Hi all.I am working on a flow with heating in a channel and I use Comsol when I use a small mesh The solution works fine when I increase the mesh the calculation is diverged.does anyone can help me how to vary the numerical diagrams and the convergence criterion. and thank you
Using small mesh will result in more better and accurate solutions. Using bigger mesh will converge to a solution quicker but will not serve the purpose of Finite Element Method as the design or product's behaviour is more thoroughly sampled across its physical realm.
1-Try to recalculate the solution (refined mesh) by taking the coarse mesh solution as initial solution.
2-Ramp viscosity convergence; by adoption parametric sweep study; multiplying the viscosity by a number (1000....................1).
If this does not work ) please inbox me
This document could be helpful; please go through the given link once:
https://www.comsol.com/blogs/improving-convergence-multiphysics-problems/