[Gmsh] merge surface

[Geordie McBain]

2011/10/27 isettagi at libero.it <isettagi at libero.it>:
> Hi all,
> thank you again for support and for the possibility to use this programm.
>
> I'd like to know if there is a command to merge different surface in one.

I'm not sure if this will exactly answer your question, but I do have
an example of creating a volume bounded by multiple surfaces.  (I
preferred to keep the surfaces distinct so I could put different
boundary conditions on them later.)  Hopefully you'll be able to
modify this to achieve your end.

You can "Merge" multiple Stl surfaces and then call "CreateTopology".
This latter command doesn't appear in the manual
<http://geuz.org/gmsh/doc/texinfo/gmsh.html>, but is mentioned at
https://geuz.org/trac/gmsh/wiki/STLRemeshing.

Here's a complete example.  I have three STL files, corresponding to
the different boundary conditions in my finite element problem:
inlet.stl, outlet.stl, and wall.stl.  I get Gmsh to create the volume
that they jointly enclose and then mesh the volume and the three
surfaces and export the mesh.

%<---
Merge "inlet.stl";
Merge "outlet.stl";
Merge "wall.stl";

CreateTopology;

Physical Surface (1) = {1};
Physical Surface (2) = {2};
Physical Surface (3) = {3};

Surface Loop (1) = {1, 2, 3};
Volume (1) = {1};
Physical Volume (4) = {1};
%<---

Hope this helps.
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