cell shapes

guy_smiling · September 12, 2010, 15:24

I'm trying to use blockMesh (and create a blockMeshDict file) with keywords other than "hex". There seems to be conflicting documentation: in http://www.openfoam.com/docs/user/blockMesh.php I see that I need to have 8 vertices, and all blocks are inherently hexahedral; in order to make a prism I need to collapse two vertices, and still use hex.

However, here http://www.openfoam.com/docs/user/mesh-description.php apparently I can use any of these keywords listed (such as prism) to generate a prism with only 6 vertices. I have found that the keyword prism in blockMeshDict still gives me 8 vertices (two of which are garbage) or 7 (one of which is garbage) if I order the vertices in a wrong way.

Is there some way to get a different geometry besides hex in blockMesh? Does anyone know how to use blockMesh without just hex?

mturcios777 · September 13, 2010, 16:49

The cellShapes tools only apply when you writing your own mesh conversion utility, or using a mesh conversion utility. From the link you provided:

The vast majority of mesh generators and post-processing systems support only a fraction of the possible polyhedral cell shapes in existence. They define a mesh in terms of a limited set of 3D cell geometries, referred to as cell shapes. The OpenFOAM library contains definitions of these standard shapes, to enable a conversion of such a mesh into the polyMesh format described in the previous section.

blockMesh only ever uses hexes, and all other degenerate hexa are created by collapsing points. Hope this clears up your question.

September 12, 2010, 15:24	cell shapes	#1
guy_smiling New Member Join Date: Aug 2010 Posts: 11 Rep Power: 15	I'm trying to use blockMesh (and create a blockMeshDict file) with keywords other than "hex". There seems to be conflicting documentation: in http://www.openfoam.com/docs/user/blockMesh.php I see that I need to have 8 vertices, and all blocks are inherently hexahedral; in order to make a prism I need to collapse two vertices, and still use hex. However, here http://www.openfoam.com/docs/user/mesh-description.php apparently I can use any of these keywords listed (such as prism) to generate a prism with only 6 vertices. I have found that the keyword prism in blockMeshDict still gives me 8 vertices (two of which are garbage) or 7 (one of which is garbage) if I order the vertices in a wrong way. Is there some way to get a different geometry besides hex in blockMesh? Does anyone know how to use blockMesh without just hex?

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September 13, 2010, 16:49		#2
mturcios777 Senior Member Marco A. Turcios Join Date: Mar 2009 Location: Vancouver, BC, Canada Posts: 740 Rep Power: 28	The cellShapes tools only apply when you writing your own mesh conversion utility, or using a mesh conversion utility. From the link you provided: The vast majority of mesh generators and post-processing systems support only a fraction of the possible polyhedral cell shapes in existence. They define a mesh in terms of a limited set of 3D cell geometries, referred to as cell shapes. The OpenFOAM library contains definitions of these standard shapes, to enable a conversion of such a mesh into the polyMesh format described in the previous section. blockMesh only ever uses hexes, and all other degenerate hexa are created by collapsing points. Hope this clears up your question.