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How to unite objects with assembly mode?
Posted Aug 13, 2013, 4:24 p.m. EDT Low-Frequency Electromagnetics, Geometry Version 4.3a 4 Replies
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Hi everyone,
I'm modelling coils using the Multi-Turn Coil Domain, and I'm having trouble getting the magnetic fields to work when I finalize the geometry with an assembly (I need to use assembly mode because I need to import some CAD files with very complex geometry). I'm doing a frequency domain study.
I've got a cylindrical coil surrounded by a spherical domain of air (see attached file). The problem seems to be that the Magnetic Insulation boundary condition is automatically applied to the boundaries of the coil, so the magnetic fields are trapped inside. But I can't figure out how to get rid of it. When I do a Form Union instead, the Magnetic Insulation is only applied to the boundaries of the sphere, which is what I want.
I think the reason it's not working in assembly mode is because the coil and the air sphere need to be linked/continuous, but how do I do this? Does it involve pairs somehow? I've tried applying an Identity pair between the boundaries of the coil and sphere, but that didn't work. Then I applied continuity to the pair, but it still didn't work. I've also tried adding a Boolean Operations > Union to the geometry, but that didn't work either.
Can anyone please help me?
Thanks in advance,
Neil
I'm modelling coils using the Multi-Turn Coil Domain, and I'm having trouble getting the magnetic fields to work when I finalize the geometry with an assembly (I need to use assembly mode because I need to import some CAD files with very complex geometry). I'm doing a frequency domain study.
I've got a cylindrical coil surrounded by a spherical domain of air (see attached file). The problem seems to be that the Magnetic Insulation boundary condition is automatically applied to the boundaries of the coil, so the magnetic fields are trapped inside. But I can't figure out how to get rid of it. When I do a Form Union instead, the Magnetic Insulation is only applied to the boundaries of the sphere, which is what I want.
I think the reason it's not working in assembly mode is because the coil and the air sphere need to be linked/continuous, but how do I do this? Does it involve pairs somehow? I've tried applying an Identity pair between the boundaries of the coil and sphere, but that didn't work. Then I applied continuity to the pair, but it still didn't work. I've also tried adding a Boolean Operations > Union to the geometry, but that didn't work either.
Can anyone please help me?
Thanks in advance,
Neil
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4 Replies Last Post Aug 15, 2013, 10:13 a.m. EDT
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Posted:
1 decade ago
Neil,
Right now, you have the default "magnetic insulation" applied to all boundaries. The boundaries between the coil and the air however should have "perfect magnetic conductor" boundary conditions (I believe). Also, I think you do need to specify continuity as well so the assembly bodies "know" how to communicate (ie pass dep. variables on the nodes).
By the way, why do you need to use the Form Assembly? The geometry is pretty simple in what you've uploaded. Using Form Union is much simpler.
Best regards,
Josh Thomas
AltaSim Technologies
Right now, you have the default "magnetic insulation" applied to all boundaries. The boundaries between the coil and the air however should have "perfect magnetic conductor" boundary conditions (I believe). Also, I think you do need to specify continuity as well so the assembly bodies "know" how to communicate (ie pass dep. variables on the nodes).
By the way, why do you need to use the Form Assembly? The geometry is pretty simple in what you've uploaded. Using Form Union is much simpler.
Best regards,
Josh Thomas
AltaSim Technologies
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Posted:
1 decade ago
Hi Josh, thanks for your reply.
The model I attached is not my actual model, it's just to test if I can model coils in assembly mode. In my actual model I will have very complex geometry from CAD files, which needs an assembly (Form Union gives an "internal geometry error").
Anyway, I don't think Perfect Magnetic Conductor is the correct boundary condition. According to the documentation it sets the tangential component of the magnetic field to zero, which is not what I want. I tried applying it (in union mode) and you can see from the attached image that the current density in the coil is not right.
Yes, I think I do need to specify continuity, but how? The coil and the air don't actually have any touching boundaries, so I can't use Identity Pairs, can I? I need to somehow pair the coil boundaries with the air domain, but I can't find any way to do this...
Thanks,
Neil
The model I attached is not my actual model, it's just to test if I can model coils in assembly mode. In my actual model I will have very complex geometry from CAD files, which needs an assembly (Form Union gives an "internal geometry error").
Anyway, I don't think Perfect Magnetic Conductor is the correct boundary condition. According to the documentation it sets the tangential component of the magnetic field to zero, which is not what I want. I tried applying it (in union mode) and you can see from the attached image that the current density in the coil is not right.
Yes, I think I do need to specify continuity, but how? The coil and the air don't actually have any touching boundaries, so I can't use Identity Pairs, can I? I need to somehow pair the coil boundaries with the air domain, but I can't find any way to do this...
Thanks,
Neil
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Posted:
1 decade ago
Neil,
You are right. I was wrong about the perfect magnetic conductor boundary condition.
You will need to specify continuity on the touching boundaries. To use form assembly mode properly, you will need to perform a Boolean Operations>Difference operation where you subtract the coil object from the air object. Then you will have the air object and the coil object before you "Form Assembly." Then you can specify continuity on the duplicated boundaries where the air touches the coils.
My guess however is that if you have trouble with the Boolean union operation that you will also have trouble with the Boolean difference operations.
You may consider trying to simply your CAD geometry or playing with the CAD defeaturing options in COMSOL to get the Union operation to work properly. This would solve your difficulties.
Best regards,
Josh Thomas
AltaSim Technologies
You are right. I was wrong about the perfect magnetic conductor boundary condition.
You will need to specify continuity on the touching boundaries. To use form assembly mode properly, you will need to perform a Boolean Operations>Difference operation where you subtract the coil object from the air object. Then you will have the air object and the coil object before you "Form Assembly." Then you can specify continuity on the duplicated boundaries where the air touches the coils.
My guess however is that if you have trouble with the Boolean union operation that you will also have trouble with the Boolean difference operations.
You may consider trying to simply your CAD geometry or playing with the CAD defeaturing options in COMSOL to get the Union operation to work properly. This would solve your difficulties.
Best regards,
Josh Thomas
AltaSim Technologies
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Posted:
1 decade ago
Ah yes, the difference operation is what I needed. Now the Multi-Turn Coil Domain is giving the correct results.
And yes, the difference operation will also cause problems with the complex geometry. I've already tried CAD defeaturing and it's not able to remove a lot of the small edges/faces. I'll just have to rework the CAD files to simplify them a bit.
Thanks so much for your help.
Neil
And yes, the difference operation will also cause problems with the complex geometry. I've already tried CAD defeaturing and it's not able to remove a lot of the small edges/faces. I'll just have to rework the CAD files to simplify them a bit.
Thanks so much for your help.
Neil