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snappyHexMesh utility does not work correctly

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Old   March 20, 2013, 09:17
Default snappyHexMesh utility does not work correctly
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sandy
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Dear foamers,
I am trying to simulate a liquid jet from an injector, I draw my geometry in blender, two cylinder, the big one for my domain, the small one for the my injector shape and I connected them together by using Ctrl+j in blender to make them one stl ASCII format, I attached the picture as I visualized in paraview. My problem is when I try to use the snappyhexmesh utility, I do not get the snap for the small cylinder(injector) I do not even see it in the result, I just get snap for the long big cylinder.. Can any body help me please.
My dimensions for the big cylinder(my domain) are D= 0.001 m, L =0.012 m. the I built my injector above it and my dimensions for the small cylinder(my injector) are D= 0.0004 m, L =0.0002 m
I attached picture for my geometry(as visualized in paraview and it had done in blender) and the next picture for what I get after I ran snappyhexmesh
Sandy,
Attached Images
File Type: jpg injector.jpg (10.1 KB, 53 views)
File Type: jpg snappy picture.jpg (12.9 KB, 52 views)
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Old   March 24, 2013, 15:04
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Bruno Santos
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Greetings Sandy,

I can only guess that you did not remove the faces that connect the two cylinders.
The other possibility is that your cells were too large for the smaller pipe, which lead snappy to not find the smaller pipe.

Best regards,
Bruno
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Old   April 1, 2013, 05:11
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David Haces
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Hi Sandy,
I think you can try to build your domain (the big cylinder) with blockmesh and then mesh the rest with snappy. My experience is that most of the errors come from the .STL file so the simpler the better.

I hope this helps,
David
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Old   April 1, 2013, 11:01
Default snappy does not snap all the geometry
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Quote:
Originally Posted by wyldckat View Post
Greetings Sandy,

I can only guess that you did not remove the faces that connect the two cylinders.
The other possibility is that your cells were too large for the smaller pipe, which lead snappy to not find the smaller pipe.

Best regards,
Bruno
Dear wyldckat,
Yes indeed I did not remove the faces, but I manged to solve out this problem and my snappy works perfectly for all the geometry. know I run the case but I still get the same error and my running stops after a few iterations. I had a many goes with the time step and the courant number with out any benefit. could you please help me, any thoughts would be helpful...
sandy,
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Old   April 1, 2013, 11:04
Default my running still stops after fixing snappy utility
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Quote:
Originally Posted by Haces View Post
Hi Sandy,
I think you can try to build your domain (the big cylinder) with blockmesh and then mesh the rest with snappy. My experience is that most of the errors come from the .STL file so the simpler the better.

I hope this helps,
David
Dear Hances,
Thank you so much for your replay. Yes I manged to solve out this problem and my snappy works perfectly for all the geometry, I ran checkMesh, every thing is ok. know I run the case but I still get the same error and my running stops after a few iterations. I had a many goes with the time step and the courant number with out any benefit. could you please help me, any thoughts would be helpful...
sandy,
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Old   April 1, 2013, 12:12
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Hi Sandy,

You're not giving us much information to work with. You haven't even mentioned which specific solver you're trying to use, or on which thread you have more details about this!

Last but not least, try running checkMesh with a full check:
Code:
checkMesh -allTopology -allGeometry
Best regards,
Bruno
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Old   April 2, 2013, 06:37
Default STL geometry problems
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Quote:
Originally Posted by wyldckat View Post
Hi Sandy,

You're not giving us much information to work with. You haven't even mentioned which specific solver you're trying to use, or on which thread you have more details about this!

Last but not least, try running checkMesh with a full check:
Code:
checkMesh -allTopology -allGeometry
Best regards,
Bruno
Dear wyldckat,
I am sorry, recently I had a family issues and I was not concentrating, sorry again and this her is my case.
I am doing simulation for a liquid jet from a small orifice(cylinder) inside domain(big cylinder) from above(in the z direction), laminar, velocity=1 m/s. I am using interFoam, I set the boundary condition for the alpha1=1 at the inlet and the velocity=-1 m/s. I did the geometry by using blender STL then I used snappy for the mesh, I ran checkMesh and the result is ok. I had no idea about your code, but now I run your code:checkMesh -allTopology -allGeometry, and I found errors...

