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Note: This discussion is about an older version of the COMSOL Multiphysics® software. The information provided may be out of date.

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streamline problem

Posted 2013年2月16日 GMT-5 15:36 Version 4.3a 18 Replies

Celia Xiao
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Hey, i am having some problems creating the steamlines for my Helmholtz coil. I followed the steps for the one of the model on comsol website for Helmholtz coil except other than revolve to create the coils i did extrusion instead. Now i am getting something really weird for my streamline and I compared with the Helmholtz coil file i downloaded from the website and i looks like I did the exact same thing with the example. I couldn't figure out what might possibly go wrong. I have attached a picture of the streamline I have now. Can you tell me what I did wrong and help me fix it? Thank you.

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18 Replies Last Post 2013年3月9日 GMT-5 21:20
Edgar Kaiser
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Posted: 1 decade ago 2013年2月16日 GMT-5 16:49
Hi,

it looks like you used a geometry parameter for the components of the flux lines. You must use the magnetic flux density components instead and assign proper start coordinates.

Cheers
Edgar
Hi, it looks like you used a geometry parameter for the components of the flux lines. You must use the magnetic flux density components instead and assign proper start coordinates. Cheers Edgar
Celia Xiao
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Posted: 1 decade ago 2013年2月18日 GMT-5 19:06
Hey! Thanks for you reply. I got this fixed.

I have another question for my model. in this Helmholtz coil, i build another permanent magnet at the center of this coil system. Do I need to edit something about interface or sth else? I built another mesh for the permanent magnet and I am able to compute. But when I was trying to plot the 3D arrow volume for this permanent magnet, it gives me a error saying "failed to evaluate variable :mod1.mfnc.Bx". I am not sure how to fix this. And also, when i did slice for this magnet as how i did it for the helmholtz coil, it didn't give me a error but there is nothing plotted on the model either. I feel like I am missing something here when I add this permanent magnet. Can you tell me what I did wrong here?

Thank you.
Hey! Thanks for you reply. I got this fixed. I have another question for my model. in this Helmholtz coil, i build another permanent magnet at the center of this coil system. Do I need to edit something about interface or sth else? I built another mesh for the permanent magnet and I am able to compute. But when I was trying to plot the 3D arrow volume for this permanent magnet, it gives me a error saying "failed to evaluate variable :mod1.mfnc.Bx". I am not sure how to fix this. And also, when i did slice for this magnet as how i did it for the helmholtz coil, it didn't give me a error but there is nothing plotted on the model either. I feel like I am missing something here when I add this permanent magnet. Can you tell me what I did wrong here? Thank you.
Celia Xiao
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Posted: 1 decade ago 2013年2月18日 GMT-5 20:32
Hey,

I have followed another post and made some changes to my model. and now i have things shown for arrow,slice and streamline for the permanent magnet. But the plot doesn't really look reasonable to me. is there anyway I can send this file to you and you can take a look at it for me? (the file size is too big it won't let me attach it). maybe you can help me find out what i did wrong after you look at my file.

and also, at first, i thought i should choose magnetic field, no current for the magnet, like it is said for model 78,but when i used that, it shows me a error that the variable mfnc.Bx can not found. then I changed to magnetic field(like said in another post), things show up but weird. which exactly should I choose for the permanent magnet?

Thank you in advance for your help!

Hey, I have followed another post and made some changes to my model. and now i have things shown for arrow,slice and streamline for the permanent magnet. But the plot doesn't really look reasonable to me. is there anyway I can send this file to you and you can take a look at it for me? (the file size is too big it won't let me attach it). maybe you can help me find out what i did wrong after you look at my file. and also, at first, i thought i should choose magnetic field, no current for the magnet, like it is said for model 78,but when i used that, it shows me a error that the variable mfnc.Bx can not found. then I changed to magnetic field(like said in another post), things show up but weird. which exactly should I choose for the permanent magnet? Thank you in advance for your help!
Edgar Kaiser
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Posted: 1 decade ago 2013年2月19日 GMT-5 04:57
Celia,

clear the mesh and the solutions, then the file will be small enough to allow an upload to the forum.

