[Gmsh] Holes in curved surfaces / merging surfaces

[Sean Victor Hum]

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 
multiple extrusions a daunting task.

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