|
[Sponsors] |
[snappyHexMesh] snappyHexMesh does not remove internal cells |
![]() |
|
LinkBack | Thread Tools | Search this Thread | Display Modes |
![]() |
![]() |
#1 | |
New Member
Binglian Hu
Join Date: Jun 2017
Location: Shanghai,China
Posts: 4
Rep Power: 9 ![]() |
Hi everyone. I would really appreciate your help.
I use snappyHexMesh to create a grid around a pile. The pile is in stl format. But when I apply castellatedMesh it does not remove the cells inside. The geometry doesn't have any holes and I have execute the checkmesh, it seems eveything is OK. Here is my snappyHexMeshDict: Quote:
|
||
![]() |
![]() |
![]() |
![]() |
#2 | |
New Member
Binglian Hu
Join Date: Jun 2017
Location: Shanghai,China
Posts: 4
Rep Power: 9 ![]() |
This is the results of surfaceCheck command:
Quote:
|
||
![]() |
![]() |
![]() |
![]() |
#3 |
Member
Join Date: Nov 2014
Posts: 92
Rep Power: 11 ![]() |
1) Is your stl geometry fully closed?
2) Is the locationInMesh coordinate inside the domain but out of the box? 3) Are you viewing the latest time step in paraview? Sent from my LG-H818 using CFD Online Forum mobile app |
|
![]() |
![]() |
![]() |
![]() |
#4 |
New Member
Binglian Hu
Join Date: Jun 2017
Location: Shanghai,China
Posts: 4
Rep Power: 9 ![]() |
Thank you sooo much, I just made a silly mistake. The refinementSurfaces should be "big" but not "big.stl".
|
|
![]() |
![]() |
![]() |
![]() |
#5 | |
New Member
Binglian Hu
Join Date: Jun 2017
Location: Shanghai,China
Posts: 4
Rep Power: 9 ![]() |
Quote:
Thx a lot!I've fixed it. |
||
![]() |
![]() |
![]() |
![]() |
#6 |
Member
Amir Abbas Aliabadi
Join Date: Mar 2013
Posts: 33
Rep Power: 13 ![]() |
I would like to also thank the contributors to this entry. I had a similar issue and came across the following techniques to resolve it:
1- Always make sure of the quality of the surface before running snappyHexMesh. Under the triSurface directory, run: surfaceCheck object.stl This should confirm the following: a: surface must be close b: all edges must be connected to two faces c: number of unconnected parts = 1 d: number of zones = 1 2- In snappyHexMeshDict and under refinementSurfaces, you must have the name of the surface e.g. object, NOT the filename of the surface object.stl. 3- Make sure you use locationInMesh with a coordinate that is NOT on a face or edge even after refinement, but always inside a cell. |
|
![]() |
![]() |
![]() |
![]() |
#7 |
Senior Member
|
Hello Amir,
Thank you for your valuable addition. Is there a way before meshing to make sure that locationInMeeesh is within the cell rather than on face or on the edge of the cell. Regards |
|
![]() |
![]() |
![]() |
![]() |
#8 |
New Member
Jalil
Join Date: Nov 2018
Posts: 8
Rep Power: 7 ![]() |
Hello everyone,
I have the same problem. However, I multiple stl files. They are not closed individually but all of them together closes all the boundaries. I need your help. |
|
![]() |
![]() |
![]() |
![]() |
#9 |
Senior Member
|
Hello Jalil,
Little information about your case and problem would be beneficial to give some suggestions. In general, if overall body is closed, then there should not be any problem. Open your all stl files in paraview and check again if they are water tight. Regards |
|
![]() |
![]() |
![]() |
![]() |
#10 | |
New Member
mh
Join Date: May 2013
Posts: 5
Rep Power: 13 ![]() |
Quote:
I dont know how I can check if the whole geometry is "water tight" or not, should I do that visually or there is a way to do it properly? |
||
![]() |
![]() |
![]() |
![]() |
#11 | |
Senior Member
Franco
Join Date: Nov 2019
Location: Compiègne, France
Posts: 129
Rep Power: 6 ![]() |
Quote:
this is not a problem, you should do the following: create a folder that contains only your muliple stls (no other stls files at least) I am assuming they a re assci stls (and not binary) 1. you open terminal $ cat *.stl >> model.stl (this will create a only stl that if your surface meshes are correct, this should give a water tight mesh you can check it with surfaceChek command.) 2. you use a region stl configuration in snappy hex inside the geometry dict. example bellow. 3. one really important thing to take in accound is that you should give a refiment level, even if it is (0 0) to each region in castellated if you dont do this snappy will have problems. Code:
