|
[Sponsors] |
[snappyHexMesh] SnappyHexMesh and 2 Phase Modelling |
|
LinkBack | Thread Tools | Search this Thread | Display Modes |
September 21, 2008, 07:13 |
SnappyHexMesh and 2 Phase Modelling
|
#1 |
New Member
Axel Mohr
Join Date: Mar 2009
Location: Kiel, Schleswig-Holstein, Germany
Posts: 24
Rep Power: 17 |
Hello All,
I would like to use OpenFOAM for shiptank-modeling, now after using icoFoam and turbFoam, with rasInterFoam. Now my actual problem, where I stuck, is to create a sharp interface in the model-mesh, which should act as boundary-surface of the two phases in the rasInterFoam case. First with blockMesh I created a hexahedronal quadratic mesh with the dimensions of the tank. The ship-hull is available as a geometry in iges or step format. Gmesh (http://www.geuz.org/gmsh/) creates a triangular surface mesh out of this, which is saved as STL-File. These parts are needed by snappyHexMesh to build the desired mesh of the model area. So far, this works fine (nevertheless until now not all arguments are perfectly understood by me) but the resulting mesh is satisfactory - for single phase modeling the top patch is set to the water-level, the part of the hull that lies over the surface will be truncated. But for 2 phase modeling I think an internal face or patch is needed, which marks the water-level and separates these phases in the resulting mesh. So far I've tried a lot of things. The last had been using snappyHexMesh first with the water-phase, then the same with the air-phase, then merging these resulting meshes with 'mergeMeshes' - but at last stitchMesh failed. Now I hope, that someone here has an idea, suggestion or a solution for my problem. Something like a "How-To" for creating an boundary layer between two phases for usage in snappyHexMesh would be great. (what about the layer sub-dict in the snappyHexMeshDict? but here an internal face is needed?) Maybe there is a simple apparently solution, but I can't see it ... Thanks in advance for your help! bye and greetings, Axel |
|
September 23, 2008, 18:49 |
Hello All,
now I've learned
|
#2 |
New Member
Axel Mohr
Join Date: Mar 2009
Location: Kiel, Schleswig-Holstein, Germany
Posts: 24
Rep Power: 17 |
Hello All,
now I've learned, how to create internal face. Even though it does not solve my problem, I would like to give a short description: 1. creating a hexahedronal mesh with blockMesh, not to forget to ensure, that there will be faces at the desired position 2. using faceSet with a faceSetDict, including: name f0; action new; boxToFace // or another ... { box (x1, y1, z1) (x2, y2, z2); } 3. adding the new face to "boundary": n+1 { . . . { intern-A type patch; nFaces 0; startFace ; } 4. createBaffles f0 intern-A Don't forget -case <path> at each utility. A more detailed description of this is here: http://www.cfd-online.com/OpenFOAM_D...es/1/5108.html But, unfortunately the result is not that what I wanted. snappyHexMesh realize these internal face as external boundary, not just as a flat plane in the interior of the new mesh --- as I hoped. Any other idea? greeting, Axel ... nevertheless, snappyHesMesh is a great tool. |
|
September 25, 2008, 11:45 |
oh, i think we have the same p
|
#3 |
Guest
Posts: n/a
|
oh, i think we have the same problem, i did just post something above!
are you getting anywhere? Erik Ekedahl |
|
September 25, 2008, 16:24 |
the last thing I've tried had
|
#4 |
New Member
Axel Mohr
Join Date: Mar 2009
Location: Kiel, Schleswig-Holstein, Germany
Posts: 24
Rep Power: 17 |
the last thing I've tried had been partitioning the problem in two cases, one for the water-phase and one for the air-phase and applying snappyHexMesh on both cases. But so far, after merging both meshes, unfortunately stitchMesh failed.
=> http://www.cfd-online.com/OpenFOAM_D.../126/8450.html |
|
October 2, 2008, 09:32 |
I'd also like to test snappyHe
|
#5 |
New Member
Nicola Parolini
Join Date: Mar 2009
Posts: 4
Rep Power: 17 |
I'd also like to test snappyHexMesh in the context of free-surface flows.
I'm encountering problems to understand how the tool works. Running the tutorial iglooWithFridges I'd like to see wath happen increasing the number of layers on the fridges from 1 to 5. The code runs through the different steps including the layers generation, and from the log it seems that a layer mesh is generated Writing 8540 added cells to cellSet addedCells Writing 6720 faces inside added layer to faceSet layerFaces Layer mesh : cells:18953 faces:61079 points:23729 However, as far as I can see in paraFoam, no boundary layer mesh is showing up around the fridges. Am I missing something ? Thanks a lot. nico |
|
October 2, 2008, 15:43 |
Try displaying the cellSet onl
|
#6 |
Senior Member
Mattijs Janssens
Join Date: Mar 2009
Posts: 1,419
Rep Power: 26 |
Try displaying the cellSet only (convert with "foamToVTK -cellSet addedCells"). Use the clip filter in Paraview to e.g. cut through the fridge.
