Discussion Forum

I try to understand the difference between FSI and acoustic-structure interaction (including thermoviscous acoustics and pressure acoustics).

After exploring some blogs articles and examples, I have an impression that FSI is more "complete" since it starts from the lower level-- the properties of the solid and the fluid, with moving mesh in general. So it can handle all kinds of fluid structure interaction problems, including the ones in which the sturcture vibrates in fairly high frequency (~kHz). As long as the time step is small enough (1/nth of a period of the vibration), FSI time depent solver should be able to find all the behavior of this system, including dampling. The only practical problem is that it can be expensive and be even inpractical for very high frequency vibration, and must be carefully setup when dealing with fast changing conditions, like shocks.

Thermoviscous acoustics and structure coupling, howerer, is a weaker solution compared to the FSI one, as it doesn't have moving mesh. So, it can't handle motions or vibrations with large amplitude. But it is more efficient than FSI for vibration scenarios, as long as the vibration amplitude is not large enough. This case condisers both added mass due to the fliud to the structure and the thermal damping due to the fliud.

The pressure acoustic and structure coupling is further simplied thermoviscous acoustics structure coupling, because it simply drops the thermal damping part. For macrosopic systems, that parts is in genearl insignificant.

If the above is in general correct, I had a laminar flow--solid mechanics coupling problem. And I tried to find the eigenfrequency of the coupled system using eigenfrequency solver, but it seems the result is not much different from the same system without the laminar flow part. Did I choose the wrong coupling (FSI)? or did I choose the wrong, laminar flow?