How to overcome highly distorted elements problem in fluid-structure interaction anal

N mollaahmadi · April 28, 2018, 09:37

Dear All,
I'm involving in a 2-way FSI problem simulation of blood flow in arteries(transient structural + CFX) which includes big structural deformation. I have used very small time step for transient structural part as well as system coupling part. However, system coupling delivers "highly distorted elements error" or " Element has excessive thickness change." every time I run the problem. when I run system coupling it return highly distorted elements error for the first iteration, even for very small time steps (1e-7sec).I change the "under-relaxation factor" less than 1 to 0.0001 but this error did not remove.Anyone has any idea how to solve this issue??
Thanks,

ghorrocks · April 29, 2018, 08:02

This suggests that despite your efforts so far the motion is still numerically unstable. Try even smaller time steps. If that does not work then get a little more desperate by modifying your material to be stiffer and heavier to see if that stabilises things - if you can get that to run you might be able to complete a time step and then you can see the motion and might be able to see what has gone bezerk.

April 28, 2018, 09:37	How to overcome highly distorted elements problem in fluid-structure interaction anal	#1
N mollaahmadi New Member Nazanin mollahmadi Join Date: Feb 2018 Posts: 1 Rep Power: 0	Dear All, I'm involving in a 2-way FSI problem simulation of blood flow in arteries(transient structural + CFX) which includes big structural deformation. I have used very small time step for transient structural part as well as system coupling part. However, system coupling delivers "highly distorted elements error" or " Element has excessive thickness change." every time I run the problem. when I run system coupling it return highly distorted elements error for the first iteration, even for very small time steps (1e-7sec).I change the "under-relaxation factor" less than 1 to 0.0001 but this error did not remove.Anyone has any idea how to solve this issue?? Thanks,

April 29, 2018, 08:02		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	This suggests that despite your efforts so far the motion is still numerically unstable. Try even smaller time steps. If that does not work then get a little more desperate by modifying your material to be stiffer and heavier to see if that stabilises things - if you can get that to run you might be able to complete a time step and then you can see the motion and might be able to see what has gone bezerk. micheldang likes this. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

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