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 The information provided may be out of date.

Discussion Closed This discussion was created more than 6 months ago and has been closed. To start a new discussion with a link back to this one, click here.

Static magnetic model

Please login with a confirmed email address before reporting spam

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)

Please login with a confirmed email address before reporting spam

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

Note that while COMSOL employees may participate in the discussion forum, COMSOL® software users who are on-subscription should submit their questions via the Support Center for a more comprehensive response from the Technical Support team.