At AltaSim, we await COMSOL’s improvements to their software with great anticipation. We take time to evaluate these changes to determine what we can use to better serve our clients. Based on our review, we also pass on our insights via Tips & Tricks.
Version 5.6 of COMSOL Multiphysics has introduced serval solver improvements that may help you to solve your models faster – especially if you are doing computational fluid dynamics (CFD). One feature that AltaSim has found to be a particularly helpful improvement is the Block Navier-Stokes preconditioner.
AltaSim recommends iterative linear system solvers for medium to large size models that have greater than about 200-500k degrees of freedom. The COMSOL Multiphysics default solver sequences for iterative methods will automatically include preconditioners to improve the conditioning of the system of equations, allowing for faster and more robust convergence. Preconditioners are particularly helpful for ill-conditioned systems that are sensitive to small changes in the inputs.
If you are solving the incompressible Navier-Stokes equations in the transient regime, the best option for a preconditioner, before version 5.6, was most likely the Multigrid preconditioner. However, if you are using version 5.6, we recommend switching to the Block Navier-Stokes preconditioner as this will likely produce noticeable speed up. An example of the speed up that can be obtained for a jet flow model is shown below.
This approach is activated by clicking on Laminar Flow, expanding the section Advanced Settings and checking the box for ‘Use Block Navier-Stokes preconditioner in time dependent studies’.
Consider attending AltaSim’s Solver Setting for Effective Analysis in COMSOL Multiphysics for training in solver strategy, including best practices for incorporating the other v5.6 solver improvements into your modeling approaches.