Discussion Forum

Hi, I am struggling with the simulation results from a model which considers a 0.5x0.4 m^2 aluminium plate (with 0.004 m thickness). In particular, I am performing an eigenfrequency study through a pure FEM simulation. The plate is therefore sourrounded by a sphere with a spherical wave radiation condition. My issues are the following: -Imaginary part in the eigenfrequency computed values. Some eigenfrequenciers show an imaginary part. I understand that this come from some sort of damping which comes from considering the energy loss caused by the radiation of the sphere. What bothers me is that some frequencies remain purely real, and that there seems to be no logic in the mixture of real and complex frequency values. -Strange results for some eigenfrequencies. Some eigenfrequencies produce a completely unexpected (irregular) mode shape, associated with an unreal acoustic pressure fields which is zero above the plate and increases towards the sphere boundaries. - Different simulated modal shapes between a pure mechanical study and a coupled mechanical acoustics study. In the first case I am able to obtain only some of the frequencies I can obtain from the complete acoustic coupled system. I would expect some differences because of air coupling, but the coupled system find way more mode shapes than the pure mechanical study. I need to find which modes are correct and which are not, as I need to collect the correct shapes outside of comsol. I attach the model with the two studies for better understanding. Thank you to anyone would help me figuring out what is going on.

Riccardo