Frequency sweep in a magnetic field interface

Topics: 4.3, AC/DC Module, 3.5a

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Venkatram Pepakayala

Venkatram Pepakayala

January 17, 2013 9:34pm UTC

Frequency sweep in a magnetic field interface

Hello everyone,
This should be seemingly siomple problem. I am trying to model the AC magnetic field due to a coil in 3D. I am using a magnetic field interface on a simple cylinder (acting as the coil) kept in air. A current has been given to this cylinder axially using "external current density feature". Now if I run a stationary solver, it is able to solve for a magnetic field without hassle. Even if I give a periodic current to the coil and solve for time-dependent solution at a particular frequency, I am getting an answer. But when I want to do a frequency sweep analysis I am getting the following error:
"Failed to find a solution for the initial parameter.
Matrix has zero on diagonal.
Returned solution is not converged."
Now I know that usually this kind of error is due to inadequate boundary condition. But that does not explain to me how the simulation is successful with a stationary and time domain analysis.

Also if I try to make the coil using a 2D axisymmetric simulation, I am able to do even the frequency sweep giving the exact same boundary conditions that I am using for 3D simulation. I am at loss to see what could be the problem. Any suggestions or advice will be highly appreciated.
I have attached the model file in case anyone wants to check it out.
Venkat

Attachments:   mf_test.mph  

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Sergei Yushanov

Sergei Yushanov
Certified Consultant
AltaSim Technologies, LLC

January 17, 2013 10:25pm UTC in response to Venkatram Pepakayala

Re: Frequency sweep in a magnetic field interface

Venkat,

Set air conductivity to small value compared to the conductivity of copper (say, sig_air=10[S/m]) and re-run analysis. This helps solver to be more stable.

Regards,
Sergei

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Venkatram Pepakayala

Venkatram Pepakayala

January 18, 2013 3:38am UTC in response to Sergei Yushanov

Re: Frequency sweep in a magnetic field interface

Thanks Sergei! Works like a charm. Makes me wonder why this was not the case in COMSOL 3.5. The conductivity values even if 0 seem to pose no problem in 3.5.

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Sergei Yushanov

Sergei Yushanov
Certified Consultant
AltaSim Technologies, LLC

January 18, 2013 1:46pm UTC in response to Venkatram Pepakayala

Re: Frequency sweep in a magnetic field interface

Venkat,

Good question – I am also wondering about the difference between 3.5 and 4.3 in this regard. May be you can submit this question to Comsol Support?

Regards,
Sergei

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