[Gmsh] Trying to create a structured quad mesh in 2D

[Christophe Geuzaine]

On 05 Nov 2012, at 14:36, Jorge Milhazes <milhazes at gmail.com> wrote:

>    Hello!
>    I'm new to Gmsh and I've been struggling with structured meshes. I
> read the hex.geo example and when I try to apply same rule with
> transfinite+recombine surface I get almost-squared elements with
> distortions here and there.

A single transfinite interpolation will get you a pretty poor mesh

(Just define Transfinite Surface {30} = {1,4,2,3}; and set e.g. Mesh.Smoothing = 500;)

If you want a fully regular mesh, you'll have to subdivide the surface into pieces.

Otherwise you can recombine an unstructured triangular mesh, using Blossom.



>    I'm using the all-quads subdivision algorithm and tried Delaunay
> for quads and frontal with no success. Bellow is my code. Will be glad
> if someone could help me with this.
>    Cheers,
> 
>    Jorge Milhazes
> 
> 
>    ##################
> 
>    cl1 = 1;
> Point(1) = {0, 0, 0, cl1};
> Point(2) = {0.9, 0.9, 0, cl1};
> Point(3) = {0, 0.9, 0, cl1};
> Point(4) = {0.9, 0, 0, cl1};
> Point(5) = {0.9, 0.4, 0, cl1};
> Point(6) = {0.9, 0.425, 0, cl1};
> Point(7) = {0.9, 0.6, 0, cl1};
> Point(8) = {0.9, 0.625, 0, cl1};
> Point(9) = {0.9, 0.8, 0, cl1};
> Point(10) = {0.9, 0.825, 0, cl1};
> Point(11) = {0.75, 0.4, 0, cl1};
> Point(12) = {0.75, 0.425, 0, cl1};
> Point(13) = {0.75, 0.6, 0, cl1};
> Point(14) = {0.75, 0.625, 0, cl1};
> Point(15) = {0.75, 0.8, 0, cl1};
> Point(16) = {0.75, 0.825, 0, cl1};
> Point(17) = {0, 0.4, 0, cl1};
> Point(18) = {0, 0.425, 0, cl1};
> Point(19) = {0, 0.6, 0, cl1};
> Point(20) = {0, 0.625, 0, cl1};
> Point(21) = {0, 0.8, 0, cl1};
> Point(22) = {0, 0.825, 0, cl1};
> Point(23) = {0.15, 0.4, 0, cl1};
> Point(24) = {0.15, 0.425, 0, cl1};
> Point(25) = {0.15, 0.6, 0, cl1};
> Point(26) = {0.15, 0.625, 0, cl1};
> Point(27) = {0.15, 0.8, 0, cl1};
> Point(28) = {0.15, 0.825, 0, cl1};
> Line(1) = {1, 17};
> Transfinite Line {1} = 17Using Bump 1;
> Line(2) = {17, 23};
> Transfinite Line {2} = 7Using Bump 1;
> Line(3) = {23, 24};
> Line(4) = {24, 18};
> Transfinite Line {4} = 7Using Bump 1;
> Line(5) = {18, 19};
> Transfinite Line {5} = 8Using Bump 1;
> Line(6) = {19, 25};
> Transfinite Line {6} = 7Using Bump 1;
> Line(7) = {25, 26};
> Line(8) = {26, 20};
> Transfinite Line {8} = 7Using Bump 1;
> Line(9) = {20, 21};
> Transfinite Line {9} = 8Using Bump 1;
> Line(10) = {21, 27};
> Transfinite Line {10} = 7Using Bump 1;
> Line(11) = {27, 28};
> Line(12) = {28, 22};
> Transfinite Line {12} = 7Using Bump 1;
> Line(13) = {22, 3};
> Transfinite Line {13} = 4Using Bump 1;
> Line(14) = {4, 5};
> Transfinite Line {14} = 17Using Bump 1;
> Line(15) = {5, 11};
> Transfinite Line {15} = 7Using Bump 1;
> Line(16) = {11, 12};
> Line(17) = {12, 6};
> Transfinite Line {17} = 7Using Bump 1;
> Line(18) = {6, 7};
> Transfinite Line {18} = 8Using Bump 1;
> Line(19) = {7, 13};
> Transfinite Line {19} = 7Using Bump 1;
> Line(20) = {13, 14};
> Line(21) = {14, 8};
> Transfinite Line {21} = 7Using Bump 1;
> Line(22) = {8, 9};
> Transfinite Line {22} = 8Using Bump 1;
> Line(23) = {9, 15};
> Transfinite Line {23} = 7Using Bump 1;
> Line(24) = {15, 16};
> Line(25) = {16, 10};
> Transfinite Line {25} = 7Using Bump 1;
> Line(26) = {10, 2};
> Transfinite Line {26} = 4Using Bump 1;
> Line(27) = {1, 4};
> Transfinite Line {27} = 37Using Bump 1;
> Line(28) = {3, 2};
> Transfinite Line {28} = 37Using Bump 1;
> Line Loop(30) = {28, -26, -25, -24, -23, -22, -21, -20, -19, -18, -17,
> -16, -15, -14, -27, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13};
> Plane Surface(30) = {30};
> Transfinite Surface {30};
> Recombine Surface {30};
> Physical Line(0) = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13};
> cl1 = 1;
> Physical Line(cl1) = {14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26};
> Physical Line(2) = {27};
> Physical Line(3) = {28};
> Physical Surface(35) = {30};
> 
>    ####################
> 
> _______________________________________________
> gmsh mailing list
> gmsh at geuz.org
> http://www.geuz.org/mailman/listinfo/gmsh

-- 
Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science 
http://www.montefiore.ulg.ac.be/~geuzaine