# Structured meshing in Gmsh

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 May 10, 2011, 16:31 Structured meshing in Gmsh #1 New Member   Matt Join Date: May 2011 Posts: 2 Rep Power: 0 After some digging online, it appears there are only two ways to generate a structured mesh in Gmsh; extrusion and applying "Recombine Surface" on an unstructured surface. Here is my simple mesh, that I am trying to mesh structured: cl1 = 0.5; cl2 = 0.002; cl3 = 0.005; Point(1) = {23.5, 0.02, 0, cl1}; Point(2) = {23.5, 10, 0, cl1}; Point(3) = {59.5, 10, 0, cl2}; Point(4) = {59.5, 0.02, 0, cl1}; Point(5) = {0, 0, 0, cl1}; Point(6) = {0, 23.75, 0, cl1}; Point(7) = {24, 23.75, 0, cl1}; Point(8) = {16.052083, 14.122111, 0, cl3}; Point(9) = {24, 14.122111, 0, cl1}; Point(10) = {16.052083, 14.059611, 0, cl1}; Point(11) = {16, 14.025063, 0, cl3}; Point(13) = {23.5, 19, 0, cl1}; Point(14) = {16.017535, 14.111694, 0, cl3}; Line(1) = {2, 1}; Line(2) = {2, 3}; Transfinite Line {2} = 72Using Progression 1; Line(3) = {3, 4}; Line(4) = {4, 1}; Transfinite Line {4} = 72Using Progression 1; Line(5) = {1, 5}; Line(6) = {5, 6}; Line(7) = {6, 7}; Line(8) = {9, 7}; Line(9) = {8, 9}; Transfinite Line {1,3,8} = 45 Using Progression 1.2; Transfinite Line {5,6,7} = 49Using Progression 1.0; Transfinite Line {9} = 55Using Progression 1.1; Circle(10) = {11, 13, 2}; Transfinite Line {10} = 65Using Progression 1.07; Circle(11) = {11, 10, 14}; Transfinite Line {11} = 19Using Progression 1.0; Circle(12) = {14, 10, 8}; Transfinite Line {12} = 9Using Progression 1.0; Line Loop(1) = {-1, 2, 3, 4}; Plane Surface(1) = {1}; Transfinite Surface {1} = {1,2,3,4}; Recombine Surface {1}; Line Loop(2) = {1, 5, 6, 7, -8, -9, -12, -11, 10}; Plane Surface(2) = {2}; Physical Line(13) = {5, 6, 7}; Physical Line(14) = {9, 12, 11, 10}; Transfinite Surface {2} = {1,13,8,14}; Recombine Surface {2}; As you can see, Surface 1 recombines properly into a nice structured domain, but on Surface 2, the Recombine algorithm fails. As far as I can tell, the four entities that make up the boundary of Surface 2 (1,13,8,14) should form a structured half O-mesh around the lip feature, with dimensions 145x45. What am I doing wrong? Thanks P.S.-Structured meshing seems very cumbersome in Gmsh; can anyone recommend a free meshing program that is more conducive to structured meshes?

 September 18, 2011, 07:44 #2 New Member   jb Join Date: Jun 2009 Posts: 10 Rep Power: 9 Hello Matt, The surface 2 of your model has 9 lines as boundary. You can create structured mesh only on surfaces defined by 3 or 4 border lines. The only way for you, in that example, is to divide the surface 2 into smaller surfaces, and apply the transfinite/recombine command on them. Yes, you are right: structured meshing is very cumbersome, but that is a general fact. An alternative is the unstructured quadrilateral meshing. For instance, the Q-Morph algorithm provides unstructured quadrilateral meshes with well-aligned rows of quadrilaterals parallel to the boundary of the domain. In my album "Q-Morph example 1" you will find pictures of the application of the Q-Morph algorithm on the surface 2 of your domain. For more informations, see the following thread: Q-Morph: an unstructured quadrilateral mesh generator embedded in gmsh. Regards, JB

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