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Hi all,

First a disclaimer, I am an electrical engineer, but I am adventuring myself into this as it is need for an ongoing project. I am trying to understand how to work this problem in Comsol 5.0. I will try to explain where I want to get by steps:

1. I have a homegenous nanosphere made of an elastic material and I need to find its natural frequencies. This has been done and verified. I am interested in one of the modes, which I will call frequency . This was obtained using the solid mechanics module using the eigenfrequency sutdy.
2. I put this sphere inside a box containing a fluid (air, in this case). This box already contains another sphere with the exact dimensions and elastic properties of the first one,
3. What I want to know is: if the first starts to vibrate with frequency , the movement in the fluid should affect the second one and they will couple. How can I actually verify that in Comsol? At first, I just want a simple eigenfrequency study as I have with only one sphere, see if immersing both spheres in a fluid would change , if other modes appear, and so on.

I have tried the fluid solid interaction module, as well as putting together the Solid Mechanics and Acoustic Pressure modules together, trying different studies (eigenfrequency, stationary, frequency domain, etc) without success.

Here is an image of the problem

The only thing that I have so far is that one vibrates, the other one stays fixed and the fluid moves, but without occuping the void space when the sphere is 'squeezed'.

Any light on this would be highly appreciated.

Kind regards, Gabriel