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Lorentz Term for Ferromagnetic Bodies
Posted May 20, 2015, 4:15 p.m. EDT Low-Frequency Electromagnetics 5 Replies
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Dear All,
Going through the "Magnet Falling Through Copper Tube" example (www.comsol.com/model/magnet-falling-through-copper-tube-13875), I saw the following sentence explaining where the "Lorentz term" can be applied in Comsol to model the movement of solid bodies:
"The use of the Lorentz term to include the motion is a valid approach in situations when the moving domains do not contain magnetic sources such as currents or magnetization (fixed or induced) that
move along with the material, and when the moving domains are invariant in the
direction of motion. "
I am a little confused about the statement "[...] when the moving domains do not contain [...] magnetization (fixed or induced) that move along with the material [...]". Could anyone please explain what this (especially induced magnetization) means?
In specific, can I use the same modeing approach when the tube is not made of copper, but made of iron with (MuR>>1, conductivity >>0)? How about iron with nonlinear B-H relationship, may I still use the Lorentz term if the tube is made of saturating iron which is modeled using a BH curve?
Finally, just curious if the Lorentz term would still be applicable then the PM is replaced by some current carrying wire where the current is changing with time. Could then the movement of a (copper or iron) tube around an AC current carrying wire be modeled using the Lorentz term?
Thanks in advance!
Going through the "Magnet Falling Through Copper Tube" example (www.comsol.com/model/magnet-falling-through-copper-tube-13875), I saw the following sentence explaining where the "Lorentz term" can be applied in Comsol to model the movement of solid bodies:
"The use of the Lorentz term to include the motion is a valid approach in situations when the moving domains do not contain magnetic sources such as currents or magnetization (fixed or induced) that
move along with the material, and when the moving domains are invariant in the
direction of motion. "
I am a little confused about the statement "[...] when the moving domains do not contain [...] magnetization (fixed or induced) that move along with the material [...]". Could anyone please explain what this (especially induced magnetization) means?
In specific, can I use the same modeing approach when the tube is not made of copper, but made of iron with (MuR>>1, conductivity >>0)? How about iron with nonlinear B-H relationship, may I still use the Lorentz term if the tube is made of saturating iron which is modeled using a BH curve?
Finally, just curious if the Lorentz term would still be applicable then the PM is replaced by some current carrying wire where the current is changing with time. Could then the movement of a (copper or iron) tube around an AC current carrying wire be modeled using the Lorentz term?
Thanks in advance!
5 Replies Last Post May 22, 2015, 1:41 p.m. EDT
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Posted:
9 years ago
Dear Arda,
please note that the Lorentz term formulation has indeed the described limitations.
If you want to model more complex scenarios as the one you describe you may want to tke
the following tutorial as a reference:
ch.comsol.com/model/voltage-induced-in-a-coil-by-a-moving-magnet-14163
I uses the moving mesh interface and handles the equations in a similary way as do the
rotating machinery interfaces for generators and motors where you have not the
limitations of the Lorentz term approach.
Best regards,
Sven
please note that the Lorentz term formulation has indeed the described limitations.
If you want to model more complex scenarios as the one you describe you may want to tke
the following tutorial as a reference:
ch.comsol.com/model/voltage-induced-in-a-coil-by-a-moving-magnet-14163
I uses the moving mesh interface and handles the equations in a similary way as do the
rotating machinery interfaces for generators and motors where you have not the
limitations of the Lorentz term approach.
Best regards,
Sven
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Posted:
9 years ago
Dear Sven
Thank you very much for your reply! It is a very helpful tutorial you have mentioned, showing the option of a moving mesh. However, I would once more like to inquire about the possibility of having a model without moving mesh.
Coming back to the tutorial about magnet falling through copper tube where the Lorentz term is used, would Lorentz term be applicable if the tube was made of magnetic material such as steel (with relative peremability of, say, 1000 instead of 1)? Or -in a further step- a material with nonlinear (single-valued) BH curve?
