[Gmsh] Strucutred mesh for 1/8th of a hollow sphere with quads and 8-node Hexahedron

[Rahul Sharma]

Hello,

I am trying to mesh 1/8th of a hollow sphere which consists of three plane
surfaces and two ruled surfaces, I am trying to get a mesh with all quads
and 8-node Hexahedron elements however when I use transfinite surface and
recombine surface and volume command ,tip of the sphere section is
converted into prism elements that is what I don't want.

Please take a look at the geo file

Point(1)  = {0, 0, 0, 1};
Point(2)  = {1, 0, 0, 1};
Point(3)  = {2, 0, 0, 1};
Point(4)  = {0, 1, 0, 1};
Point(5)  = {0, 2, 0, 1};
Point(6)  = {0, 0, 1, 1};
Point(7)  = {0, 0, 2, 1};

Line(1) = {4, 5};
Line(2) = {2, 3};
Line(3) = {6, 7};
Circle(4) = {5, 1, 3};
Circle(5) = {3, 1, 7};
Circle(6) = {5, 1, 7};
Circle(7) = {4, 1, 2};
Circle(8) = {2, 1, 6};
Circle(9) = {4, 1, 6};

Line Loop(10) = {6, -3, -9, 1};
Plane Surface(11) = {10};
Line Loop(12) = {1, 4, -2, -7};
Plane Surface(13) = {12};
Line Loop(14) = {3, -5, -2, 8};
Plane Surface(15) = {14};
Line Loop(16) = {9, -8, -7};
Ruled Surface(17) = {16};
Line Loop(18) = {6, -5, -4};
Ruled Surface(19) = {18};

Surface Loop(20) = {19, 11, 15, 13, 17};
Volume(21) = {20};

Transfinite Line{1:3}     = 3 Using Progression 1;
Transfinite Line{4,6,7,9} = 6 Using Progression 1;
Transfinite Line{5,8}     = 7 Using Progression 1;

Transfinite Surface{11,13,15,17,19};
Recombine Surface{11,13,15,17,19};

Transfinite Volume{21};
Recombine Volume{21};

--------------------------------------
The mesh I want is similar to this (
http://res.cloudinary.com/engineering-com/image/upload/v1437412966/tips/Mesh_Sphere_h01ftf.jpg
).

Looking forward to your comments. Thanks in advance.

-- 
Warm Regards,

*Rahul Sharma*
Graduate Student
Structural Optimization and computaion mechanics
Delft University of Technology
Netherlands
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