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I am trying to do the same in 4.0. By selecting the fsi module, you automatically setup certain defaults that are in conflict with the contact option. The fluid-solid interaction region will be written over when you declare these surface to be contact surfaces. Therefore, you have to re-insert the fluid surface load using using boundary load. Also, it seems like some prescribed mesh displacement for some surface is set to zero and this causes contact surfaces to go through each other. With limited success, I am able to run an fsi problem with contact. However, in many instances I am getting inverted mesh elements. So I am having convergence issues. I will be contacting COMSOL support group soon.

I am trying to do the same in 4.0. By selecting the fsi module, you automatically setup certain defaults that are in conflict with the contact option. The fluid-solid interaction region will be written over when you declare these surface to be contact surfaces. Therefore, you have to re-insert the fluid surface load using using boundary load. Also, it seems like some prescribed mesh displacement for some surface is set to zero and this causes contact surfaces to go through each other. With limited success, I am able to run an fsi problem with contact. However, in many instances I am getting inverted mesh elements. So I am having convergence issues. I will be contacting COMSOL support group soon.

I have the same problem during my modeling in 3.5a. What do you mean about "re-insert the fluid surface load using boundary load" ?

Hi,
I'm also trying to model a fluid structure interaction with contact (also in the case of a beating reed).
Contact pairs seem difficult to define.
Did you make any progress? Have you any advices for me?
Thanks

I was unable to get the "contact" feature to work along with FSI; however, you can simulate the effect by adding in a large "spring" load to the surface that comes in contact. I don't remember the exact function, but add in a force such that F = K*X with a large K (simulating a large contact stiffness) and X as the displacement variable (only apply this to the reed closing, i.e. X < some small gap length).

Did that make sense? I don't have time at the moment to work out step-by-step directions and I have not attempted this in a 3-D case, but I had it working for 2-D and could probably make up an example later this week.

Note that:
1.) You need to apply the force such that the valve does not close fully. COMSOL can't handle redefining the domains like that (i.e. separating 1 fluid domain to 2).
2.) This is probably not an accurate way to model contact forces. If you are just concerned about the fluid flow that shouldn't be an issue, but don't use this method to do a stress analysis on your reed.

Thanks John
I'm more concerned about the fluid flow so I will try your solution.
If you could send an example that would be great!

John,

Your solution was very helpful because for a long time, I was in a trouble when I was using a contact pair in a FSI model. but still I don't know how to add in a spring between two boundaries which come in contact. Should I define forces (F=-K.X) on both boundaries? How can I calculate the distance between the boundaries? I guess by defining identity contact but don't know how. And finally the forces we put on a boundary works on that boundary not on an approaching boundary!!

I really really appreciate if you help me on this and give me a steps direction.