When solving a Multiphysics problem, it is necessary to ensure that the solvers behave correctly. It is especially important to check if a model is solved Fully Coupled or in a Segregated way. COMSOL has built in logic to handle most multiphysics problems when the predefined multiphysics couplings are used, ensuring that the model solves correctly. If many physics or couplings are added at the same time, this logic can fail and manual settings should be performed. For large models COMSOL generates Iterative Solver Suggestions (see below).

It is also possible to enable and disable both physics and couplings from within a Study Step. This can be done in the Physics and Variables Selection section in Settings. This functionality can be used to solve a model both coupled and uncoupled by adding two Studies: one where the Multiphysics coupling is active and one where it has been deactivated.

Multiphysics models can in 3D easily grow rapidly in size and become difficult to solve with a direct solver, simply because you run out of RAM. In this case, it can be necessary to switch to an iterative solver approach. For most multiphysics couplings, iterative solver suggestions are automatically generated. Set up a new solver configuration (first time the model is solved) or right-click the study node and select Show Default Solver, then expand the Solver Configuration tree under Stationary Solver or Time-Dependent Solver. The predefined iterative solver suggestions that are automatically generated can be seen here. In the predefined cases, a direct solver is used as default and iterative solvers are suggested and disabled. To turn on one of these approaches, right-click the solver and select Enable (or press F4).

All solver suggestions have a tag that makes it possible to see which physics feature that has generated them, for example, (asb1) means that the suggestion comes from the Acoustic–Structure Boundary 1 feature.

When a multiphysics model is solved in the time domain, it is important to update the Transient Solver Settings section of the acoustics interface (and structural interfaces if present) used in the model. The time stepping settings generated by these settings will also be applied to the coupled problem when a Multiphysics couplings is used.