Surface as a body in 3D

General discussion about Elmer
Post Reply
adoldesa
Posts: 9
Joined: 26 Sep 2018, 18:46
Antispam: Yes
Contact:

Surface as a body in 3D

Post by adoldesa »

Hi all,
I am still a novice in Elmer and FEM in general and I have a fundamental question. I need to simulate current flowing along a surface surrounded by dielectrics (two different fro top and bottom). I need the problem to be in three dimensions since I want to map the electric field in space and calculate the capacitance of the system but my surface has to be 2D. It there a way to do so? Can I use a surface as a body, or shall I make a very thin box to approximate it?

Thanks for your help!
Last edited by adoldesa on 08 Oct 2018, 12:17, edited 1 time in total.
mzenker
Posts: 1999
Joined: 07 Dec 2009, 11:49
Location: Germany

Re: Surface as a body in 3D

Post by mzenker »

Hi,

I am not sure to understand correctly. Is your current flowing through the surface, i.e. from dielectric 1 to dielectric 2, or along the surface without flowing through the dielectric? In the latter case, the "surface" would need a finite thickness anyway, wouldn't it?

Matthias
adoldesa
Posts: 9
Joined: 26 Sep 2018, 18:46
Antispam: Yes
Contact:

Re: Surface as a body in 3D

Post by adoldesa »

Sorry, my mistake. The current is flowing along the surface (I amended the original post).
mzenker
Posts: 1999
Joined: 07 Dec 2009, 11:49
Location: Germany

Re: Surface as a body in 3D

Post by mzenker »

Then I would give the surface a thickness, else you would have infinite current density...
mzenker
Posts: 1999
Joined: 07 Dec 2009, 11:49
Location: Germany

Re: Surface as a body in 3D

Post by mzenker »

N.B. It would be practical to be able to use a surface as a body giving it a thickness in the Elmer settings, so that thin layers can be simulated without too much challenge in meshing. AFAIK this is currently only possible in mechanics, not in electric simulations.
adoldesa
Posts: 9
Joined: 26 Sep 2018, 18:46
Antispam: Yes
Contact:

Re: Surface as a body in 3D

Post by adoldesa »

Thanks, I thought so, I will try with a thin layer. However, I know that other FEM software allows to define a surface as a body and therefore give it a different material. Do you know if this is doable in elmer? I use gmsh to define geometry and mesh but I don't know how to define a surface as a separate body.
mzenker
Posts: 1999
Joined: 07 Dec 2009, 11:49
Location: Germany

Re: Surface as a body in 3D

Post by mzenker »

This must be done in Elmer. I had not remembered quite correctly, it is currently possible only in the Heat solver, see viewtopic.php?f=11&t=4210#p14890. I am not sure if it can be done within the GUI. Anyway, AFAIK it is currently not possible for the Static Current Solver. To implement it one would have to change the source code of StatCurrentSolve. I don't know if it there are plans in the Elmer team to do it in the foreseeable future...
adoldesa
Posts: 9
Joined: 26 Sep 2018, 18:46
Antispam: Yes
Contact:

Re: Surface as a body in 3D

Post by adoldesa »

Thanks mzenker, I have also posted in the thread you linked in case some developers see it! For now I will try and mesh a finite-thickness layer and look at the result.
raback
Site Admin
Posts: 4812
Joined: 22 Aug 2009, 11:57
Antispam: Yes
Location: Espoo, Finland
Contact:

Re: Surface as a body in 3D

Post by raback »

Hi

Basically you can have a boundary partipaciting in the PDE as a bulk. Just give for the boundary the next free body index, for example

Code: Select all

Body Id = 2
This way you the layer can be included (just make the equation active in this new body).

Now what you should do by yourself is to multiply the effective parameters with the thickness such that the formulation is consistent (and units match in 2D and 3D). Therefore you cannot have the same material parameters in 2D and 3D even though they would in reality be the same. Create also a new material for your new body.

The case Matthias was probably referring to was test case "ThermalPipe3D". For HeatSolve the geometric multplier was added after request but this has not been done for any other equation hence the multiplication of material parameters.

Hope this helps.

-Peter
adoldesa
Posts: 9
Joined: 26 Sep 2018, 18:46
Antispam: Yes
Contact:

Re: Surface as a body in 3D

Post by adoldesa »

Hi raback,
thanks a lot, this is exactly what I was looking for. Indeed it was under my nose all the time in ElmerGUI! By clicking on the surface whilst defining the boundary conditions you can just click on "Use as body" and it will automatically appear as a body with the ID of the surface!

Thanks,

Adolfo.
Post Reply