FSI convergence problem

YY

Hi guys,

I'm not sure if this would be the best place but I'm desperately in need of help.

Okay, so I'm modelling this FSI problem of a flow in a collapsible tube. Tube is circular with a constant external pressure acting on it. The pressure inside the tube is less than the external pressure applied causing the tube to deform inwards.Deformations are expected to be large and post-buckling effects are supposed to be captured. I'm modelling this in Workbench using the Ansys and CFX code coupling. This problem is a 2-way FSI.

So the problem is:

When I run the structural part alone, the net pressure acting on the solid is much higher than in the coupled solution which would mean than the deformation is larger but yet I could get the result to converged. However when I solve it together with the fluid part the structural part could not converged and there is always the error of elements turning inside out. Can anyone explain to me what's happening and how do I fix this. Thanks.

Regards, YY