[Gmsh] gmesh // char. lenth, unv format

[Christophe Geuzaine]

Alper Corlu wrote:
> 
> Hi ,
> 
> thanks for the answer. But to tell the truth I am a beginner on finite
> element method and mesh generation, so the only thing I know about mesh
> size in a mesh is the max of the diameters of the elements (diameter of an
> element defined as the largest edge of the element) in the volume.
>  1)So what do you mean by mesh sizes at each point? (you may just show me
> a reference on meshing or finite element)

In Gmsh, the mesh size is defined as

- the length of the segment for lines
- the radius of the circumscribed circle for triangles
- the radius of the circumscribed sphere for tetrahedra

A nice book on mesh generation is 

@book{georges-delaunay-97,
  author =	 "P. L. Georges and H. Borouchaki",
  title =	 "Triangulation de Delaunay et maillage",
  publisher =	 HERMES,
  year =	 1997
}

It's in french, but I think there is an english translation, too.

>  2) What is the unv format? Is it some standard file output for
> meshes? Can you supply info or reference on this format?

The unv format is the "universal" file format produced by IDEAS (from
SDRC). If you don't know this format, my advice is: don't use it! :-)
The native Gmsh file format is much simpler, and much smaller...


Christophe



>  thanks a lot
> alper
> 
> On Thu, 26 Jul 2001, Christophe Geuzaine wrote:
> 
> > Alper Corlu wrote:
> > >
> > > Hi
> > >
> > > I am Alper Corlu. I am a physics Phd student at university of
> > > Pennsylvania. I am currently working on finite element method and the code
> > > I have is using your Gmesh program. We are trying to understand the
> > > program and asking you if there is a manual for the program? The tutorial
> > > is fine but we cant find answers to all the questions in tutorial like
> > > characteristic length, how to set it, how to use it ..etc.
> >
> > Unfortunately, there is no complete manual for Gmsh at the moment. But
> > don't hesitate to send specific questions to the mailing list
> > (mailto:gmsh at geuz.org). As for the characteristic lengths, there are
> > three main possibilities:
> >
> > 1) Specify a target mesh size as the fourth coordinate of the geometry
> > points. These mesh sizes will be linearly interpolated in the structure
> > to produce the actual mesh sizes at each point in the volume.
> >
> > 2) Use attractors with the anisotropic mesh generator (see
> > tutorial/t7.geo).
> >
> > 3) Define a real background mesh, from which the actual mesh sizes will
> > be interpolated. Try for example 'gmsh tutorial/t1 -bgm
> > tutorial/bgmesh.pos -2'.
> >
> > Christophe
> >
> > --
> > Christophe Geuzaine
> >
> > Tel: 32 (0) 4 366 37 10    http://geuz.org
> > Fax: 32 (0) 4 366 29 10    mailto:Christophe.Geuzaine at ulg.ac.be
> >
> 
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-- 
Christophe Geuzaine

Tel: 32 (0) 4 366 37 10    http://geuz.org
Fax: 32 (0) 4 366 29 10    mailto:Christophe.Geuzaine at ulg.ac.be