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Permanent magnet force calculation error

Posted 03.07.2012, 07:33 GMT-4 Low-Frequency Electromagnetics Version 4.2a 5 Replies

Lorenz Eberhardt
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Hello everybody,
I'm trying to compute the force between a sphere permanent magnet and a iron ball.
The system is successfully solved but when i try to compute the force I get a lot of failed to evaluate variable errors.
Anybody has an idea why I get this error?
Model is attached.

Attachments:

5 Replies Last Post 04.07.2012, 07:39 GMT-4
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 03.07.2012, 09:27 GMT-4
Hi

if you include the total force of source and destination = magnet and iattracted ron you should get a net "0" or thereabout. What about trying to solve for two forces, one for each shpere and compare the two (with opposed signes)

--
Good luck
Ivar
Hi if you include the total force of source and destination = magnet and iattracted ron you should get a net "0" or thereabout. What about trying to solve for two forces, one for each shpere and compare the two (with opposed signes) -- Good luck Ivar
Lorenz Eberhardt
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Posted: 1 decade ago 03.07.2012, 09:46 GMT-4
Thank you for your reply.
I don't get any result, I get the error message that the variable dnphi cannot be evaluated at the boundaries of the sphere no matter which sphere I choose.
The thing worked in 3 d, but I wanted to save computing force, so I did it in 2d axisymmetric.
The name of the variable (dnphi) shows also that I have probably done something wrong with the 2d axisymmtric geometry.
Thank you for your reply. I don't get any result, I get the error message that the variable dnphi cannot be evaluated at the boundaries of the sphere no matter which sphere I choose. The thing worked in 3 d, but I wanted to save computing force, so I did it in 2d axisymmetric. The name of the variable (dnphi) shows also that I have probably done something wrong with the 2d axisymmtric geometry.
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 04.07.2012, 03:04 GMT-4
Hi

it did solve OK for me but I have v4.3, when I split the force (with different 2 names) into two.
But, I noticed that the error(differences) was quite large, I didnt have time to check out why. Back in 4.2 sometimes I got more preciese results with MF rather than MFNC, even if I had no curent. And from v3.5 I know that force estimation is very mesh density and mesh shape dependent

--
Good luck
Ivar
Hi it did solve OK for me but I have v4.3, when I split the force (with different 2 names) into two. But, I noticed that the error(differences) was quite large, I didnt have time to check out why. Back in 4.2 sometimes I got more preciese results with MF rather than MFNC, even if I had no curent. And from v3.5 I know that force estimation is very mesh density and mesh shape dependent -- Good luck Ivar
Lorenz Eberhardt
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Posted: 1 decade ago 04.07.2012, 07:17 GMT-4
Thank you, it worked when I took MF.
Thank you, it worked when I took MF.
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 04.07.2012, 07:39 GMT-4
Hi

Interesting, I wounder what is so different between MF and MFNC, in case you find out pls report back

--
Good luck
Ivar
Hi Interesting, I wounder what is so different between MF and MFNC, in case you find out pls report back -- Good luck Ivar

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