Build : 2.1.1-221db2718bbb
Exec : checkMesh -allTopology -allGeometry
Date : Apr 02 2013
Time : 11:30:31
Host : "l031"
PID : 5164
Case : /home/atheel/interFoamvalidation/laminar/liquidjetinjector
nProcs : 1
sigFpe : Enabling floating point exception trapping (FOAM_SIGFPE).
fileModificationChecking : Monitoring run-time modified files using timeStampMaster
allowSystemOperations : Disallowing user-supplied system call operations

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
Create time

Create polyMesh for time = 0

Time = 0

Mesh stats
points: 653667
faces: 1719316
internal faces: 1577348
cells: 532960
boundary patches: 7
point zones: 0
face zones: 0
cell zones: 0

Overall number of cells of each type:
hexahedra: 506128
prisms: 0
wedges: 0
pyramids: 0
tet wedges: 0
tetrahedra: 0
polyhedra: 26832

Checking topology...
Boundary definition OK.
Cell to face addressing OK.
Point usage OK.
Upper triangular ordering OK.
Face vertices OK.
Topological cell zip-up check OK.
Face-face connectivity OK.
Number of regions: 1 (OK).

Checking patch topology for multiply connected surfaces ...
Patch Faces Points Surface topology Bounding box
leftWall 0 0 ok (empty)
rightWall 0 0 ok (empty)
frontWall 0 0 ok (empty)
backWall 0 0 ok (empty)
atmosphere 0 0 ok (empty)
inlet 208 241 ok (non-closed singly connected) (-0.0001984 -0.0001984 0.0122) (0.0001984 0.0001984 0.0122)
injector_ExportedfromBlender-2.65(sub8)141760 141793 ok (non-closed singly connected) (-0.000499981 -0.000499981 0) (0.000499981 0.000499981 0.0122)

Checking geometry...
Overall domain bounding box (-0.000499981 -0.000499981 0) (0.000499981 0.000499981 0.0122)
Mesh (non-empty, non-wedge) directions (1 1 1)
Mesh (non-empty) directions (1 1 1)
Boundary openness (3.82255e-17 1.66236e-16 6.6499e-17) OK.
Max cell openness = 3.21018e-16 OK.
Max aspect ratio = 5.49452 OK.
Minumum face area = 9.29097e-11. Maximum face area = 1.03589e-08. Face area magnitudes OK.
Min volume = 1.97022e-15. Max volume = 5.75331e-13. Total volume = 9.42301e-09. Cell volumes OK.
Mesh non-orthogonality Max: 52.0704 average: 6.9085
Non-orthogonality check OK.
Face pyramids OK.
Max skewness = 2.21305 OK.
Coupled point location match (average 0) OK.
***Error in face tets: 32 faces with low quality or negative volume decomposition tets.
<<Writing 32 faces with low quality or negative volume decomposition tets to set lowQualityTetFaces
Min/max edge length = 6.85999e-06 0.000101803 OK.
All angles in faces OK.
Face flatness (1 = flat, 0 = butterfly) : average = 0.999989 min = 0.881762
All face flatness OK.
Cell determinant (wellposedness) : minimum: 0.0866447 average: 8.82645
Cell determinant check OK.
***Concave cells (using face planes) found, number of cells: 15637
<<Writing 15637 concave cells to set concaveCells

Failed 2 mesh checks.
Thank you so much for this code, I will try to fix it, but still I need to use STL, do you recommend any thing that can push me...
Sandy,
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Old   April 2, 2013, 17:16
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Hi Sandy,

Check the tutorials section on this page: http://openfoamwiki.net/index.php/Sn...als_and_Guides

In addition, I would suggest that you simplify your case first and use the simpler case for figuring out how the solver works with your settings. In essence, gradually increase the complexity of the case, instead of trying to solve everything in a single case.

Best regards,
Bruno
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