> On 09 Feb 2016, at 21:21, Kópházi József <[email protected]> wrote:
>
> Dear list members,
>
> I have encountered some unusual behavior while trying to generate a very
> simple structured tetrahedral mesh for two boxes. The attached images show
> the surface (triangle) and volumetric (tetrahedron) elements of the same
> mesh. However, some of the triangles do not "sit" properly on the face of the
> corresponding tetrahedron but they are "laid across" on two tetrahedra. This
> is marked with red arrows on the images. I have also attached the script
> resulting this mesh.
>
Yes : the "Transfinite Volume" algorithm in automatic mode (when the corner
vertices are not explicitly specified) will not try to match the surface mesh
(because in some cases it's impossible, depending on the surface mesh). Without
"Recombine" you should thus specify the orientions by hand:
lc = 0.3;
// example of a purely hexahedral mesh using only transfinite
// mesh constraints
Point(1) = {-2,0,0,lc};
Point(2) = {-1,0,0,lc};
Point(3) = {-1,1,0,lc};
Point(4) = {-2,1,0,lc};
Point(5) = {-2,0,1,lc};
Point(6) = {-1,0,1,lc};
Point(7) = {-1,1,1,lc};
Point(8) = {-2,1,1,lc};
Line(1) = {4,3};
Line(2) = {3,2};
Line(3) = {2,1};
Line(4) = {1,4};
Line(6) = {5,6};
Line(7) = {6,7};
Line(8) = {7,8};
Line(9) = {8,5};
Line(10) = {1,5};
Line(11) = {4,8};
Line(12) = {2,6};
Line(13) = {3,7};
Line Loop(14) = {3,4,1,2};
Plane Surface(15) = {14};
Line Loop(16) = {6,7,8,9};
Plane Surface(17) = {16};
Line Loop(18) = {10,-9,-11,-4};
Plane Surface(19) = {18};
Line Loop(20) = {8,-11,1,13};
Plane Surface(21) = {20};
Line Loop(22) = {12,7,-13,2};
Plane Surface(23) = {22};
Line Loop(24) = {6,-12,3,10};
Plane Surface(25) = {24};
Surface Loop(1) = {17,-25,-23,-21,19,15};
Volume(1) = {1};
Transfinite Line{1:4,6:13} = 5;
// need to specify orientation (through vertex list) by hand to have correctly
// matching volume/surface edges
Transfinite Surface {15} = {1,2,3,4};
Transfinite Surface {17} = {5,6,7,8};
Transfinite Surface {19} = {1,5,8,4};
Transfinite Surface {21} = {4,8,7,3};
Transfinite Surface {23} = {2,6,7,3};
Transfinite Surface {25} = {1,5,6,2};
Transfinite Volume{1} = {1,2,3,4,5,6,7,8};
Note that it's often less tedious to use "Extrude" with "Layers" instead of
Transfinite.
Christophe
> I generated these pictures using gmsh version 2.9.1 but some other versions
> also produce the same problem.
>
> Thank you for your help,
>
> Jozsef Kophazi
>
>
> <surfaces marked.png><twobox.geo><volumes
> marked.png>_______________________________________________
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--
Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science
http://www.montefiore.ulg.ac.be/~geuzaine
Tetrahedron V, July 4-5 2016: http://tetrahedron.montefiore.ulg.ac.be
Free software: http://gmsh.info | http://getdp.info | http://onelab.info
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