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[snappyHexMesh] Troubles with layer adding in my mesh |
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August 27, 2012, 19:18 |
Troubles with layer adding in my mesh
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#1 |
New Member
Pierre Crepier
Join Date: Aug 2012
Location: Wageningen
Posts: 3
Rep Power: 14 |
Hello everybody,
So I've been starting using OPENFoam those last days and I am a bit stuck at the layer insertion in my mesh. First of all : I'm meshing a 3D profile (clarkypt) for some remote controlled device to know more about the ground effect on such slender body ... slender because for 1m long, I have only 0.1m of width! so it is 3D since I'm interested in 3D effects. So for now I generated a mesh without surface layers, to keep it simple, but know, I'd like to add it to capture accurately my boundary layer. The problem : sHM seems to be detecting that he needs to add layers ... but it clearly says : no layer extruded ... so my question is: why ? here is the dictionnary I'm using: http://pastebin.com/rDVyc9wt and the output of SHM: http://pastebin.com/NkCNnzXz So if someone could give me a hint of were it could go wrong ... I would really appreciate it! for now what I tried is : play with feature Angle up to 180° : result is above, play a bit with the mesh quality : reduce the tolerance to allow bad cells ... doesn't seem to have an effect. I have to say that I am a bit lost! Thanks for reading, Pierre |
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August 27, 2012, 20:54 |
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#2 |
Senior Member
Marco A. Turcios
Join Date: Mar 2009
Location: Vancouver, BC, Canada
Posts: 740
Rep Power: 28 |
Looking at the output, this appears to hold the key:
Code:
Checking mesh with layer ... Checking faces in error : non-orthogonality > 60 degrees : 0 faces with face pyramid volume < -1e+13 : 0 faces with face-decomposition tet quality < 0.01 : 1067680 faces with concavity > 80 degrees : 0 faces with skewness > 4 (internal) or 20 (boundary) : 0 faces with interpolation weights (0..1) < 0.05 : 0 faces with volume ratio of neighbour cells < 0.01 : 0 faces with face twist < 0.05 : 0 faces on cells with determinant < 0.001 : 0 Detected 1067680 illegal faces (concave, zero area or negative cell pyramid volume) Extruding 0 out of 66660 faces (0%). Removed extrusion at 37854 faces. |
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August 29, 2012, 10:36 |
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#3 |
Senior Member
Eloïse
Join Date: Jul 2012
Location: Trondheim, Norway
Posts: 113
Rep Power: 14 |
Hi Pierre,
Try to deactivate all the mesh quality controls for the layer insertion Code:
maxNonOrtho 180; maxBoundarySkewness -1; maxInternalSkewness -1; maxConcave 180; minVol -1e33; minTetQuality -1e30; minTwist -1e30; minDeterminant -1; minFaceWeight -1; minVolRatio -1; Good luck! Eloïse |
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August 30, 2012, 17:50 |
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#4 |
New Member
Pierre Crepier
Join Date: Aug 2012
Location: Wageningen
Posts: 3
Rep Power: 14 |
Hi everyone,
So first, after the remark of mturcios, I rounded the trailing edge of my profile to get a better there (I can understand that adding such a layer on such a sharp corner can lead to sh***y cells). It did not helped a lot, so I tried by using some more permissive orthogonality settings ... and still didn't worked. And I just tried the solution of Éloïse ... and WOW, it worked! that was a good solution! but know, new problem : how do I visualize the bad cells in paraView ? I enabled the sets, choose the nonorthoblabla set ... and nothing appeared when in the checkMesh I have this : Code:
/*---------------------------------------------------------------------------*\ | ========= | | | \\ / F ield | OpenFOAM: The Open Source CFD Toolbox | | \\ / O peration | Version: 2.1.1 | | \\ / A nd | Web: www.OpenFOAM.org | | \\/ M anipulation | | \*---------------------------------------------------------------------------*/ Build : 2.1.1-221db2718bbb Exec : checkMesh -latestTime Date : Aug 30 2012 Time : 22:33:16 Host : "zib-desktop" PID : 7225 Case : /home/zib/OpenFOAM/zib-2.1.1/run/openDomainRefined 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 = 3 Time = 3 Mesh stats points: 2420646 faces: 7011837 internal faces: 6939387 cells: 2296002 boundary patches: 7 point zones: 0 face zones: 0 cell zones: 0 Overall number of cells of each type: hexahedra: 2211760 prisms: 6906 wedges: 0 pyramids: 0 tet wedges: 0 tetrahedra: 0 polyhedra: 77336 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 patch topology for multiply connected surfaces ... Patch Faces Points Surface topology outlet 450 506 ok (non-closed singly connected) inlet 100 121 ok (non-closed singly connected) outer 1450 1516 ok (non-closed singly connected) leadingEdge_OBJECT 17122 17303 ok (non-closed singly connected) foil_OBJECT 28512 28878 ok (non-closed singly connected) trailingEdge_OBJECT 22770 23368 ok (non-closed singly connected) trailingEdgeEnd_OBJECT2046 2311 ok (non-closed singly connected) Checking geometry... Overall domain bounding box (-2 -1 -1) (7 1 1) Mesh (non-empty, non-wedge) directions (1 1 1) Mesh (non-empty) directions (1 1 1) Boundary openness (-3.57353e-18 7.56963e-16 -7.41408e-16) OK. Max cell openness = 2.10983e-14 OK. Max aspect ratio = 428.46 OK. Minumum face area = 1.93605e-09. Maximum face area = 0.0402104. Face area magnitudes OK. Min volume = 5.90847e-13. Max volume = 0.00804138. Total volume = 35.9919. Cell volumes OK. Mesh non-orthogonality Max: 82.6553 average: 5.93784 *Number of severely non-orthogonal faces: 976. Non-orthogonality check OK. <<Writing 976 non-orthogonal faces to set nonOrthoFaces Face pyramids OK. Max skewness = 1.84672 OK. Coupled point location match (average 0) OK. Mesh OK. End thanks a lot! |
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August 30, 2012, 18:24 |
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#5 |
Senior Member
Marco A. Turcios
Join Date: Mar 2009
Location: Vancouver, BC, Canada
Posts: 740
Rep Power: 28 |
You'll need to do a foamToVTK and include the set. Open your mesh case in paraview, then open the VTK file that contains your cellSet (will be in the VTK folder by default)
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August 31, 2012, 04:37 |
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#6 |
Senior Member
Eloïse
Join Date: Jul 2012
Location: Trondheim, Norway
Posts: 113
Rep Power: 14 |
It is not a cell set but a face set. Use the command:
foamToVTK -faceSet nonOrthoFaces -latestTimeand import the created VTK in paraView |
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August 31, 2012, 16:31 |
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#7 |
New Member
Pierre Crepier
Join Date: Aug 2012
Location: Wageningen
Posts: 3
Rep Power: 14 |
thanks for the tips, I saw the command in one of your posts Éloïse. And so now it raises new questions!
