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Static magnetic model

Posted Dec 29, 2010, 4:30 p.m. EST Low-Frequency Electromagnetics, Modeling Tools & Definitions, Parameters, Variables, & Functions, Results & Visualization Version 4.1 1 Reply

Floyd Knapp
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I'm trying to get familiar with COMSOL. I modeled 2 ea 2" cube NdFeB magnets stacked 0.1" apart on the Z axis, opposite poles facing, inside a 10" boundary cube. solving for Force of attraction I get 335N and -332N. This seems a bit small as another program calculates the force at 1551N. What am I doing wrong?
1 Reply Last Post Dec 30, 2010, 4:48 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 30, 2010, 4:48 a.m. EST
Hi

you are not necesarily doing something "wrong" but force calculation, if you are using the Maxwell stress tensor, are rather shape and mesh dependent (in fact gradient resolution dependent) so you should run several models with different mesh and check the conergence and stability of your results.
I have noticed that quad regular meshes gives often better results, as well as rounding the edges of "square" shapes, as these corners make field concetration points and singularities for the gradient estimations, hence easily wrong results.

Another trick is to estimate the maxwell tensor values for each edge, and see how they differ, for symmetric cases you often see large differences, mostly related to the mesh. There are also other ways to estimate the force via effective work, cehck the doc. there are many treads on the Forum about Maxwell stress tensor do a search

--
Good luck
Ivar
Hi you are not necesarily doing something "wrong" but force calculation, if you are using the Maxwell stress tensor, are rather shape and mesh dependent (in fact gradient resolution dependent) so you should run several models with different mesh and check the conergence and stability of your results. I have noticed that quad regular meshes gives often better results, as well as rounding the edges of "square" shapes, as these corners make field concetration points and singularities for the gradient estimations, hence easily wrong results. Another trick is to estimate the maxwell tensor values for each edge, and see how they differ, for symmetric cases you often see large differences, mostly related to the mesh. There are also other ways to estimate the force via effective work, cehck the doc. there are many treads on the Forum about Maxwell stress tensor do a search -- Good luck Ivar

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