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Magnetic flux through a coil, with a permanent magnet
Posted 07.09.2010, 10:46 GMT-4 Low-Frequency Electromagnetics Version 4.1 1 Reply
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Hello I'm new using COMSOL and although I've been reading the manual there are some questions I still cannot find an answer. If anyone knows the answer please help me out.
I'm modeling a permanent magnet, cylindrical magnet, and I'm going to put a coil outside the magnet and moving it to model the voltage in the coil.
The question I have are the following.
1. The magnetic lines should be closed paths, but inside the magnet the direction is the opposite to the direction outside the magnet. Is that normal in COMSOL? By the way, why if I set the residual magnetism of the permanent magnet, Br, to 1T, the maximum value of magnetic field is not 1 anywhere?
2. I'm testing with a value of 1T for residual magnetism in the permanent magnet. I think that's a value, not an expression, but if I write 1 in the value field the magnetic field seems to be parallel to "r" (horizontal axis) and if I write 1 in the "value" field, the magnetic field seems to be parallel to "z" vertical axis. Can you tell me how should I deal with this? Is there any part in COMSOL manual where it is specified how COMSOL assigns values for this? What if a want to set the magnetic field with 45 degrees respect to the r axis? or set a magnetic field in a magnet where the upper half is north pole, and the lower half is south pole?
3. I need to calculate the magnetic flux (in this case sum of all the "z" component of magnetic field multiplied with the area of transversal section (in this case pi* R^2). I'm working in the axisymmetry mode, but although I'm reading the manual, I still don't understand how to do the integration, because I need to integrate over an area perpendicular to the plane I'm working at. Can you give me some help with this? I need to integrate the z component of magnetic field through a circular area, with radius R and which center is over the z axis. I need the integration of the z component of the magnetic field through the perpendicular area the vectors are crossing (magnetic flux) for all the z values along the axis. I'm still reading but I'd really appreciate your help, specially in this topic!
P.S. I'm attaching some pictures of my screen, showing the permanent magnet and the physic domain settings to better explain my questions.
Thank you all
I'm modeling a permanent magnet, cylindrical magnet, and I'm going to put a coil outside the magnet and moving it to model the voltage in the coil.
The question I have are the following.
1. The magnetic lines should be closed paths, but inside the magnet the direction is the opposite to the direction outside the magnet. Is that normal in COMSOL? By the way, why if I set the residual magnetism of the permanent magnet, Br, to 1T, the maximum value of magnetic field is not 1 anywhere?
2. I'm testing with a value of 1T for residual magnetism in the permanent magnet. I think that's a value, not an expression, but if I write 1 in the value field the magnetic field seems to be parallel to "r" (horizontal axis) and if I write 1 in the "value" field, the magnetic field seems to be parallel to "z" vertical axis. Can you tell me how should I deal with this? Is there any part in COMSOL manual where it is specified how COMSOL assigns values for this? What if a want to set the magnetic field with 45 degrees respect to the r axis? or set a magnetic field in a magnet where the upper half is north pole, and the lower half is south pole?
3. I need to calculate the magnetic flux (in this case sum of all the "z" component of magnetic field multiplied with the area of transversal section (in this case pi* R^2). I'm working in the axisymmetry mode, but although I'm reading the manual, I still don't understand how to do the integration, because I need to integrate over an area perpendicular to the plane I'm working at. Can you give me some help with this? I need to integrate the z component of magnetic field through a circular area, with radius R and which center is over the z axis. I need the integration of the z component of the magnetic field through the perpendicular area the vectors are crossing (magnetic flux) for all the z values along the axis. I'm still reading but I'd really appreciate your help, specially in this topic!
P.S. I'm attaching some pictures of my screen, showing the permanent magnet and the physic domain settings to better explain my questions.
Thank you all
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1 Reply Last Post 07.09.2010, 10:55 GMT-4
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Posted:
1 decade ago
Hi igor
first of all note the naming Br is the "remananet B" and not the "r" component of the B field ! so the first block of Br is the "r" radial component, and the second is the "z" component (in 2D axi)
2nd if you have a magnet you should set "M" and not "Br" to the value of the "Magnetisation" of your magnet, change the formula by selecting it in the respecive field on the window, and then update M either along r or Z (or both vector components if you want it at an angle such as 45°)
in 2D axi a line is in afct a surface obtained by integrating any "value* 2*pi*r" along an edge, use the integration coupling Variables (in V3.5a) or Definitions Model Coupling Integrations in V4
Good luck
Ivar
first of all note the naming Br is the "remananet B" and not the "r" component of the B field ! so the first block of Br is the "r" radial component, and the second is the "z" component (in 2D axi)
2nd if you have a magnet you should set "M" and not "Br" to the value of the "Magnetisation" of your magnet, change the formula by selecting it in the respecive field on the window, and then update M either along r or Z (or both vector components if you want it at an angle such as 45°)
in 2D axi a line is in afct a surface obtained by integrating any "value* 2*pi*r" along an edge, use the integration coupling Variables (in V3.5a) or Definitions Model Coupling Integrations in V4
Good luck
Ivar