Solvers for BEM Models
The default for The Pressure Acoustics, Boundary Mode Interface is to use an iterative solver for 3D models and a direct dense matrix solver for 2D problems. If the Far-Field Approximation is turned off, the direct dense matrix solver will be used in all situations.
The boundary element method (BEM) used in the Pressure Acoustics, Boundary Elements interface is based on the direct method with Costabel’s symmetric coupling. The adaptive cross approximation (ACA) fast summation method is used for solving the resulting linear system. This method uses partial assembly of the matrices where the effect of the matrix vector multiplication is computed. The default iterative solver used is GMRES.
For multiphysics problems that combine BEM and FEM interfaces and are set up with one of the multiphysics couplings; the default approach is to use hybridization with ACA for BEM and an appropriate preconditioner for the FEM part of the problem (direct or multigrid). Several solver suggestions are given for the multiphysics FEM-BEM problems.
Further details about the BEM formulation are found in The PDE, Boundary Elements Interface documentation in the COMSOL Multiphysics Reference Manual.