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Eddy current simulation considering skin effects

Posted Dec 11, 2011, 10:16 a.m. EST Low-Frequency Electromagnetics Version 4.2 3 Replies

Zhiqiu Lu
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My simulation goal is to simulate two solenoids with AC signal and 180 degree phase shift respectively, with the freq between 10MHz and 100MHz, and see the Lorrentz force of a Al plate over the two coils.
The method in official tutorial ppts I found is to add surface current condition on the coils with the excitation value of Current/(circle length).
However,the results are not good. the z component of electromagnetic force over the Al plate is too small, only 1/1000 of the real situation. The second is the r component of electromagnetic force. The force theoritically should point to the center of the system, and the whole force over the volume of Al plate should be 0 because the system is axis-symmetric. Actually, by integrating the r component of electromagnetic force what I got is a non-zero value. And I cannot understand why this happened.
3 Replies Last Post Dec 12, 2011, 2:05 a.m. EST
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Dec 11, 2011, 10:26 a.m. EST
Hi

have you done your homework ? have you checked that the wavelength at your frequency is large compared to the geometry, and that your mesh resolves correctly all gradients ? what about the skin effect in the coils and the plate, are they resolved correctly 5-10 meshes across 90% of the skin depth for all cases.

For me this looks like the first issue in your model.

Your little air gap between the coils is also plying you games with the mesh density, this is not ideal, try to make the mesh more uniform, you need anyhow a denser mesh on the coil surfaces

As I no longer have 3.5a up running I cannot say much more

--
Good luck
Ivar
Hi have you done your homework ? have you checked that the wavelength at your frequency is large compared to the geometry, and that your mesh resolves correctly all gradients ? what about the skin effect in the coils and the plate, are they resolved correctly 5-10 meshes across 90% of the skin depth for all cases. For me this looks like the first issue in your model. Your little air gap between the coils is also plying you games with the mesh density, this is not ideal, try to make the mesh more uniform, you need anyhow a denser mesh on the coil surfaces As I no longer have 3.5a up running I cannot say much more -- Good luck Ivar
Zhiqiu Lu
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Posted: 1 decade ago Dec 11, 2011, 3:26 p.m. EST
thanks!
I will try to have a much finer mesh.

And how to explain the r component force integration value is non-zero? Is it due to the software?
thanks! I will try to have a much finer mesh. And how to explain the r component force integration value is non-zero? Is it due to the software?

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Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Dec 12, 2011, 2:05 a.m. EST
Hi

I would rather use "boundary mesh" on the coils and the plate, as this allows you to have a fine structures mesh across the skin effect region, and get a coarser mesh outside, hence less elements

Then force integration is based on flux integration and flux are difficult to calculate, these are very dependent on the mesh and on field concentrations. Typically in corners you have easily singularities, try rounding (fillet) your plate corners.

Then check the relation with the mesh density (but only in the region of the coils and levitation ring

--
Good luck
Ivar

--
Good luck
Ivar
Hi I would rather use "boundary mesh" on the coils and the plate, as this allows you to have a fine structures mesh across the skin effect region, and get a coarser mesh outside, hence less elements Then force integration is based on flux integration and flux are difficult to calculate, these are very dependent on the mesh and on field concentrations. Typically in corners you have easily singularities, try rounding (fillet) your plate corners. Then check the relation with the mesh density (but only in the region of the coils and levitation ring -- Good luck Ivar -- Good luck Ivar

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