Elmer Discussion Forum

Hi,
My simulation diverges after 900 iteration and I can't explain this weird behaviour. Until that moment, the result are good and physically correct. Have you got any idea of this behaviour? I have tried also to reduce the domain and to refine the mesh, nevertheless the divergence always occurs. I attached an image that shows the evolution of the profile and the convergence history with the case.sif in a zip folder. The actual mesh I am using is: https://we.tl/t-drNNRZxPlc
Regards,
Andrea

I don't understand why the convergence occurs in this problem viewtopic.php?f=3&t=7507 and in the simulation, I am doing it doesn't.
-Andrea

Hi Andrea,

You've been working hard with a very complex case that would deserve some closer attention! Unfortunately I haven't had time to look it that closely. It is easier for some cases where you get an idea just by reading through the sif file. Convergence issues are more difficult.

Could you maybe classify a little to a post what all you have tried, what has been succesfull, where are your struggling and need the most help. There are quite a few cases on the forum now to choose from

-Peter

raback wrote: ↑20 Jul 2021, 01:46 Hi Andrea,

You've been working hard with a very complex case that would deserve some closer attention! Unfortunately I haven't had time to look it that closely. It is easier for some cases where you get an idea just by reading through the sif file. Convergence issues are more difficult.

Could you maybe classify a little to a post what all you have tried, what has been succesfull, where are your struggling and need the most help. There are quite a few cases on the forum now to choose from

-Peter

First of all, I tried to reduce the domain and refine the mesh, but these measures didn't work.
Secondly, I used the Mumps direct method, indeed an iterative method doesn't work (maybe due to the level set, I don't know honestly). I launched a paralleling simulation with Mumps. It worked but it diverged. So, I decided to keep on with Umfpack.
For a couple of days, I have been trying to reduce the relaxation factor(<=0.1) and using the Picard method, instead of Newton one. Apparently, the convergence behavior is pretty good, nevertheless, the obtained velocity profile is far from the exact one. Perhaps, a very low relaxation factor reduces the convergence velocity even if improving it.
Instead, with the relaxation factor of 0.1, the differences between the velocity computed by Elmer and the reference one were negligible. However, the divergence in this case occurred. I attach some images and case.sif just to show us the results. My uniform magnetic fields are B=0.5 T and B=1 T. I adopted a Gaussian magnetic field as the third example too. Thanks in advance for your help.
Regards,
Andrea

I have noted that if I use either a relaxation factor <0.1 or the Picard method, the convergence of the problem gets really slow. Indeed the velocity profiles are pretty different from the ones computed in the reference paper.
-Andrea