Even in the most complicated example I mentioned earlier (where the magnet is replaced by AC current-carying coils - coils are fixed in position), there is no moving magnet, therefore I wanted to respectfully post this follow-up question inquiring whether the Lorentz term could be used when the magnetic field applied to the tube (made of iron or copper) changes in time.
Therefore, I would be happy if you could please comment on the applicability of the Lorentz term in the above mentioned three cases, summarized as:
1) when permeability of tube >>1
2) when nonlinear BH curve of tube
3) time dependent field being applied the tube
Thank you very much again, for looking into this case. It is greatly appreciated.
Best regards
Thank you very much for your reply! It is a very helpful tutorial you have mentioned, showing the option of a moving mesh. However, I would once more like to inquire about the possibility of having a model without moving mesh.
Coming back to the tutorial about magnet falling through copper tube where the Lorentz term is used, would Lorentz term be applicable if the tube was made of magnetic material such as steel (with relative peremability of, say, 1000 instead of 1)? Or -in a further step- a material with nonlinear (single-valued) BH curve?
Even in the most complicated example I mentioned earlier (where the magnet is replaced by AC current-carying coils - coils are fixed in position), there is no moving magnet, therefore I wanted to respectfully post this follow-up question inquiring whether the Lorentz term could be used when the magnetic field applied to the tube (made of iron or copper) changes in time.
Therefore, I would be happy if you could please comment on the applicability of the Lorentz term in the above mentioned three cases, summarized as:
1) when permeability of tube >>1
2) when nonlinear BH curve of tube
3) time dependent field being applied the tube
Thank you very much again, for looking into this case. It is greatly appreciated.
Best regards
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Posted:
9 years ago
Dear Arda,
please find my answers in your support case.
Best regards,
Sven
please find my answers in your support case.
Best regards,
Sven
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Posted:
9 years ago
Hi Sven, Arda,
why not going ahead with this thread in the forum? The applicability of the Lorentz term is a very interesting subject to many COMSOL users.
Cheers
Edgar
--
Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
why not going ahead with this thread in the forum? The applicability of the Lorentz term is a very interesting subject to many COMSOL users.
Cheers
Edgar
--
Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
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Posted:
9 years ago
Hallo Edgar,
schön wieder mal von Dir zu hören! And you are right - let's continue:
Moving magnetic sources (permanent magnets, magnetized materials, etc.) induce an electric field due to Faraday's Law, so they cannot be modeled using the Lorentz term only in the moving region. A "correction" that takes into account the induced field would need to be added. Also, since the mesh is not really moving, the Lorentz term is only applicable for "steady state" movements (this is the meaning of "domains invariant in the direction of motion").
Permeable or saturable materials would exhibit an induced magnetization. In general one cannot use the Lorentz term for a iron tube since the moving magnetic sources induced in the tube would in turn induce an electric field in the surrounding region, which is not modeled by the Lorentz term feature.
So for all those cases that Arda described - a thorough formulation using a moving mesh would be appropriate.
Kind regards and Schöne Pfingsten!
Sven Friedel
schön wieder mal von Dir zu hören! And you are right - let's continue:
Moving magnetic sources (permanent magnets, magnetized materials, etc.) induce an electric field due to Faraday's Law, so they cannot be modeled using the Lorentz term only in the moving region. A "correction" that takes into account the induced field would need to be added. Also, since the mesh is not really moving, the Lorentz term is only applicable for "steady state" movements (this is the meaning of "domains invariant in the direction of motion").
Permeable or saturable materials would exhibit an induced magnetization. In general one cannot use the Lorentz term for a iron tube since the moving magnetic sources induced in the tube would in turn induce an electric field in the surrounding region, which is not modeled by the Lorentz term feature.
So for all those cases that Arda described - a thorough formulation using a moving mesh would be appropriate.
Kind regards and Schöne Pfingsten!
Sven Friedel