|
|
October 3, 2008, 01:35 |
Also, make sure you load the r
|
#7 |
Member
Martin Aunskjaer
Join Date: Mar 2009
Location: Denmark
Posts: 53
Rep Power: 17 |
Also, make sure you load the right time directory; snappyHexMesh writes outputs from different stages to different time directories (probably unless you have purgeWrite in controlDict). The final mesh is in the last one.
|
|
October 16, 2008, 23:40 |
I want to use interFoam to mod
|
#8 |
New Member
Robert Manning
Join Date: Mar 2009
Posts: 12
Rep Power: 17 |
I want to use interFoam to model air/water transport. I have a STL file which contains the initial liquid region. I can use snappyHexMesh to create a mesh of the liquid. What do people recommend to add the mesh of the air? I've used mapFields to a new grid. However when viewed in paraview, it seems to not properly copy the wall patches from one grid to the target mesh.
|
|
October 17, 2008, 05:18 |
Since you're doing interFoam y
|
#9 |
Senior Member
Mattijs Janssens
Join Date: Mar 2009
Posts: 1,419
Rep Power: 26 |
Since you're doing interFoam you should generate both regions as one mesh and then set the fluid part using e.g. setFields or funkySetFields (see Wiki).
setFields can use any cell source that the cellSet application can so have a look at the sample cellSetDict in the application directory (mesh/manipulation/cellSet/cellSetDict). There is a surfaceToCell option there which might be useful. |
|
October 22, 2008, 10:28 |
Thanks Mattijs for the suggest
|
#10 |
New Member
Robert Manning
Join Date: Mar 2009
Posts: 12
Rep Power: 17 |
Thanks Mattijs for the suggestion to use surfaceToCell. It works well but only sets gamma to 0 or 1. I've tried refineHexMesh to refine the mesh but to get a smooth interface requires a large number of cells. Essentially I want the gamma to vary as the fraction of the cell volume that is cut by the STL file. Is there anything out there? If not, where should I begin to write a code that performs this?
|
|
November 10, 2008, 08:09 |
Thanks Mattijs, and sorry for
|
#11 |
New Member
Nicola Parolini
Join Date: Mar 2009
Posts: 4
Rep Power: 17 |
Thanks Mattijs, and sorry for the late reply. I've been far from OF for a few weeks. I've actually understood the problem which is related to parafoam. When I load the case, it first shows the level 1 grid (before snapping), if I increase the mesh level to 2 it shows the snapped grid, but when I further increase to 3 nothing changes. To visualize the boundary layer grid, I have to go back to 2 and then again to 3 and magically my layer grid is there. Don't know why it behaves like this, but it works.
Now I have another question related to feature edges. Reading other posts, it seems that feature edges are not supported at the moment. On the other hand, it exists (and it is described in the user guide) a featureEdgeMesh option in the snappy dictionary which should allow refinement based on edge definition. Is this option inactive in the current release ? If it is already active, is there any example showing how the file someLine.eMesh should be define ? Thanks a lot. nicola |
|
November 10, 2008, 14:18 |
There is only refinement based
|
#12 |
Senior Member
Mattijs Janssens
Join Date: Mar 2009
Posts: 1,419
Rep Power: 26 |
There is only refinement based on feature edges. No snapping to feature edges.
Have a look at the source code for featureEdgeMesh so see how to read/write them or there is the surface/surfaceFeatureConvert utility. This is all still in state of flux though. |
|
November 11, 2008, 05:18 |
Thanks Mattijs. If anyone as a
|
#13 |
New Member
Nicola Parolini
Join Date: Mar 2009
Posts: 4
Rep Power: 17 |
Thanks Mattijs. If anyone as already tried to use the featureEdgeMesh tool, I would be glad to see the format needed for the file someLine.eMesh to work.
thanks a lot. nicola |
|
December 9, 2008, 03:45 |
Hello All,
A problem simila
|
#14 |
Senior Member
Mark Couwenberg
Join Date: Mar 2009
Location: Netherlands
Posts: 130
Rep Power: 17 |
Hello All,
A problem similar to what is described here: SHM works fine but know I want to add some cell layers which are aligned with the local surfaces, as described in the User Manual (hood of the car). It should be doable with the fields under "layer" in the SHMdict. I tried it in the iglo tutorial. After some playing around I found that when adding 4 or more layers, the alyers are actually created. Probably with less than 4 some constraints are not met (?). However, the added layers are not added in the actual mesh but stored separately in a layerFaces set. The layers are visualised below: And the bottom of the iglo (in the final timestep): Question: how shall these layers be incorporated in the actual mesh? For reference here the SHM dict: snappyHexMeshDict Thanks for any advice, Mark |
|
December 9, 2008, 05:30 |
Short answer: since you can se
|
#15 |
Senior Member
Mattijs Janssens
Join Date: Mar 2009
Posts: 1,419
Rep Power: 26 |
Short answer: since you can see the added faces in your faceSet they are also in the mesh. A faceSet/cellSet/pointSet is just a subset of mesh items.
