Learning Forum

[Farah]

Hi,

I am working on a two-way FSI of a complex physiological geometry. I've read online about using an "under relaxation factor," but I'm unsure if I should define it for data transfer, the fluid domain (blood), or the solid domain (wall). Any advice would be appreciated.

Thank you!

 

[Rahul]

Hello Farah,

Which data transfer is unstable out of 'force' and 'displacement'? You can apply URF to the corresponding data transfer. 
You can refer user guide to learn more about improving the stability of coupled analysis. Data Transfer Relaxation (ansys.com)

[Farah]

Hey Rahul,

Im not sure which one but here is what i know: 

my simulation keep fails due to "excessive thickness change" so the shell element (structural) can not tolerate this pressure. now can u help me which data transfer is unstable? 

thanks

[Rahul]

Okay. Here you can apply it on force data transfer. 
How good is the mesh? Ensure that you have good mesh quality.
What is your working fluid? I assume you are using a liquid (blood) for your application. Make sure your material is set as a compressible liquid. An incompressible fluid will have infinite sound speed, which in cases with deforming fluids can lead to pressure spikes at the FSI interfaces resulting in excessive deformation. If you still experience high pressure oscillations at the FSI interface, consider using Solution Stabilization 12.6.9.8 Solution Stabilization for Dynamic Meshes Boundary Zones (ansys.com)