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faraday34 June 13, 2013 16:18

FSI analysis for blood vessel
5 Attachment(s)
Since it says turn on element shape checking, in mechanics shape checking is on standard mechanical. By the way it says to change if error message occurs after first step. The error occurs after 6th iteration.

Hi everybody

I am trying to simulate an aneurysm in a vessel. At the very beginning of simulations I encountered with problems. In the threads I have seen similar problems but can not get a solution, unless I missed it.

First of all when performing on the CFX Setup it warned as:

In Analysis 'Flow Analysis 1' - Output Control: No intermediate transient results files have been defined.

In Analysis 'Flow Analysis 1': Export results are unavailable as no suitable boundaries exist for use as export surfaces. Mesh motion on a boundary invalidates its use as an export surface.

I ignored those.

Then in the out file when solving structural before cfx:

A wall has been placed at portion(s) of an OUTLET |
| boundary condition (at 95.7% of the faces, 96.6% of the area) |
| to prevent fluid from flowing into the domain. |
| The boundary condition name is: Outlet. |
| The fluid name is: Fluid 1. |
| If this situation persists, consider switching |
| to an Opening type boundary condition instead.

And then:
Fatal error occurred when requesting Total Mesh Displacement for Interface.

In the error file it says:

*** ERROR *** CP = 62.931 TIME= 12:34:42
One or more elements have become highly distorted. Excessive
distortion of elements is usually a symptom indicating the need for
corrective action elsewhere. Try ramping the load up instead of step
applying the load (KBC,1). You may need to improve your mesh to
obtain elements with better aspect ratios. Also consider the behavior
of materials, contact pairs, and/or constraint equations. If this
message appears in the first iteration of first substep, be sure to
run shape checking of elements.

I am attaching the out and error file.

When I increase the mesh quality nothing changed. Only I get the error after waiting a little longer :))

I will really really appreciate if someone can answer.

PS: I also attach the fluid & solid mesh with the weird picture in the results ( in case it may give some idea what is wrong)

faraday34 June 18, 2013 17:08

For the ones who also questions such kind of question

Increasing young modulus of elasticity of the wall, making it in GPa made the solution converge.

Lance June 19, 2013 03:25


Originally Posted by faraday34 (Post 434724)
Increasing young modulus of elasticity of the wall, making it in GPa made the solution converge.

Sure, but how realistic is an arterial wall stiffness on the order of GPa? I doubt that you will have a realistic wall displacement.

faraday34 June 19, 2013 11:54

It is not realistic, but since I am at the beginning I was even not using blood, just water and trying to see if the model works. Geometry, mesh, fsi interface etc. Bcs are also need to be modified.

ghorrocks June 19, 2013 19:09

I think Lance's comment is important - if the stiffness you use is a long way from the real stiffness then the setup is not going to be relevant for the real simulation. Change the stiffness to be at close to the actual stiffness.

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