[Gmsh] Unexpected behaviour with Geometry.AutoCoherence=0 and duplicatedsurfaces.

[Christophe Geuzaine]

On 30/04/10 12:46, Mark Starnes wrote:
> Hi everyone,
>
> For various reasons, the meshes I produce use Geometry.AutoCoherence=0
> to prevent the collapsing of coincident objects.  I perform collapsing
> at a later point when needed.
>
> When copying a surface, however, extra nodes seem to appear on the
> duplicated surface and when meshed, Gmsh shows a Seg. Fault.  I tried
> this on windows and linux, and am using version 2.5.0-svn.
>
> The following script shows the issue.  The behaviour can be turned on or
> off by commenting the Geometry.AutoCoherence=0 command:
>
> -----------------
> Geometry.AutoCoherence = 0;
>
> Point(1) = {0,0,0}; // centre
> Point(2) = {1,0,0};
> Point(3) = {0,1,0};
> Point(4) = {-1,0,0};
> Point(5) = {0,-1,0};
>
> Circle(1) = {2, 1, 3};
> Circle(2) = {3, 1, 4};
> Circle(3) = {4, 1, 5};
> Circle(4) = {5, 1, 2};
>
> Line Loop(5) = {2, 3, 4, 1};
> Plane Surface(6) = {5};
>
> test[] = Translate{0,0,-0.1} {Duplicata{Surface{6};}};
> -----------------

Hi Mark - Indeed: the old internal CAD engine translates surfaces by 
translating its boundaries separately first; so without the 
"RemoveDuplicate" phase, the resulting geometry is not correct (the 
meshing algorithm should not crash anyway, but... well ;-)

In any case, just translating the geometry will *not* give you identical 
meshes. Currently you would have to use a hack based on extrusion for 
this: see

http://www.geuz.org/pipermail/gmsh/2009/004416.html

In the very near future we will also add true "mesh copying" facilities 
to generate periodic grids.

Best,

Christophe


>
> I noticed this, as I have coincident faces which need identical
> meshes for coupling to occur on a node to node basis between different
> domains.
>
> If anybody has a suggestion for how to match meshes on coincident but
> numerically separate faces, I'd love to hear it!  Currently, all I can
> think of is the Duplicata approach above.
>
> As a side, I have just been awarded my Doctorate of Aeronautics from
> Imperial College, London:  I used Gmsh throughout the project (and
> referenced it as requested!), and have posted a few times, receiving
> much help from the community.  So, thanks for this great software and
> thanks for the support over the years!
>
> Best regards,
>
> Mark.
>
> FT Technologies Limited is registered in England and Wales under registered number 01603909. Its registered office is at Church Lane, Teddington, Middlesex, TW11 8PA.
> The information in this message is confidential and is intended only for the use of the intended recipient(s). If you are not an intended recipient, you should not disclose, use or copy this information. Please contact the sender immediately if you have received this message in error.
>
> _______________________________________________
> gmsh mailing list
> gmsh at geuz.org
> http://www.geuz.org/mailman/listinfo/gmsh
>
>


-- 
Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science
http://www.montefiore.ulg.ac.be/~geuzaine