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Magnetic force on magnetic particle by permanent magnet
Posted Oct 21, 2014, 10:35 p.m. EDT Low-Frequency Electromagnetics Version 4.4 2 Replies
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Hello everyone,
I am completely new to comsol. And these days I am trying to use comsol to simulate the magnetic force on iron oxide magnetic particle by permanent magnet. In theory, the magnetization direction of particle follows the direction of magnetic field generated by permanent magnet. And due to the gradient of magnetic field, the y component of magnetic force is much stronger than the x component. But my simulation does not work fine. In addition, the y component of magnetic force should be negative rather than positive. Maybe there is some place where my setting is wrong. Is there somebody who can help me regarding the following issue?
1. How to set the magnetic property of magnetic particle, whose magnetization direction follows that of magnetic field?
2. Why is the magnetic force on magnetic particle wrong? What is the problem?
3. How to edit the model of magnetic force on magnetic particle when I know the magnetization and magnetic field strength?
Attached is my model. I appreciate it very much if someone can take his/her time to help me.
Best regards,
Jing
I am completely new to comsol. And these days I am trying to use comsol to simulate the magnetic force on iron oxide magnetic particle by permanent magnet. In theory, the magnetization direction of particle follows the direction of magnetic field generated by permanent magnet. And due to the gradient of magnetic field, the y component of magnetic force is much stronger than the x component. But my simulation does not work fine. In addition, the y component of magnetic force should be negative rather than positive. Maybe there is some place where my setting is wrong. Is there somebody who can help me regarding the following issue?
1. How to set the magnetic property of magnetic particle, whose magnetization direction follows that of magnetic field?
2. Why is the magnetic force on magnetic particle wrong? What is the problem?
3. How to edit the model of magnetic force on magnetic particle when I know the magnetization and magnetic field strength?
Attached is my model. I appreciate it very much if someone can take his/her time to help me.
Best regards,
Jing
Attachments:
2 Replies Last Post Oct 22, 2014, 8:12 a.m. EDT
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Posted:
1 decade ago
Jing,
1. Use Remanent flux density instead of Magnetization to define constitutive relation for magnetic particle (this would allow you to avoid circular dependency) and define remanent flux as following:
Brx=Br0*mfnc.Hx/sqrt(mfnc.Hx^2+mfnc.Hy^2+eps)
Bry=Br0*mfnc.Hy/sqrt(mfnc.Hx^2+mfnc.Hy^2+eps)
where Br0 is remanent flux density magnitude for the magnetic particle. This definition means that remanent flux density of the particle is aligned with magnetic field. Comsol has special variable name “eps” for the small number and you need to add this number to avoid division by zero. If you use the above expressions, then magnetic force in the y-direction will be negative and several times higher in magnitude than force in the x-direction.
2. Your mesh for the particle is too coarse – you can’t expect any meaningful result for the force calculation based on the Maxwell stress tensor with such coarse mesh. Set mesh size for the particle with maximum element size several times smaller than the radius of the particle.
Regards,
Sergei
1. Use Remanent flux density instead of Magnetization to define constitutive relation for magnetic particle (this would allow you to avoid circular dependency) and define remanent flux as following:
Brx=Br0*mfnc.Hx/sqrt(mfnc.Hx^2+mfnc.Hy^2+eps)
Bry=Br0*mfnc.Hy/sqrt(mfnc.Hx^2+mfnc.Hy^2+eps)
where Br0 is remanent flux density magnitude for the magnetic particle. This definition means that remanent flux density of the particle is aligned with magnetic field. Comsol has special variable name “eps” for the small number and you need to add this number to avoid division by zero. If you use the above expressions, then magnetic force in the y-direction will be negative and several times higher in magnitude than force in the x-direction.
2. Your mesh for the particle is too coarse – you can’t expect any meaningful result for the force calculation based on the Maxwell stress tensor with such coarse mesh. Set mesh size for the particle with maximum element size several times smaller than the radius of the particle.
Regards,
Sergei
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Posted:
1 decade ago
Hello Sergei,
Thank you very much for your time to help me.
1. According to your suggestion, I improved the meshing for the particle and used the equations, and the x component and y component of magnetic force on magnetic particle are right now. In addition, I tried to use the equations you have mentioned, which would improve my simulation accuracy. But by using the constitutive relation of remanent flux density, the magnetic force of y component is about 10^-18 N(really weak, maybe not right) whereas that is about 10^(-7) N (seems right) by using the constitutive relation of magnetization and the same equations. Maybe there is some problem about my setting parameters. Could you please help me?
2. To improve my simulation, I'd better import a magnetization curve of the magnetic particle or an equation to describe the relation between magnetic field and particle magnetization, such as Mag_particle=Ms*(coth(B/B0)-B0/B). What constitutive relation I should choose? also remanent flux density?
Could you please take your time to help me regarding this?
Thank you again.
best regards,
Jing
Thank you very much for your time to help me.
1. According to your suggestion, I improved the meshing for the particle and used the equations, and the x component and y component of magnetic force on magnetic particle are right now. In addition, I tried to use the equations you have mentioned, which would improve my simulation accuracy. But by using the constitutive relation of remanent flux density, the magnetic force of y component is about 10^-18 N(really weak, maybe not right) whereas that is about 10^(-7) N (seems right) by using the constitutive relation of magnetization and the same equations. Maybe there is some problem about my setting parameters. Could you please help me?
2. To improve my simulation, I'd better import a magnetization curve of the magnetic particle or an equation to describe the relation between magnetic field and particle magnetization, such as Mag_particle=Ms*(coth(B/B0)-B0/B). What constitutive relation I should choose? also remanent flux density?
Could you please take your time to help me regarding this?
Thank you again.
best regards,
Jing
Attachments: