Unstructured Grid, 3d Face Swapping
Hello;
What is a good criteria for a triangular face of a tetrahedron unstructured cell to be swapped? Any information on tetrahedron face swapping is greatly appreciated. Thank You, Saied 
Re: Unstructured Grid, 3d Face Swapping
(1). I am not sure whether we are talking about the same thing or not. (2). If you have a pair of triangular surfaces sharing a long common edge, then the skewness of both triangles will be high. (3). By swapping the diagonal common edge, the resultant triangles will have lower skewness, still using the same original four vertices. (4). If this is not your question, then please define the "swapping" more clearly.

Re: Unstructured Grid, 3d Face Swapping
Dear John, thank you for respondig. Yes, we are talking about the same thing. 1 replacing a common face between two tetrahedral cells 2 by connecting the opposite (diagonal) vertices to form a new edge and 3 creating three new faces that all share this new edge. The question is: When do we do this? What should be the criteria to swap? should I only consider the skewness of the face? or its relation with other faces has to be taken into account

Re: Unstructured Grid, 3d Face Swapping
(1). To make it simple, you can go through the loop once. And then come back second time to do the second loop, and so on. Until, there is no more triangles to swap. (based on the skewness, I hope. Unless you have some new ideas?)

Re: Unstructured Grid, 3d Face Swapping
How can we be certain that the new edge passes through the original face? Would the three new cells replacing the two old cells have equivelent total volume? How is a skewed face defined?(two edges being larger than a third edge by a factor for example. If so what is a good factor?)

Re: Unstructured Grid, 3d Face Swapping
(1). Well, if a trangle has three equal edges, then it it not skewed. The angle between two edges is 60 degrees. (2). Sometimes it is easier to use the minimum angle to set the requirement, for example, 20 degrees as a minimum. I guess, it depends on the solver, whether it can handle it accurately or not with certain skewness. (3). You may have to read the user's manual of a particular code to find out the specific definition of the skewness. (4). In 2D, when you swap the edges, the two new triangles are brand new. So, they will have completely different properties of their own. (hopefully better than the original triangles.)

Re: Unstructured Grid, 3d Face Swapping
Dear John, I am intrested in 3d, thank you

Re: Unstructured Grid, 3d Face Swapping
Hi,
I am still working on the 2D swapping problem. It appears to me that edge swapping in 2D is a very sensitive process. For example, if I have an isotropic mesh, and then introduce a matrix which can result in grids at any aspect ratio I need. I find that for aspect ratio >10, edge swapping itself can result in a very bad mesh, while AR < 10, it works pretty well together with edge splitting and node removal. I don't which kind of application you are doing, hope it helps. Guoping 
Re: Unstructured Grid, 3d Face Swapping
Hi,
Paul Louis George's book on Delaunay triangulation might be interesting for you: PaulLouis George, Houman Borouchaki: Delaunay Triangulation and meshing. Editions Hermes (1998), ISBN 2866016920. http://www.editionshermes.fr/Wlivre.asp?qid=934 Best regards, Robert Robert Schneiders MAGMA Giessereitechnologie GmbH D52072 Aachen Kackertstr. 11 Germany Tel.: +492418890113 email: R.Schneiders@magmasoft.de www: http://wwwusers.informatik.rwthaachen.de/~roberts/ 
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