Now it is more about the mesh quality than inserting the viscous layer but I keep posting on this topic, if a moderator thinks I should start another topic, then I'll do so! So here is my 3D profile: the bad faces are those ones: as seen from the top: and some interior mesh details: Now I am wondering why I get those bad faces (and by the way, I do not see 976 faces ... some are missing, where do they go ?) in such "easy" location ?? what are the parameters to tune up to get a very correct mesh (and you can also see that the snapping kinda deform the geometry but I have to play with sHM to solve this with featureEdges I guess) So every advice is appreciated! And by the way a more general question on the limits of OpenFOAM : what is a very bad grid (orthogonality, skewness etc ..) for openfoam ? Thanks a lot for your time, Cheers, Pierre |
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September 20, 2012, 10:31 |
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#8 |
Member
Join Date: Jul 2012
Posts: 66
Rep Power: 14 |
Have you tried Feature Edge Handling
http://www.openfoam.com/news/snappyH...ature-edge.php http://www.cfd-online.com/Forums/ope...ture-edge.html I guess this will fix your problem |
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October 21, 2012, 10:06 |
same topic, different problem
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#9 |
New Member
Nils
Join Date: Oct 2012
Posts: 2
Rep Power: 0 |
Hi everyone, I've got a problem with my layer addition in SHM. I've read a lot about the whole topic, but never heard something about this problem. Perhaps you could help me out.
I am meshing a wind turbine an therefore used SHM, especially the new snapEdge feature of SHM (nFeatureSnapIter). The results for time 2 are very good, but when it comes to layer addition, some "undo"-iterations occur which destroy some of the snapped edges. Furthermore in some of these regions (and only there!) no layers are added. All my checkMesh controls are disabled. I am using a featureAngle of 180. |
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February 10, 2013, 11:04 |
Problem with featureEdge feature
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#10 | |
Member
P.A.
Join Date: Mar 2009
Location: Germany
Posts: 83
Rep Power: 17 |
Quote:
I don't know if this thread is still being watched, but I will give it a try anyway... Did you solve this problem? I am experiencing the same behaviour of SHM with a ship hull geometry, and the more layer addition iterations I allow to SHM, the less cells are extruded, resulting in a grid almost without any layers. I experimented a lot with all the settings in the layer addition part, but I cannot get better than about 85% of extruded cell layers. Unfortunately, the 15% of layers are missing in quite essential parts. Do you have any helpful hint? Cheers, Pascal. |
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April 4, 2017, 20:21 |
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#11 |
Senior Member
Yuehan
Join Date: Nov 2012
Posts: 142
Rep Power: 14 |
Hi,
Sorry to pop up this thread again. I just would like to know if there is any improvment in SHM's layer addtion in new versions of OF. Layer addtion failure, at least to me, has been a persisting problem when handling complex geometries using SHM. |
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June 21, 2019, 12:18 |
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#12 |
New Member
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Hello everyone,
I'm a newbie in CFD and I've been using OpenFoam with HELYX-OS interface just since 3 months, so I'm no expert at all however, I just wanted to share my experience on this subject. I've had problems in layer insertion from the start, so I set up a very simple case (a bended pipe) and then, using the advice by Eloise in this thread, I've played around with the parameters. In the end, I identified that in my case the quality control parameters that were forbidding boundary layer insertion were mainly the following 3: maxBoundarySkewness - which I ended up leaving deactivated (-1) maxInternalSkewness - which I ended up leaving deactivated (-1) minTetQuality - which I ended up leaving at a very small value (1E-30) (even if the skewness limits are deactivated, if the mesh dimensions are specified correctly the resulting mesh doesn't suffer any skewness - at list in my experience with the simplified geometry) Furthermore, I've also seen that (maybe it's obvious to you) the simulation geometry quality can have a significant impact on meshing: the process of exporting a parametric CAD file (e.g. STEP) to STL can give very different results depending on the software (in my experience, for example, between FreeCad and SALOME) and this in turn applies to the mesh. ...just my 2 cents Andrea |
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Tags |
addlayers, shm, snappyhexmesh, viscous layer |
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