Hi David,
The error message for the stl importation is the following:
Info : Running '/Applications/Gmsh.app/Contents/Resources/bin/gmsh -2 reparam.geo'
Info    : Started on Mon Dec 14 07:31:09 2009
Info    : Reading 'reparam.geo'
Info    : Reading 'ChunkOfGeometry.msh'
Info    : 214164 vertices
Info    : Vertex numbering is dense
Info    : 426736 elements
Info    : Read 'ChunkOfGeometry.msh'
Error   : Incorrect face in compound surface -1000

So I may have to clean my stl a bit

ae-jh1406a:DUCT_VORTICES jh1406$

As far as the prisms are concerned, it is a little bit weird: if I run gmsh -3, I get the following errors:
Error   : Degenerated prism in extrusion of volume 5
Error   : Degenerated prism in extrusion of volume 5
Error   : Degenerated prism in extrusion of volume 5
Error   : Degenerated prism in extrusion of volume 5
Error   : Degenerated prism in extrusion of volume 5
Error   : Degenerated prism in extrusion of volume 5
Error   : Degenerated prism in extrusion of volume 5
Error   : Degenerated prism in extrusion of volume 5
Error   : Degenerated prism in extrusion of volume 5
Error   : Degenerated prism in extrusion of volume 5
Error   : Degenerated prism in extrusion of volume 5
Error   : Degenerated prism in extrusion of volume 5
Error   : Degenerated prism in extrusion of volume 5
Error   : Degenerated prism in extrusion of volume 5
Error   : Degenerated prism in extrusion of volume 5
Info    : Mesh 3D complete (0.018726 s)
Info    : 2083 vertices 5682 elements
Error   : ------------------------------
Error   : Mesh generation error summary
Error   :     0 warnings
Error   :  1698 errors
Error   : Check the full log for details
Error   : ------------------------------
Info    : Writing 'test_curved.msh'
Info    : Wrote 'test_curved.msh'
Info    : Stopped on Mon Dec 14 07:39:45 2009

If I run gmsh -2, I generate the same mesh without errors. I attached the test case.


I also get a lot of warnings if I try to switch to order 2 to get the curvature of the elements. It seems to work though as mesh file only contains 2d order prisms
Warning : We don't have a valid parameter on curve 23-529
Warning : We don't have a valid parameter on curve 529-530
Warning : We don't have a valid parameter on curve 530-531
Warning : We don't have a valid parameter on curve 531-532
Warning : We don't have a valid parameter on curve 532-533
Warning : We don't have a valid parameter on curve 533-534
Warning : We don't have a valid parameter on curve 534-21
Warning : We don't have a valid parameter on curve 22-535
Warning : We don't have a valid parameter on curve 535-536
Warning : We don't have a valid parameter on curve 536-537
Warning : We don't have a valid parameter on curve 537-538
Warning : We don't have a valid parameter on curve 538-539
Warning : We don't have a valid parameter on curve 539-540
Warning : We don't have a valid parameter on curve 540-24
Warning : We don't have a valid parameter on curve 24-541
Warning : We don't have a valid parameter on curve 541-542
Warning : We don't have a valid parameter on curve 542-543
Warning : We don't have a valid parameter on curve 543-23
Warning : We don't have a valid parameter on curve 14-544
Warning : We don't have a valid parameter on curve 544-545
Warning : We don't have a valid parameter on curve 545-546
Warning : We don't have a valid parameter on curve 546-23
Warning : We don't have a valid parameter on curve 13-547
Warning : We don't have a valid parameter on curve 547-548
Warning : We don't have a valid parameter on curve 548-549
Warning : We don't have a valid parameter on curve 549-24

Attachment: test_curved.geo
Description: Binary data



Best regards,
Julien

On 12 Dec 2009, at 17:09, David Colignon wrote:


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 [[email protected]]
Date d'envoi : vendredi 11 décembre 2009 14:40
À : Hoessler, Julien
Cc : [email protected]
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
CÉCI - Consortium des Équipements de Calcul Intensif
ACE - Applied&  Computational Electromagnetics
Sart-Tilman B28
Université de Liège
4000 Liège - BELGIQUE
Tél: +32 (0)4 366 37 32
Fax: +32 (0)4 366 29 10
WWW:    http://hpc.montefiore.ulg.ac.be/
Agenda: http://www.google.com/calendar/embed?src=david.colignon%40gmail.com



Julien Hoessler
PhD Student
Department of Aeronautics
Imperial College London

Phone: +44 (0) 20759 45042
Email:   [email protected]

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