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May 30, 2012, 20:07 |
Negative ELEMENT Volume Problem-FSI
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#1 |
Senior Member
Ashkan Javadzadegan
Join Date: Sep 2010
Posts: 255
Rep Power: 16 |
Dear All,
I am doing FSI modelling in arteries. I encountered with following error at the beginning of second stagger iteration. A negative ELEMENT volume has been detected. This is a fatal | error and execution will be terminated. The location of the first | negative volume is reported below. | Volume: -0.9954E-12 I got this error when I specified frictionless support at one end of the model. When I fix both ends, the solution converges; however, when I specify frictionless support at one end, the above error is given. Could anyone help me to fix it pls. Kind regards, AshtonJ |
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May 30, 2012, 21:28 |
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#2 |
Member
Peter Galimutti
Join Date: May 2012
Posts: 37
Rep Power: 13 |
'Friction-less support' means you are restricting the face to displace in its normal direction. Hence, you have displacement in other two directions. When the solid displaces in other two directions say 'y' and 'x', the fluid mesh also needs to be displaced accordingly. The mesh motion should be set to 'unspecified' for that boundary.
This is my initial view of you model, but we can not go further with out more input from you! Which means please post as much information as you can regarding your model, setup, bc's, a ccl file etc.. |
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May 30, 2012, 21:46 |
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#3 |
Senior Member
Ashkan Javadzadegan
Join Date: Sep 2010
Posts: 255
Rep Power: 16 |
Thanks for your helpful comments.
For my next questions regarding the FSI modelling, I will provide more information. Thank you. Regards, AshtonJ |
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May 31, 2012, 19:21 |
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#4 |
Senior Member
Ashkan Javadzadegan
Join Date: Sep 2010
Posts: 255
Rep Power: 16 |
Thanks for your help. I could converge my model with fixed support at inlet and frictionless support at outlet. I tried to use frictionless supports at both inlet and outlet; however, it diverged.
Here is the settings of my model; Structural Model: Young module: 1MPa Poisson ratio: 0.3 Density: 1050 kg/m^3 Structural setting Tetrahedral-Patch Conforming Mesh Analysis Settings: Autotime stepping: Off Define by: substeps Number of substeps: 1 Time Integration: Off Boundary Conditions: Inlet and outlet: Frictionless support Inner surface of the wall: Fluid-solid interface Fluid setting Tetrahedral-Patch Conforming Mesh Boundary Conditions: Inlet: Static Pressure 100 mmHg, Mesh Motion: Unspecified Outlet: Static Pressure 50 mmHg, Mesh Motion: Unspecified Wall: fluid-solid interface Initial conditions: Automatic Solver Control: Fluid part: Advection scheme: High resolution transient scheme :Second order backward max loops: 10 convergence criteria:0.0001 Structural part: max iteration: 45 Under relaxation factor: 0.25 Convergence target: 0.01 In CFX-Pre, the following warning is given: 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 would be too please if you could help me to fix this problem. Regards, AshtonJ |
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