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-   -   find degenerated cells (http://www.cfd-online.com/Forums/cd-adapco/54527-find-degenerated-cells.html)

Pete April 19, 2005 03:38

find degenerated cells
 
I have made a mesh with proam. Unfortunately there are some ployhedral cells which have 5 edges. For some reasons I cannot use the boundaries attached to these cells. So I have got two questions: - how can I find these cells? - is there a way to remesh these cells for exmaple with tetrahedrals?

Volker April 19, 2005 05:12

Re: find degenerated cells
 
Tricky one. You can do a boundary check, but I am not sure if the faulty boundaries will be put into a bset. You will definitely get a list of them on your screen maybe together with the attached cells. You can put them in a set with

bset news blis

or cset news clis.

From the bset you get to the cells by

vset news bset

cset news vset face

This can be very tedious if you have lots of those boundaries. Once you got your problem cells you could either remesh them as tets or fix them by hand (e.g. split them into tets, hexas or prisms). If you have the problem on your inlet/outlet, you could just extrude one cell layer and redefine your boundaries. Hope that helps,

volker

Pete April 19, 2005 06:32

Re: find degenerated cells
 
thanks, volker

but bcheck did not find these cells. but i have got them with the trimmed option in cset.

how can I split trimmed cells in tets without deleting them by hand?

Volker April 22, 2005 05:49

Re: find degenerated cells
 
You can use the tetgen command in proam to do this. Take the cell you want to replace (and maybe the cells around this one) and create a surface around them with livesurf. Check that this surface has no errors (self-intersection, orientation, cuts), then run tetgen. You have to have a fluid cell type active when you do that. It is advisable to give the cells you want to replace a new cell ID. When you have your new tets, delete the old cells and connect the new cells to the rest of the mesh. Alternatively you can use TetFix in Mesh Tools. It's made for unresolved cells but it should work for your problem as well, if you give your bad cells the ID 2. Alternatively, use the cdx command to generate new cells by hand. Most of the times you can replace your trimmed cell by a few standard shape cells. Just get your bad cell and the neighbouring cells, delete the bad cell and fill the hole with new cells with:

setadd, on

ctype, 1 (or whatever ID you choose)

cdx, hexa (or tetr or prism...)

cplot

When you do the cdx you have to be careful to choose the vertices in the right order (see Appendix A in the proam User guide). This method has the advantage of fewer cells and total control over the quality of your newly generated cells. It's a bit tricky the first time you do it, but it's worth getting used to if you regularly work with trimmed meshes.

Good luck,

Volker


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