[Gmsh] Fails to mesh 3d region with hole.

[Martin Aunskjær]

Hi,

I'm having trouble generating a 3D mesh of a bounding
box with a hole (another closed volume) embedded
inside of it. Gmsh does generate a mesh, but it meshes
the entire bounding box, including the inside of the
hole. I believe this will happen if the volume
enclosing the hole is not closed. Thus, I tried
dumping the 2D surface mesh, converted it to a .poly
file for TetGen and sure enough TetGen detects an open
face in the interior volume and no mesh is generated
as all tets are eaten away. I would appreciate some
assistance in understanding the following:

1) Is there something foolish about the way I generate
the geometry (see included nose_in_box.geo)? The
surface bounding the interior hole seems to me to be
closed. Or is it gmsh that produces an erroneous
surface mesh that will make the 3D meshing fail ?

2) I do not understand the remark in the user guide
about consistent orientation of surfaces when creating
a surface loop. Supposedly, this means that the
normals of all elementary surfaces of a surface loop
should all either point into or out of the volume it
encloses. Is it so that the surface normals should
point into the volume being meshed; i.e. for an
exterior bounding box they should point inward, and
for an inside hole they should point outward? And what
determines the direction of a surface normal compared
to the way its underlying line loop is defined ?

Thanks in advance,
Martin Aunskjaer


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