CFD Online Discussion Forums - [snappyHexMesh] Defining boundary condition for stl imported

Hi Pablo,

Thank you for your quick reply.
Yes, I saw the constant/polyMesh/boundary file, but I think it is generated by blockMesh. Thus, the sphere does not appear in this file but it is probably normal. Or should I modify this file ?
Here is the content of my boundary file at the moment :

Code:

FoamFile

{

    version     2.0;

    format      ascii;

    class       polyBoundaryMesh;

    location    "constant/polyMesh";

    object      boundary;

}

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



3

(

    inlet

    {

        type            patch;

        nFaces          625;

        startFace       90625;

    }

    outlet

    {

        type            patch;

        nFaces          625;

        startFace       91250;

    }

    walls

    {

        type            wall;

        nFaces          5000;

        startFace       91875;

    }

)



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

I think the problem might come from my snappyHexMeshDict file. Here it is:

Code:

/*--------------------------------*- C++ -*----------------------------------*\

| =========                 |                                                 |

| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |

|  \\    /   O peration     | Version:  2.2.2                                 |

|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |

|    \\/     M anipulation  |                                                 |

\*---------------------------------------------------------------------------*/

FoamFile

{

    version     2.0;

    format      ascii;

    class       dictionary;

    object      autoHexMeshDict;

}



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



// 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

{

    sphere4.stl

    {

        type triSurfaceMesh;

        regions

        {

            boule

            {

                name sphere;

            }

        }

    }

    

    boite

    {

        type searchableBox;

        min (-0.5 -0.25 -0.25);

        max (0.5 0.25 0.25);

    }

    

    boiteFine

    {

        type searchableBox;

        min (-0.3 -0.1 -0.1);

        max (0.3 0.1 0.1);

    }

    

}







// 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 4000000;



    // 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 20;



    // 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 "sphere4.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

    {

        sphere

        {

            // Surface-wise min and max refinement level

            level (2 2);

        }

    }



    resolveFeatureAngle 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

    {

        boiteFine

        {

            mode inside;

            levels ((0.1 1));

        }

        

        sphere

        {

            mode distance;

            levels ((0.1 1));

        }

    }





    // 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.

    // This is an outside point locationInMesh;

    locationInMesh (-0.4 0 0); // Inside point



    // 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 1.0;



    //- Number of mesh displacement relaxation iterations.

    nSolveIter 300;



    //- 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) features by sampling the surface

        implicitFeatureSnap false;



        //- Use castellatedMeshControls::features

        explicitFeatureSnap true;



        //- Detect features between multiple surfaces

        //  (only for explicitFeatureSnap, default = false)

        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

    {

        "sphere_.*"

        {

            nSurfaceLayers 1;

        }

    }



    // Expansion factor for layer mesh

    expansionRatio 1.0;





    // 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 0.3;



    // Minimum thickness of cell layer. If for any reason layer

    // cannot be above minThickness do not add layer.

    // See relativeSizes parameter.

    minThickness 0.25;



    // 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 0;





    // Advanced settings



    // When not to extrude surface. 0 is flat surface, 90 is when two faces

    // are perpendicular

    featureAngle 30;



    // 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 0.3;



    // Angle used to pick up medial axis points

    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;



    //- 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 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-9;



    //- 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;



    //- 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 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;





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

Here is the beginning and the end of my sphere4.stl file :

Code:

solid boule

  facet normal -0.382156 -0.0525255 -0.922604

    outer loop

       vertex -0.012941 0 -0.0482963

……

       vertex -3.06162e-18 0 -0.05

    endloop

  endfacet

endsolid boule

Now when I run paraFoam, I cannot see the sphere anymore. It shuts itself down and gives:

HTML Code:

--> FOAM FATAL IO ERROR: 

Cannot find patchField entry for inlet

Any idea on how to solve the problem?