Cheers
Edgar
Celia, clear the mesh and the solutions, then the file will be small enough to allow an upload to the forum. Cheers Edgar
Celia Xiao
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Posted: 1 decade ago 2013年2月19日 GMT-5 10:32
Hey Edgar,

I have attached my file below. What I did for this model is I have a mesh for the Helmholtz coil and one for the permanent magnet(zone 7). and I also have another setup to generate another magnetic field below the permanent magnet(I disable that for now). Can you check the parameters and properties I choose for both the Helmholtz coil and permanent magnet? The plots for these model is really important for my research. Thank you for you help!


Hey Edgar, I have attached my file below. What I did for this model is I have a mesh for the Helmholtz coil and one for the permanent magnet(zone 7). and I also have another setup to generate another magnetic field below the permanent magnet(I disable that for now). Can you check the parameters and properties I choose for both the Helmholtz coil and permanent magnet? The plots for these model is really important for my research. Thank you for you help!

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Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 2013年2月20日 GMT-5 03:01
Hi

you should start to use only 1 MF as now you solve for two magnetic vector potentials over the same model, but these are not linked

--
Good luck
Ivar
Hi you should start to use only 1 MF as now you solve for two magnetic vector potentials over the same model, but these are not linked -- Good luck Ivar
Edgar Kaiser
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Posted: 1 decade ago 2013年2月20日 GMT-5 04:02

Yes Ivar is right. I moved the permanent magnet's Ampere's Law into the first mf model (where the coils are defined) and it looks good to my taste. I assume you want to see the interaction between coils and magnet?

Cheers
Edgar
Yes Ivar is right. I moved the permanent magnet's Ampere's Law into the first mf model (where the coils are defined) and it looks good to my taste. I assume you want to see the interaction between coils and magnet? Cheers Edgar
Celia Xiao
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Posted: 1 decade ago 2013年2月26日 GMT-5 10:11
Hey Edgar!

Thanks for you reply. and yes, I want to see the the orientation of the permanent magnet in the magnetic field caused by the Helmholtz coil. Is there any study or method in comsol that can tell me the orientation of the permanent magnet in the field?(like where is the north pole, where is south?) Thank you!

Celia
Hey Edgar! Thanks for you reply. and yes, I want to see the the orientation of the permanent magnet in the magnetic field caused by the Helmholtz coil. Is there any study or method in comsol that can tell me the orientation of the permanent magnet in the field?(like where is the north pole, where is south?) Thank you! Celia
Celia Xiao
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Posted: 1 decade ago 2013年2月26日 GMT-5 10:14
and also, what do you mean by moving the permanent magnet's amperer's law to the first mf model? is it mean those two will be linked after I do that? and how to moe it to the first mf model? and what is the Imf to start where mean?

Thanks!
and also, what do you mean by moving the permanent magnet's amperer's law to the first mf model? is it mean those two will be linked after I do that? and how to moe it to the first mf model? and what is the Imf to start where mean? Thanks!
Celia Xiao
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Posted: 1 decade ago 2013年2月27日 GMT-5 22:21
Hey Ivar!

what do you mean by start to use only IMF? where should I change this parameter? and also, as you said, the two coils are not linked, so how should I change this to have them linked? Thank you!
Hey Ivar! what do you mean by start to use only IMF? where should I change this parameter? and also, as you said, the two coils are not linked, so how should I change this to have them linked? Thank you!
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 2013年2月28日 GMT-5 02:39
Hi

sorry for the typo, I meant 1x MF.
I never like to have 2 physics solving the same dependent variables on the same geometry, as everything mixes up. But I might have misunderstood something from your model.
--
Good luck
Ivar
Hi sorry for the typo, I meant 1x MF. I never like to have 2 physics solving the same dependent variables on the same geometry, as everything mixes up. But I might have misunderstood something from your model. -- Good luck Ivar
Ralf Tschiesche
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Posted: 1 decade ago 2013年2月28日 GMT-5 04:03
Hello!

I have modified your model; is this what you are looking for?

Ralf
Hello! I have modified your model; is this what you are looking for? Ralf
Celia Xiao
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Posted: 1 decade ago 2013年3月3日 GMT-5 22:34
Hey Ralf!

Sorry for the late reply. and YES! it is what I am looking for (by looking at the .png picture). but somehow, when I opened the mph file, i can't see anything in the graphic. Do you know why?...... and also, what changes you have made to the model to make it looks like this? Can you also explain why? Thanks a lot!

