CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > OpenFOAM Native Meshers: snappyHexMesh and Others

snappyHexMesh surface refinement bugs

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

Reply
 
LinkBack Thread Tools Display Modes
Old   November 9, 2012, 14:50
Default snappyHexMesh surface refinement bugs
  #1
Member
 
Cong
Join Date: Nov 2012
Posts: 77
Rep Power: 4
wc34071209 is on a distinguished road
Hi everyone,

I found that something wrong with the surface refinement. I wanted to refine a surface and it got refined, but another surface very close to this surface also got refined. Details can be seen from the figure.

In the figure, I only wanted to refine the surface of duct but the surface of box close to the duct also got refined. It is really strange.

Anyone knows why ?

Thank you in advance !
Attached Images
File Type: jpg 11.jpg (81.1 KB, 98 views)
wc34071209 is offline   Reply With Quote

Old   November 10, 2012, 19:22
Default
  #2
Member
 
Cong
Join Date: Nov 2012
Posts: 77
Rep Power: 4
wc34071209 is on a distinguished road
no body takes interest?
wc34071209 is offline   Reply With Quote

Old   November 10, 2012, 21:18
Default
  #3
Super Moderator
 
Bruno Santos
Join Date: Mar 2009
Location: Lisbon, Portugal
Posts: 8,251
Blog Entries: 34
Rep Power: 84
wyldckat is just really nicewyldckat is just really nicewyldckat is just really nicewyldckat is just really nice
Greetings Cong and welcome to the forum!

I can only guess what the problem is - since the surfaces are too close, the one you don't want as refined as the other one is still getting caught thanks to the number of cells between each level... namely this parameter:
Code:
nCellsBetweenLevels
For more information, see "A Comprehensive Tour of snappyHexMesh - 7th OpenFOAM Workshop (25 June 2012)", accessible through here: http://openfoamwiki.net/index.php/Sn...als_and_Guides

Best regards,
Bruno
wyldckat is offline   Reply With Quote

Old   November 11, 2012, 10:44
Default
  #4
Member
 
Cong
Join Date: Nov 2012
Posts: 77
Rep Power: 4
wc34071209 is on a distinguished road
Hi,
Thank you so much !

I am using default setting for nCellsBetweenLevels --- 2. According to you, I should decrease this value ?
wc34071209 is offline   Reply With Quote

Old   November 11, 2012, 10:46
Default
  #5
Member
 
Cong
Join Date: Nov 2012
Posts: 77
Rep Power: 4
wc34071209 is on a distinguished road
Hi Bruno,

Could you give me some hints about how to avoid concave cells?

The following attached is the output after I run checkMesh. It seems my mesh is really bad.


Mesh stats
points: 5640879
faces: 15861281
internal faces: 15183609
cells: 5116777
boundary patches: 15
point zones: 0
face zones: 0
cell zones: 0

Overall number of cells of each type:
hexahedra: 4884773
prisms: 47139
wedges: 23
pyramids: 16
tet wedges: 987
tetrahedra: 0
polyhedra: 183839

Checking topology...
Boundary definition OK.
Cell to face addressing OK.
Point usage OK.
Upper triangular ordering OK.
Face vertices OK.
Number of regions: 1 (OK).

