CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Open Source Meshers: Gmsh, Netgen, CGNS, ...

Null determinant cells in Netgen

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Display Modes
Old   January 20, 2013, 11:55
Default Null determinant cells in Netgen
  #1
Senior Member
 
Daniele Vicario
Join Date: Mar 2009
Location: Novara, Italy
Posts: 142
Rep Power: 7
danvica is on a distinguished road
Meshing a simple geometry using Netgen I obtained some null-determinant cells that crash a solver (see Questions on dynamicTopoFvMesh)

Enclosed you can find pictures of the mesh and the file of the .brep geometry.

The white coloured cells are the null-determinant ones.

Is there anyone able to solve this problem ? Is there any guideline to follow to avoid this cells ?

More: Why did they come in such a simple case ?

Thanks.
Attached Images
File Type: jpg pict1.jpg (17.6 KB, 6 views)
File Type: jpg pict2.jpg (15.6 KB, 4 views)
File Type: jpg pict3.jpg (19.7 KB, 3 views)
Attached Files
File Type: zip dom.zip (18.7 KB, 2 views)
__________________
Daniele Vicario

blueCFD2.1 - Windows 7
danvica is offline   Reply With Quote

Old   January 24, 2013, 07:23
Default Success in SALOME
  #2
Member
 
Ilya
Join Date: Dec 2011
Location: Russia
Posts: 65
Blog Entries: 34
Rep Power: 4
skeptik is on a distinguished road
I generated both meshes in SALOME without any problem.

1. Simple mesh NETGEN 1D-2D-3D with very fine settings.
asd.jpg
2. Mesh with refinement on edges.
v2ref.jpg

I did not mesh conversion due to i have not OF on my working computer, but SALOME didn't detect zero volumes so i think there is no elements with negative determinant.

P.S. I use SALOME on Win7
skeptik is offline   Reply With Quote

Old   January 24, 2013, 09:34
Default
  #3
Senior Member
 
Daniele Vicario
Join Date: Mar 2009
Location: Novara, Italy
Posts: 142
Rep Power: 7
danvica is on a distinguished road
Hi,
Thanks for your time. Have you tried to check your mesh with:

checkMesh -allGeometry -allTopology

and see how many (and if...) undeterminet cells it has ?


BTW: I use Salome but just to preprocess existing STEP geometry. Then usually I use SHM. I tried several times meshing with it but I found it quite instable (i.e. lots of crash), above all making submesh.

Which version are you using ? Do you download it from the official site ?
__________________
Daniele Vicario

blueCFD2.1 - Windows 7
danvica is offline   Reply With Quote

Old   January 24, 2013, 11:55
Default Mesh OK
  #4
Member
 
Ilya
Join Date: Dec 2011
Location: Russia
Posts: 65
Blog Entries: 34
Rep Power: 4
skeptik is on a distinguished road
Here my checkMesh output:

Code:
Checking geometry...
    Overall domain bounding box (-0.05 -0.05 0) (0.05 0.05 0.375)
    Mesh (non-empty, non-wedge) directions (1 1 1)
    Mesh (non-empty) directions (1 1 1)
    Boundary openness (-8.45579e-18 -2.98649e-18 -1.5611e-17) OK.
    Max cell openness = 2.74985e-16 OK.
    Max aspect ratio = 4.80757 OK.
    Minumum face area = 6.88965e-07. Maximum face area = 0.000152252.  Face area magnitudes OK.
    Min volume = 3.02192e-10. Max volume = 6.23914e-07.  Total volume = 0.00198994.  Cell volumes OK.
    Mesh non-orthogonality Max: 50.6206 average: 15.2056
    Non-orthogonality check OK.
    Face pyramids OK.
    Max skewness = 0.557965 OK.
    Coupled point location match (average 0) OK.

Mesh OK.
Mesh is good. In this case i checked mesh with refinement. I think the problem in your mesher. However SALOME uses NETGEN algorythm. May be you did something wrong in NETGEN settings.

Quote:
I tried several times meshing with it but I found it quite instable (i.e. lots of crash), above all making submesh.

Which version are you using ? Do you download it from the official site ?
Yes, It could be unstable due to big mesh and unsufficient memory. So i just restart it and save my projects before each operation with mesh.

I use version 6.4 32-bit from official website.
skeptik is offline   Reply With Quote

Old   January 24, 2013, 13:34
Default
  #5
Senior Member
 
Daniele Vicario
Join Date: Mar 2009
Location: Novara, Italy
Posts: 142
Rep Power: 7
danvica is on a distinguished road
Can you please execute checkMesh with -allGeometry -allTopology options ?

PS. I really hope you had find a good way to avoid these cells...

Thanks.
__________________
Daniele Vicario

blueCFD2.1 - Windows 7
danvica is offline   Reply With Quote

Old   January 25, 2013, 10:19
Default
  #6
Member
 
Ilya
Join Date: Dec 2011
Location: Russia
Posts: 65
Blog Entries: 34
Rep Power: 4
skeptik is on a distinguished road
OK!

I executed it with options -allGeometry -allTopology and got an undetermined cells as you describe.

It was pretty strange so i did checkMesh with the same options but on my nozzle head case. The mesh was also generated using SALOME.

So i got same cells in the similar positions as in your case.

There is:

funny.jpg

So i think you need keep it simple) it's not your fault
skeptik is offline   Reply With Quote

Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
SnappyHexMesh for internal Flow vishwa OpenFOAM Native Meshers: snappyHexMesh and Others 23 August 6, 2014 04:50
No layers in a small gap bobburnquist OpenFOAM Native Meshers: snappyHexMesh and Others 2 November 25, 2012 09:54
Import netgen mesh to OpenFOAM hsieh Open Source Meshers: Gmsh, Netgen, CGNS, ... 32 September 13, 2011 06:50
snappyHexMesh won't work - zeros everywhere! sc298 OpenFOAM Native Meshers: snappyHexMesh and Others 2 March 27, 2011 22:11
physical boundary error!! kris CD-adapco 2 August 3, 2005 01:32


All times are GMT -4. The time now is 21:44.