negative element volume problem in CFX/icem-cfd
 

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)

Hi,

Usually this occurs in a deforming mesh simulation when an element turns itself inside out but in my experience it is possible in ICEM to use poor smoothing and also generate negative volume elements. You have to be careful with smoothing in ICEM, it can generate negative volume elements using the default settings. The problems are usually at the interface between prism layers and tet elements in tricky bits of the geometry.

Make sure you do a element volume check in ICEM, and don't do too much smoothing.

Glenn Horrocks

Glenn, you've saved me before, hopefully you can again.

Despite that I have used minimal smoothing in ICEM (I just smoothed for orthogonality, being that it is a hexahedral grid), my grid appears to have negative volume elements, as shown below.

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

As shown on the left in blue writing and in the histogram, there are almost 63 negative volume elements (8 + 55), with the smallest being -18.7586 mm^3. I need to get rid of these, but am not sure how.

Any ideas?

just a guess,

reassociate the edges/lines AND then try to move the verticies on the line. If done right you´ll see the verticies snapping on the edges. i my case while encountering such problems, i did a edge/line association, so everything was looking good but the verticies haven´t been moved to the linelocation ending up in meshverticies out of the surface -->(distorted elements-->neg. element)

neewbie

Hi Neewbie -

Thanks for the reply.

I did re-associate the edges/lines before moving the vertices. The vertices did snap on the edges, as shown with my blocking here:

http://img171.imageshack.us/img171/9...t7block.th.jpg

In these situations then I do not smooth in ICEM. Just mesh and proceed. Smoothing can be more harm than good sometimes.

Thanks for the reply, Glenn.

Oddly enough, I ran another test case without any smoothing, and STILL had negative volume elements.

More details about this situation can be found in this thread:
http://www.cfd-online.com/Forums/ans...tml#post255073

Don't give up yet! Meshing is a complicated skill.

Although this post is best discussed on the thread you link to as it is really a meshing question, not a CFX question.