[filpucfd]

Hello everyone,

I am trying to generate a mesh with snappyHexMesh for a chtMultiRegionFoam case having two fluid regions and one solid region.
The geometries are generated as triply-periodic-minimal-surfaces (TPMS) and the solid is in contact with both fluid domains, which should never mix.

I am using FOAM-EXTEND 5.0

I am generating a cylindrical blockMesh from which I intend to derive the solid phase ( hence I put in the blocks keyword the name 'solid'). I hope it is possible to do it in such way. It would act as a flows separator but also it has a diameter such that to include the outer pipe/tube.

For my snappyHexMesh I am inputting 4 geometries:
A. The entire fluid1 domain, with three patches defined: input, output, walls.
B. The entire fluid2 domain, with three patches defined: input, output, walls.
C. The walls from fluid1 domain, which I will use as a faceZone and cellZone
to get the solid
D. The walls from the fluid2 domain, which I will use as a faceZone and
cellZone to get the solid

I am having a problem, which is not letting me complete the snapping process:

--> FOAM FATAL ERROR:
Face 2621440 fc:(-0.0258851 -0.0909335 0.17375) in zone solid is in patch fluid1ToSolid_walls1 and in patch fluid2ToSolid_walls2

    From function getZoneBafflePatches(const bool)
    in file autoHexMesh/autoHexMeshDriver/autoSnapDriver.C at line 106.

FOAM aborting

How can it be solved?
EDIT - SOLVED : I needed two different faceZone names.


Thank you in advance everyone!!!

Below there is my snappyHexMeshDict:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | foam-extend: Open Source CFD                    |
|  \\    /   O peration     | Version:     5.0                                |
|   \\  /    A nd           | Web:         http://www.foam-extend.org         |
|    \\/     M anipulation  | For copyright notice see file Copyright         |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      autoHexMeshDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

// 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
{
    unrem_fluid1_cat.stl
    {
        type triSurfaceMesh;
        name fluid1;
    }

    unrem_fluid2_cat.stl
    {
        type triSurfaceMesh;
        name fluid2;
    }
    
    unrem_fluid1_walls.stl
    {
        type triSurfaceMesh;
        name fluid1ToSolid;
    }

    unrem_fluid2_walls.stl
    {
        type triSurfaceMesh;
        name fluid2ToSolid;
    }
    
};

// Settings for the castellatedMesh generation.
castellatedMeshControls
{

    // 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 999999999;

    // 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 999999999;

    // 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 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
    (
    );

    // 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
    {
        fluid1
        {
            // Surface-wise min and max refinement level
            level (1 1);

            faceZone fluid1;
            cellZone fluid1;
            faceType boundary;
            zoneInside true;
            regions
            {
                inlet1     { level ( 0 0 ); patchInfo { type patch; } }
                outlet1    { level ( 0 1 ); patchInfo { type patch; } }
		walls1    { level ( 1 2 ); patchInfo { type wall; } }
	    }
        }

        fluid2
        {
            // Surface-wise min and max refinement level
            level (1 1);

            faceZone fluid2;
            faceType boundary;
            cellZone fluid2;
            zoneInside true;
            regions
            {
                inlet2     { level ( 0 0 ); patchInfo { type patch; } }
                outlet2    { level ( 0 1 ); patchInfo { type patch; } }
		walls2    { level ( 1 2 ); patchInfo { type wall; } }
	    }
        }
	
        fluid1ToSolid
        {
            // Surface-wise min and max refinement level
            level (1 1);
            faceZone solToF1;
            cellZone solid;
            //faceType baffle;
            regions
            {
            	walls1 {level (1 2); patchInfo {type wall;} }
            };
            zoneInside true;
        }

        fluid2ToSolid
        {
            // Surface-wise min and max refinement level
            level (1 1);
	    //faceType baffle;
            faceZone solToF2;
            cellZone solid;
            regions
            {
            	walls2 {level (1 2); patchInfo {type wall;} }
            };
            zoneInside true;
        }
	
    }

    // Resolve sharp angles
    resolveFeatureAngle 5;

