[Gmsh] Problems with structured meshing

[Christophe Geuzaine]

> On 15 Oct 2016, at 19:02, Kushagra Vidyarthi <kushagra.vidyarthi at ymail.com> wrote:
> 
> Dear Sir/Madam,
> 
> I am working on a CFD analysis around an ellipse. For this purpose, I have created a circular domain around the geometry, and I am trying to create a structured mesh around it, so that I can have some control over the boundary layer. My .geo file is below:
> 
> // Gmsh project created on Fri Oct 14 10:40:40 2016
> 
> //geometry creation
> //ellipse: major axis 0.075, minor axis 0.009375
> // 1st arc
> Point(1) = {-0.0375, 0, 0, 0.01};
> Point(2) = {0, 0, 0, 0.01}; //global center
> Point(3) = {-0.02, 0, 0, 0.1};
> Point(4) = {-0.026516504, 0.003314563, 0, 0.01};
> Ellipse(1) = {1, 2, 3, 4};
> 
> //arc 2
> Point(5) = {0, 0.0046875, 0, 0.01};
> Point(6) = {0.02, 0, 0, 0.01};
> Ellipse(2) = {4, 2, 3, 5};
> 
> //arc3
> Point(7) = {0.026516504, 0.003314563, 0, 0.01};
> Ellipse(3) = {5, 2, 6, 7};
> 
> //arc4
> Point(8) = {0.0375, 0, 0, 0.01};
> Ellipse(4) = {7, 2, 6, 8};
> 
> //arc5
> Point(9) = {0.026516504, -0.003314563, 0, 0.01};
> Ellipse(5) = {8, 2, 6, 9};
> 
> //arc6
> Point(10) = {0, -0.0046875, 0, 0.01};
> Ellipse(6) = {9, 2, 6, 10};
> 
> //arc7
> Point(11) = {-0.026516504, -0.003314563, 0, 0.01};
> Ellipse(7) = {10, 2, 3, 11};
> 
> //arc8
> Ellipse(8) = {11, 2, 3, 1};
> 
> //circle
> Point(12) = {-1.7677669, -1.7677669, 0, 0.01};
> Point(13) = {-1.7677669, 1.7677669, 0, 0.01};
> Point(14) = {1.7677669, 1.7677669, 0, 0.01};
> Point(15) = {1.7677669, -1.7677669, 0, 0.01};
> 
> Circle(9) = {12, 2, 13};
> Circle(10) = {13, 2, 14};
> Circle(11) = {14, 2, 15};
> Circle(12) = {15, 2, 12};
> 
> //blocking lines
> Line(13) = {11, 12};
> Line(14) = {4, 13};
> Line(15) = {7, 14};
> Line(16) = {9, 15};
> 
> //splitting lines
> Transfinite Line {9} = 100 Using Progression 1;
> Transfinite Line {10} = 100 Using Progression 1;
> Transfinite Line {11} = 100 Using Progression 1;
> Transfinite Line {12} = 100 Using Progression 1;
> Transfinite Line {14} = 100 Using Progression 1;
> Transfinite Line {15} = 100 Using Progression 1;
> Transfinite Line {16} = 100 Using Progression 1;
> Transfinite Line {13} = 100 Using Progression 1;
> Transfinite Line {8} = 100 Using Progression 1;
> Transfinite Line {1} = 100 Using Progression 1;
> Transfinite Line {2} = 100 Using Progression 1;
> Transfinite Line {3} = 100 Using Progression 1;
> Transfinite Line {4} = 100 Using Progression 1;
> Transfinite Line {5} = 100 Using Progression 1;
> Transfinite Line {6} = 100 Using Progression 1;
> Transfinite Line {7} = 100 Using Progression 1;
> Line Loop(17) = {13, 9, -14, -1, -8};
> Plane Surface(1) = {17};
> Line Loop(19) = {15, -10, -14, 2, 3};
> Plane Surface(2) = {19};
> Line Loop(21) = {16, -11, -15, 4, 5};
> Plane Surface(3) = {21};
> Line Loop(23) = {13, -12, -16, 6, 7};
> Plane Surface(4) = {23};
> Transfinite Surface {1} = {4, 13, 12, 11};
> Transfinite Surface {2} = {7, 14, 13, 4};
> Transfinite Surface {3} = {9, 15, 14, 7};
> Transfinite Surface {4} = {11, 12, 15, 9};
> 
> Recombine Surface {1};
> Recombine Surface {2};
> Recombine Surface {3};
> Recombine Surface {4};
> 
> When I run this file in gmsh, I get errors like: "Error   : Surface 4 cannot be meshed using the transfinite algo". I also get a warning stating: "Warning : Cannot apply Blosson: odd number of triangles (15167) in surface 4". My error log and .geo files are attached. Please advise on what I can do to fix these errors.
> 

Transfinite Surface meshes require matching number of vertices on opposite sides. Add e.g. this to your file:

N = 10;
Transfinite Line {1:8} = N;
Transfinite Line {9:12} = 2*N-1;
Transfinite Line {13:16} = 50 Using Progression 1.2;


> Thanks and Regards,
> 
> Kushagra Vidyarthi
> 
> <ellipse+domain_geom_o-grid (copy)-msgs.geo><ellipse+domain_geom_o-grid (copy).geo>_______________________________________________
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-- 
Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science 
http://www.montefiore.ulg.ac.be/~geuzaine

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