Discussion Forum

Hello all,

I am new to COMSOL and I am trying to simulate a metal cylinder in a stationary magnetic field. First with a solid cylinder, then for a hollow cylinder.

The solid cylinder model converges nicely and gives reasonable results. However, the hollow cylinder model is considerably slower and only converges sometimes. Increased computing time for the increased complexity is fair, but the inconsistency is troubling.

I am using the fully coupled, iterative solver. And I have tried the five available solvers (GMRES, FGMRES, BiCGStab, Conjugate Gradients, and TFQMR). For the hollow cylinder model, the runs sometimes take around 10 seconds and produce a nice result. But when I try to compute the same problem again (with the same solver to check for consistency) it takes 15 minutes and fails to converge. Sometimes it completes the computation but presents an unphysical result.

The two errors I most often see are: - Failed to find a solution. Maximum number of Newton iterations reached. There was an error message from the linear solver. Maximum number of intermediate iterations reached. Returned solution is not converged. Not all parameter steps returned - Failed to find a solution. Divergence of the linear iterations. Returned solution is not converged. Not all parameter steps returned.

I have tried varying the mesh size between normal, finer, and even up to extremely fine. But that did not solve the issue.

I am starting to wonder if I have made some basic mistake in setting up the model that makes it difficult to converge. I have attached the project files for the solid and hollow cylinder models, and I would appreciate if a more experienced user could take a look at them.

Thanks, Linus