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Vibrating Sample Magnetometer model, will not solve
Posted 13 mar 2012, 12:26 GMT-4 Low-Frequency Electromagnetics, Mesh, Studies & Solvers, Structural Mechanics Version 4.2a 2 Replies
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All, thank you before hand for your help.
I am modeling a vibrating sample magnetometer (trying to) from what I understand of the device. As I understand it, the concept is that a piece of magnetic material is vibrated vertically (z, i am defining this here) at about 80Hz, and the sample is magnetized in the horizontal direction, x in this case (this could be anything, but I am currently working with permanent magnets magnetized out of plane as in the model and the 0 initial applied H field should give the remanence/remanent magnetization left in the material, the same as the input magnetization).
The VSM uses pickup coils (yes, similar to those you'd find in a guitar). I modeled them as 4 matching coils with a high permeability material for a core (soft magnets to guide the magnetic field and changes thereof into the core. The change in magnetic field should cause a voltage to be sensed in the coils (i know the coils in my model are short and simple, but I felt that since COMSOL can use idealities that an increase in wire count and windings wouldn't make a difference).
My problem is this, i don't have experience using the moving mesh or solid mechanics for that matter and don't know if I should be using time-dependent (over a single period of motion) or frequency solvers. I am using 4.2a and the model is attached. The model just stalls around 60-70%, from what the process window tells me.
Thank you again for your help. If you have further suggestions, such as how to do this without moving the sample in the model or anything else, that would be great.
Brock
I am modeling a vibrating sample magnetometer (trying to) from what I understand of the device. As I understand it, the concept is that a piece of magnetic material is vibrated vertically (z, i am defining this here) at about 80Hz, and the sample is magnetized in the horizontal direction, x in this case (this could be anything, but I am currently working with permanent magnets magnetized out of plane as in the model and the 0 initial applied H field should give the remanence/remanent magnetization left in the material, the same as the input magnetization).
The VSM uses pickup coils (yes, similar to those you'd find in a guitar). I modeled them as 4 matching coils with a high permeability material for a core (soft magnets to guide the magnetic field and changes thereof into the core. The change in magnetic field should cause a voltage to be sensed in the coils (i know the coils in my model are short and simple, but I felt that since COMSOL can use idealities that an increase in wire count and windings wouldn't make a difference).
My problem is this, i don't have experience using the moving mesh or solid mechanics for that matter and don't know if I should be using time-dependent (over a single period of motion) or frequency solvers. I am using 4.2a and the model is attached. The model just stalls around 60-70%, from what the process window tells me.
Thank you again for your help. If you have further suggestions, such as how to do this without moving the sample in the model or anything else, that would be great.
Brock
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2 Replies Last Post 3 apr 2012, 13:16 GMT-4
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Posted:
1 decade ago
I am also a beginner, but I took a look at your model and I have a few suggestions:
If you do not have a strong nonlinear influence you can assume that all variations in time occur as sinusoidal signals. So, I think you should use a Frequency Domain study for it will be less time consuming.
In the MEF you should apply the Ampere’s law and current conservation only to the conducting domain. For the rest of the space you should apply only Ampere´s law (instead of the Current conservation you applied).
You specified a circuit terminal type but you did not couple it to the circuits interface. You should either change the terminal type or consider the cir. Also, you should consider a floating potential, but I am not sure. You could also manually do a line integral to evaluate the induced voltage in the terminals.
I have a problem with the convergence of the segregated solvers when I couple some interface with the circuits interface in 3D. So I tried to solve your model without the solid mechanics and it converges. Maybe you missed something when coupling the physics and I am keen to know about the solution.
Please be critic about what I am saying and let others evaluate that as well for I am also starting to use Comsol.
I cannot help with the moving mesh nor the solid mechanics physics.
I am curious to know if you tried to use a 2D Asymmetric approach. It would reduce significantly the computational time and allow you to better debug your model. I had a similar model and I did not manage to make it work (I had results, but they did not make sense). Please tell me if you tried it.
If you do not have a strong nonlinear influence you can assume that all variations in time occur as sinusoidal signals. So, I think you should use a Frequency Domain study for it will be less time consuming.
In the MEF you should apply the Ampere’s law and current conservation only to the conducting domain. For the rest of the space you should apply only Ampere´s law (instead of the Current conservation you applied).
You specified a circuit terminal type but you did not couple it to the circuits interface. You should either change the terminal type or consider the cir. Also, you should consider a floating potential, but I am not sure. You could also manually do a line integral to evaluate the induced voltage in the terminals.
I have a problem with the convergence of the segregated solvers when I couple some interface with the circuits interface in 3D. So I tried to solve your model without the solid mechanics and it converges. Maybe you missed something when coupling the physics and I am keen to know about the solution.
Please be critic about what I am saying and let others evaluate that as well for I am also starting to use Comsol.
I cannot help with the moving mesh nor the solid mechanics physics.
I am curious to know if you tried to use a 2D Asymmetric approach. It would reduce significantly the computational time and allow you to better debug your model. I had a similar model and I did not manage to make it work (I had results, but they did not make sense). Please tell me if you tried it.
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Posted:
1 decade ago
Carlos, thank you for your reply. I have tried implementing a few different things since you responded (the reason I didn't respond right away). My model doesn't really make for simplifications as the materials (permanent magnets in particular) are non linear and making coils in 2D, I don't know quite how to do that. The rectangle in the center is vibrated sinusoidally at 80Hz, so maybe each H-field value can be used in a parameterized variable in a frequency domain setup. The reason I would like this model of a VSM is that it helps to plot out the magnetization left in the material as the H-field is varied from +Hmax to -Hmax. However, I did implement the Ampere's Law as suggested, any simplification can help in models of this size.
As for the circuits interface. All I want to do is read a voltage that is induced in the coil due to the shift in magnetic field (in this case due to a moving magnet). How would I then measure that? You mentioned a floating potential?
I hope that answers some questions. Further help is appreciated. :)
As for the circuits interface. All I want to do is read a voltage that is induced in the coil due to the shift in magnetic field (in this case due to a moving magnet). How would I then measure that? You mentioned a floating potential?
I hope that answers some questions. Further help is appreciated. :)