# [Gmsh] Quadrangular mesh with flat faces from ruled surface

Julien ERCOLANELLI julien.ercolanelli at ensta-bretagne.org
Mon Jul 18 14:20:57 CEST 2016

```Ok thanks,

I tried what you explained for a basic structured pattern but with no results.

Mesh a non flat surface always produces non flat quadrangular elements.

If you have a counter-example, let me know

________________________________
De : Felix Salazar <felix.a.salazar at gmail.com>
Envoyé : vendredi 8 juillet 2016 17:53:58
À : Julien ERCOLANELLI
Cc : gmsh at onelab.info
Objet : RE: [Gmsh] Quadrangular mesh with flat faces from ruled surface

I don't have a gmsh installation to test. But there is a 2D meshing algorithm for quads. Delaunay Quad. And you might have to set the recombine option in the geometry script, before actually meshing anything.

I've done what you need but with transfinite mesh for a structured pattern.

I'll try to get ahold of a GMsh install and run some test.

Good luck

On Jul 8, 2016 5:05 AM, "Julien ERCOLANELLI" <julien.ercolanelli at ensta-bretagne.org<mailto:julien.ercolanelli at ensta-bretagne.org>> wrote:

Hi Felix,

Yes a ruled surface that is not flat.

I did what you explained. Recombine + 1 st order

But Gmsh gives non-flat quadrangular mesh elements since the four points of an element are not in a same plane. All the elements are composed of two triangles with different normals (see attached file).

Is Gmsh is able to do what I want?

or Do I need a trick to get quadrangular mesh with flat faces? I though transform my ruled curved surfaces into multiple plane surfaces approximating my real geometry but it might not be so simple.

________________________________
De : Felix Salazar <felix.a.salazar at gmail.com<mailto:felix.a.salazar at gmail.com>>
Envoyé : jeudi 7 juillet 2016 20:13:38
À : Julien ERCOLANELLI
Cc : gmsh at onelab.info<mailto:gmsh at onelab.info>
Objet : Re: [Gmsh] Quadrangular mesh with flat faces from ruled surface

You mean a ruled surface that isn't flat itself?

Recombine the mesh for that surface to get the quads. And pay attention to specify 1st order elements in the mesh options. If you want structured quads, check the documentation and the tutorials to get the transfinite lines and surfaces.

You should get a non-planar surface with flat first order elements.

Hope this helps

On Jul 7, 2016 7:32 AM, "Julien ERCOLANELLI" <julien.ercolanelli at ensta-bretagne.org<mailto:julien.ercolanelli at ensta-bretagne.org>> wrote:

Dear Gmsh users,

I am working with ruled surfaces and at the end I would like to get a quadrangular mesh with only flat faces.

Is there a way to mesh a ruled surface with flat quadrangular faces?

Thanks,

Julien

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