Calculating force from coil on permanent magnet

Posted Jul 5, 2024, 8:54 a.m. EDT 0 Replies

F S

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Dear Team,

Really appreciate your help with everything!

Attached is a model of a homogenized multi turn coil, with a ferrite core, and a permanent cube magnet on top of it. I have been having some difficulty with calculating force and setting up infinite domain meshes for the air.

Firstly, can you please show me how to setup an infinite domain on this system? I have tried a lot and followed the tutorials but can't seem to get it to work. If you can edit my model I would be so grateful.

I am struggling with understanding how the forces are being calculated (I am looking at everything from the xz-plane view):

1- In this scenario, The the cube magnet has north and south faces along the y-axis. In my system I give a max of 0.25A current, when I switch the polarity and give a -0.25A of current, I am expecting the y-axis force evaluated to become a repulsive force, with a positive force value on the cube magnet, instead its still a negative force value albeit smaller than when the current is 0.25A, why is that? Am I right to assume that the cube magnet is being attracted to the copper and ferrite core material more than it being repulsed by the magnetic pole created by the coil? Or is there something else?

2- In this scenario, I setup the magnet, so that the cube magnet has north and south faces along the x-axis. When I excite the coil, why does the z-axis have a force? shouldn't it be negligible? I would expect that the south face along the x-axis would be greater attracted to the North Pole creating coil, and so why isn't there a larger x-axis force? Having the biggest force in the y-axis makes sense, but then I would expect the x-axis force to be second biggest, as the cube magnet tries to rotate its south face to align with the north face of the coil. But instead I get small x-axis forces?? and worse I also get z-axis forces, yet my system is symmetrical, so why z-axis? (I tried all the meshing to make it very fine, so I don't think its that tbh)

3- In reference to question 2 above, does changing where the center of the magnet is, affects the force vector calculations? because when I moved everything so that global center (0,0,0) is in the middle of the cube magnet, the values changed? why? Im so confused to be honest, I need to use this force calculation, but I can't trust anything. Perhaps all my assumptions are wrong, please enlighten me.

4- There also seems to be a lack of symmetry with the force calculations, in this scenario with north and south faces in the x-axis, if I switch the current from + to -, why aren't the forces for the x-axis also switching from positive to negative? I would expect it as above to be the case, where one face is being pulled more, and hence a greater x-axis force in the opposite direction when the coil Polarity changes? To help make sense, imagine the cube magnet was fixed and free to rotate along the z-axis, that's the system I am trying to model, I would imagine that as I changed the polarity of the coil, the cube magnet rotates either left or right to align its faces with the polarity of the coil.

5- Why are there jumps and non-continuity in my line plots of the magnetic flux along the 3D cut lines I defined? why is it not smooth?

I hope I am making sense, and there is a simple fix for this. I have attached my model as well. Please help me with the infinite mesh as well, I am trying to keep my hope with this haha, but its getting so hard to get predictable results.

Best wishes and appreciate all your support, Femos

Attachments:

MabelCoilLarge10mm.mph

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0 Replies Last Post Jul 5, 2024, 8:54 a.m. EDT

COMSOL Moderator

Hello F S

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