[Getdp] Simple electrostatic simulation yields nan values everywhere

[Théo Mathurin]

Hello everyone,

I've encountered a strange issue with my electrostatic computation. I'm
using the V formulation with the electric potential v saved as a
post-operation output (see pro file attached).

The geometry is desperately simple: two conductors in a square surrounding
medium, each with its insulation. When the conductors are round,
everything's fine and the electric potential is computed correctly. But
when their shape is changed to rectangular, for some reason I get nan
values everywhere in the domain.

My msh file is generated using the Gmsh Python API. Attached is the
corresponding Python script, where one can switch the shape from circles to
rectangles. For debugging purposes, the script is written so that the
minimal amount of code that is not shared by the two cases is isolated
behind a conditional statement.

Apparently, the problem arises when and only when one or several of the
left or right insulation outer curves are straight lines. I have checked
that there is nothing wrong with physical regions.

In both cases I'm using the same pro file, and the command to run GetDP is
the following:

getdp -pro electrostatics.pro -msh test_geom.msh -solve EleSta_vf -pos get_v
>

Note that I was able to carry out the very same computation successfully in
a different, much more complicated geometry with rectangular conductors. I
sincerely have no idea as to the root of this seemingly intractable
problem, and therefore any help would be greatly appreciated. If needed, I
can also provide the msh files I get when I'm running my Python script.

Other potentially relevant information below
- Python API from Gmsh 4.4.1 Linux 64 bits SDK
- GetDP 3.2.0 Linux 64 bits
- Python 3.7
- Ubuntu 18.04.3

Best regards,

Théo Mathurin

Research engineer
Laboratoire Systèmes Electrotechniques et Environnement (LSEE) - Université
d'Artois
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