Numerical Damping value in Transient Analysis — Lesson 3

The default 0.1 numerical damping value used in the transient analysis must have a reason. Is there any test correlation to validate the damping values? Or is it just a random number the program picks?

Numerical damping, it is numerical - not physical - so it's not related to test correlation.

Please see Section 5.6.3 "Transient Dynamic Analysis Settings Based on Application" below:

Ansys Help

There, one will see different default values. MAPDL defaults to gamma = 0.005 while Ansys Mechanical™ structural finite element analysis software defaults to gamma = 0.1. The setting for Ansys Mechanical software is the same as in the "Moderate Speed Simulation" case.

To provide some background, when we have transient structural analyses, we can often get additional 'noise' - for example, spurious high-frequency content can be excited. Models may not be set up 'perfectly' by the user (not through any fault of the user, but to get an efficient solution, there may be some modeling short-cuts taken, such as using a coarse mesh). Using numerical damping can reduce such 'noise'. It can also have a different effect - faster convergence. These benefits come at the expense of some numerical dissipation (larger numerical damping means larger numerical dissipation).

The defaults in Ansys Mechanical software of gamma = 0.1 are a tradeoff between these effects (pros and cons) for structural simulations. Note that for purely acoustic simulations, it's a bit different - we don't have contact/impact in purely acoustic simulations, and everything is always linear. Thus, using no numerical damping (no numerical dissipation) is probably desired for this situation Albert has where amplitude is lower than expected.

In short, numerical damping comes about mainly for structural analyses, and defaults are with structural analyses in mind. For purely acoustic simulations, numerical damping can add unwanted numerical dissipation, so user may wish to set it to zero.