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-   -   [ICEM] negative mesh volume problem (icem-cfd/cfx) (http://www.cfd-online.com/Forums/ansys-meshing/67000-negative-mesh-volume-problem-icem-cfd-cfx.html)

adam2008 July 30, 2009 15:01

negative mesh volume problem (icem-cfd/cfx)
 
hi,
Got an error as below in CFX. I am using Icem-CFD to generate mesh. But in Icem-cfd, i already did smoothing and all determinant values in icem-cfd are above zero. I am wondering, how can I find this mesh problem in icem-cfd? Which mesh quality parameter should i check in icem-cfd? Because each time, cfx takes a long time to read in icem-cfd mesh due to large size, it is really waste of time when this error comes out. So if I can know this problem in icem-cfd, that would be very helpful. thanks a lot


ERROR #002100012 has occurred in subroutine cVolSec. |
| Message: |
| A negative ELEMENT volume has been detected. This is a fatal |
| error and execution will be terminated. The location of the first |
| negative volume is reported below. |
| Volume : -0.5637E-12 |
| Location : ( 0.10718E+01, 0.61251E-02, -0.61110E-01)

PSYMN July 31, 2009 13:53

Check the unstructured mesh before exporting...
 

I asked around to be sure, but we are guessing that you did the check in ICEM CFD on the Pre-mesh and not the Unstructured mesh.



We recommend that you do your mesh checks on the unstructured mesh before outputting to an unstructured solver…


For some reason, checking the mesh before this conversion is made does not always show the same errors you will find in an unstructured solver (like CFX).



I am guessing that the problem is in a refined boundary layer. You probably have a misalignment of parts (curves not aligned with surfaces to the same tolerance as your first cell height) and the mesh is trying to follow too closely. In certain situations, this can invert the boundary layer in the last element when projection changes from one entity to the other. If that is what you find, setting projection limit can really help.



Josh April 14, 2010 19:42

Simon -

I did check on the unstructured mesh and found negative elements, likely because of the sharp airfoil-wall interaction in my domain as seen below.

http://img90.imageshack.us/img90/459...ttempt1.th.jpg

Here are the volume check results:

http://img72.imageshack.us/img72/816...empt4negat.jpg

As you can see, the negative volumes interact primarily at the leading and trailing edges of the rotor I am studying.

How would you recommend eliminating these negative elements? I haven't performed any smoothing in these pictures, though when I performed orthogonality smoothing (it's a hexa mesh), the negative element issue was worsened.

mbell10 April 15, 2010 06:32

is there a chance that your mesh isnt interfacing correctly causing your negative volumes?

Josh April 15, 2010 15:00

I appreciate your prompt response, Mark, though I'm not sure what you mean by "interfacing correctly."

As I mentioned in the other thread you replied to, there appears to be both degenerative elements (e.g. the one shown below) and negative volume elements.

http://img515.imageshack.us/img515/5...t4degen.th.jpg

Also, there is a poor interaction between the inflated boundary on the blade surface and the structured H-grid preceding it. The second picture is zoomed-in to the stagnation point.

http://img138.imageshack.us/img138/6...ttempt4.th.jpg

http://img59.imageshack.us/img59/256...t4stagn.th.jpg

PSYMN April 16, 2010 12:21

Other string...
 
Not sure why, but Josh started two strings on the same question...

The other one has more of a solution...

http://www.cfd-online.com/Forums/ans...-elements.html


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