# [Gmsh] Holes in curved surfaces / merging surfaces

Sean Victor Hum svhum at ucalgary.ca
Tue Jan 4 07:07:58 CET 2005

```Hello,

First off I would like to commend the gmsh team on an amazing piece of
software.  I have found many uses for gmsh ranging from electromagnetic
scattering problems to mechanical problems.  Thanks for making it
publically available.

I have a question about the geometry module.  All the problems I use
gmsh for involve surfaces (no 3D elements).  I have not found a way to
easily make a hole in a curved surface.  I know it is quite easy for
plane surfaces since holes can be defined in the expression list, but I
am interested in making a hole in a curved surface, specifically a hole
in a surface that was made by extruding a curve.  If cutting a hole in a
surface extruded from a spline is a problem, I can reformulate the
problem using a series of lines for the extrusion instead of a spline,
thus using a piecewise linear model of the curve (but it would still
involve many, many points, making defining the hole 'manually' using

On a similar topic, I am also learning if there is a way to merge 2D
meshes from two intersecting surfaces.  For example, in the problem
above, if I had a hole in a surface and wanted to attach a curved
surface to cover the hole, how would I go about defining the
geometry/mesh so that the mesh flows smoothly over the composite
surface?  If I were to use an example from the gmsh website, I would use
the famous fighter jet screen shot: the problem I am trying to solve is
very similar to trying to attach the canopy of the fighter jet to the
fuselage starting with two separate surfaces defining those two objects.

Any help on how to approach these tasks would be appreciated.

Thanks, and best regards,

Sean

```