Frequency Domain, Modal and Time-Dependent, Modal Studies
The Frequency Domain, Modal study type () is used to do modal analysis in the frequency domain and the Time-Dependent, Modal study () is used to do time-dependent modal analysis. Both study types can also be used for multiphysics models like a vibroacoustic problem. These problems can result in nonsymmetric matrices for which both left and right eigenvectors are automatically stored.
When defining sources in models solved with the modal solvers, the source expressions (magnitude) need to be wrapped with the linper() operator. For example, a pressure source of amplitude 1[Pa] should be defined as linper(1[Pa]).
To obtain a sufficient basis, it is in most cases necessary to include eigenmodes representing eigenfrequencies up to twice the maximum frequency to be resolved. Note also that in many acoustic problems you need to include the 0 Hz mode (DC mode) to get the correct behavior at low frequencies.
Frequency Domain, Modal and Time Dependent, Modal in the COMSOL Multiphysics Reference Manual
Helmholtz Resonator Analyzed with Different Frequency Domain Solvers: Application Library path Acoustics_Module/Tutorials,_Pressure_Acoustics/helmholtz_resonator_solvers