Capacitance matrix calculation
Posted: 25 May 2018, 20:25
Hello everyone,
Apologies in advance if what I'm about to ask has been asked before and if this post would be more suitable in another category.
What I'm trying to do:
Ultimately, I'd like to use Elmer to calculate the capacitance matrix for 17 electrodes within an ionisation chamber. I've attached the .step file that I created in Freecad.
What I've done so far:
Firstly, I followed the tutorial relevant to this problem (2 balls inside a larger ball), and the results matched those given in the instructions. I planned to generate the mesh for the chamber by exporting the .step file from freecad, create the mesh with gmsh, convert with Elmergrid and then load into Elmer. I therefore tried to replicate the '2 balls in a larger ball' calculation by making a similar geometry in freecad and following the steps that I intended to take to get to the capacitance matrix, closely following the steps in the tutorial after I had created the mesh. A screen shot of the geometry in the GUI with the convergence and results is attached for the case where I followed the tutorial exactly and where I tried to replicate it using freecad. Unfortunately, the results are very different. The problem obviously lies somewhere within the creation of the step file and meshing in gmsh. My exact procedure is:
1) draw three spheres in freecad, one enlosing the other two, which are separated.
2) selecting these shapes in the 'model' tab, and then export as a .step
3) open the .step in gmsh and choosing: mesh -> 3D -> optimise 3D -> refine by splitting.
4) save mesh.
5) Elmergrid 14 2 mymesh.msh -autoclean
There is a problem somewhere in here, and I suspect that it is something to do with the number of bodies - in my attempt at the problem, I apply the Equation to 3 bodies whereas in the tutorial example, you only apply the equation to 1 body. Please could someone define exactly what a body is? I'm not sure as to how 3 distinct spheres can be treated as one 'body' in the tutorial example.
Any suggestions as to where I've gone wrong and what I might to do solve this would be very much appreciated!!
Thanks in advance,
Sam.
Apologies in advance if what I'm about to ask has been asked before and if this post would be more suitable in another category.
What I'm trying to do:
Ultimately, I'd like to use Elmer to calculate the capacitance matrix for 17 electrodes within an ionisation chamber. I've attached the .step file that I created in Freecad.
What I've done so far:
Firstly, I followed the tutorial relevant to this problem (2 balls inside a larger ball), and the results matched those given in the instructions. I planned to generate the mesh for the chamber by exporting the .step file from freecad, create the mesh with gmsh, convert with Elmergrid and then load into Elmer. I therefore tried to replicate the '2 balls in a larger ball' calculation by making a similar geometry in freecad and following the steps that I intended to take to get to the capacitance matrix, closely following the steps in the tutorial after I had created the mesh. A screen shot of the geometry in the GUI with the convergence and results is attached for the case where I followed the tutorial exactly and where I tried to replicate it using freecad. Unfortunately, the results are very different. The problem obviously lies somewhere within the creation of the step file and meshing in gmsh. My exact procedure is:
1) draw three spheres in freecad, one enlosing the other two, which are separated.
2) selecting these shapes in the 'model' tab, and then export as a .step
3) open the .step in gmsh and choosing: mesh -> 3D -> optimise 3D -> refine by splitting.
4) save mesh.
5) Elmergrid 14 2 mymesh.msh -autoclean
There is a problem somewhere in here, and I suspect that it is something to do with the number of bodies - in my attempt at the problem, I apply the Equation to 3 bodies whereas in the tutorial example, you only apply the equation to 1 body. Please could someone define exactly what a body is? I'm not sure as to how 3 distinct spheres can be treated as one 'body' in the tutorial example.
Any suggestions as to where I've gone wrong and what I might to do solve this would be very much appreciated!!
Thanks in advance,
Sam.