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Anyone?

This is what I have tried:

In model wizard choose 2D, solid mechanics, eigenfrequency. Then I draw a circle to represent the infinite beam and I choose some material for it. In the solid mechanics (solid) I create a new rigid connector and in the rigid domain I choose the entire circle. In the rigid connector I check a prescribed displacement in the Y-direction and set it to 0. In the rigid connector I add an applied force, and in the x-direction I give a value -100*u[N/m]. Create the mesh and try to solve. The solver gives the following error:

The source selection for the operator intrig11 must be nonempty. Error in multiphysics compilation.
-Feature: Compile Equations: Eigenfrequency (sol1/st1)
-Error: The source selection for the operator intrig11 must be nonempty

Any ideas?

Hi

First I would say its a 1D problem as you have a constant section, it solves even quicker.
Then, I'm nut sure you can truely represent "INF" in a FEM (Finite Elements ...). You need to find a way to define your BC i.e. by a periodic condition. Have you checked the model library about PDE examples ?

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Good luck
Ivar

Thanks for the reply. You're right, it is a 1D problem at the moment, but once I couple it with a fluid, it's 2D. The "infinity" here is just that the problem is 2D.

I can make everything work just fine if I won't make the circle (cylinder) a rigid domain (i.e. so that the cylinder is also allowed to deform). I wonder why this is.. I suppose I could use it this way as well, but I would probably save some computational effort if the rigid body would actually be rigid.

Hi

Ok but then I missed something, if you are in 2D and you see along the axis, your cylinder is a circle indeed, but by default ist NOT infinite in Z (out of the paper) it's rather finite and by default COMSOL uses 1[m] depth, most values comes out as values "per meter" depth, up to you to multiply by the thrue depth.

This does not really apply to eigenfrequencies, as thes are restrained truely to 2D and you do not see any Z, Rx, Ry modes (only X,Y, & Rz modes) by symmetry, so in fact you are missing many modes.

Now, you say you have a fluid around, this will indeed interact, but that is rather tricky, you have the added mass for "small deformations" but also the visosity. I'm not sure what is the best to use Acoustics or FSI ... ? and for eigenfrequencies ?

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Good luck
Ivar

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