[Gmsh] RE : stl and prism extrusion

[David Colignon]

On 12/12/09 14:18, Hoessler, Julien wrote:
> Hi David,
> Thanks for the quick answer. The stl importation crashes with the stl file or a msh file obtained from the stl,

Hi Julien,

does it print an error message before crashing ?

> but I guess that's because my stl is too fine (214K elements), I'll try again with a coarser mesh.
> As far as the prism extrusion is concerned,it works well and after recombining, the prism look perfectly fine on a curved surface, except that I get errors telling me that the prisms are degenerated. Is it an unnecessary warning or should I be worried?


Can you send a copy of these warnings ?


> I also have a bonus question if you don't mind.

You're welcome

>When I generate the extrusion of the surfaces and put them on a list surf[], is it possible to access the edges and vertices of the top surfaces to define the volume above?

No. But the Tools -> Visibility -> Tree browser can help tou to quickly retrieve it.

>I could extrude the edges and vertices too but it would mean that some entities would be duplicated.

Not necessarily, after each extrusion operation, Gmsh issues the "Coherence;" command which should eliminate duplicated 
entities.

Regard,

Dave


> Best regards
> Julien
> ________________________________________
> De : David Colignon [David.Colignon at ulg.ac.be]
> Date d'envoi : vendredi 11 décembre 2009 14:40
> À : Hoessler, Julien
> Cc : gmsh at geuz.org
> Objet : Re: [Gmsh] stl and prism extrusion
>
> On 11/12/09 15:00, Hoessler, Julien wrote:
>> Good afternoon all,
>> First of all, thanks for writing this code, I'm using it a lot to generate 2D/3D meshes for DNS and stability analysis. I was wondering if it is possible to extrude a layer of prisms using the surface normals instead of a specific direction. I need to generate a layer of prisms out of a wall which is curved and there is more than 80 degrees of angular difference between the two extreme locations of the surface (it is smooth, but twists a bit like a sinh).
>
>
> Hi Julien,
>
> it is still experimental and quite hidden in the documentation
>    ( http://www.geuz.org/gmsh/doc/texinfo/gmsh.html#Structured-grids ),
> but you can try:
>
> Extrude { Surface { expression-list }; layers }
>
> which extrudes a boundary layer along the normals of the specified surfaces (if they are smooth and do not form acute
> angles).
>
>> My second question is about the stl importation. I have a stl file which is a 3D box that I can read and visualise without problems, but I'd like to remesh it
>
> The undocumented "Compound Surface" command is also very experimental, but you can try the attached file (reparam.geo)
> which here use a .msh file but should also work with a .stl file.
>
>
> , mesh the volume inside  and split the box surface to assign different physical groups for boundary conditions (and add
> a layer of prisms on one of the surfaces). Is it possible with Gmsh? I've searched through the questions in this mailing
> list, do I need the opencascade support for this?
>
>
> Regards,
>
> Dave
>
>
> --
> David Colignon, Ph.D.
> Collaborateur Logistique du F.R.S.-FNRS
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