CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > OpenFOAM > OpenFOAM Meshing & Mesh Conversion

[snappyHexMesh] SnappyHexMesh refine but does not snap

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   December 14, 2012, 12:37
Default SnappyHexMesh refine but does not snap
  #1
Member
 
Malik
Join Date: Dec 2012
Location: Austin, USA
Posts: 53
Rep Power: 13
malaboss is on a distinguished road
Hi FOAMers,

I am trying tu study an air foil case in 2D.
The geometry is defined by an stl file.
To design the mesh I decided to use snappyHexMesh.

However when i run it, i get a refined geometry but not snapped.
I already saw few threads about it but no solution given what right for my case.

I use Open Foam 2.1.1
My background mesh size is closed to 1x1x1
I defined a refinement box around the air foil
I defined well the location in mesh

And i just don't know what i am doing wrong.

You can find enclosed my blockMeshDict and my snappyHexMeshDict, and a picture of the situation.

blockMeshDict
Code:
/*---------------------------------------------------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  1.0                                   |
|   \\  /    A nd           | Web:      http://www.openfoam.org               |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/

FoamFile
{
    version         2.0;
    format          ascii;

    root            "";
    case            "";
    instance        "";
    local           "";

    class           dictionary;
    object          blockMeshDict;
}

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //


convertToMeters 1;

vertices        
(
    (-17000.0 3500  -5750.0)
    ( 8000.0 3500  -5750.0)
    ( 8000.0  6000  -5750.0)
    (-17000.0  6000  -5750.0)
    (-17000.0 3500   6750.0)
    ( 8000.0 3500   6750.0)
    ( 8000.0  6000   6750.0)
    (-17000.0  6000   6750.0)
);

blocks          
(
    hex (0 1 2 3 4 5 6 7) (10 1 5) simpleGrading (1 1 1)
);

edges           
(
);

patches         
(
    patch maxY 
    (
        (3 7 6 2)
    )
    patch minX
    (
        (0 4 7 3)
    )
    patch maxX
    (
        (2 6 5 1)
    )
    patch minY
    (
        (1 5 4 0)
    )
    patch minZ
    (
        (0 3 2 1)
    )
    patch maxZ
    (
        (4 5 6 7)
    )
);

mergePatchPairs 
(
);


// ************************************************************************* //
snappyHexMeshDict
Code:
/*---------------------------------------------------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  1.0                                   |
|   \\  /    A nd           | Web:      http://www.openfoam.org               |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/

FoamFile
{
    version         2.0;
    format          ascii;

    root            "/home/penfold/mattijs/foam/mattijs2.1/run/icoFoam";
    case            "cavity";
    instance        "system";
    local           "";

    class           dictionary;
    object          autoHexMeshDict;
}

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

// Which of the steps to run
castellatedMesh true;  // true;
snap            true;   // true;
addLayers       true;   // true;


// 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
{
    surfacemesh.stlb
    {
        type triSurfaceMesh;
        name stlSurface;
    }

    refinementBox
    {
        type searchableBox;
        min (0 3425 0);
        max (2418.4 16500.4 2171.11);
    }
};



// Settings for the castellatedMesh generation.
castellatedMeshControls
{
	allowFreeStandingZoneFaces true;
    // Refinement parameters
    // ~~~~~~~~~~~~~~~~~~~~~

    // While refining maximum number of cells per processor. This is basically
    // the number of cells that fit on a processor. If you choose this too small
    // it will do just more refinement iterations to obtain a similar mesh.
    maxLocalCells 1000000;

    // 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 2000000;

    // 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 10;

    // Number of buffer layers between different levels.
    // 1 means normal 2:1 refinement restriction, larger means slower
    // refinement.
    nCellsBetweenLevels 2;   // 2;



    // 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 "someLine.eMesh";
        //    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
    {
        stlSurface
        {
            // Surface-wise min and max refinement level
            level (2 4);  // 5 6
        }
    }

    // Resolve sharp angles
    resolveFeatureAngle 15;   // 30;


    // Region-wise refinement
    // ~~~~~~~~~~~~~~~~~~~~~~

    // Specifies refinement level for cells in relation to a surface. One of
    // three modes
    // - distance. 'levels' specifies per distance to the surface the
    //   wanted refinement level. The distances need to be specified in
    //   descending order.
    // - inside. 'levels' is only one entry and only the level is used. All
    //   cells inside the surface get refined up to the level. The surface
    //   needs to be closed for this to be possible.
    // - outside. Same but cells outside.

    refinementRegions
    {
        refinementBox
        {
            mode inside;   // inside;
            levels ((1.0e+15 4));  //1E15 4
        }
    }


    // Mesh selection
    // ~~~~~~~~~~~~~~

    // After refinement patches get added for all refinementSurfaces and
    // all cells intersecting the surfaces get put into these patches. The
    // section reachable from the locationInMesh is kept.
    // NOTE: This point should never be on a face, always inside a cell, even
    // after refinement.
    locationInMesh (-3023.55 4000 -103.606); 
}



