数，而不是一个IF函数。               An IF condition is often used in an Expression. However, since this is a discontinuous change, it can cause a numerical instability which can slow down the simulation. Using a continuous change, if possible, can improve the stability and simulation speed. For example, STEP(time,1,1,1.1,2) is more stable than IF(time-1:1,1,2).

表达式中经常使用IF函数。然而，由于这是一个不连续的变化，它可以导致可降低仿真速度的数值不稳定。使用一个连续的变化，如果可能，可以提高稳定性和仿真速度。例如，STEP（time,1,1,1.1,2）比IF(time-1:1,1,2)更稳定。

• Expression    出现概率:中等       

表达式   Use a sufficiently large time duration to transition the values in a Step function.

在Step函数中使用足够大的持续时间来转换数值。               A Step function is the recommended method for transitioning from one value to another within an Expression. The Step function is inherently smooth, but if the time duration of the transition is too small the value can change radically and cause a numerical instability which can slow the simulation. Please check that the time duration of the transition is reasonable, considering that transitions in physical systems tend to require a noticeable amount of time.

 Step函数一个表达式内从一个值与转换到另一个值的推荐方法。阶跃函数本质上是光滑的，但如果过渡的时间持续时间太短，值可能会迅速改变，导致可降低仿真速度的数值不稳定。请检查持续时间是否合理，考虑到物理系统内的转换往往需要一个明显的时间。

•   Friction   出现概率:高     

摩擦       Check if the threshold velocity of a friction parameter is set appropriately.

检查摩擦参数的门槛速度是否设置合适。                  The Threshold Velocities in the friction definition are used to distinguish between zero friction and static friction, and static friction and dynamic friction. When the ‘Static Threshold Velocity’ and ‘Dynamic Threshold Velocity’ parameters of a joint friction or a contact friction are too small and/or too close in value, it sometimes slows the simulation speed. If Stiction is not important, increasing the Static Threshold Velocity can improve the simulation speed. Note that the default threshold velocities for some contacts are quite large (100mm and 150mm). It can be reasonable to reduce these values to 10mm and 15mm or even 1mm and 1.5 mm, but make these reductions incrementally and check whether or not the lower values have caused a significant slowing of the simulation.

在摩擦定义中的门槛速度被用来区分零摩擦和静态摩擦，以及静态摩擦和动态摩擦。当一个关节摩擦或接触摩擦的“静态门槛速度”和“动态门槛速度”参数太小和/或数值太接近时，有时会降低仿真速度。如果静摩擦不重要，增加静态门槛速度可以提高仿真速度。注意，一些接触的默认门槛速度是相当大的（100mm和150mm）。可以合理降低这些值到10mm和15mm或甚至1mm和1.5mm，但逐渐做出这些减少，并检查较小的值是否引起了仿真速度的严重降低。