Selecting Iterative Solvers
The default solver for structural mechanics is the MUMPS direct solver in both 2D and 3D. For large 3D problems (several hundred thousands or millions of degrees of freedom) it is beneficial to use iterative solvers when possible to save time and memory. The drawback is that they are more sensitive and might not converge if the mesh quality is low. The iterative solvers also have more options than the direct solvers.
For Stationary, Time Dependent studies and Frequency Domain studies in 3D, a GMRES iterative solver is preconfigured and available as an alternative solver suggestion for solid mechanics models.
If the model is set up using quadratic (default) or higher order elements for the displacement dependent variable, this GMRES solver will use geometric multigrid (GMG) as the preconditioner.
For slender geometries, changing to SOR Line as presmoother and postsmoother can give better results compared to SOR that is the default for GMG preconditioner.
For models using linear elements for the displacement dependent variable, the preconditioner will be changed to smoothed aggregated algebraic multigrid (AMG). This is to avoid remeshing when creating the discretization on the coarse level. Note that you need to manually regenerate the solver sequence after you change the element order if you want to make use of such change in the predefined iterative solver configuration.
For eigenfrequency/eigenvalue studies, use the default direct solver (MUMPS).
Specifying a shift frequency greater than the lowest eigenfrequency results in indefinite matrices.
Studies and Solvers
in the
COMSOL Multiphysics Reference Manual