// Settings for the snapping.
snapControls
{
    //- Number of patch smoothing iterations before finding correspondence
    //  to surface
    nSmoothPatch 10;

    //- Relative distance for points to be attracted by surface feature point
    //  or edge. True distance is this factor times local
    //  maximum edge length.
    tolerance 1.0;

    //- Number of mesh displacement relaxation iterations.
    nSolveIter 30;

    //- Maximum number of snapping relaxation iterations. Should stop
    //  before upon reaching a correct mesh.
    nRelaxIter 10;
}



// Settings for the layer addition.
addLayersControls
{
    relativeSizes true;  //true;   // v 1.6
    // Per final patch (so not geometry!) the layer information
    layers
    {
        //minZ
        //{
        //    nSurfaceLayers 3;
        //}
        stlSurface_patch0   // a_surface_name
        {
            nSurfaceLayers 5;
        }
    }

    // Expansion factor for layer mesh
    expansionRatio 1.4;   // 1.0;

    //- Wanted thickness of final added cell layer. If multiple layers
    //  is the
    //  thickness of the layer furthest away from the wall.
    //  Relative to undistorted size of cell outside layer.
    //finalLayerRatio FINALLAYERRATIO;   // 0.3; 
    finalLayerThickness 0.6;   // 0.3;    // v 1.6

    //- Minimum thickness of cell layer. If for any reason layer
    //  cannot be above minThickness do not add layer.
    //  Relative to undistorted size of cell outside layer.
    minThickness 0.001;   // 0.1;

    //- If points get not extruded do nGrow layers of connected faces that are
    //  also not grown. This helps convergence of the layer addition process
    //  close to features.
    nGrow 1;   // 1;


    // Advanced settings

    //- When not to extrude surface. 0 is flat surface, 90 is when two faces
    //  make straight angle.
    featureAngle 179;   // 30; 

    //- Maximum number of snapping relaxation iterations. Should stop
    //  before upon reaching a correct mesh.
    nRelaxIter 3;

    // Number of smoothing iterations of surface normals 
    nSmoothSurfaceNormals 1;

    // Number of smoothing iterations of interior mesh movement direction  
    nSmoothNormals 3;

    // Smooth layer thickness over surface patches
    nSmoothThickness 10;

    // Stop layer growth on highly warped cells 
    maxFaceThicknessRatio 0.5;

    // Reduce layer growth where ratio thickness to medial 
    // distance is large 
    maxThicknessToMedialRatio 0.3;

    // Angle used to pick up medial axis points
    minMedianAxisAngle 130;

    // Create buffer region for new layer terminations
    nBufferCellsNoExtrude 0;

    // Overall max number of layer addition iterations   // v 1.6
    nLayerIter 50;   // v 1.6
}



// Generic mesh quality settings. At any undoable phase these determine
// where to undo.
meshQualityControls
{
    //- Maximum non-orthogonality allowed. Set to 180 to disable.
    maxNonOrtho 65;

    //- Max skewness allowed. Set to <0 to disable.
    maxBoundarySkewness 20;
    maxInternalSkewness 4;

    //- Max concaveness allowed. Is angle (in degrees) below which concavity
    //  is allowed. 0 is straight face, <0 would be convex face.
    //  Set to 180 to disable.
    maxConcave 80;

    //- Minimum projected area v.s. actual area. Set to -1 to disable.
    minFlatness 0.5;

    //- Minimum pyramid volume. Is absolute volume of cell pyramid.
    //  Set to very negative number (e.g. -1E30) to disable.
    minVol 1e-13;

    //- Minimum face area. Set to <0 to disable.
    minArea -1;

    //- Minimum face twist. Set to <-1 to disable. dot product of face normal
    //- and face centre triangles normal
    minTwist 0.02;

    //- minimum normalised cell determinant
    //- 1 = hex, <= 0 = folded or flattened illegal cell
    minDeterminant 0.001;

    //- minFaceWeight (0 -> 0.5) 
    minFaceWeight 0.02;

    //- minVolRatio (0 -> 1)
    minVolRatio 0.01;

    //must be >0 for Fluent compatibility
    minTriangleTwist -1;

	//- Minimum quality of the tet formed by the face-centre
    //  and variable base point minimum decomposition triangles and
    //  the cell centre. This has to be a positive number for tracking
    //  to work. Set to very negative number (e.g. -1E30) to
    //  disable.
    //     <0 = inside out tet,
    //      0 = flat tet
    //      1 = regular tet
    minTetQuality 1e-30;

    // Advanced

    //- Number of error distribution iterations
    nSmoothScale 4;
    //- amount to scale back displacement at error points
    errorReduction 0.75;
}


