# [Gmsh] Normals

Nacho Andres de la Fuente nacho.andres at deos.tudelft.nl
Wed Feb 25 21:03:45 CET 2004

```Many thanks for your rapid response.

Yes I tried that already but I thought that gmsh did not save it
correctly to the mesh file because when generating the 3D mesh (saving
and opening the mesh file again), gmsh does not show the additional
Physical Surfaces with the same geometrical location. Afterwards, I have
checked up the *.msh file and there they are ..  :-)

Many thanks Cristophe,
NAcho

On Sun, 2004-02-22 at 17:31, Christophe Geuzaine wrote:
> Nacho Andres de la Fuente wrote:
>
> > Dear all,
> >
> > I am using gmsh in combination with getdp and I am a newbie so I would
> > (i.e. passing from conductivity_1 to conductivity_2) in getdp and
> > therefore I need the normals defined outwards for all the surfaces to
> > impose the appropriate boundary conditions.
> >
> > I have done two things in gmsh:
> > 1) define the inner surface and the outer surface different (i.e. with
> > different geometrical elements) corresponding to the same geometrical
> > location => gmsh gets crazy when meshing since it finds out that the
>
> Yes, you cannot do that...
>
> > 2) create an inner volume giving it the right normals and the outer
> > volume being the first one with the gap of the second => the problem
> > with the normals appear: the outwards direction for the inner volume is
> > right but for the outer volume gets the inwards direction (opposite to
> > what I would need for the boundary condition for getdp)
> >
> > I am certainly doing something wrong and sure some of you have the right
> >
>
> Simply define two Physical Surfaces for the boundary:
>
> // interior boundary:
> Physical Surface(1) = {10,11,-12};
>
> // exterior boundary, with opposite orientation:
> Physical Surface(2) = {-10,-11,12};
>
> Christophe

```