Celia
Hey Ralf! Sorry for the late reply. and YES! it is what I am looking for (by looking at the .png picture). but somehow, when I opened the mph file, i can't see anything in the graphic. Do you know why?...... and also, what changes you have made to the model to make it looks like this? Can you also explain why? Thanks a lot! Celia
Celia Xiao
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Posted: 1 decade ago 2013年3月3日 GMT-5 22:36
I mean when I clicked on model 1, i can see the coil and everything, but when I click on the plots under results, I can't see anything. why is that? Thank you again.
I mean when I clicked on model 1, i can see the coil and everything, but when I click on the plots under results, I can't see anything. why is that? Thank you again.
Ralf Tschiesche
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Posted: 1 decade ago 2013年3月5日 GMT-5 05:25
Hello!

You have to solve it again; the model is clean (deleted mesh and solution to keep the file small).
As Ivar said I use only one MF physic to define all things.
Look at the 3D plotgroup 2 how the definition of streamlines is used (also limits for data range and color...).

Ralf
Hello! You have to solve it again; the model is clean (deleted mesh and solution to keep the file small). As Ivar said I use only one MF physic to define all things. Look at the 3D plotgroup 2 how the definition of streamlines is used (also limits for data range and color...). Ralf
Celia Xiao
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Posted: 1 decade ago 2013年3月5日 GMT-5 11:25
Hey!

I resolved the model as you said and now I got the graph you did. it look good! thank you!

I still have some questions.
first, I see in this model we only have one mesh which has both the coil and the permanent magnet in between. So is the arrow volume and streamline for magnetische flussdichte has considered the interaction between the coil and the permanent magnet already? it looks like it has because i see the arrow near the permanent magnet is so much bigger than the other ones. Just want to make sure;
and also, what is the little circular thing attach to the cylinder in the middle? (i have attached a screen shot of it)

and also, if I want to treat the middle part as a permanent magnet which will have north pole and south pole, will I be able to know the orientation of the magnet from the computation?

Thanks!

Celia
Hey! I resolved the model as you said and now I got the graph you did. it look good! thank you! I still have some questions. first, I see in this model we only have one mesh which has both the coil and the permanent magnet in between. So is the arrow volume and streamline for magnetische flussdichte has considered the interaction between the coil and the permanent magnet already? it looks like it has because i see the arrow near the permanent magnet is so much bigger than the other ones. Just want to make sure; and also, what is the little circular thing attach to the cylinder in the middle? (i have attached a screen shot of it) and also, if I want to treat the middle part as a permanent magnet which will have north pole and south pole, will I be able to know the orientation of the magnet from the computation? Thanks! Celia

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Ralf Tschiesche
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Posted: 1 decade ago 2013年3月6日 GMT-5 01:46
Hello!

Yes, the solution is for all parts; they produce one mag. field.
The little ring is one streamline. Since you have a strong magnet and a little coil current, the field from the magnet is much stronger. My streamlines depend on field strength...
If you increase the currents from 5 to 50A, you will see better images. Play with streamline parameters - you have several options!
The arrows will show you the orientation of the magnet. If you reverse the magnetization, the arrows near the magnet will also be reversed.
It would be better, to use a finer mesh...

Ralf
Hello! Yes, the solution is for all parts; they produce one mag. field. The little ring is one streamline. Since you have a strong magnet and a little coil current, the field from the magnet is much stronger. My streamlines depend on field strength... If you increase the currents from 5 to 50A, you will see better images. Play with streamline parameters - you have several options! The arrows will show you the orientation of the magnet. If you reverse the magnetization, the arrows near the magnet will also be reversed. It would be better, to use a finer mesh... Ralf
Celia Xiao
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Posted: 1 decade ago 2013年3月9日 GMT-5 21:20
Hey!

The arrow for the orientation of the permanent magnet, can you be more specific? are you talking about the red ones in the field or the one I have attached on my previous reply? Btw, what is the little red thing attached at the side of the permanent magnet?

Thanks!
Hey! The arrow for the orientation of the permanent magnet, can you be more specific? are you talking about the red ones in the field or the one I have attached on my previous reply? Btw, what is the little red thing attached at the side of the permanent magnet? Thanks!

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