[Gmsh] creating patch on sphere

[Max Orok]

Hello Peter,

I took a bit of a different approach and hopefully it is similar to what
you'd like to do.
This short script makes a "sphere patch" by subtracting one sphere from
another.

SetFactory("OpenCASCADE");

// arbitrary angle selections here
Sphere(1) = {0, 0, 0, 0.5, -Pi/9, Pi/9, Pi/4};
Sphere(2) = {-.25, 0, 0, 0.5, -Pi/9, Pi/9, Pi/4}; // shift sphere 2

// use sphere 2 to cut sphere 1
BooleanDifference{ Volume{1}; Delete; }{ Volume{2}; Delete; }

[image: image.png]
[image: image.png]

I hope this is helpful! If I missed the point please let me know.

Sincerely,
Max

On Wed, Apr 24, 2019 at 7:22 PM Peter Johnston <p.johnston at griffith.edu.au>
wrote:

> Thanks Max and Christophe,
>
> I have attached a simple sample .geo file. For some reason it creates even
> more volumes than the more complicated script I was working on. However, it
> still displays similar problems.
>
> If you have any further questions, please let me know.
>
> Thanks again,
>
> Peter.
>
> ---------------------------------------------------------------------
>
> 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
> On 25 Apr 2019, 1:36 AM +1000, Max Orok <morok at mevex.com>, wrote:
>
> Hi Peter,
>
> Scripts are always helpful! It is nice to be able to see the steps as you
> go along.
>
> Max
>
> On Wed, Apr 24, 2019 at 8:36 AM Peter Johnston <p.johnston at griffith.edu.au>
> wrote:
>
>> 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.
>>
>> ---------------------------------------------------------------------
>>
>> 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
>> _______________________________________________
>> gmsh mailing list
>> gmsh at onelab.info
>> http://onelab.info/mailman/listinfo/gmsh
>>
>
>
> --
> Max Orok
> Contractor
> www.mevex.com
>
>
>

-- 
Max Orok
Contractor
www.mevex.com
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