[Gmsh] Surface Patches on Extruded Surfaces (e.g.: Cylinder)

[David Colignon]

On 04/03/12 23:27, James Snyder wrote:
> I have looked around on the list a bit yesterday and have noticed that
> the question of doing intersections or surface patches has come up
> quite a few times.  I realize that Gmsh is not a solid modeler
> (although I might be interested in hearing of a simple, perhaps open
> source, command line, solid modeler that one could provide geometry to
> and get a file importable to Gmsh for meshing... is this essentially
> Open CASCADE?)

Hi James,

you can have a look at FreeCAD, http://sourceforge.net/projects/free-cad/ , which is based on OpenCascade. You can 
easily export your geometry in brep format and import it in Gmsh.

Regards,

Dave

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David Colignon, Ph.D.
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, and I've also seen that there is the ruled surface
> functionality that provides a mechanism for interpolating or pinning a
> patch to a sphere, but there isn't a convenient way of doing this with
> cylinders.
>
> For me this has become of interest for doing electrostatics
> simulations where one would like to have patches to define as
> electrodes rather than points or ad-hoc selection of neighboring faces
> to fit a geometry after mesh generation, e.g.:
> http://eidors3d.sourceforge.net/tutorial/netgen/netgen_gen_models.shtml
> or http://eidors3d.sourceforge.net/tutorial/EIDORS_basics/forward_solvers_3d.shtml
>
> What I've come to ask/suggest is perhaps something could be done with
> fields/attractors/thresholds for defining these patches?  Since this
> functionality already provides a way to control element sizes as a
> function of distance, including restrictions of whether to apply these
> parameters to given surfaces or volumes, could there not be a
> relatively simple way to define a patch from these or the code that is
> providing this functionality (with or without actually varying mesh
> density).  Maybe there's already a convenient way to select elements
> resulting from the current functionality just based on size and
> distance, but it would be nice to have form a clean line/arc rather
> than just selecting triangles under a given distance (either in the
> surface or euclidean distance would be fine).
>
> It seems like the easiest way to get the desired effects currently is
> to use splines where one calculates out the line/arc along curved
> surfaces and the resulting spline can be used, but this has some
> downsides in that I'm not completely sure if the splines really do
> always end up in the desired curved face.  It seems like if one uses
> enough or if the geometry is correct it may just fall below the
> threshold of complaint one might find from embedding a line in a
> surface if enough points are used?
>
> Best.
>
> -jsnyder
>
>
>