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Merging Meshes / Multiple Bodies
Posted: 28 Feb 2018, 20:26
by rschaefer
Dear Elmer-community,
First of all, the context: I'd like to use Elmer for static electrical field calculations for a particle physics detector. I started with GMSH and created my detector in SINGLE parts (basically a tube with wires in it). The reason why I chose single parts were my geometric constraints. Since the wires are very thin compared to their length, the meshing didn't go properly when I constructed the wole detector in GMSH. So I did it 1-by-1.
Now I want to import this in Elmer to make the field calculations. I managed to "unite" all wires into a single mesh. These should be kept at a constant potential (e.g. .30V). However, the tube, which corresponds to the detector casing, should be at a different potential (e.g. 0V).
Now my problem is: If I unite the mesh of "all wires" and the "casing" mesh, I only get one body in ElmerGUI - so I can't apply different potentials. Are there different ways of uniting or adding two meshes? Preferrably in a way, that the wires are "body 1" and the casing is "body 2"?
Cheers,
Robert
Re: Merging Meshes / Multiple Bodies
Posted: 28 Feb 2018, 20:33
by mzenker
Hi,
Elmer's capability to treat meshes being limited, I would try to make the mesh ready with an external mesher. You could post your problem on the gmsh mailing list, or try if you can solve it with another mesher, e.g. Salomé.
Concerning the potential, I would impose it on the boundaries. Your mesh should have the surfaces limiting your geometry as boundaries where you can set the potential as boundary condition.
HTH,
Matthias
Re: Merging Meshes / Multiple Bodies
Posted: 05 Mar 2018, 16:19
by raback
Hi,
try
Code: Select all
ElmerGrid 2 2 wires -bulktype 1 10 1 ! make bodies [1,10] to 1
ElmerGrid 2 2 casing -bulktype 1 10 2 ! make bodies [1,10] to 2
ElmerGrid 2 2 wires -in casing -out finalmesh -unite -merge 1.0e-10
I would be concerned that your united mesh is not conforming and then the merging does not work.
-Peter
Re: Merging Meshes / Multiple Bodies
Posted: 16 Mar 2018, 16:15
by rschaefer
Dear Peter,
thanks for your reply. I tried it, and it worked.
Basically what I would like is the electrostatic field of: a -30V - potential on the 4 wires and a 0V - potential on the mantle.
Since I assume that the electrical field calculation is a very simple task, is there a tutorial how to do it?
Best regards,
Robert
Re: Merging Meshes / Multiple Bodies
Posted: 16 Mar 2018, 16:24
by rschaefer
Sorry, I forgot a sketch of the layout. See the attachment.
Re: Merging Meshes / Multiple Bodies
Posted: 16 Mar 2018, 16:35
by raback
Hi
Try to add this to your sif,
Code: Select all
Solver 2
Equation = ComputeFlux
Procedure = "FluxSolver" "FluxSolver"
Calculate Grad = Logical True
Target Variable = String Potential
Linear System Solver = "Iterative"
Linear System Iterative Method = "cg"
Linear System Preconditioning = ILU0
Linear System Residual Output = 10
Linear System Max Iterations = Integer 1000
Linear System Convergence Tolerance = 1.0e-10
End
and modify
-Peter
Re: Merging Meshes / Multiple Bodies
Posted: 16 Mar 2018, 17:35
by rschaefer
Hi Peter,
thanks for the hint. Well in my sif file, your second suggestion is implemented by default.
Also, regarding your first suggestion, there is already a "solver 2" part in my sif. Would you like me to just replace the default part with yours or additionally place it in my sif.
Also, regarding the mesh, when I add the boundary conditions (= potentials of the surfaces) to my surfaces, there is a strange connection, see the image/attachment.
The inner red surface (lower left) should be on -30V and the outer larger surface should be at 0V - is there a method to decouple this?
Cheers,
Robert
Re: Merging Meshes / Multiple Bodies
Posted: 18 Mar 2018, 21:57
by raback
Hi Robert
Even the GUI has tool to separate BCs by feature angle. You could use that.
To be on the safe side, do you have any mesh between the outer cylinder and the wire at the center? In finite elements the whole volume must be meshed.
-Peter
Re: Merging Meshes / Multiple Bodies
Posted: 21 Mar 2018, 13:32
by rschaefer
Hi Peter,
thanks for the info. I don't have a mesh between the outer cylinder and the inner wires. I'll put in something and come back to you.
Cheers,
Robert
Re: Merging Meshes / Multiple Bodies
Posted: 03 May 2018, 12:20
by rschaefer
Hi Peter,
well I managed to implement your hint, as well as splitting/uniting the surfaces accodingly. However for the assignment of the materials I only have one "body" available, where I need 3 (the casing made from Al, the wires made from Cu and the "inner part" made from air). Is there a possibility to generate a body (maybe from a selection of surfaces)?
Cheers,
Robert