/*--------------------------------*- C++ -*----------------------------------*\ | ========= | | | \\ / F ield | OpenFOAM: The Open Source CFD Toolbox | | \\ / O peration | Version: v2012 | | \\ / A nd | Website: www.openfoam.com | | \\/ M anipulation | | \*---------------------------------------------------------------------------*/ FoamFile { version 2.0; format ascii; class dictionary; object snappyHexMeshDict; } // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // // Which of the steps to run castellatedMesh true; snap true; addLayers false; // Geometry. Definition of all surfaces. All surfaces are of class // searchableSurface. // Surfaces are used // - to specify refinement for any mesh cell intersecting it // - to specify refinement for any mesh cell inside/outside/near // - to 'snap' the mesh boundary to the surface geometry { model.stl // name of the file in the constant/triSurface/ { type triSurfaceMesh; name InnerCylinder; // name that it will be called thought the simulation (it is also used in the castellatedMeshDict) regions //if the stl is divided in region the regions can be used to create patchs { regionSTL_i //this is the name of the different regions in the stl, if the workflow will be with stl with regions create a patch for each region, do not leave // a regionSTL without a name. if thats the case, snappy will create a patch named nameOfModel_regionSTL_i. { name patchNameOfRegion_i; // this is the name of the patch that snappy will create for the regionSTL_i (the type of patch/boundary can be assigned in the castellatedMeshDict) } Inlet { name Inlet; } Outlet { name Outlet; } Walls { name Walls; } sym_1 { name symm_1; } sym_2 { name symm_2; } } } }; // Settings for the castellatedMesh generation. castellatedMeshControls { // Refinement parameters // ~~~~~~~~~~~~~~~~~~~~~ // If local number of cells is >= maxLocalCells on any processor // switches from from refinement followed by balancing // (current method) to (weighted) balancing before refinement. maxLocalCells 2000000000; // Overall cell limit (approximately). Refinement will stop immediately // upon reaching this number so a refinement level might not complete. // Note that this is the number of cells before removing the part which // is not 'visible' from the keepPoint. The final number of cells might // actually be a lot less. maxGlobalCells 200000000; // The surface refinement loop might spend lots of iterations refining just a // few cells. This setting will cause refinement to stop if <= minimumRefine // are selected for refinement. Note: it will at least do one iteration // (unless the number of cells to refine is 0) minRefinementCells 5; // Allow a certain level of imbalance during refining // (since balancing is quite expensive) // Expressed as fraction of perfect balance (= overall number of cells / // nProcs). 0=balance always. maxLoadUnbalance 0.10; // Number of buffer layers between different levels. // 1 means normal 2:1 refinement restriction, larger means slower // refinement. nCellsBetweenLevels 1; // Explicit feature edge refinement // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ // Specifies a level for any cell intersected by its edges. // This is a featureEdgeMesh, read from constant/triSurface for now. features ( { file "model.extendedFeatureEdgeMesh"; //this should be created using the surfaceFeatureExtract application (combined with system/surfaceFeatureExtractDict) level 2; } ); // Surface based refinement // ~~~~~~~~~~~~~~~~~~~~~~~~ // Specifies two levels for every surface. The first is the minimum level, // every cell intersecting a surface gets refined up to the minimum level. // The second level is the maximum level. Cells that 'see' multiple // intersections where the intersections make an // angle > resolveFeatureAngle get refined up to the maximum level. refinementSurfaces { InnerCylinder //here we use the name designated to the stl in the geometryDict section { level (1 1); // This is the min and maximum refiment of the background mesh that intersect the geometry at the boundaries of the stl the minimum refiment // is the refiment over a surface (boundary of the stl) and the maximum is the refiment over a feature (corner/wire of the stl) regions { regionSTL_i // Here we need to use the regionSTL_i name, and not the name assignated in the geometryDict section! { level ( 1 2 ); // Same as before the min and max refiment but only over this boundary, so in this way we can refine over a boundary if necessary patchInfo { type patch; // Here we define the boundary type patch, wall, etc, be aware snappy does not accept contrainst type boundaries // so, no: symmetry, symmetryPlane, cyclic, clyclicAMI, etc. For these type of boundaries or they are carried out from the backgroundMesh (from the blockMeshDict) // or it should be created after the snappyHexMesh with createPatch application (combined with system/createPatchDict) } } Inlet { level ( 1 2 ); patchInfo { type patch; } } Outlet { level ( 1 2 ); patchInfo { type patch; } } sym_1 { level ( 1 2 ); patchInfo { type patch; } } sym_2 { level ( 1 2 ); patchInfo { type patch; } } Walls { level ( 1 2 ); patchInfo { type wall; } } } } } best regards. |
