[Gmsh] double surfaces/lines between adjacent bodies

[Zenker, Dr. Matthias]

Hi Elmer and gmsh  list,

I use gmsh and Elmer to simulate an electrical current flowing through a
conductive medium between two electrodes. I get the geometry from my CAD
colleagues in STEP format, import it in gmsh, mesh it, read the mesh
with Elmer and do the FEM calculation there. Most of the time, the
calculations are 2D. This works in principle, but there is the following
problem: 
Electrode and medium have common surfaces (resp. lines in 2D). When I
get the geometry in STEP format, every part (Electrodes and Medium) has
its own outer surface (line). This leads to double surfaces (lines)
between the adjacent bodies. For geometry and mesh import, this is no
problem, neither for gmsh nor for elmer - the mesh is imported OK in
Elmer. But when I do the simulation, I see that no current flows through
this double surface (although only one of them is defined as physical in
gmsh, and only that one is seen in Elmer).
Removing the double surface/line in gmsh is rather tedious (Identify the
problematic regions where there is a double line between adjacent
surfaces. Delete at least one of the adjacent surfaces. Delete the
corresponding line at the interface. Delete its points. Redefine the
surface(s) which was (were) deleted before. It gets more complicated in
case of only partially overlapping lines which have to be partially
reconstructed.).

Question: How do I deal with this problem? Is there a more elegant (and
less time consuming) way than manual removal of the double lines? (The
autocoherence function in gmsh which is intended to remove double
duplicate entities in geometries is switched on, but does not seem to
have any effect.)
I imagine that this must be a known problem, since doing simulations
with geometries imported from 3D CAD systems is not so uncommon after
all.
Further it is not totally clear to me where the problem really comes
from. I suspect non-identical mesh nodes at the interface, which inhibit
current flow across the border.

Ideas and suggestions are more than welcome...

Thank you,

Matthias

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ERBE Elektromedizin GmbH
Dr.rer.nat. Matthias Zenker
Dipl. Phys.
Grundlagenentwicklung Technologie
Waldhoernlestrasse 17
72072 Tuebingen
Phone + 49 7071 - 755 226
Fax + 49 7071 - 755 5226
mailto:Matthias.Zenker at ERBE-med.de
www.ERBE-med.de
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