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help needed: magnetic force calculation

Posted 25.02.2014, 06:46 GMT-5 Low-Frequency Electromagnetics, Results & Visualization Version 4.4 5 Replies

Qu Cangyu
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Hi,
I tried to use COMSOL 4.4 to model the magnetic field surrounding a permanent magnet and calculate the force acting on an object nearby. ( in 3D case )
The geometry is simple, a block ( the "object" ) is placed next to a block-shaped permanent magnet. I used mfnc, and the magnet is defined by a "remanent flux density" constitutve relation. The force acting on the "object" is calculated by adding a "force calculation".

The results of magnetic field is reasonable, but then I came up with a problem about the magnetic force.
I assigned the material "air" (with mur = 1) to all the domains, so theoretically the force acting on the "object" has to be ZERO. But the results gives a force of ~30 N.

I've read some of the posts about "force calculation" and " Maxwell stress tensor", but still cannot fix the problem.
Really appreciate it if anyone can help me on this.
5 Replies Last Post 25.02.2014, 11:22 GMT-5
Edgar J. Kaiser Certified Consultant
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Posted: 1 decade ago 25.02.2014, 07:00 GMT-5

It is difficult to give an advice without seeing the model.

--
Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
It is difficult to give an advice without seeing the model. -- Edgar J. Kaiser emPhys Physical Technology http://www.emphys.com
Qu Cangyu
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Posted: 1 decade ago 25.02.2014, 07:15 GMT-5
so sorry but the model file seems too large (~7 MB) that i can't upload it
so sorry but the model file seems too large (~7 MB) that i can't upload it
Edgar J. Kaiser Certified Consultant
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Posted: 1 decade ago 25.02.2014, 07:17 GMT-5
Clear meshes and solutions before uploading.

--
Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
Clear meshes and solutions before uploading. -- Edgar J. Kaiser emPhys Physical Technology http://www.emphys.com
Florian Oberhauser
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Posted: 1 decade ago 25.02.2014, 10:00 GMT-5
Hello,

I made similar simulations with a cylindrical magnet above a metalplate with different relative permeability.

I made a 2D axisymmetric and a 3D simulation with the same geometry and get different results when i made a parametric sweep for the relative permeability from 1..20.
It seems that the 3D simulation has a constat offset with the value calculted from the relative permeability of 1.
I have olso tried to solve the problem but not get a real solution or explanation for the difference.

Maybe this helps a little.
Hello, I made similar simulations with a cylindrical magnet above a metalplate with different relative permeability. I made a 2D axisymmetric and a 3D simulation with the same geometry and get different results when i made a parametric sweep for the relative permeability from 1..20. It seems that the 3D simulation has a constat offset with the value calculted from the relative permeability of 1. I have olso tried to solve the problem but not get a real solution or explanation for the difference. Maybe this helps a little.
Edgar J. Kaiser Certified Consultant
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Posted: 1 decade ago 25.02.2014, 11:22 GMT-5

Florian,

I would suggest to report this to the COMSOL support.

Cheers
Edgar

--
Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
Florian, I would suggest to report this to the COMSOL support. Cheers Edgar -- Edgar J. Kaiser emPhys Physical Technology http://www.emphys.com

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