[Rasmusiwersen]

Hi all,

I am struggling with adding layers around a cylinder through addLayer controls in snappy.

Following is a snip of the snappyHexMesh log-file, where the layer addition phase starts. My snappyHexMesh is attached in this thread. As you see, the layer thickness is initially calculated, however in the end it is not added (layer thickness is set to zero in the end).

I am not sure where the error is, or if there is a numerical "limit switch" somewhere that i cannot see. If i change "firstLayerThickness" from 0.0016 (required by ypluys calculation) to say 0.005 the layer is added nicely.

Do any of you know what the problem is?

Thank you!
/Rasmus
__________________________________________________ ___________

Layer thickness specified as final layer and expansion ratio.

Shrinking and layer addition phase
----------------------------------

Using mesh parameters
{
maxNonOrtho 70;
maxBoundarySkewness 20;
maxInternalSkewness 4;
maxConcave 180;
minVol 1e-13;
minTetQuality 1e-30;
minArea -1;
minTwist 0.05;
minDeterminant 0.0001;
minFaceWeight 0.05;
minVolRatio 0.01;
minTriangleTwist -1;
nSmoothScale 4;
errorReduction 0.75;
relaxed
{
maxNonOrtho 75;
}
}



Merging all faces of a cell
---------------------------
- which are on the same patch
- which make an angle < 180 degrees (cos:-1)
- as long as the resulting face doesn't become concave by more than 90 degrees
(0=straight, 180=fully concave)

Merging 0 sets of faces.

No faces merged ...

Merging all points on surface that
- are used by only two boundary faces and
- make an angle with a cosine of more than -1.

No straight edges simplified and no points removed ...

Checking mesh manifoldness ...

Checking initial mesh ...
Checking faces in error :
non-orthogonality > 70 degrees : 0
faces with face pyramid volume < 1e-13 : 0
faces with face-decomposition tet quality < 1e-30 : 0
faces with skewness > 4 (internal) or 20 (boundary) : 0
faces with interpolation weights (0..1) < 0.05 : 0
faces with volume ratio of neighbour cells < 0.01 : 0
faces with face twist < 0.05 : 0
faces on cells with determinant < 0.0001 : 0
Detected 0 illegal faces (concave, zero area or negative cell pyramid volume)
Duplicating 0 points on faceZones of type boundary

Handling points with inconsistent layer specification ...
dupNonManifoldPoints : Found : 0 non-manifold points (out of 1247256)

Adding in total 0 inter-processor patches to handle extrusion of non-manifold processor boundaries.

Handling points with inconsistent layer specification ...

Handling non-manifold points ...

Checking patch manifoldness ...
Outside of local patch is multiply connected across edges or points at 0 points.
Set displacement to zero for all 0 non-manifold points

Handling feature edges (angle < 180) ...

Growing non-extrusion points by one layer ...
Set displacement to zero for an additional 0 points.

Growing non-extrusion points by one layer ...
Set displacement to zero for an additional 0 points.

Growing non-extrusion points by one layer ...
Set displacement to zero for an additional 0 points.

Growing non-extrusion points by one layer ...
Set displacement to zero for an additional 0 points.

Growing non-extrusion points by one layer ...
Set displacement to zero for an additional 0 points.

patch faces layers avg thickness[m]
near-wall overall
----- ----- ------ --------- -------
cylinder2 36800 5 0.00154 0.0104

Selecting externalDisplacementMeshMover displacementMedialAxis
displacementMedialAxis : Calculating distance to Medial Axis ...
--> FOAM IOWarning :
Found [v1712] 'minMedianAxisAngle' entry instead of 'minMedialAxisAngle' in dictionary "/mnt/c/Users/rli/Desktop/3D_2x2/system/snappyHexMeshDict.addLayersControls"

This keyword is deemed to be 18 months old.

