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ashtonJ April 18, 2012 20:56

FSI Wall Expansion Problem
Dear All,

I did steady FSI in a straight pipe with 50pa inlet pressure and 0 outlet pressure. Someone else for his thesis did the same simulation few years ago, there is a big difference between my results and his results. For me, the pipe wall is expanded close to inlet and outlet, however, for him, the wall is expanded in the middle of the pipe. Does anybody know where the problem originates from.

An image regarding this issue is attached.

Kind regards,

Gweher April 19, 2012 00:45

1 Attachment(s)
Dear Ashkan,

How did you create your geometry, and can you be more specific about your problem setup. If you have the exact same setup you should find the same, from your image I suppose that your BC aren't well imposed.

I'm investigating the static instability of your pipe conveying fluid using Ansys 14, if your setup is done properly you can have some results like buckling.

ashtonJ April 19, 2012 01:04

Dear Gweher,

Thanks for your reply. Let me explain my problem.

I am doing steady FSI in a simple straight pipe.

Pipe length: 8cm
Diameter: 2cm
Wall thickness: 0.1cm

The material of the wall is:

Young module: 10MPa
Poisson ratio: 0.3
Density: 1050 kg/m^3

Structural setting

Hex dominant (Quad) mesh with 1188 Elements

Analysis Settings:

Autotime stepping: Off
Define by: substeps
Number of substeps: 1
Time Integration: Off

Boundary Conditions:
Inlet and outlet: Fixed support
Inner surface of the wall: Fluid-solid interface

Fluid setting

Hex dominant (Quad) mesh with 8800 Elements

Boundary Conditions:
Inlet: Static Pressure 50Pa

Outlet: Static Pressure 0Pa
Wall: fluid-solid interface

Initial conditions:

Solver Control:
Fluid part:
Advection scheme: High resolution
transient scheme :Second order backward
max loops: 100
convergence criteria:0.0001
Structural part:
max iteration: 25
Under relaxation factor: 0.75
Convergence target: 0.01

I went through all the thesis settings and am sure that I used the same settings.

Kind regards,

Gweher April 19, 2012 03:36

When you imposed your boundary condition (Structural) did you select the inner radius edge, the outer edge or the surface thickness?

If you send me your files I can have a quick look.

ashtonJ April 19, 2012 04:43

Thank you very much for your kind attention.

Can I have your email address plz to send my case. I am in the Uni and here I don't have access to the file sharing website like Rapishare.

Kind regards,

Gweher April 19, 2012 07:14

I've send you an e-mail, I'll try to have a look tomorrow.

ashtonJ April 19, 2012 08:04

Thank you very much. The file is sent.

Kind regards,

kok2945 November 26, 2012 10:12

Hi Ashkan, I am also working a very similar geometry as yours by using ANSYS CFX V12 solver. I was wondering if you have figured out how to solve the boundary conditions that you mentioned here? Or, was that the boundary issues that caused your mesh deformation different than the one simulated by the author?
Thank you.

kmgraju December 5, 2012 08:07

Dear friend
I am working on similar problem . I am doing transient two fsi problem.
I don't know how to do Analysis settings in the transient structural
Kindly help me to figure out time step , number of steps etc



kmgraju December 5, 2012 08:18

Dear friend

I confuse with step control settings. Is it necessary for pulsatile flow through the pipe?



kok2945 December 5, 2012 14:19


Originally Posted by kmgraju (Post 395902)
Dear friend

I confuse with step control settings. Is it necessary for pulsatile flow through the pipe?



I Govind, for the structural part, ANSYS CFX Tutorial - Chap.23 for FSI may give you some idea how to set it up. For my case, the only change I made was instead of using timestep, i used Substeps. and no. of substep=1. I hope this helps. May i know what is your topic about?

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