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-   -   Cracks in 2D grid (https://www.cfd-online.com/Forums/siemens/52952-cracks-2d-grid.html)

jonw June 27, 2002 16:47

Cracks in 2D grid
 
I'm just starting out with STAR-CD.

When I enter a patch with variable spacing in both the x and y directions and then extrude them, I get cracks near the edges where the cells are thinly spaced.

Why is this and how can I fix it?

Thanks

Jon

Jamie June 27, 2002 19:02

Re: Cracks in 2D grid
 
before you extrude the patch, try smoothng the vertices using the vsmooth command. for more information type 'help vsmooth' on the command line.

Anton Lyaskin July 1, 2002 10:10

Re: Cracks in 2D grid
 
It's an error in checking algorithm. If you are sure that there are no actual cracks there you can just ignore it.

Karim Loueslati July 1, 2002 11:54

Re: Cracks in 2D grid
 
Compress the Cell Delete the unused vertices and compress the vertices The matter would be eliminated

Jiaying Xu July 4, 2002 15:05

Re: Cracks in 2D grid
 
Hello,

I encounter a similiar problem. I built up everything and run the simulations fine. But after I refine the grid, I got cracks.

I have to say, I *did* compress the cells and merged vertexes.

Is this like what Anton Lyaskin said an unreal error message due to the wrong algorithm of checking cells?

Thanks,

JY

LOUESLATI Karim July 5, 2002 04:00

Re: Cracks in 2D grid
 
Hi,

In your case, it's possible that the "false crack" was due to the refinement algorithm or probably because you didn't choose the create couple option in the refinement command.

Jiaying Xu July 5, 2002 06:39

Re: Cracks in 2D grid
 
I *did* choose the couple option 1 before doubling the mesh. I think it is proper.

Also, I collect the "crack" cells after the cell check and zoom out to see the detail. But I could not find anything strange.

Any idea? (May I just igonre as Anton said?)

Thanks,

Jiaying


LOUESLATI Karim July 5, 2002 06:45

Re: Cracks in 2D grid
 
My only last idea is the following : select the all entire cells select attached vertices invert the vertices selection delete (+merge +compress)this last selection if not empty After : merge couple and compress it launch the check tools

What did u got ??

Karim

Anton Lyaskin July 9, 2002 03:58

Re: Cracks in 2D grid
 

Anton Lyaskin July 9, 2002 04:12

Re: Cracks in 2D grid
 
Sorry for the empty post above. I just want to ask, which version do you use? I've had such problems with versions 3.10, 3.10a and early releases of 3.10b. Looks like later the algorithm was corrected.

To my mind the error comes from the nature of crack test - ProSTAR takes a point in the center of every cell face, moves it along the outer normal for some small value "delta" and if it resides in the neighbore cell than there is no crack. In your case the thickness of the cell is less than "delta".

You can try a simple check: "Enlarge" your model (using vscale command) say 1000 times and check it again. If there will be no crack than it's an error in the algorithm and you'll just have to set the geometry scale factor 0.001 before you'll run the calculation.

Regards, Anton


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