# [Gmsh] Problem with 2D mesh generation for a cracked domain

Christophe Geuzaine cgeuzaine at ulg.ac.be
Wed Apr 1 21:30:14 CEST 2009

```olivier jamond wrote:
> Hello,
>
> I am a french phd student and I am working on multiscale simulations of
> propagation of critical areas within the Arlequin framework
> (www.mssmat.ecp.fr/IMG/pdf/BenDhia.pdf). I use Gmsh to generate meshes
> at each step of the propagation of cracked domains. I'am working with 2D
> closed crack, so I would like to have duplicated points in the .geo
> file. So I have unchecked the option
> "remove duplicated entities in GEO models", but it seams to exists a
> feature which deals with the intersection of the 1D mesh of the edges
> ("There are 4 intersections in the 1d mesh/Gmsh splits those edges and
> tries again"). Is there any way to disable this function, or to allow
> duplicated points or self-crossed edge?
>

Hi Olivier - No... Maybe a better way to do this would be to actually
declare your crack as an embedded curve in your surface. This way you
still have perfectly nice manifolds and the cracks are only incorporated
at the meshing stage.

Here's an example:

Point(1) = {0.5, 0.5, 0};
Point(2) = {0, 0.5, 0};
Point(3) = {0.5, 1, 0};
Point(4) = {0.5, 0, 0};
Point(5) = {1, 0.5, 0};
Point(6) = {0.8, 0.6, 0};
Line(1) = {2, 1};
Line(2) = {1, 4};
Line(3) = {1, 6};
Circle(4) = {4, 1, 5};
Circle(5) = {5, 1, 3};
Circle(6) = {3, 1, 2};
Line Loop(7) = {5, 6, 1, 2, 4};
Plane Surface(8) = {7};
Line{3} In Surface{8};

Of course with this approach you don't get duplicate vertices. Do you
really need the duplication?

(If you do I guess you could quite easily generate the duplicates after
reading the mesh file, e.g. by declaring 2 physical curves with opposite
orientations on the crack and then checking which triangle shares which
edge?)

> A  problematic .geo file is attached.
>
> Thanks a lot,
>
> Best regards,
>
> Olivier Jamond
>
>
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>
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--
Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science
http://www.montefiore.ulg.ac.be/~geuzaine

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