Christophe Geuzaine Christophe.Geuzaine at
Fri Jul 31 14:41:25 CEST 1998

Hello S.K.Choi,

> I'm a student of graduate school in Korea majoring on the
> high-voltage engineering in electrical department.
> I'm now interested on the analysis of electromagntic
> phenomena such as electric field, magnetic field, and
> elctromagnetic force of vacuum circuit breaker using finite
> element method with tetrahedron elements,however I'm very
> poor at dealing with software because I've been researched
> mainly by experiments.
> Surveying on the web to obtain 3-d automesh program, I
> happily found theGMSH software for Windows and downloaded
> successfully. After installingthis software, I have met
> several problems as follows.
>   i) I could not save on line help files such items as
>      Creating a Mesh & Visualiztion. So I don't analyse
>      what the data outputs saved in gref, msh,and unv
>      format mean.

When you mesh something, you can save the elements (points, lines,
triangles, tetrahedra, etc) into a file. The format of this file is
either gref, unv (the universal mesh data format) or msh (the internal
format of gmsh). Jean-Francois Remacle is currently writing some
actualized manual pages (You'll have to be a little patient...). For the
two first formats, you can search the web for some documentation. The
gmsh format is very simple: it consists of a several fields, the most
important being:

- the nodes :

num x y z
num x y z
num x y z

- the elements :

num type physical_entity_num elementary_entity_num nb_nodes node node
num type physical_entity_num elementary_entity_num nb_nodes node node
num type physical_entity_num elementary_entity_num nb_nodes node node


type = 1 for lines
       2 for triangles
       3 for quadrangles
       4 for tetrahedra

>   ii) Because of the reason relating with clause i), I havd
>       tried to download GMSH for Unix system but I failed to
>       download. I think the files seem to be broken or
>       damaged.

Strange. Several people downloaded theses files without any problem. A
new version (consisting of separate libraries to be linked by the user)
will be available next month (or a little bit later)

>   iii) During check the samlpe geo files I can hardly
>      understand the means of some commands such as
>       coherance, complex, transfinite, recombine, physical,
>       , and other uncommented commands in on line help.

cf. i). In brief:

- coherence stands for geometry checking (it's automatically added in
the geo file after an extrusion, etc, when multiple geometrical entities
which have been generated could coincide)
- complex: always part of something else, as in 'complex volume'
- transfinite: gmsh can deal with transfinite meshes of lines, surfaces
or volumes. 
- recombine: recombine triangles into quadrangles
- physical: the physical entities are those for which the mesh is saved
in the file. If no physical entities are defined, your output file will
only contain the generated points.

> Please let me obtain on line documents and files as follows,
> ifpossible.
>     i) some helpful text files for using GMSH in English
>     ii) GMSH software for AIX-4
>     iii) some helpful documents, papers, sample geo files,
>        and so on for me to use GMSH
>     iv) some helpful materials including FEM source program
>         related with electrical research, if possible.
> In addition I'd like to obtain your comments on the
> procedures from creation and analyse of the output for
> tetrahedron elements as follows.
>     i) creation of 3-d tetrahedron elements
>     II) what the output data formatted with gref, msh, and
>        unv means.

cf. i)

> Your helpful actions will be highly appreciated.
> Thank you in advance and hoping your response

Best regards,

Christophe Geuzaine         

Tel: +32-(0)4-366.37.10     mailto:Christophe.Geuzaine at
Fax: +32-(0)4-366.29.10