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Static magnetic force
Posted Jan 28, 2015, 11:46 a.m. EST Low-Frequency Electromagnetics Version 4.4, Version 5.0 2 Replies
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Dear all,
I have a model with two magnets and one coil. The two magnets are as one component. I am interested the force between the two magnets and the coil. However, when the current is zero in the coil, the force on the two magnets is not zero. I am wondering, is this force the inner force between the two magnets?
Thanks!
Ruijun
I have a model with two magnets and one coil. The two magnets are as one component. I am interested the force between the two magnets and the coil. However, when the current is zero in the coil, the force on the two magnets is not zero. I am wondering, is this force the inner force between the two magnets?
Thanks!
Ruijun
2 Replies Last Post Jan 29, 2015, 11:04 a.m. EST
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Posted:
10 years ago
Hi Ruijun,
can it be that it is non-zero due to coarse mesh or round-off errrors? Nummerically these
forces are almost never extactly zero and mesh sensitive. But they should be small compared
to a situation with current on.
Also if the magnets are to close to an outer boundary of the simulation domain they will be repelled.
Regards
Jens
can it be that it is non-zero due to coarse mesh or round-off errrors? Nummerically these
forces are almost never extactly zero and mesh sensitive. But they should be small compared
to a situation with current on.
Also if the magnets are to close to an outer boundary of the simulation domain they will be repelled.
Regards
Jens
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Posted:
10 years ago
I can recommend viewing this problem in the light of Linus's blog post: www.comsol.com/blogs/fillet-away-your-electromagnetic-field-singularities/
If you're sure the magnets are meshed properly, have fillets and are kept far enough from the walls (using infinite elements perhaps), or centred between the walls (so that the forces from the walls cancel out), there should be no net. force on the combination of the two magnets.
Otherwise, a combination of two magnets would be a self-propelling mechanism and you could build a Perpetuum mobile with it.
As Jens Krause suggests: If it's non zero, but small compared to the force when selecting only one magnet or when activating the current, you could also consider it a numerical error.
If you're sure the magnets are meshed properly, have fillets and are kept far enough from the walls (using infinite elements perhaps), or centred between the walls (so that the forces from the walls cancel out), there should be no net. force on the combination of the two magnets.
Otherwise, a combination of two magnets would be a self-propelling mechanism and you could build a Perpetuum mobile with it.
As Jens Krause suggests: If it's non zero, but small compared to the force when selecting only one magnet or when activating the current, you could also consider it a numerical error.