fieldSmoother : Smoothing normals ...
Iteration 0 residual 0.0205345346075574
displacementMedialAxis : Inserting points on patch atmosphere if angle to nearest layer patch > 30 degrees.
displacementMedialAxis : Inserting points on patch inlet if angle to nearest layer patch > 30 degrees.
displacementMedialAxis : Inserting points on patch outlet if angle to nearest layer patch > 30 degrees.
displacementMedialAxis : Inserting points on patch top if angle to nearest layer patch > 30 degrees.
displacementMedialAxis : Inserting points on patch bottom if angle to nearest layer patch > 30 degrees.
displacementMedialAxis : Inserting points on patch back if angle to nearest layer patch > 30 degrees.
displacementMedialAxis : Inserting points on patch front if angle to nearest layer patch > 30 degrees.
fieldSmoother : Smoothing normals in interior ...
Iteration 0 residual 0.0215657546950029

Layer addition iteration 0
--------------------------

Determining displacement for added points according to pointNormal ...
Detected 0 points with point normal pointing through faces.
Reset displacement at 0 points to average of surrounding points.

displacementMedialAxis : Smoothing using Medial Axis ...
displacementMedialAxis : Reducing layer thickness at 0 nodes where thickness to medial axis distance is large
displacementMedialAxis : Removing isolated regions ...
- if partially extruded faces make angle < 90
- if exclusively surrounded by non-extruded faces
displacementMedialAxis : Number of isolated points extrusion stopped : 0
fieldSmoother : Smoothing field ...
Iteration 0 residual 1.0013611341402e-12
Iteration 10 residual 4.14830931198911e-13
displacementMedialAxis : Moving mesh ...
displacementMedialAxis : Iteration 0
Moving mesh using displacement scaling : min:1 max:1
Checking faces in error :
non-orthogonality > 70 degrees : 0
faces with face pyramid volume < 1e-13 : 0
faces with face-decomposition tet quality < 1e-30 : 0
faces with skewness > 4 (internal) or 20 (boundary) : 0
faces with interpolation weights (0..1) < 0.05 : 0
faces with volume ratio of neighbour cells < 0.01 : 0
faces with face twist < 0.05 : 0
faces on cells with determinant < 0.0001 : 0
displacementMedialAxis : Successfully moved mesh
displacementMedialAxis : Finished moving mesh ...
truncateDisplacement : Unextruded 0 faces due to non-consecutive vertices being extruded.
truncateDisplacement : Unextruded 0 faces due to stringed edges with inconsistent extrusion.

Setting up information for layer truncation ...
Detected 0 baffles across faceZones of type internal


Checking mesh with layer ...
Checking faces in error :
non-orthogonality > 70 degrees : 0
faces with face pyramid volume < 1e-13 : 0
faces with face-decomposition tet quality < 1e-30 : 0
faces with skewness > 4 (internal) or 20 (boundary) : 0
faces with interpolation weights (0..1) < 0.05 : 16032
faces with volume ratio of neighbour cells < 0.01 : 0
faces with face twist < 0.05 : 0
faces on cells with determinant < 0.0001 : 0
Detected 16032 illegal faces (concave, zero area or negative cell pyramid volume)
Extruding 11168 out of 36800 faces (30.3478260869565%). Removed extrusion at 12010 faces.
Added 184000 out of 184000 cells (100%).

Growing non-extrusion points by one layer ...
Set displacement to zero for an additional 6400 points.

Growing non-extrusion points by one layer ...
Set displacement to zero for an additional 1572 points.

Growing non-extrusion points by one layer ...
Set displacement to zero for an additional 0 points.

Growing non-extrusion points by one layer ...
Set displacement to zero for an additional 0 points.

Growing non-extrusion points by one layer ...
Set displacement to zero for an additional 0 points.


