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[Gmsh] Gmsh. I want a mesh with Quadrangle (9 nodes instead of 8 nodes)

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Old   December 13, 2014, 15:59
Default Gmsh. I want a mesh with Quadrangle (9 nodes instead of 8 nodes)
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Guiliguili
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Hi,

I tried the Transfinite Surface "*" and Recombine Surface "*" to get Quadrangle9 but I still obtained 8 nodes instead of 9 nodes.
Please, how do I get only Quadrangle9 elements as illustrated below with gmesh command line?

3-----6-----2
7-----8-----5
0-----4-----1

Thanks.
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Old   July 5, 2016, 06:48
Default 8 node quads mesh
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Tshering Lhamo
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Hello, I don't know if it's too late. However, I wanted to ask if it is possible to generate 8 node quads elements mesh with GMSH. I have a file from Lagamine with only 8 node elements. Thank you
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Old   June 23, 2017, 12:17
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Hello,
If it's not too late you need a second order element (Check at http://gmsh.info/doc/texinfo/gmsh.ht...r-options-list)

Does Gmsh support curved elements? Yes, Gmsh can generate both 1st order and 2nd order elements. To generate second order elements, click on ‘High order’ in the mesh menu after the mesh is completed. To always generate 2nd order elements, select ‘Generate second order elements’ in the mesh option panel. From the command line, you can also use -order 2.


If you're using the command line, you will need first to combine triangles into rectangles by using Recombine function in the geometry file:
Recombine Surface { expression-list } | "*" < = expression >; Recombines the triangular meshes of the surfaces listed in expression-list into mixed triangular/quadrangular meshes. The optional expression on the right hand side specifies the maximum difference (in degrees) allowed between the largest angle of a quadrangle and a right angle (a value of 0 would only accept quadrangles with right angles; a value of 90 would allow degenerate quadrangles; default value is 45).

At last, from a command line:
gmsh t1.geo -3 -order 2 mesh.msh

where
t1.geo is you geometry file
-2 for a 2D
-order 2 for a second order element (-order int: set mesh order(1, ..., 5))
mesh.msh is the name of your output file
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