[Gmsh] Trouble Meshing Open Surface

Hayan Nasser hayannasser at gmail.com
Tue Jun 30 16:10:31 CEST 2015


Hello,

I am trying to mesh a surface that presents itself as a 2D flexible surface
embedded in a 3D domain.
The surface is homemorphic to a disk and saved as an .stl file (attached).

Can these types of surfaces be meshed?
I'm following along with this wiki page:
https://geuz.org/trac/gmsh/wiki/STLRemeshing
and also the examples I have managed to find in the mailing list.

My procedure so far is:
1) load .stl file (attached) into Gmsh.

2) Reclassify the mesh (using GUI) Mesh->Reclassify 2D.

After reclassifying the mesh, I check the Elementary Entities (Tools ->
Visibility) and I see two Surfaces* (listed as Surface 2 and Surface 3 on
my machine) and a Lines (shown as Line 3 and 6).
*This is a confusing part to me, as should I not be expecting a single
surface?

3) I save the reclassified mesh as a .msh file
4) I create a .geo file named flexible_sheet.geo with the following
contents:

-------------------------------------------------------
-------------------------------------------------------
Mesh.RemeshAlgorithm=1;
CharacteristicLengthFactor = 0.5;

Merge "reclassified_flexible_sheet.msh";
CreateTopology;

Compound Surface(100) = {3};
--------------------------------------------------------
--------------------------------------------------------

5) I then run: gmsh -2 flexible_sheet.geo

The output in the terminal reads as an error:

---------------------------------------------------------------------
Info    : Started on Tue Jun 30 15:02:00 2015
Info    : Reading 'flexible_sheet.geo'...
Info    : Reading 'flexible_sheet_thicker_reclassified.msh'...
Info    : 96 vertices
Info    : Vertex numbering is dense
Info    : 286 elements
Info    : Done reading 'flexible_sheet_thicker_reclassified.msh'
Info    : Creating topology from mesh...
Info    : Removing duplicate mesh vertices...
Info    : Found 0 duplicate vertices
Info    : No duplicate vertices found
Info    : Done creating topology from mesh (0.000411 s)
Info    : Done reading 'flexible_sheet.geo'
Info    : Meshing 1D...
Info    : Done meshing 1D (9e-06 s)
Info    : Meshing 2D...
Info    : Meshing surface 12 (Compound surface, MeshAdapt)
Info    : Parametrizing surface 12 with 'convex map'
[0]PETSC ERROR: --------------------- Error Message
--------------------------------------------------------------
[0]PETSC ERROR: Object is in wrong state
[0]PETSC ERROR: Not for unassembled matrix
[0]PETSC ERROR: See http://www.mcs.anl.gov/petsc/documentation/faq.html for
trouble shooting.
----------------------------------------------------------------------------

Something clearly has gone wrong with the classification of the surface as
the output seems to suggest that there are 286 elements?

If you could help with getting this surface meshed I would be incredibly
grateful as I have been trying for sometime...

Many Thanks,
Dr Hayan Nasser
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