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 force
Posted 28.01.2015, 11:46 GMT-5 Low-Frequency Electromagnetics Version 4.4, Version 5.0 2 Replies
Please login with a confirmed email address before reporting spam
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 29.01.2015, 11:04 GMT-5
Please login with a confirmed email address before reporting spam
Posted:
1 decade 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
Please login with a confirmed email address before reporting spam
Posted:
1 decade 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.