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Electric Fields In Air - Balloon Boundary

Posted Nov 26, 2010, 7:03 a.m. EST 5 Replies

Dominic Clarke
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I am looking to model the electric field given off by a steel disk held at a fixed potential in air.

I have tried drawing a large box around my model and specifying its material as air. What i really want to have is something equivalent to a Balloon boundary, where the charge at infinity balances the charge in the problem area, or the voltage is zero at infinty.

How do i specify these kinds of boundary conditions, what are the best solvers for this problem?
I am new to Comsol so apologies if this is a rather primitive question.

Thankyou.
5 Replies Last Post Nov 26, 2010, 10:01 a.m. EST
Dominic Clarke
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Posted: 1 decade ago Nov 26, 2010, 7:47 a.m. EST
I have just come across the "infinite elements" node, which i presume acts like a balloon boundary. Still strugling with my main goal which is to plot mag[E] in the space around my model.
I have just come across the "infinite elements" node, which i presume acts like a balloon boundary. Still strugling with my main goal which is to plot mag[E] in the space around my model.
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Nov 26, 2010, 8:22 a.m. EST
Hi
depending on version (v3.5 and v4) and "application modes"/"physics" choosen you have the "Infinite elements" and the PML (Perfectly Matched Layers), but check carefully the doc on how to define them (incl. coordinate system) and set up correct mesh

--
Good luck
Ivar
Hi depending on version (v3.5 and v4) and "application modes"/"physics" choosen you have the "Infinite elements" and the PML (Perfectly Matched Layers), but check carefully the doc on how to define them (incl. coordinate system) and set up correct mesh -- Good luck Ivar
Dominic Clarke
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Posted: 1 decade ago Nov 26, 2010, 8:56 a.m. EST
I am on v4.0a

I am in AC/DC module, "electrostatics"
though i have tried with "magnetic and electric fields" too.

I want 3D plot of mag[E] due to steel disk floating at a set potential (e.g. +30V)

So my best plan is to draw a box around it and specify that box as the infinite element and also as the zero charge boundary?

Initial/Boundary conditions are just the voltage on the disk.

The solver reports errors such as "singular matrix" when the box is present but solves fine without it. Does this mean my BC's IC's and perhaps Mesh are wrong?

I'm sorry if this question isn't specific enough, but there is so little information about what the user has done wrong when the error occurs...

Thanks for the help.
I am on v4.0a I am in AC/DC module, "electrostatics" though i have tried with "magnetic and electric fields" too. I want 3D plot of mag[E] due to steel disk floating at a set potential (e.g. +30V) So my best plan is to draw a box around it and specify that box as the infinite element and also as the zero charge boundary? Initial/Boundary conditions are just the voltage on the disk. The solver reports errors such as "singular matrix" when the box is present but solves fine without it. Does this mean my BC's IC's and perhaps Mesh are wrong? I'm sorry if this question isn't specific enough, but there is so little information about what the user has done wrong when the error occurs... Thanks for the help.
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Nov 26, 2010, 9:27 a.m. EST
Hi

I have still the 4.1 from the conference, some 6h left ;) but this should be the same:

I choose 2D, ES, and make 1 squares and 2 concentric circles one inside the other with no common borders

I define a default material with er=1

in the ES physics main node I deselect the inner box domain "3"= your metal I'm not solving for the interiour

I set 30V on the interiour boundary (the empty box bundary)

and I select Infinite elements for the outer box in spherical/circular coordinates

I set GND on the outer external boundary (not only 0 charge as by default)

I mesh with a "finer" mode to have a fem elements across the volumes

solve and I'm rather happy with the results, but I havent checked by any analytical calculations, one should do ;)


isnt this what you wanted ?
--
Good luck
Ivar
Hi I have still the 4.1 from the conference, some 6h left ;) but this should be the same: I choose 2D, ES, and make 1 squares and 2 concentric circles one inside the other with no common borders I define a default material with er=1 in the ES physics main node I deselect the inner box domain "3"= your metal I'm not solving for the interiour I set 30V on the interiour boundary (the empty box bundary) and I select Infinite elements for the outer box in spherical/circular coordinates I set GND on the outer external boundary (not only 0 charge as by default) I mesh with a "finer" mode to have a fem elements across the volumes solve and I'm rather happy with the results, but I havent checked by any analytical calculations, one should do ;) isnt this what you wanted ? -- Good luck Ivar
Dominic Clarke
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Posted: 1 decade ago Nov 26, 2010, 10:01 a.m. EST
Yes, very much, but i would like to do it in 3D as i will be introducing asymmetries later on.
Thankyou for your help though, i will start again and see what i can come up with.

Dominic.
Yes, very much, but i would like to do it in 3D as i will be introducing asymmetries later on. Thankyou for your help though, i will start again and see what i can come up with. Dominic.

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