Layer addition iteration 1
--------------------------

Determining displacement for added points according to pointNormal ...
Detected 0 points with point normal pointing through faces.
Reset displacement at 0 points to average of surrounding points.

displacementMedialAxis : Smoothing using Medial Axis ...
displacementMedialAxis : Reducing layer thickness at 0 nodes where thickness to medial axis distance is large
displacementMedialAxis : Removing isolated regions ...
- if partially extruded faces make angle < 90
- if exclusively surrounded by non-extruded faces
displacementMedialAxis : Number of isolated points extrusion stopped : 0
fieldSmoother : Smoothing field ...
Iteration 0 residual 0
Iteration 10 residual 0
displacementMedialAxis : Moving mesh ...
displacementMedialAxis : Iteration 0
Moving mesh using displacement scaling : min:1 max:1
Checking faces in error :
non-orthogonality > 70 degrees : 0
faces with face pyramid volume < 1e-13 : 0
faces with face-decomposition tet quality < 1e-30 : 0
faces with skewness > 4 (internal) or 20 (boundary) : 0
faces with interpolation weights (0..1) < 0.05 : 0
faces with volume ratio of neighbour cells < 0.01 : 0
faces with face twist < 0.05 : 0
faces on cells with determinant < 0.0001 : 0
displacementMedialAxis : Successfully moved mesh
displacementMedialAxis : Finished moving mesh ...
truncateDisplacement : Unextruded 0 faces due to non-consecutive vertices being extruded.
truncateDisplacement : Unextruded 0 faces due to stringed edges with inconsistent extrusion.

Setting up information for layer truncation ...
Detected 0 baffles across faceZones of type internal


Checking mesh with layer ...
Checking faces in error :
non-orthogonality > 70 degrees : 0
faces with face pyramid volume < 1e-13 : 0
faces with face-decomposition tet quality < 1e-30 : 0
faces with skewness > 4 (internal) or 20 (boundary) : 0
faces with interpolation weights (0..1) < 0.05 : 0
faces with volume ratio of neighbour cells < 0.01 : 0
faces with face twist < 0.05 : 0
faces on cells with determinant < 0.0001 : 0
Detected 0 illegal faces (concave, zero area or negative cell pyramid volume)
Extruding 0 out of 36800 faces (0%). Removed extrusion at 0 faces.
Added 0 out of 184000 cells (0%).
Edge intersection testing:
Number of edges : 3581019
Number of edges to retest : 0
Number of intersected edges : 36800

patch faces layers overall thickness
[m] [%]
----- ----- ------ --- ---
cylinder2 36800 0 0 0

Writing 0 added cells to cellSet addedCells
Writing 0 faces inside added layer to faceSet layerFaces

Writing fields with layer information:
nSurfaceLayers : actual number of layers
thickness : overall layer thickness
thicknessFraction : overall layer thickness (fraction of desired thickness)

Layer mesh : cells:1167070 faces:3581019 points:1247256
Cells per refinement level:
0 719790
1 44080
2 94400
3 308800
Writing mesh to time constant
Wrote mesh in = 52.98 s.
Layers added in = 52.98 s.
Checking final mesh ...
Checking faces in error :
non-orthogonality > 70 degrees : 0
faces with face pyramid volume < 1e-13 : 0
faces with face-decomposition tet quality < 1e-30 : 0
faces with skewness > 4 (internal) or 20 (boundary) : 0
faces with interpolation weights (0..1) < 0.05 : 0
faces with volume ratio of neighbour cells < 0.01 : 0
faces with face twist < 0.05 : 0
faces on cells with determinant < 0.0001 : 0
Finished meshing without any errors
Finished meshing in = 70.48 s.
End

[Rasmusiwersen]

So I managed to find a solution to this, see attached picture.

The solution was to add a slightly more corase layer prior to the final layer. In this case I tried to create a layer with first cell thickness = 0.001 [m]. This was done by following procedure:
- Run snappyHexMesh having enabled castellated and snap controls only in snappyhexmesh
- Run snappyHexMesh with addlayers control enabled only with firstlayerthickness = 0.003 [m]
- Run snappyHexMesh with addlayers control enabled only with firstlayerthickness = 0.001 [m].

Hope this help any who might have the same problem.