Checking geometry...
Overall domain bounding box (-3 -3.049999952 -0.03999999911) (3.440000057 3.049999952 2.160000095)
Mesh (non-empty, non-wedge) directions (1 1 1)
Mesh (non-empty) directions (1 1 1)
Boundary openness (-4.370968924e-15 -3.928455669e-19 1.96277524e-15) OK.
Max cell openness = 1.095394505e-15 OK.
Max aspect ratio = 64.0748539 OK.
Minimum face area = 1.548521309e-09. Maximum face area = 0.381110741. Face area magnitudes OK.
Min volume = 4.377205473e-13. Max volume = 0.1300759831. Total volume = 74.34968174. Cell volumes OK.
Mesh non-orthogonality Max: 64.98871264 average: 5.814950331
Non-orthogonality check OK.
Face pyramids OK.
***Max skewness = 4.476212227, 745 highly skew faces detected which may impair the quality of the results
<<Writing 745 skew faces to set skewFaces
Coupled point location match (average 0) OK.
***Error in face tets: 74 faces with low quality or negative volume decomposition tets.
<<Writing 70 faces with low quality or negative volume decomposition tets to set lowQualityTetFaces
*Edges too small, min/max edge length = 0 0.8384450559, number too small: 4
<<Writing 4 points on short edges to set shortEdges
*There are 1390 faces with concave angles between consecutive edges. Max concave angle = 53.12549247 degrees.
<<Writing 1390 faces with concave angles to set concaveFaces
Face flatness (1 = flat, 0 = butterfly) : average = 0.9999261207 min = 0.7680335307
*There are 8 faces with ratio between projected and actual area < 0.8
Minimum ratio (minimum flatness, maximum warpage) = 0.7680335307
<<Writing 8 warped faces to set warpedFaces
Cell determinant (wellposedness) : minimum: 0 average: 6.956499987
***Cells with small determinant found, number of cells: 4768
<<Writing 4768 under-determined cells to set underdeterminedCells
***Concave cells (using face planes) found, number of cells: 36302
<<Writing 36302 concave cells to set concaveCells

Failed 4 mesh checks.

End
wc34071209 is offline   Reply With Quote

Old   November 11, 2012, 16:41
Default
  #6
Super Moderator
 
Bruno Santos
Join Date: Mar 2009
Location: Lisbon, Portugal
Posts: 8,251
Blog Entries: 34
Rep Power: 84
wyldckat is just really nicewyldckat is just really nicewyldckat is just really nicewyldckat is just really nice
Hi Cong,

Quote:
Originally Posted by wc34071209 View Post
Could you give me some hints about how to avoid concave cells?
Sorry but I haven't figured out how concave cells can be avoided. All I know is that sometimes it's just a warning and those cells are OK.

Nonetheless, I believe that you might be able to find the solution if you read the tutorials referred to in the link I posted.

Good luck!
Bruno
wyldckat is offline   Reply With Quote

Old   November 11, 2012, 18:28
Default
  #7
Senior Member
 
sail's Avatar
 
Vieri Abolaffio
Join Date: Jul 2010
Location: Always on the move.
Posts: 308
Rep Power: 7
sail is on a distinguished road
with so many errors, chances are that sHM have not produced a mesh witt your quality criterion before the maximum snapping phases and it gave up.

try to take a look at the sHM log to find if there have been any error messages.
__________________
http://www.leadingedge.it/
Naval architecture and CFD consultancy
sail is offline   Reply With Quote

Old   November 11, 2012, 22:07
Default
  #8
Member
 
Join Date: Nov 2010
Posts: 50
Rep Power: 6
Doug68 is on a distinguished road
Hi wc34071209,

From my point of view if the mesh finishes at the boundary surface and its what's going on side the mesh that is important.
I think it's easy to get fixated on getting a perfect representation of the surface at the edge of the mesh but if you un-refine immediately away from the surface then the chances of getting good results about what's happening close to and then onto the surface are surely diminished?

In the case of your box close to the surface, if its not going to have real effect on the flow i.e. it represents a probe or something that shouldn't have a major effect on the simulation then remove it from the model. If on the other hand it is important then you should refine around it also I would have thought?
Doug68 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
Number of cells in mesh don't match with size of cellLevel colinB OpenFOAM Native Meshers: snappyHexMesh and Others 11 January 13, 2015 12:47
SnappyHexMesh for internal Flow vishwa OpenFOAM Native Meshers: snappyHexMesh and Others 23 August 6, 2014 03:50
killed "snappyHexMesh" parkh32 OpenFOAM Pre-Processing 2 April 8, 2012 17:12
refinementregion in the snappyhexmesh hei@ge OpenFOAM 7 March 25, 2012 14:50
[ICEM] Problems with coedge curves and surfaces tommymoose ANSYS Meshing & Geometry 0 August 5, 2011 16:02


All times are GMT -4. The time now is 06:40.