FSI - highly distorted elements
 

Good morning,

I am currently simulating a fluid-structure interaction of a channel driven cavity flow and a plate with pulsatile flow. The velocity profile is sinusoidal. With a sine frequency of 1 Hz, everything worked. But now I raised the frequency to 2 Hz and I get the error highly distorted element every time.
The mesh quality of the solid plate and the fluid domain is really good with aspect ratios < 1.3 and element quality > 0.98.
What I am wondering about is the huge change in the receiving force within one coupling step:

Coupling Iteration 2
RECEIVING FORCE FX SUM = -0.31654E-02
RECEIVING FORCE FY SUM = 6.3474
RECEIVING FORCE FZ SUM = -0.16165E-05
Coupling Iteration 3
RECEIVING FORCE FX SUM = 26551.
RECEIVING FORCE FY SUM = -0.32817E+11
RECEIVING FORCE FZ SUM = -0.25715E+06

Can anyone help to find the reason for the errors? I defined the material Aluminum only with density, Young's Modulus and Poisson ratio - is that enough?

Thanks in advance!