You might look at where they are collapsed. Slice through your mesh and you'll see them. |
|
February 18, 2009, 06:05 |
here are some hints how to add
|
#16 |
Senior Member
Wolfgang Heydlauff
Join Date: Mar 2009
Location: Germany
Posts: 136
Rep Power: 21 |
here are some hints how to add the layers.
the finalLayerRatio 0.1; is in my opinion is the thickness of the complete boundarlayer in ratio to the blockMesh-created cell thickness. don't make the value too big or small. otherwise the added layer do not have enough space to fit in. just play around with it a little bit. according to the original size of the backgroundmesh, your minThickness 0.000001; should not bee the big. otherwise the added layers are too small and will not be created. |
|
February 18, 2009, 06:07 |
here are some hints how to add
|
#17 |
Senior Member
Wolfgang Heydlauff
Join Date: Mar 2009
Location: Germany
Posts: 136
Rep Power: 21 |
here are some hints how to add the layers.
the finalLayerRatio 0.1; is in my opinion is the thickness of the complete boundarlayer in ratio to the blockMesh-created cell thickness. don't make the value too big or small. otherwise the added layer do not have enough space to fit in. just play around with it a little bit. according to the original size of the backgroundmesh, your minThickness 0.000001; should not bee the big. otherwise the added layers are too small and will not be created. |
|
February 18, 2009, 06:14 |
Here I try to add image of the
|
#18 |
Senior Member
Wolfgang Heydlauff
Join Date: Mar 2009
Location: Germany
Posts: 136
Rep Power: 21 |
Here I try to add image of the Igloo Tutorial with its snappyHexMeshDict.
As you can see, several boundary layers are being added. snappyHexMeshDict |
|
February 18, 2009, 06:26 |
some more information:
it i
|
#19 |
Senior Member
Wolfgang Heydlauff
Join Date: Mar 2009
Location: Germany
Posts: 136
Rep Power: 21 |
some more information:
it is a very unsure thing with the boun darylayer addition of snappyHexMesh, but furthermore I think, that the expansionRation mustn't be too small. if it is e.g. 1.0, meaning the layers won't grow at all, sHM has no chance to add those layers while the over all thickness (finalLayerRatio) is too small (e.g. also 1.0). in this case sHM doesn't add the layers. So always pay attention, that the expansion factor as well as the overallthickness, as well as the minimumthickness is in a healthy balance with the thickness of the cells which are created with blockMesh. here I'm not sure which cells are meant, the original blockMesh cells or the already refined cells by sHM. |
|
June 18, 2009, 19:07 |
|
#20 |
Senior Member
|
Hi Wolfgang,
First, thanks for posting all this information. Second, are these prisms I see in the boundary layer? Or are they hexahedrons rendered as prisms by paraview? I am trying to mesh my boundary layer with mostly hexahedrons using snappyHexMesh but it seems all the boundary layer cells are 5-face prisms. Any thoughts on this? Am I wasting my time trying to get hexahedrons because prisms are better? My colleagues here are all using hexahedrons in their boundary layers, not prisms... thanks and have a good day! -Louis EDIT: for clarification, here is the output of my checkMesh: Number of cells of each type: hexahedra: 143741 prisms: 1454 wedges: 0 pyramids: 0 tet wedges: 92 tetrahedra: 0 polyhedra: 43413 and I attach a screenshot of a slice through my vehicle.. Seems like paraview is only showing me prisms but there are only 1454 according to checkMesh... so I am confused! Thanks again. -Louis Last edited by louisgag; June 18, 2009 at 23:46. Reason: clarification |
|
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
[snappyHexMesh] snappyhexmesh error in refinement phase | ianjikar | OpenFOAM Meshing & Mesh Conversion | 2 | May 11, 2018 14:27 |
[snappyHexMesh] Running snappyHexMesh in parallel - optimizing | peterhess | OpenFOAM Meshing & Mesh Conversion | 2 | January 3, 2018 03:54 |
[snappyHexMesh] Tutorial crashes: snappyHexMesh floating point exception. | jasv | OpenFOAM Meshing & Mesh Conversion | 4 | May 10, 2016 03:55 |
[snappyHexMesh] Problem with snappyhexMesh: modelling a pore chamber and pore throat model | Saideep | OpenFOAM Meshing & Mesh Conversion | 5 | May 10, 2015 15:46 |
[snappyHexMesh] problemes modelling surfaces with snappyhexmesh | gija79 | OpenFOAM Meshing & Mesh Conversion | 5 | June 30, 2010 14:50 |