// Advanced

// Flags for optional output
// 0 : only write final meshes
// 1 : write intermediate meshes
// 2 : write volScalarField with cellLevel for postprocessing
// 4 : write current intersections as .obj files
debug 0;


// Merge tolerance. Is fraction of overall bounding box of initial mesh.
// Note: the write tolerance needs to be higher than this.
mergeTolerance 1E-6;


// ************************************************************************* //
Attached Images
File Type: jpg airfoil.jpg (46.3 KB, 164 views)
malaboss is offline   Reply With Quote

Old   November 12, 2014, 10:08
Default Same here
  #2
New Member
 
Lilly
Join Date: May 2014
Posts: 11
Rep Power: 11
5tern is on a distinguished road
Hey,

did you find a solution then?
I have the same problem for my 2D-geometry.

Similar cases only give solutions for 3D (featured edge).

Thanks in advance
5tern is offline   Reply With Quote

Old   November 25, 2014, 18:04
Default
  #3
Super Moderator
 
Tobi's Avatar
 
Tobias Holzmann
Join Date: Oct 2010
Location: Tussenhausen
Posts: 2,708
Blog Entries: 6
Rep Power: 51
Tobi has a spectacular aura aboutTobi has a spectacular aura aboutTobi has a spectacular aura about
Send a message via ICQ to Tobi Send a message via Skype™ to Tobi
Hi Stern,
As you See from the date, it's a long time ago. On my homepage you find 2d mesh generation tutorials ...

Good luck
__________________
Keep foaming,
Tobias Holzmann
Tobi is offline   Reply With Quote

Old   December 9, 2014, 04:23
Default Found Problem
  #4
New Member
 
Lilly
Join Date: May 2014
Posts: 11
Rep Power: 11
5tern is on a distinguished road
Hello Tobias,

thank you for your reply. I found my .stl-file to be the problem, for I assumed to get the 3D-effect simply by extruding after snapping. But snappy already requires a volume mesh.
5tern is offline   Reply With Quote

Old   December 10, 2014, 02:44
Default
  #5
Super Moderator
 
Tobi's Avatar
 
Tobias Holzmann
Join Date: Oct 2010
Location: Tussenhausen
Posts: 2,708
Blog Entries: 6
Rep Power: 51
Tobi has a spectacular aura aboutTobi has a spectacular aura aboutTobi has a spectacular aura about
Send a message via ICQ to Tobi Send a message via Skype™ to Tobi
Yes sHM require a 3d mesh.
Where is the problem?
__________________
Keep foaming,
Tobias Holzmann
Tobi is offline   Reply With Quote

Old   December 10, 2014, 06:27
Default
  #6
New Member
 
Lilly
Join Date: May 2014
Posts: 11
Rep Power: 11
5tern is on a distinguished road
Hello Tobi,

you're right and there was no problem except me forgetting to extrude the 2D-mesh BEFORE snapping :-) I just wrote it in case someone experiences the same "problem".
5tern is offline   Reply With Quote

Old   December 10, 2014, 06:31
Default
  #7
Super Moderator
 
Tobi's Avatar
 
Tobias Holzmann
Join Date: Oct 2010
Location: Tussenhausen
Posts: 2,708
Blog Entries: 6
Rep Power: 51
Tobi has a spectacular aura aboutTobi has a spectacular aura aboutTobi has a spectacular aura about
Send a message via ICQ to Tobi Send a message via Skype™ to Tobi
Quote:
Originally Posted by 5tern View Post
Hello Tobi,

you're right and there was no problem except me forgetting to extrude the 2D-mesh BEFORE snapping :-) I just wrote it in case someone experiences the same "problem".
Well you also can make the following steps:
  • castellatedMesh
  • snap the mesh
  • (flattenMesh [optional])
  • extrudeMesh by using front or back patch


That is my standard procedure if I want to generate normal 2d or rotational 2d meshes.
Never did extruding before snapping.
__________________
Keep foaming,
Tobias Holzmann
Tobi is offline   Reply With Quote

Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
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 Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
[snappyHexMesh] Run snappyHexMesh steps (castellated, snap, addlayer) separately Glc OpenFOAM Meshing & Mesh Conversion 6 October 8, 2021 03:50
[snappyHexMesh] snappyHexMesh does not snap everywhere flowris OpenFOAM Meshing & Mesh Conversion 7 February 17, 2019 06:17
[snappyHexMesh] snappyHexMesh doesnt snap staustrahltriebwerk OpenFOAM Meshing & Mesh Conversion 47 March 18, 2018 15:19
[snappyHexMesh] snappyHexMesh. irregular cells on snap stage Svensen OpenFOAM Meshing & Mesh Conversion 0 April 3, 2015 04:12
[snappyHexMesh] snappyHexMesh failure to snap to geometry Yadasol OpenFOAM Meshing & Mesh Conversion 1 November 17, 2014 06:00


All times are GMT -4. The time now is 17:57.