[Gmsh] Points seem to move on transfinite surface after the recombination

Bojan Niceno bojan.niceno.scientist at gmail.com
Wed Jul 8 13:21:28 CEST 2020

```Dear Christophe,

Oh great, thanks a lot for the fast reply :-)

Best regards,

Bojan

On Wed, Jul 8, 2020 at 1:08 PM Christophe Geuzaine <cgeuzaine at uliege.be>
wrote:

>
>
> > On 8 Jul 2020, at 12:46, Bojan Niceno <bojan.niceno.scientist at gmail.com>
> wrote:
> >
> > Dear all,
> >
> > I have a problem when trying to mesh planar structured surfaces.
> Although points seem to be uniformly placed on a transfinite surface, they
> move a bit when recombining the mesh to change triangles to quadrilateral
> cells.
> >
> > Here is a simple script which demonstrates it:
> >
> > // Define points
> > Point(1) = {0.0,  0.0,  0.0};
> > Point(2) = {0.5,  0.0,  0.0};
> > Point(3) = {0.0,  0.5,  0.0};
> > Point(4) = {0.7,  0.0,  0.0};
> > Point(5) = {0.0,  0.7,  0.0};
> >
> > // Define connectors from points ...
> > Line  (1) = {2, 4};
> > Circle(2) = {4, 1, 5};
> > Line  (3) = {5, 3};
> > Circle(4) = {3, 1, 2};
> >
> > // ... and set them as transfinite
> > Transfinite Curve {1, 2, 3, 4} = 11 Using Progression 1;
> >
> > // Define surface ...
> > Curve Loop(1) = {1, 2, 3, 4};  Plane Surface(1) = {1};
> >
> > // ... and set it as transfinite too
> > Transfinite Surface {1};
> >
> > So, as I said, generating a 2D mesh over the surface places points
> properly, but command recombine moves them a bit :-/  Is there a way to
> prevent these movements of points?
> >
> > I am also attaching a screenshot of a mesh before and after
> recombination, to illustrate my problem better.
> >
>
> Indeed, recombination a posteriori applies some smoothing. You should add
>
> Recombine Surface{1};
>
> after "Transfinite Surface {1};", which will directly create a quad mesh.
>
> Christophe
>
>
>
>
> >     Best regards,
> >
> >     Bojan
> >
> > P.S.  I am not sure if attachments go to the mailing list, I've never
> used a mailing list before.
> >
> >
> <points_after_generation.png><points_after_recombination.png>_______________________________________________
> > gmsh mailing list
> > gmsh at onelab.info
> > http://onelab.info/mailman/listinfo/gmsh
>
> —
> Prof. Christophe Geuzaine
> University of Liege, Electrical Engineering and Computer Science
> http://www.montefiore.ulg.ac.be/~geuzaine
>
>
>
>
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