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Posted:
9 years ago
14 avr. 2015, 08:26 UTC−4
You can use either the impedance and/or transition boundary conditions. Provided the skin depth is less than metal thickness these should work.
You can use either the impedance and/or transition boundary conditions. Provided the skin depth is less than metal thickness these should work.
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Posted:
9 years ago
14 avr. 2015, 13:09 UTC−4
On rare occasions in simple problems, I have gotten that to work. But usually COMSOL won't let you assign the needed boundary conditions, and even in those cases where you can apply impedance boundaries, I haven't been able to figure out how to control the boundary meshes.
On rare occasions in simple problems, I have gotten that to work. But usually COMSOL won't let you assign the needed boundary conditions, and even in those cases where you can apply impedance boundaries, I haven't been able to figure out how to control the boundary meshes.
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Posted:
9 years ago
14 avr. 2015, 17:05 UTC−4
Any chance that you could upload a sample file of what you want to do? Does not have to be proprietary but something to help see the problem a bit more.
Any chance that you could upload a sample file of what you want to do? Does not have to be proprietary but something to help see the problem a bit more.
Walter Frei
COMSOL Employee
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Posted:
9 years ago
16 avr. 2015, 14:55 UTC−4
Hello David,
The appropriate approach here is to only solve for the electromagnetic wave equations in the air domain. Generally the easiest way to set up such a model would be to only select your air domains when you are selecting the domains for which the electromagnetic waves physics interface is being used. That is, never introduce the metallic domains into the problem. You can then apply a single impedance boundary condition on all of the metal surfaces. (Of course you will need to assign different material properties to the different surface in the materials branch.)
Boundary layer meshing should not be used unless the skin depth is a significant fraction of the part dimensions. You will always want to use the impedance boundary condition if the skin depth is small (~10x or less) of the characteristic size of your metallic objects.
Also, with the automatic meshing available in version 5.0, the domains in which you are not solving the electromagnetic waves physics will not be meshed at all unless you are also solving other physics such as heat transfer on these domains.
Best Regards,
Walter
Hello David,
The appropriate approach here is to only solve for the electromagnetic wave equations in the air domain. Generally the easiest way to set up such a model would be to only select your air domains when you are selecting the domains for which the electromagnetic waves physics interface is being used. That is, never introduce the metallic domains into the problem. You can then apply a single impedance boundary condition on all of the metal surfaces. (Of course you will need to assign different material properties to the different surface in the materials branch.)
Boundary layer meshing should not be used unless the skin depth is a significant fraction of the part dimensions. You will always want to use the impedance boundary condition if the skin depth is small (~10x or less) of the characteristic size of your metallic objects.
Also, with the automatic meshing available in version 5.0, the domains in which you are not solving the electromagnetic waves physics will not be meshed at all unless you are also solving other physics such as heat transfer on these domains.
Best Regards,
Walter
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Posted:
9 years ago
16 avr. 2015, 17:15 UTC−4
Hello Walter,
Yes, thanks. I've made this work on cases with relatively simple geometries - where there are only a few hundred metal boundaries, and they're not too hard to select. Just did it for a case involving several different types of dielectrics and several different types of metals - but with only about a hundred metal surfaces, and none of them too hard to get to. It's a nice little fully parameterized shielded solenoid, tuned and matched to 50-ohms, in this case at 50 MHz. (Was going to attach it, thinking it might be a useful demo, but couldn't figure out how to make that work.)
There are two problems. First of all, I don't know how to control the meshing near the surface of various metal parts independently that are not part of the emw solution and thus are not meshed. There is only a single set of settings for meshing the air in contact with many different metal parts, which have different requirements.
Secondly, it becomes prohibitively difficult in a case where there are 500 domains and 6000 surfaces, most of which are very difficult to select. It seems like COMSOL should be able to do this automatically - with a default surface conductivity the same as that of the adjacent unmeshed metal domain.
Since we can't get our 4-socket 512GB 32-core computer to run rf problems more than about half as fast as our single-processor 8-core 64GB computer (where we are at memory limits), we might have no choice but to try to manually select thousands of surfaces deep inside a complex system so we can avoid meshing the metal parts. But I'm very worried (from experience thus far) that without the ability to control the meshing independently at all these metal surfaces, we won't be able to get it to build a mesh in the vacuum.
Best regards,
David Doty
Hello Walter,
Yes, thanks. I've made this work on cases with relatively simple geometries - where there are only a few hundred metal boundaries, and they're not too hard to select. Just did it for a case involving several different types of dielectrics and several different types of metals - but with only about a hundred metal surfaces, and none of them too hard to get to. It's a nice little fully parameterized shielded solenoid, tuned and matched to 50-ohms, in this case at 50 MHz. (Was going to attach it, thinking it might be a useful demo, but couldn't figure out how to make that work.)
There are two problems. First of all, I don't know how to control the meshing near the surface of various metal parts independently that are not part of the emw solution and thus are not meshed. There is only a single set of settings for meshing the air in contact with many different metal parts, which have different requirements.
Secondly, it becomes prohibitively difficult in a case where there are 500 domains and 6000 surfaces, most of which are very difficult to select. It seems like COMSOL should be able to do this automatically - with a default surface conductivity the same as that of the adjacent unmeshed metal domain.
Since we can't get our 4-socket 512GB 32-core computer to run rf problems more than about half as fast as our single-processor 8-core 64GB computer (where we are at memory limits), we might have no choice but to try to manually select thousands of surfaces deep inside a complex system so we can avoid meshing the metal parts. But I'm very worried (from experience thus far) that without the ability to control the meshing independently at all these metal surfaces, we won't be able to get it to build a mesh in the vacuum.
Best regards,
David Doty
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Posted:
9 years ago
16 avr. 2015, 19:19 UTC−4
How are you building your geometry? If you can build / import your metal parts as separate steps in the geometry, then you can create selections as they are built so you don't have to select things by hand after the fact.
How are you building your geometry? If you can build / import your metal parts as separate steps in the geometry, then you can create selections as they are built so you don't have to select things by hand after the fact.
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Posted:
9 years ago
16 avr. 2015, 19:57 UTC−4
Thanks. We haven't used that feature yet. Sounds like it should be helpful.
David
Thanks. We haven't used that feature yet. Sounds like it should be helpful.
David
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Posted:
9 years ago
20 août 2015, 13:24 UTC−4
Hi every body,
I have an issue with meshing my geometry, 3 cubic blocks putted each on the other and they have different heights with the same contact area, the upper and bottom surfaces of the first and last blocks includes channels, serpentine ones. I am still getting weird results from solving the problem and once I stop running it I got a lot of error messeges related to the mesh at either domains, surfaces or points, specific x y z dimension points.
Any idea or help of how to mesh like this kind of geometries will be really appreciated!
Thanks in advance.
Mohammed
Hi every body,
I have an issue with meshing my geometry, 3 cubic blocks putted each on the other and they have different heights with the same contact area, the upper and bottom surfaces of the first and last blocks includes channels, serpentine ones. I am still getting weird results from solving the problem and once I stop running it I got a lot of error messeges related to the mesh at either domains, surfaces or points, specific x y z dimension points.
Any idea or help of how to mesh like this kind of geometries will be really appreciated!
Thanks in advance.
Mohammed