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-   -   Negative Volume Mesh (http://www.cfd-online.com/Forums/fluent/38845-negative-volume-mesh.html)

MANOJKUMAR December 6, 2005 03:15

Negative Volume Mesh
 
Hi all friends, My problem is how to solve negative volume. When i mesh the volume and chek in Gambit it show NAGETIVE vOLUME.if any one know to solve this problem please tell me. Thanking all, From MANOJKUMAR

pah December 6, 2005 04:20

Re: Negative Volume Mesh
 
Hi MANOJKUMAR!

This Prolem can be solved with the Running Solve of the Grid system. Actually, I do not know what is the results of the problem. However, I suggest to you in the Solving grid system don't solve with much iterations. If you solve with 100, appears Negative volume, and then You try with 50 iterations, maybe it will disappear. :)

Goodluck!

Pah

zxaar December 6, 2005 04:27

Re: Negative Volume Mesh
 
actually (as i think), he is facing the probelm when he reads the mesh for the first time into fluent. I guess this is coming because of handedness of the cells. When you do the grid check, it should show some handedness probelm.


Rajesh December 6, 2005 21:02

Re: Negative Volume Mesh
 
If you get negative volumes when you perform the grid check, as Zxaar told, then you have to look into the curved portions of your geometry. Negative volumes are normally reported when your geometry contains very small "loops"(the first cell of the boundary layer extends beyond the edge of your geometry)near the curved edges. I have had this problem and I observed that this may be solved by adjusting the first cell height of the boundary layer.

Good Luck

Rajesh

MANOJKUMAR December 7, 2005 06:32

Re: Negative Volume Mesh
 
thanks all.

i have created virtual volume in my geametry to mesh my geometry. now when i delete the negative volume and try with other type of mesh then meshing is not done.can negative volume be removed by changing the type of mesh.


MANOJKUMAR December 7, 2005 06:36

Re: Negative Volume Mesh
 
Thanks ,

As zxaar said that i get negative volume in the Gambit as well as in Fluent. In Gambit when I check the Volume then it say negatve volume and in Fluent when i read the Name.msh file then it show the negative volume.Thanks once again.I want e-mail address of u because u help me for this problem my email address is ms_project05@rediffmail.com

And Rajesh said that when geometry is samall then it occur ,it is true my Geometry is very large box 2100 length,1900 width and 756 mm height and in this there is 0.672 mm thickness and 770 mm width sheet is held.U told u have a problem like this if don't mind please give me this type of problem or any paper for help me.

And Pah told that iterate means i nod understand.I think u say i give boundary condition and iterate.Is there is problem in result.

Rajesh December 7, 2005 06:59

Re: Negative Volume Mesh
 
Dear Manoj,

I had this problem when I was doing the meshing on an ejector geometry which had a highly curved surface. I could solve it by changing the first cell size of the boundary layer and dividing the geometry(curved edge) into more number of edges. I haven't seen any papers describing this problem, but I could get some useful information from this forum. Try searching the forum for "negative volumes"

All the best

Rajesh

Mahesh Masurkar December 8, 2005 07:14

Re: Negative Volume Mesh
 
What is the output of grid check? Left handed cells:- try to resolve it vie TUI. -ve cells:- Remesh again.

Mahesh

wangyifei April 7, 2009 09:50

I also met the same problem , but I did not find a Effective solution, generally ,first of all the negative volume aslo Appeared in the hex .But some of the negative volume do not impact on the calculation results ,and you can ignore the existence of them. In addition,you can aslo change the parameters of the boundary conditions to reduce the impact of the negative volume.
May be what i said can help you ,your friends yifei


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