Multiphysics analysis is one of the strengths of COMSOL. And, they have put a lot of time and energy into tuning the default solver sequences to handle as many problems as possible as efficiently as possible. However, it is important to be able to understand how to tune your solver set-up because the default settings don't always offer the optimum approach. In all cases, COMSOL by default will solve all
active equations simultaneously (using either a segregated or fully coupled solution approach). But, did you know that if your equations are one-way coupled (aka sequentially coupled) that you can manually set-up COMSOL to solve in a step-wise fashion? This can be a big memory saver and, if you are running a number of simulations, this can be a time saver as well.
One
classic example of one-way coupled equations uses the heat transfer and solid mechanics equations when thermal expansion is involved. A good assumption for this physical situation is that the temperature solution to the heat transfer equations affects the solid mechanics solution but not the reverse. In other words, temperature affects expansion but expansion does not affect
temperature. In this case, the equations can be solved sequentially using a two step process.
The trick to implementing this 2 step process is knowing the correct way of passing the solution to the 1st step into the solver for the 2nd step. Often COMSOL will "intelligently" set things up properly, but it's always a
good idea to know how to check yourself that things are how you want them. For this two step process, the following image shows the proper solver settings for Step 2.
