# How to make sure the mesh numbers are the same for two identical faces?

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April 23, 2012, 23:16
How to make sure the mesh numbers are the same for two identical faces?
#1
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Join Date: Apr 2012
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Hi guys. I'm having some problems with Gambit.

I'm trying to mesh a half cylinder (I have several hundreds of this kind of structure in my case). I started with meshing the top and bottom faces. I selected these two faces at the same time (I didn't mesh the lines of the half circle first) and use the "Mesh Faces" option. And I got some funny results. The mesh numbers of these two faces are different. One is 26 and the other is 28.

As you can see in the attached file, the total interval numbers of the lines of these two half circles are exactly the same. But the interval numbers for the two bottom lines and for the half circles are different. Is there any ways to solve the problem? I know one solution is to mesh the lines first to make sure the interval numbers are always the same for the same types of lines. But like I said, I have hundreds of half cylinders in my case. It would be more time-saving if I can directly mesh the faces. Thanks for your kind help in advance.
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April 24, 2012, 01:20
#2
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Lucky Tran
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Quote:
 Originally Posted by beastieboys6 Hi guys. I'm having some problems with Gambit. I'm trying to mesh a half cylinder (I have several hundreds of this kind of structure in my case). I started with meshing the top and bottom faces. I selected these two faces at the same time (I didn't mesh the lines of the half circle first) and use the "Mesh Faces" option. And I got some funny results. The mesh numbers of these two faces are different. One is 26 and the other is 28. As you can see in the attached file, the total interval numbers of the lines of these two half circles are exactly the same. But the interval numbers for the two bottom lines and for the half circles are different. Is there any ways to solve the problem? I know one solution is to mesh the lines first to make sure the interval numbers are always the same for the same types of lines. But like I said, I have hundreds of half cylinders in my case. It would be more time-saving if I can directly mesh the faces. Thanks for your kind help in advance.
Do you need to mesh both faces for any reason? If the mesh is extruded, the opposite face should be left free so that the extrusion can be copied to it.

You can link/group edges together so that whatever is applied to one edge is automatically applied to the other. From the edge pane (it is the bottom left, underneath mesh edge). Pay attention to the edge direction (the arrows). You want the arrows to point in the same pattern (usually means the arrows are pointing in same direction). Other than that the only option is to mesh the edges directly.

 April 26, 2012, 21:00 #3 New Member   Join Date: Apr 2012 Posts: 16 Rep Power: 6 Thanks for your suggestions. They are very helpful. Now I finally know what the "Link Edge" option is for. One more question, if I want to extrude the mesh from one side to the other, I should choose Cooper scheme. Is that right? And if I want to go with Cooper Scheme, then I should use "Quad" element, rather than "Tri" element. Which one is better between "Quad" and "Tri" elements to mesh a circle or half a circle? Or there will not be any difference if the mesh desnity and quality is good enough? Thanks for your kind help again.

April 26, 2012, 21:13
#4
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Quote:
 Originally Posted by beastieboys6 Thanks for your suggestions. They are very helpful. Now I finally know what the "Link Edge" option is for. One more question, if I want to extrude the mesh from one side to the other, I should choose Cooper scheme. Is that right? And if I want to go with Cooper Scheme, then I should use "Quad" element, rather than "Tri" element. Which one is better between "Quad" and "Tri" elements to mesh a circle or half a circle? Or there will not be any difference if the mesh desnity and quality is good enough? Thanks for your kind help again.
Cooper mesh is correct. If you cannot do a direct mapped mesh of all quads, then copper mesh is the next best thing you can do.

Quad is always preferred to Tri but sometimes meshing in quad is not possible (for complicated geometries). When the meshing is complex, tri is needed to maintain reasonable mesh quality. In general, less cells are needed for a quad mesh than a tri mesh of similar quality, so that is why quad is preferred. Likewise, for quad and tri mesh of similar cell sizes, quad mesh normally has better quality. Many more and smaller tri cells are needed for an equivalent quad mesh (if quad is possible).

For complicated geometries, using quads to form a hexahedral mesh is an art. Usually many control edges are added in order to form a set of unstructured blocks that are each structured so that purely quad mapped meshes can be used inside each block. It is sometimes difficult but definitely worth it, if done properly.

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