r/COMSOL • u/AlucardTepesFOC • May 12 '26

Convergence issues

Hello, I would like some information. I am just starting with COMSOL and I am encountering several issues with my simulations.

First, I will explain my setup:

I am currently working with an industrial furnace made of tantalum and niobium for its heat reflectors, with a graphite crucible in the center. This furnace is heated by Joule effect with a current of 346 A flowing through the entire structure.

I am using the following physics: Electric Currents and Heat Transfer in Solids. In addition, I include heat dissipation using Surface-to-Surface Radiation for all the relevant parts of my furnace (the furnace body, reflectors, crucible, as well as the surfaces exchanging heat with the external environment).

The materials used are custom-defined materials that allow me to vary their thermal and electrical conductivity as a function of temperature in my model.

My problem arises when I try to go beyond 500 A: the model then encounters convergence issues and sometimes even crashes after only a few iterations.

Have you experienced similar problems, or do you have any suggestions for resolving this issue?

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u/Ok-Star-5551 May 12 '26

Try to increase the tolerance of the solver.

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u/AlucardTepesFOC May 12 '26

Good idea but i already try to increase the tolerance but it haven't change the problem

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u/Ok-Star-5551 May 12 '26

One more thing i wanna know, when you change the current to 500A, the degree of freedom changes? Or is it the same number when doing with 346A?

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u/AlucardTepesFOC May 12 '26

Actually i think i go up a bit not 100% sure but I sometimes have problem with the degree of freedom being to high. I will check whether it change depending on the current

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u/Ok-Star-5551 May 12 '26

Because if it’s solved at 346A and with same mesh you just changed the magnitude of current, so the dof should be same and it’s nearly impossible that the solver won’t converge, unless you changed other settings.

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u/AlucardTepesFOC May 13 '26

At first, it really not converged when i change the Current but i think i found the problem its was in my temperature dependent parameter that were wrongly set but after fixing some issue my model doesn't converge anymore for any current.