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How prescribed displacement and Floquet Bloch boundary conditions in COMSOL of two-dimensional unit cell work to achieve eigenfrequencies?

Posted Jul 12, 2024, 3:24 a.m. EDT 0 Replies

Binh Pham

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Dear All,

I am trying to simulate a periodic unit cell using two studies: Study 1 and Study 2. The first study is stationary, and the second study is an eigenfrequency analysis. In the first study, I applied a tensile load (prescribed displacement) to the top-bottom and left-right faces of a two-dimensional unit cell. In the second study, all solutions from Study 1 are used as initial conditions for Study 2. This was set up in the "Values of Dependent Variables" section under "Eigenfrequency" with the following settings: User controlled; Method: Solution; Study: Study 1, Stationary; Selection: Automatic (all solutions).

I have verified that the unit cell deformed correctly under the assigned tensile load in Study 1, without the application of Floquet-periodic boundary conditions. However, after solving Study 2 with Floquet-periodic boundary conditions, the eigenmodes in all modes did not display the deformed shape from Study 1 (i.e. the undeformed shape of the unit cell is obtained at all eigenmodes). It appears that the solutions from Study 1 were not utilized as initial conditions for Study 2. I also attempted to vary the magnitude of the prescribed displacement on the faces, but the same eigenfrequencies and eigenmodes were obtained. It is important to note that when solving Study 1, I turned off the "Solve for" property in the "Physics and Variables Selection" for Study 2, and vice versa.

I would appreciate any comments or suggestions you might have on this issue. If anyone else is familiar with this problem, your assistance would also be greatly appreciated.

Thank you very much.

Best wishes, Binh

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