[Gmsh] double surfaces/lines between adjacent bodies

[Zenker, Dr. Matthias]

Hi Mark,

this would be exactly what I need...

Best regards,

Matthias 

> -----Original Message-----
> From: Mark van Doesburg [mailto:mark.van.doesburg at technolution.nl] 
> Sent: Wednesday, March 11, 2009 5:51 PM
> To: Zenker, Dr. Matthias; gmsh at geuz.org; elmerdiscussion at postit.csc.fi
> Subject: Re: [Gmsh] double surfaces/lines between adjacent bodies
> 
> Hello Matthias,
> 
> I have the same problem and am working on a solution. This 
> solution consists of an algorithm which uses OpenCASCADE to 
> find all overlapping vertices/edges and surfaces and merge 
> them.  This includes partial overlaps.
> 
> With a partial overlap I mean for example a small edge with 
> overlaps a larger edge in the middle. The algorithm will 
> split the longer edge in three pieces and the overlapping 
> section is merged. As similar method is used to merge 
> partially overlapping surfaces.
> 
> I was creating this as part of a BRL-CAD reader for gmsh, but 
> it is probably usefull for all OpenCASCADE models. 
> Unfortunately it is not yet finished.
> 
> regards,
> 
> Mark van Doesburg
> 
> "Zenker, Dr. Matthias" <Matthias.Zenker at erbe-med.de> wrote:
> 
> 	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
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> 	Dipl. Phys.
> 	Grundlagenentwicklung Technologie
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> 	ERBE Elektromedizin GmbH
> 	Firmensitz: 72072 Tuebingen
> 	Geschaeftsfuehrer: Christian O. Erbe, Reiner Thede
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_____________________________________________________________________
ERBE Elektromedizin GmbH
Firmensitz: 72072 Tuebingen
Geschaeftsfuehrer: Christian O. Erbe, Reiner Thede
Registergericht: Stuttgart HRB 380137