# FSI problem of improper constraint

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March 18, 2013, 02:45
FSI problem of improper constraint
#1
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Dr. Moloy Kumar Banerjee
Join Date: Jun 2011
Posts: 71
Rep Power: 15
Dear all,
I am trying to simulate the FSI problem where, a fluid is flowing through a pipe of dia 2cm and length 8cm. My aim is to check the behavior of the wall material under the influence of fluid flow and vice-verse. For this simulation I select the Youngs modulus for the pipe material as 10Mpa, and poissons ratio as 0.3 and density of 1050 kg/m3. For the fluid model I have selected the density as 1050kg/m3 and the viscosity as 0.003 Pas.
For fluid domain BC, I used transient pressure at inlet and zero gauge pressure at outlet.
For the structural domain I select the front faces of the wall as stationary(as shown in figure) and the two surface that in contact with the fluid domain as fluid-solid-interaction BC.
My aim is to do the 2D analysis of the problem and hence I choose 2-3 element thickness of the entire geometry in the z-direction. Both the front and Back end of the fluid domain are given the symmetry BC.
Once I start the simulation using system coupling it shows the error " improper constraint in the structural system, which results in a very high displacement Uy=10^33 and finally it stops"

Is there any correction needed in the constraint definition. Please help me to rectify the problem..
Attached Images
 wall.JPG (44.2 KB, 10 views) fluid.JPG (48.1 KB, 10 views)

 March 19, 2013, 06:13 #2 Member   Dr. Moloy Kumar Banerjee Join Date: Jun 2011 Posts: 71 Rep Power: 15 any help is highly appreciated

 March 25, 2013, 13:23 #3 Senior Member   Join Date: Apr 2009 Posts: 531 Rep Power: 21 Given the low Youngs modulus it's likely unstable coupling. "Solution stabilization" in version 14.5 would address this. If you can download the Fluent FSI training material from the ANSYS Customer Portal there's a whole chapter on convergence that covers this.

 April 4, 2013, 03:47 #4 New Member   binh Join Date: Dec 2012 Posts: 6 Rep Power: 13 Is there any download link for Fluent FSI training? I could not access the Ansys Portal. Thank you.

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