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

[snappyHexMesh] How to create internal boundaries using snappyHexMesh

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   September 6, 2014, 14:38
Default How to create internal boundaries using snappyHexMesh
  #1
Member
 
Roberto Pieri
Join Date: Feb 2012
Location: Milan
Posts: 57
Rep Power: 10
robyTKD is on a distinguished road
Hi foamers,

I am trying to mesh a duct with zero-thickness deflectors in it.

In the castellated phase snappy is able to refine cells near deflectors (as you can see in the attached figures below), but when running the snap phase, snappy doesn't morph the mesh following deflectors geometry. Moreover faceZones related to the deflectors are empty, as you can see below:
Code:
Introducing zones for interfaces
--------------------------------

Surface : deflettori_1
    faceZone : deflettori_1
    cellZone : deflettori_1
Surface : deflettori_2
    faceZone : deflettori_2
    cellZone : deflettori_2
Walking from location-in-mesh (12000 -18000 -22000) to assign cellZones - crossing a faceZone face changes cellZone

Found point (12000 -18000 -22000) in global region 0 out of 1 regions.
Only keeping zone faces inbetween different cellZones.

CellZones:
    deflettori_1        size:0
    deflettori_2        size:0

FaceZones:
    deflettori_1        size:0
    deflettori_2        size:0

Edge intersection testing:
    Number of edges             : 3596616
    Number of edges to retest   : 0
    Number of intersected edges : 170194
To be more clear the snappyHexMeshDict is the following:
Code:
/*--------------------------------*- C++ -*----------------------------------*| =========                 |                                                 |
| \      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \    /   O peration     | Version:  2.2.0                                 |
|   \  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.2;
    format      ascii;
    class       dictionary;
    object      autoHexMeshDict;
}

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

// Which of the steps to run
castellatedMesh true; // true;
snap            true; // 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
{
    condotto.stl
    {
        type triSurfaceMesh;
        name condotto;

        patchInfo
        {
            type wall;
        }
    }

    deflettori_1.stl
    {
        type triSurfaceMesh;
        name deflettori_1;

        patchInfo
        {
            type wall;
        }
    }

    deflettori_2.stl
    {
        type triSurfaceMesh;
        name deflettori_2;

        patchInfo
        {
            type wall;
        }
    }
};

// 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 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 10000000;

    // 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 0;	// 1;

    // 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 6;



    // 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 "condotto.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
    {
        condotto
        {
            // Surface-wise min and max refinement level
            level (2 2);
        }

    deflettori_1
    {
        level (2 2);
        faceZone deflettori_1;

        // Create baffles for all faces on the surface
        faceType baffle;

        cellZone deflettori_1;
        cellZoneInside none;
    } 

    deflettori_2
    {
        level (2 2);
        faceZone deflettori_2;

        // Create baffles for all faces on the surface
        faceType baffle;

        cellZone deflettori_2;

	cellZoneInside none;
    } 
    }

    resolveFeatureAngle 30;	// 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
    { 
    }


    // 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 (12000 -18000 -22000);


    // Whether any faceZones (as specified in the refinementSurfaces)
    // are only on the boundary of corresponding cellZones or also allow
    // free-standing zone faces. Not used if there are no faceZones.
    allowFreeStandingZoneFaces false; 	// true; (prima era true!)	// false;
}



// Settings for the snapping.
snapControls
{
    //- Number of patch smoothing iterations before finding correspondence
    //  to surface
    nSmoothPatch 3;	// 3;(caso MidQ-meshMix)

    //- Relative distance for points to be attracted by surface feature point
    //  or edge. True distance is this factor times local
    //  maximum edge length.
    //    tolerance 4.0;
    tolerance 4.0;	// si puņ alzare...

    //- Number of mesh displacement relaxation iterations.
    nSolveIter 100;

    //- Maximum number of snapping relaxation iterations. Should stop
    //  before upon reaching a correct mesh.
    nRelaxIter 5;

   // Feature snapping

        //- Number of feature edge snapping iterations.
        //  Leave out altogether to disable.
        nFeatureSnapIter 10;

        //- Detect (geometric only) features by sampling the surface
        //  (default=false).
        implicitFeatureSnap false;

        //- Use castellatedMeshControls::features (default = true)
        explicitFeatureSnap true;

        //- Detect points on multiple surfaces (only for explicitFeatureSnap)
        multiRegionFeatureSnap true;
}



// Settings for the layer addition.
addLayersControls
{
    // Are the thickness parameters below relative to the undistorted
    // size of the refined cell outside layer (true) or absolute sizes (false).
    relativeSizes true;

    // Per final patch (so not geometry!) the layer information
    layers
    {
    }

    // Expansion factor for layer mesh
    expansionRatio 1.2;


    //- Wanted thickness of final added cell layer. If multiple layers
    //  is the thickness of the layer furthest away from the wall.
    //  See relativeSizes parameter.
    finalLayerThickness 0.5;

