Discussion Forum

I am doing a simulation in COMSOL 5.1. A cuboid container is filled with water, I want to obtain the eigenfrequency of water (not the eigenfrequency of cuboid). The cuboid container doesn’t need to be established in Geometry and should be defined in boundary condition.
1. Which physics should I use for this problem? Structural Mechanics-Solid Mechanics- eigenfrequency? Or Pressure Acoustics Frequency domain (acpr)? Or something else?
2. If I use the water in Solid Mechanics, I need to define the Young’s modulus and Poisson’s ratio of water (maybe water’s Young’s modulus is 2.2e9 [Pa]? and water’s Poisson’s ratio is 0.5?) or I should use other physics.
3. When I use 2.2e9[Pa] and 0.5 in simulation, there will be an error:
Undefined value found.
- Detail: Undefined value found in the stiffness matrix.
There are 58765 equations giving NaN/Inf in the matrix rows for the variable comp1.u.
at coordinates: (0.35,0.0323495,0.00593529), (0.35,0.0357826,0.00560539), (0.35,0.0392158,0.00527549), (0.35,0.0340319,0.00296764), (0.35,0.037465,0.00263775), ...
There are 58765 equations giving NaN/Inf in the matrix rows for the variable comp1.v.
at coordinates: (0.35,0.0323495,0.00593529), (0.35,0.0357826,0.00560539), (0.35,0.0392158,0.00527549), (0.35,0.0340319,0.00296764), (0.35,0.037465,0.00263775), ...
There are 58765 equations giving NaN/Inf in the matrix rows for the variable comp1.w.
at coordinates: (0.35,0.0323495,0.00593529), (0.35,0.0357826,0.00560539), (0.35,0.0392158,0.00527549), (0.35,0.0340319,0.00296764), (0.35,0.037465,0.00263775), ...
and similarly for the degrees of freedom, NaN/Inf in the matrix columns.

I have searched for it on google and didn’t find answer. I will appreciate it very much if you could give me some tutorial about this problem. Thank you very much!