[Gmsh] 2D mesh generation problem

[Geordie McBain]

2011/2/21 Paavo Mäkelä <pamakela at gmail.com>:
> Hi,
>
> I have had a working workflow for making 2D meshes from trimmed NURBS
> geometry made in Aliasstudio. I use the Elmer solver to perform flow
> simulations.
>
> I recently continued my work on my personal design project and noticed that
> GMSH will produce meshes that contain 3 dimensional elements (as per Elmer
> software's log) and sometimes Elmer software detects 3 dimensional mesh,
> even though the original geometry is/was a 2D plane! What am I doing wrong
> here? Loading the original IGES file straight into Elmer software results in
> 2D mesh with 2D elements which implies the exported cad file is Ok (but
> because elmer can't handle trimmed 2d NURBS planes, I must always go through
> Gmsh). I think only 2D elements should be generated if you only use the 2D
> meshing functionality in Gmsh? I can post my IGES file if there is need for
> that.

Hello, I haven't tried Elmer (yet), but I believe Gmsh only outputs
three-dimensional meshes, even if your geometry is two-dimensional or
even one-dimensional; i.e. the nodes always have three coordinates.

Which output format do you use?  For FreeFem++, for two-dimensional
problems, I output in MEDIT .mesh from Gmsh, but then modify it in AWK
to cull the z-coordinates.  Perhaps a workaround like that would be
reasonable?