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Note: This discussion is about an older version of the COMSOL Multiphysics® software. The information provided may be out of date.

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Modeling Electromagnet

Posted 17.12.2010, 02:58 GMT-5 Low-Frequency Electromagnetics, Studies & Solvers Version 4.1 2 Replies

mb
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Hi,

attached is a model of an electromagnet (DC). The excitation happens at the coil endings via "Electric potential" and "Ground".

I managed to solve that model in v4.0a with the direct solver PARDISO with a finer mesh and linear elements. Unfortunately, this method consumes a huge amount of RAM and it is only a submodel for further investigations for me. Now I want to solve that with the iterative solver (coarser mesh but quadratic elements).

When I set a constant damping factor (see solver 1) I get "Divergence of the linear iterations". Depending on what value I set for the factor, this error occurs earlier or later.

When I set automatic damping factor (see solver 2), the solution process stops after 1 iteration without error, but the stepsize is still very large and I don't believe it is converged. Moreover, the solution process always starts with damping factor 1 although I set a smaller value.

What do you think, is this a kind of bug in COMSOL or is there something wrong with the boundaries (they changed from v4.0a to v4.1 in AC/DC module)? What can I do solve that model. I already tested various mesh sizes and solver settings.


Any comment would be appreciated.

mb
2 Replies Last Post 17.12.2010, 08:38 GMT-5
Matthias Mayer
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Posted: 1 decade ago 17.12.2010, 07:25 GMT-5
Hello Marcel,

i hope i can help

I think your problem is the small conductivity in the air gap. Try a bigger value sigma= 1e-3 then should work your constant damping solver.

For a better result make a new simulation with sigma = 1e-9 and use your last result as start conditions.

Then you can compare your result with automatic solver damping.

kind regards

Matthias



Hello Marcel, i hope i can help I think your problem is the small conductivity in the air gap. Try a bigger value sigma= 1e-3 then should work your constant damping solver. For a better result make a new simulation with sigma = 1e-9 and use your last result as start conditions. Then you can compare your result with automatic solver damping. kind regards Matthias
mb
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Posted: 1 decade ago 17.12.2010, 08:38 GMT-5
Hello Matthias,

thanks for your hint. Indeed convergence seem to improve with constant damping factor.
With damping factor set to automatic, it still stops after 1 iteration.

Thanks so far,
Marcel
Hello Matthias, thanks for your hint. Indeed convergence seem to improve with constant damping factor. With damping factor set to automatic, it still stops after 1 iteration. Thanks so far, Marcel

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