[Gmsh] creating patch on sphere

[Peter Johnston]

Hello,

I appear to have a problem for which I cannot figure out a solution.

I have an annular hemispherical volume created between to hemispheres centred on the origin. I would like to divide the volume into two parts in a special way using Boolean operations. To define a sub-volume of the initial volume by defining four points on the surface of the inner sphere, create a “quadrilateral” on the inner surface by joining the four points in order using circles through the origin. (I think that these should be parts of great circles on the inner surface?). Then I create a line loop and a surface, and finally extrude the surface away from the origin to create a volume. Perhaps a .geo script would help here?

When I perform BooleanDifferences and BooleanIntersections I end up with three volumes instead of two. The reason I get the third volume is that the surface patch that I create does not fit exactly onto the original spherical surface. Is there any way that I can force the patch to be part of the spherical surface?

A consequence of the extra volume is that I cannot create a sensible mesh.

Any ideas would be greatly appreciated.

Thanks very much,

Peter.

PS, I could send a simple script file if that would help.

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Associate Professor Peter Johnston (FAustMS, FIMA)
School of Environment and Science
Griffith University | Nathan | QLD 4111 | Technology (N44) Room 3.19
T +61 7 373 57748| F +61 7 373 57656 Email p.johnston at griffith.edu.au
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