    //- Minimum thickness of cell layer. If for any reason layer
    //  cannot be above minThickness do not add layer.
    //  See relativeSizes parameter.
    minThickness 0.002;
    
    //- 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.
    // Note: changed(corrected) w.r.t 17x! (didn't do anything in 17x)
    nGrow 0;


    // Advanced settings

    //- When not to extrude surface. 0 is flat surface, 90 is when two faces
    //  make straight angle.
    featureAngle 180; //60 puis 180

    //- Maximum number of snapping relaxation iterations. Should stop
    //  before upon reaching a correct mesh.
    nRelaxIter 5;

    // 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 0.2;

    // Angle used to pick up medial axis points
    // Note: changed(corrected) w.r.t 17x! 90 degrees corresponds to 130 in 17x.
    minMedianAxisAngle 90;

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


    // Overall max number of layer addition iterations. The mesher will exit
    // if it reaches this number of iterations; possibly with an illegal
    // mesh.
    nLayerIter 50;

    // Max number of iterations after which relaxed meshQuality controls
    // get used. Up to nRelaxIter it uses the settings in meshQualityControls,
    // after nRelaxIter it uses the values in meshQualityControls::relaxed.
    nRelaxedIter 20;
}



// 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;	// NB: mettere valore del checkMesh post castellated e separare 3 fasi

    //- Max skewness allowed. Set to <0 to disable.
    maxBoundarySkewness 4;
    maxInternalSkewness 2;

    //- 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 pyramid volume. Is absolute volume of cell pyramid.
    //  Set to a sensible fraction of the smallest cell volume expected.
    //  Set to very negative number (e.g. -1E30) to disable.
    minVol 1e-13;

    //- Minimum quality of the tet formed by the face-centre
    //  and variable base point minimum decomposition triangles and
    //  the cell centre.  Set to very negative number (e.g. -1E30) to
    //  disable.
    //     <0 = inside out tet,
    //      0 = flat tet
    //      1 = regular tet
    minTetQuality 1e-30; // ( prima era 1e-30: abilitato );

    //- 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 0.05;	// 0.05;	// -1; disattivo

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

    //- minFaceWeight (0 -> 0.5)
    minFaceWeight 0.05;

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

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

    //- if >0 : preserve single cells with all points on the surface if the
    //  resulting volume after snapping (by approximation) is larger than
    //  minVolCollapseRatio times old volume (i.e. not collapsed to flat cell).
    //  If <0 : delete always.
    //minVolCollapseRatio 0.5;


    // Advanced

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



    // Optional : some meshing phases allow usage of relaxed rules.
    // See e.g. addLayersControls::nRelaxedIter.
    relaxed
    {
        //- Maximum non-orthogonality allowed. Set to 180 to disable.
        // maxNonOrtho 180;
    }
}


// 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;


// ************************************************************************* //
I also used createBaffles but I had no luck.

Thank you very much,
Roberto
Attached Images
File Type: jpg Deflectors1.jpg (98.0 KB, 222 views)
File Type: jpg Deflectors2.jpg (98.9 KB, 162 views)
robyTKD is offline   Reply With Quote

Old   September 9, 2014, 13:31
Default
  #2
Member
 
Roberto Pieri
Join Date: Feb 2012
Location: Milan
Posts: 57
Rep Power: 10
robyTKD is on a distinguished road
Any ideas??
robyTKD is offline   Reply With Quote

Old   October 19, 2014, 10:57
Default
  #3
Member
 
Cem Albukrek
Join Date: Mar 2009
Posts: 52
Rep Power: 13
albcem is on a distinguished road
Try to use the surface feature extraction feature on the missing sufraces. This comes with the latest 2.3 version of OpenFoam and seems to be fool proof. For an example you could look in the tutorials directory, i.e. Motorcycle case.
albcem is offline   Reply With Quote

Reply

Tags
baffles, snappy

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
OpenFoam "Permission denied" and "command not found" problems. iyidaniel@yahoo.co.uk OpenFOAM Running, Solving & CFD 11 January 2, 2018 07:47
[snappyHexMesh] Modifications with SnappyHexMesh: create a beach in order to prevent reflected waves Moux OpenFOAM Meshing & Mesh Conversion 2 July 8, 2015 08:27
[snappyHexMesh] snappyHexMesh and blockMesh for internal flow (leaking geometry?) vaina74 OpenFOAM Meshing & Mesh Conversion 10 November 20, 2014 10:14
[snappyHexMesh] snappyHexMesh and cyclic boundaries Ruli OpenFOAM Meshing & Mesh Conversion 2 December 9, 2013 07:51
[snappyHexMesh] snappyHexMesh and internal flows ed_teller OpenFOAM Meshing & Mesh Conversion 2 September 20, 2012 13:38


All times are GMT -4. The time now is 12:54.