[Gmsh] Question on gmsh

[Geordie McBain]

2012/2/14 Steve Daley <steve.goodwood at virgin.net>:
> I am very interested in using gmsh to generate tet meshes for my own CFD
> code development.  I can see that gmsh will potentially be very useful to me
> to genertae my tet meshes but is it possible for gmsh to output whether a
> triangle element in a tet mesh is a surface triangle ?

Normally Gmsh only outputs triangular elements in three-dimensional
meshes if they belong to a defined surface, typically used for
boundaries and interfaces; that is, the faces of tetrahedra are not
generated or output.

In the finite element method,  the domain elements are defined in
terms of nodes and faces don't really enter; if you do need the faces,
e.g. for a finite volume method, you'll need to do further
postprocessing.

> Also can you explain what "physical 99" and "elementary 2" means in the example on Page 85.

I'm not sure what document you're referring to, but I'm guessing Page
85 is the same as Section 9.1 `MSH ASCII file format' of the on-line
manual <http://geuz.org/gmsh/doc/texinfo/gmsh.html#MSH-ASCII-file-format>.
 If so, see Section `6.2 Elementary vs. physical entities'
<http://geuz.org/gmsh/doc/texinfo/gmsh.html#Elementary-vs-physical-entities>.
 In brief: an element's elementary entity merely refers to the
geometry it meshes; its physical entity is like a subdomain or patch
that the user has deliberately tagged, e.g. in order to impose
different values of coefficients or boundary conditions.