[manoliz-]

Hi there.
I'm working on a snappyHexMesh around (thin) sails modelled as a single surface.
But I can not get proper surface layers. It seems like the added cells are collapsed again. See attached screen shot.
I've spent a day trying different addLayersControls, but I seem to be unable to get anything better than the attached.
Any Ideas of what's going on?
I don't know anymore where to search.
Thanks.
manuel

here my addLayersControls:

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
    {
        wing
        {
            nSurfaceLayers 4;
        }
    }

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

    // 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.
    // 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.
    // Note: changed(corrected) w.r.t 1.7.x! (didn't do anything in 1.7.x)
    nGrow 0;

    // Advanced settings

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

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

    // 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
    // Note: changed(corrected) w.r.t 16x! 90 degrees corresponds to 130 in 16x.
    minMedialAxisAngle 90;

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


    // mf added
    //Surface based refinement level (2 2);
    //Refinement region at the stl surface:
    //mode    distance;
    //levels  ((0.2 6));


    // 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;
}

[HPE]

Hi

- You can find the complete set of settings here for layer addition: https://www.openfoam.com/documentati...sh-layers.html
- Otherwise difficult to pinpoint and isolate the effects of each parameter for the layer addition, but I would first try to add only a single layer.

Hope it helps.

[SimonStar]

I dont really know what the mistake is because I am still a beginner.

Maybe you can play around with the featureAngle.
Or another suggestion is to add more prism layers.

I found a good tutorial here that helped me
http://www.wolfdynamics.com/wiki/meshing_OF_SHM.pdf

[manoliz-]

Thanks, I did that Wolf tutorial as a start. Good stuff, but unfortunately he doesn't really explain what the parameters really do.

HPE, that link is great. This is what I needed.

Anyway... I figured that the prism layers behave much better if I have a 2D geometry (a simple extrusion instead of a real sail). Since my goal was anyway a 2D simulation I was lucky there.

[HPE]

Hi

- Very generic extra advice: please do ensure surface mesh you use is good quality and meshed relatively densely. You can monitor the surface mesh quality metrics with `surfaceCheck` utility of OpenFOAM.

[manoliz-]

Thanks, that's good advise, too!