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modeling a magnet in 2D
Posted Oct 9, 2016, 1:36 p.m. EDT 1 Reply
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I put a magnetic flux conservation on the magnet and then specified a BH curve for the magnetic field and when solved it does not plot anything for B, M, or H.
1 Reply Last Post Oct 12, 2016, 11:47 a.m. EDT
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Posted:
8 years ago
What version of Comsol are you running? I have attached a model in version 5.2a if that would help? You can then go in and modify the model as required...
Are you using the mf or mfnc interface? The attached is created with the mfnc interface, it shows a cylindrical hard ferrite magnet (Ceramic 8 material). It shows how to add the BH curve and apply it to the model.
Note that the equations for the Magnetic Flux Conservation node have been modified as follows:
mfnc.Hz would by default be "-Vmz", but I have changed it to "-Vmz-Hc" in order to account for the shifting of the BH curve into the first quadrant. (I have added Hc, the magnet coercivity, as a parameter in this model, taken from the BH curve data).
Also, note the definition of the Magnetic Flux Conservation node, it has a user defined expression for Magnetic flux density norm, "mat2.def.int1(sqrt(mfnc.Hr^2+mfnc.Hz^2))"
Non-linear permanent magnets are not straightforward to define in Comsol... it should really be a focus point for future versions.
If your material is predominantly linear (such as for rare earth magnets) then they are much more easily defined by a relative permeability and a value for Br in the Magnetic Flux Conservation node.
The Zero Magnetic Scalar Potential point is required for a model such as this to solve. I have also added infinite element domains to the exterior of the model to better calculate the far field values...
If anyone has a better way to define permanent magnets with a BH curve, I would welcome suggestions, but this is the way I have implemented it...
Let me know how you get on!
Mark
Are you using the mf or mfnc interface? The attached is created with the mfnc interface, it shows a cylindrical hard ferrite magnet (Ceramic 8 material). It shows how to add the BH curve and apply it to the model.
Note that the equations for the Magnetic Flux Conservation node have been modified as follows:
mfnc.Hz would by default be "-Vmz", but I have changed it to "-Vmz-Hc" in order to account for the shifting of the BH curve into the first quadrant. (I have added Hc, the magnet coercivity, as a parameter in this model, taken from the BH curve data).
Also, note the definition of the Magnetic Flux Conservation node, it has a user defined expression for Magnetic flux density norm, "mat2.def.int1(sqrt(mfnc.Hr^2+mfnc.Hz^2))"
Non-linear permanent magnets are not straightforward to define in Comsol... it should really be a focus point for future versions.
If your material is predominantly linear (such as for rare earth magnets) then they are much more easily defined by a relative permeability and a value for Br in the Magnetic Flux Conservation node.
The Zero Magnetic Scalar Potential point is required for a model such as this to solve. I have also added infinite element domains to the exterior of the model to better calculate the far field values...
If anyone has a better way to define permanent magnets with a BH curve, I would welcome suggestions, but this is the way I have implemented it...
Let me know how you get on!
Mark
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