[Gmsh] Gmsh-4.0.4 Volume mesh issue

[Christophe Geuzaine]

Dear Simone,

Can you try with the latest snapshot to see if it's better?

Christophe


> On 17 Dec 2018, at 17:41, Simone GREMMO <Simone.GREMMO at umons.ac.be> wrote:
> 
> Dear Christophe,
> as you asked in your previous email, I have been testing the newly implemented quad-boundary recovery in Gmsh (at that time it was the development version, future 4.0.5 or 4.1).
> 
> I found that Gmsh works fairly well, succeeding to generate a valid mesh with sufficient overall quality (a few ill-shaped elements may be present depending on the geometry configuration).
> However, in some cases, the resulting mesh has a negative cell. All the failing cases have one negative cell only, this cell always being a flat pyramid (see attached picture). It looks like the vertex relocation cannot move the top of the pyramid inside the volume. 
> 
> Does anyone have reported a similar behaviour?
> If necessary, I can provide you with a failing test case.
> 
> Regards,
> Simone G.
> From: Christophe Geuzaine <cgeuzaine at uliege.be>
> Sent: Monday, November 12, 2018 3:33:25 PM
> To: Simone GREMMO
> Cc: gmsh at onelab.info
> Subject: Re: [Gmsh] Gmsh-4.0.4 Volume mesh issue
>  
> 
> Dear Simone,
> 
> Indeed, Gmsh 4.0.0 -> 4.0.4 do not have the ability to automatically create hybrid tetrahedral+pyramidal meshes (your surface contains quadrangles).
> 
> The latest snapshot (future Gmsh 4.0.5 or Gmsh 4.1) has a new algorithm to generate such meshes, similar but more general to what we did in Gmsh 3. Give it a try and let us know how it works out for you?
> 
> Christophe
> 
> 
> > On 12 Nov 2018, at 14:38, Simone GREMMO <Simone.GREMMO at umons.ac.be> wrote:
> > 
> > Dear all, 
> > I have just downloaded the last version of Gmsh (4.0.4), but I am facing a problem with the generation of a "simple" volume mesh.
> > 
> > I would like to mesh a volume delimited by a surface mesh in .msh format, but it looks like Gmsh cannot create the volume mesh.
> > Error Message is :
> > .....
> > Info    : Boundary Recovery...
> > Info    : Writing to GRegion...
> > Info    : Reconstruct time : 0.116395 sec
> > Error   : No tetrahedra in region 5
> > Info    : 3D point insertion terminated (3195 points created):
> > Info    :  - 0 Delaunay cavities modified for star shapeness
> > Info    :  - 0 points could not be inserted
> > Info    :  - 0 tetrahedra created in 1.6e-05 sec. (0 tets/sec.)
> > Error   : No tetrahedra in region 5 
> > Info    : Done meshing 3D (0.133228 s)
> > Info    : 4857 vertices 6617 elements
> > Error   : ------------------------------
> > Error   : Mesh generation error summary
> > Error   :     0 warnings
> > Error   :     2 errors
> > Error   : Check the full log for details
> > Error   : ------------------------------
> > 
> > I am attaching the .geo file I have created as well as the surface mesh I used. To launch the mesh generation I run the command:
> > gmsh-4.0.4 createGeom.geo -3 -o volumeMesh.msh
> > 
> > Note that the same test case is successfully meshed using Gmsh version 3.0.6.
> > 
> > Do you have any suggestion on how to solve the problem? 
> > Is it possible that the surface mesh, containing both triangles and quadrangles is at the origin of the problem?
> > 
> > Thanks in advance for your suggestions.
> > Regards,
> > Simone G.
> > 
> > <createGeom.geo><surfaceMesh.msh>_______________________________________________
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> Gmsh is a free 3D finite element mesh generator with built-in pre- and post-processing facilities. This list is for questions and discussions about Gmsh features, resources, bugs, and so forth. Useful links: Gmsh homepage (for documentation, downloads, etc.); gmsh-announce mailing list (for announcements about new Gmsh releases and major bug fixes - you probably want to subscribe to that, as well)
> 
> 
> — 
> Prof. Christophe Geuzaine
> University of Liege, Electrical Engineering and Computer Science 
> http://www.montefiore.ulg.ac.be/~geuzaine
> 
> Free software: http://gmsh.info | http://getdp.info | http://onelab.info
> 
> <negCell_.jpg>

— 
Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science 
http://www.montefiore.ulg.ac.be/~geuzaine