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SHM problem : KVLCC2 with appendage mesh

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Old   February 8, 2016, 16:46
Default SHM problem : KVLCC2 with appendage mesh
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Park
Join Date: Nov 2015
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Hi all,
I'm trying to make a mesh for KVLCC2 (an oil tanker) with its appendage(ESD, Energy Saving Device). I made an .stl file of KVLCC2 & appendage (semicircular duct) with Gridgen, and trying to make a mesh using SHM(SnappyHexMesh).
However, I cannot make fine mesh for appendage. I refined KVLCC2 hull for level 6, and made two searchable boxes for AP, FP and refined level 7, 6 for each. And, made two more searchable box for ESD zone 1&2, and refined level 8, 9 for each. Finally I refined ESD for level 11.
I changed refine level of ESD zone 1&2, and ESD itself, but it doesn't make it. Intersection of hull(stern place) and ESD always have dirty surface.
If anybody know directions to develope this mesh, please help me.
I attached some image files, SHM code of my mesh.
thanks.
(Sorry for my poor English, I'm not native speaker T.T)



SHM dict code :
Code:
/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.4.0                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      snappyHexMeshDict;
}

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

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

        patchInfo
        {
            type wall;
        }
    }
    
    ESD.stl
    {
        type triSurfaceMesh;
        name hull;

        patchInfo
        {
            type wall;
        }
    }
    /*hull_top.stl
    {
        type triSurfaceMesh;
        name hull_top;

        patchInfo
        {
            type wall;
        }
    }*/
    Box
    {
        type searchableBox;
        min (-1.48 -0.1 -1.4);
        max (8.312 2 1);
    }
    FP
    {
        type searchableBox;
        min (-0.25 -0.1 -0.26);
        max (0.36 0.5 1);
    }
    AP
    {
        type searchableBox;
        min (5.13 -0.1 -0.26);
        max (5.73 0.5 1);
    }
    ESD_zone1
    {
        type searchableBox;
        min (5.24 -0.1 -0.01);
        max (5.49 0.5 0.24); //5.49 0.5 0.26
    }
    ESD_zone2
    {
        type searchableBox;
        min (5.31 -0.1 0.05);
        max (5.44 0.5 0.19); // 5.44 0.5 0.215
    }
};



// 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 2000000;

    // 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 1;

    // Number of buffer layers between different levels.
    // 1 means normal 2:1 refinement restriction, larger means slower
    // refinement.
    nCellsBetweenLevels 3;//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 "hull.eMesh";
             level 6;
         }
         {
             file "ESD.eMesh";
             level 11;
         }
     /*{
             file "hull_top.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
    {
        hull
        {
            // Surface-wise min and max refinement level
            level (6 6);
        }
    
        ESD
        {
            // Surface-wise min and max refinement level
            level (11 11);
        }/*
    hull_top
        {
            level (1 1);
        }*/
    }


    resolveFeatureAngle 30; //25

    // 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
    {
    Box
        {
            mode inside;
            levels ((1E15 3));
        }
    FP
        {
            mode inside;
            levels ((1E15 6));
        }
    AP
        {
            mode inside;
            levels ((1E15 6));
        }
    ESD_zone1
        {
            mode inside;
            levels ((1E15 8));//7
        }
    ESD_zone2
        {
            mode inside;
            levels ((1E15 9));//8
        }
    }


    // 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 (-4 1 0);


    // 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 true;
}



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

    //- 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; //4

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

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

    nFeatureSnapIter 10;
}



// 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
    {
        hull
        {
            nSurfaceLayers 2;

        }
        ESD
        {
            nSurfaceLayers 2;

        }
        /*hull_top
        {
            nSurfaceLayers 3;

        }*/
    }

    // Expansion factor for layer mesh
    expansionRatio 1.4; //1.5

    // 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.
    // See relativeSizes parameter.
    finalLayerThickness 0.6;//0.7

    // Minimum thickness of cell layer. If for any reason layer
    // cannot be above minThickness do not add layer.
    // See relativeSizes parameter.
    minThickness 0.2; //0.3

    // 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;//0


    // Advanced settings

    // When not to extrude surface. 0 is flat surface, 90 is when two faces
    // are perpendicular
    featureAngle 130;

    // 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 interigor 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
    // Note: changed(corrected) w.r.t 17x! 90 degrees corresponds to 130 in 17x.
    minMedianAxisAngle 90;

    // Create buffer region for new layer terminations
    nBufferCellsNoExtrude 3;


    // Overall max number of layer addition iterations. The mesher will exit
    // if it reaches this number of iterations; possibly with an illegal
    // mesh.
    nLayerIter 100;

    // 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 30;
}



// Generic mesh quality settings. At any undoable phase these determine
// where to undo.
meshQualityControls
{
    #include "meshQualityDict"
}


// 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;


// ************************************************************************* //
SurfaceFeature Extract code :
Code:
/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.4.0                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      surfaceFeatureExtractDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

hull.stl
{
    // How to obtain raw features (extractFromFile || extractFromSurface)
    extractionMethod    extractFromSurface;

    extractFromSurfaceCoeffs
    {
        // Mark edges whose adjacent surface normals are at an angle less
        // than includedAngle as features
        // - 0  : selects no edges
        // - 180: selects all edges
        includedAngle   180; //150
    }

    subsetFeatures
    {
        // Keep nonManifold edges (edges with >2 connected faces)
        nonManifoldEdges       yes;

        // Keep open edges (edges with 1 connected face)
        openEdges       yes;
    }


    // Write options

        // Write features to obj format for postprocessing
        writeObj                yes;
}
ESD.stl
{
    // How to obtain raw features (extractFromFile || extractFromSurface)
    extractionMethod    extractFromSurface;

    extractFromSurfaceCoeffs
    {
        // Mark edges whose adjacent surface normals are at an angle less
        // than includedAngle as features
        // - 0  : selects no edges
        // - 180: selects all edges
        includedAngle   180; //150
    }

    subsetFeatures
    {
        // Keep nonManifold edges (edges with >2 connected faces)
        nonManifoldEdges       yes;

        // Keep open edges (edges with 1 connected face)
        openEdges       yes;
    }


    // Write options

        // Write features to obj format for postprocessing
        writeObj                yes;
}
/*hull_top.stl
{
    extractionMethod    extractFromSurface;

    extractFromSurfaceCoeffs
    {

        includedAngle   180;
    }
    subsetFeatures
    {
        nonManifoldEdges       yes;
        openEdges       yes;
    }
        writeObj                yes;
}
*/

// ************************************************************************* //
Attached Images
File Type: png 1.png (80.7 KB, 19 views)
File Type: png 2.png (52.8 KB, 19 views)
File Type: png 4.png (49.6 KB, 18 views)
File Type: png zoom_in.png (64.9 KB, 19 views)
File Type: png 5.png (69.8 KB, 18 views)
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Old   March 13, 2016, 14:28
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Hi Park,
I have a few suggestions to improve the mesh, first may be you need to check your background mesh (blockMesh) with the grid spacing in x, y and z directions. Then i would check if the hull is composed of more than one surface or you are using the complete hull as one surface (this could be a problem), as the surface feature extract cannot find a feature line. May be an alternative way is to export each hull surface as single .stl file and them merge all these files together to a sing hull file.. Then you can use that file with several patches inside it and then apply surfaceFeatureExtract. Also to me your mesh looks very coarse in the stern section of the ship and further downstream. This might give you convergence issues due to really large jumps in the cells.
Good luck.
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