I get the following error in the first iteration (or sometimes after some iterations):

CG iterations made = 5001 using tolerance of 1e-09 (error = -nan, rhs_mag = 13729.7)

Fatal   : Level 0 assertion violation
Exceeded maximum number of iterations

My question is a bit general: What are the possible causes of this error? What I understand is that the solvers are unable to converge to a solution (in finite iterations). The mesh is okay. I sometimes solve it by tweaking the initial conditions or increasing/decreasing the time step. But, this is a bit heuristic. As long-time users/developers, do you know other roots of this error? Does this type of error indicate to you a certain kind of problem?

For example, if the solver diverges quickly or doesn't even complete one iteration I usually suspect the mesh (provided all the other schemes are set reasonably). However, I am able to get results with a very similar mesh and meshing technique, so I think it is okay in this case.

Happy holidays,

Best regards,

Ilteber