||
![]() |
![]() |
![]() |
![]() |
#12 | |
Senior Member
Franco
Join Date: Nov 2019
Location: Compiègne, France
Posts: 129
Rep Power: 6 ![]() |
Quote:
surfaceCheck model.stl | tail -9 | head -1 should give you as output only that line, but in any case you will see this in surfaceCheck. as I menioned in my previous post, when using multiple stls you should fuse it into one and then use surfaceCheck to see it is waterthight. (2 separate stls can be not waterthight but their fussion can be) best regards. |
||
![]() |
![]() |
![]() |
![]() |
#13 | |
New Member
mh
Join Date: May 2013
Posts: 5
Rep Power: 13 ![]() |
Quote:
If I am not mistaken, for snappyHexMesh and simualation, I need to have separated stl file for each boundary condition. When I give the separated stl files, snappyHexMesh does not snap the outer part (I am interested in the inner part). I am sure about the locationInMesh. Do you have any advice? |
||
![]() |
![]() |
![]() |
![]() |
#14 | |
Senior Member
Franco
Join Date: Nov 2019
Location: Compiègne, France
Posts: 129
Rep Power: 6 ![]() |
Quote:
you dont need separate stls files, you need an stl with regions (one file). following the step 1. in snappyHexMesh does not remove internal cells will give you exactly that, an stl with a region for each stl that you used to create them. imagine you have 1.stl, 2.stl & 3.stl , you use cat *.stl >>model.stl you will have 4 stls in total the three originals that you will not use, and model.stl that will be separated in regions inside of the file (each region will be each of original stls). you should use the 4th stl (model.stl) for snappy, have a look at the geometryDict inside the example in snappy that I post in the post I mentionned previously. here you indicate one file, with regions inside of it. Franco |
||
![]() |
![]() |
![]() |
![]() |
#15 | |
New Member
mh
Join Date: May 2013
Posts: 5
Rep Power: 13 ![]() |
Quote:
just one more question, to add boundary layers, I modified the dictionary as below, but it didnt create the boundary layers. addLayersControls { relativeSizes true; layers { InnerCylinder { regions { "wall1" { nSurfaceLayers 3; } } } } I have also tried this, but no luck! addLayersControls { relativeSizes true; layers { "wall1" { nSurfaceLayers 3; } } |
||
![]() |
![]() |
![]() |
![]() |
#16 | |
Senior Member
Franco
Join Date: Nov 2019
Location: Compiègne, France
Posts: 129
Rep Power: 6 ![]() |
Quote:
the layers you have to define them like this: Code:
layers { patchNameOfRegion_i // Here in difference with the castellatedMeshDict section, we should use the patchNameOfRegion_i! and not the regionSTL_i! { nSurfaceLayers 3; // here we define the number of layers over the patchNameOfRegion_i } } also take in accound that if snappy does not achive the 100% of the meshQuality, it will not create layers. so in my opinion from the little info, or you defined wrong in the layer dictionary or you are not achiving the quality so snappy is able to add the layer ps please use CODE mode when posting part of dictionaries so it is easier to read. |
||
![]() |
![]() |
![]() |
![]() |
#17 | |
New Member
mh
Join Date: May 2013
Posts: 5
Rep Power: 13 ![]() |
Quote:
Thank you very much. It was indeed becasue of low quality of mesh. After refining, I got the boundary layers. The pdf is also very useful. |
||
![]() |
![]() |
![]() |
Tags |
cell removal, snappy hex mesh |
|
|
![]() |
||||
Thread | Thread Starter | Forum | Replies | Last Post |
[snappyHexMesh] snappyHexMesh <-> dynamicMeshDict problem with protected cells | Billy_16 | OpenFOAM Meshing & Mesh Conversion | 2 | November 21, 2020 03:34 |
[snappyHexMesh] Layers not growing at all | zonda | OpenFOAM Meshing & Mesh Conversion | 12 | June 6, 2020 11:28 |
[snappyHexMesh] snappyHexMesh does not create any mesh except one for the reference cell | Arman_N | OpenFOAM Meshing & Mesh Conversion | 1 | May 20, 2019 17:16 |
[blockMesh] Create internal faces as patch in blockMesh | m.delta68 | OpenFOAM Meshing & Mesh Conversion | 14 | July 12, 2018 14:43 |
[snappyHexMesh] How to create internal boundaries using snappyHexMesh | robyTKD | OpenFOAM Meshing & Mesh Conversion | 2 | October 19, 2014 09:57 |