    // 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;
        //    levels ((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 (0.07 0.065 0.01);
}

// Settings for the snapping.
snapControls
{
    explicitFeatureSnap true;
    implicitFeatureSnap false;
    multiRegionFeatureSnap true;
    //- Number of patch smoothing iterations before finding correspondence
    //  to surface
    nSmoothPatch 5;

    //- 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;
    //
    nFeatureSnapIter = 5;
    detectBaffles false;
    strictRegionSnap true;
}

// Settings for the layer addition.
addLayersControls
{
    relativeSizes true;

    // Per final patch (so not geometry!) the layer information
    layers
    {
    	".*wall.*"
    	{
    		nSurfaceLayers 15;
    	}
        //flowAirDuctReagent_flowAirDuctReagent
        //{
        //    nSurfaceLayers 1;
        //}
        //flowAirDuctReagent_inlet1
        //{
        //    nSurfaceLayers 1;
        //}
        //flowAirDuctReagent_inlet2
        //{
        //    nSurfaceLayers 1;
        //}
    }
    nLayerIter 50;
    // Expansion factor for layer mesh
    expansionRatio 1.3;

    //- 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.
    finalLayerThickness 0.05;

    //- 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;

    //- 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
    //  make straight angle.
    featureAngle 350;

    //- 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;
}

// Generic mesh quality settings. At any undoable phase these determine
// where to undo.
meshQualityControls
{
    //- Maximum non-orthogonality allowed. Set to 180 to disable.
    maxNonOrtho 70;

    //- 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 0;

    //- 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;

    // 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;

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

[filpucfd]

Hello,

I will write a new reply to point out a new issue, which looks far worse.

The snappyHexMesh process seems to work, but it looks like that the solid phase merges with the fluid1, and the fluid2 gets additional elements in the mesh that are not present in the native .stl.
These extra elements extend themselves all the way to the "tube".


How can I solve it? I thought that defining the faceType and adding the stls C and D would help keeping things separately.


_______EDIT____________:

It looks like I fixed it by changing to "zoneInside false" for all the refinement surfaces .

refinementSurfaces
    {
        fluid1
        {
            // Surface-wise min and max refinement level
            level (0 0);

            faceZone fluid1;
            cellZone fluid1;
            faceType boundary;
            zoneInside false;
            regions
            {
                inlet1     { level ( 0 0 ); patchInfo { type patch; } }
                outlet1    { level ( 0 0 ); patchInfo { type patch; } }
		walls1    { level ( 1 1 ); patchInfo { type wall; } }
	    }
        }

        fluid2
        {
            // Surface-wise min and max refinement level
            level (0 0);

            faceZone fluid2;
            faceType boundary;
            cellZone fluid2;
            zoneInside false;
            regions
            {
                inlet2     { level ( 0 0 ); patchInfo { type patch; } }
                outlet2    { level ( 0 0 ); patchInfo { type patch; } }
		walls2    { level ( 1 1 ); patchInfo { type wall; } }
	    }
        }
        
        /*
        fluid1ToSolid
        {
            // Surface-wise min and max refinement level
            level (1 1);
            faceZone solToF1;
            cellZone solid;
            faceType boundary;
            patchInfo {type wall;};
            zoneInside false;
        }

        fluid2ToSolid
        {
            // Surface-wise min and max refinement level
            level (1 1);
	    faceType boundary;
            faceZone solToF2;
            cellZone solid;
            patchInfo {type wall;};
            zoneInside false;
        }
        */
}

The only problem, now, is that I have the additional floating elements in the domain phases.
I tried to use the snappyHexMesh algorithm from OpenFoam11 and they do not appear, so I think it's not a problem of my stl geometries.

Can it be something coming from the graphical rendering of paraFoam, since I am using the one from OF11 and not the one from foam-extend-5.0, changing to OF11 via its alias?

Here are some examples of floating elements
floating.jpg

Here are some examples of missing elements + additional elements that should belong to the gray phase but that were assigned to the red and green.

additional.jpg