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-   -   snappy hangs while layer generation (http://www.cfd-online.com/Forums/openfoam-meshing-snappyhexmesh/70462-snappy-hangs-while-layer-generation.html)

bastil November 25, 2009 06:05

snappy hangs while layer generation
 
Hi group,

I have snappy hanging while layer generation quite regularely for our geometries at the following stage:

Setting up information for layer truncation

snappy is still using all the CPUs and memory but does not seem to work at all. How can I find out more about the problem? Thanks.

BastiL

bruce November 27, 2009 06:38

Hi
what i understood when i had the same issue that the Layer parameters are inconsistant to get fast extrusion.

e.g too high layer size -> takes long time to push mesh
look at how many faces were stopped during extrusion? that will give some info.

Post your Layer.log file, small test case as well.

--

subhkirti October 29, 2010 05:00

process killed while layer generation
 
Hi bruce,

I am having the same problem as bastil. The entire process of mesh generation by sHM gets killed when it starts writing the layer information in the 3rd time directory.

Specifically,

Layer addition iteration 0
--------------------------
Prevented extrusion on 0 coupled patch points during syncPatchDisplacement.

Determining displacement for added points according to pointNormal ...
Prevented extrusion on 0 coupled patch points during syncPatchDisplacement.

shrinkMeshMedialDistance : Smoothing using Medial Axis ...
shrinkMeshMedialDistance : Reduce layer thickness at 1242 nodes where thickness to medial axis distance is large
shrinkMeshDistance : Removing isolated regions ...
Number isolated points extrusion stopped : 1
shrinkMeshDistance : Smoothing field ...
Iteration 0 residual 0.301
shrinkMeshMedialDistance : Moving mesh ...
Iteration 0
Moving mesh using diplacement scaling : min:1 max:1
Checking faces in error :
non-orthogonality > 65 degrees : 0
faces with face pyramid volume < 1e-13 : 0
faces with concavity > 80 degrees : 0
faces with skewness > 4 (internal) or 20 (boundary) : 0
faces with interpolation weights (0..1) < 0.02 : 0
faces with volume ratio of neighbour cells < 0.01 : 0
faces with face twist < 0.02 : 0
faces on cells with determinant < 0.001 : 0
shrinkMeshMedialDistance : Successfully moved mesh
shrinkMeshMedialDistance : Finished moving mesh ...
Prevented extrusion on 0 coupled patch points during syncPatchDisplacement.
truncateDisplacement : Unextruded 0 faces due to non-consecutive vertices being extruded.

Setting up information for layer truncation ...
Killed

I am not able to figure out the problem. Can you help me out with this?

The layer part of my sHMDict file is given below:

/ Settings for the layer addition.
addLayersControls
{

relativeSizes true;

// Per final patch (so not geometry!) the layer information
layers
{
gondel
{
nSurfaceLayers 5;
}
}

// Expansion factor for layer mesh
expansionRatio 1.15;

finalLayerThickness 0.2;

//- 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.
finalLayerRatio 0.1;

//- 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 0.01;

//- 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 1;


// Advanced settings

//- When not to extrude surface. 0 is flat surface, 90 is when two faces
// make straight angle.
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
minMedianAxisAngle 130;

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

// Overall max number of layer addition iterations
nLayerIter 10;
}


Quote:

Originally Posted by bruce (Post 237930)
Hi
what i understood when i had the same issue that the Layer parameters are inconsistant to get fast extrusion.

e.g too high layer size -> takes long time to push mesh
look at how many faces were stopped during extrusion? that will give some info.

Post your Layer.log file, small test case as well.

--


subhkirti October 29, 2010 07:19

process killed while layer generation
 
To add to my problem that i have above, the sMH works fine when I have a grid size of 1m in each dimension. However, this particular problem arose, when I refined the grid size to 0.75m or any further above.


Quote:

Originally Posted by subhkirti (Post 281317)
Hi bruce,

I am having the same problem as bastil. The entire process of mesh generation by sHM gets killed when it starts writing the layer information in the 3rd time directory.

Specifically,

Layer addition iteration 0
--------------------------
Prevented extrusion on 0 coupled patch points during syncPatchDisplacement.

Determining displacement for added points according to pointNormal ...
Prevented extrusion on 0 coupled patch points during syncPatchDisplacement.

shrinkMeshMedialDistance : Smoothing using Medial Axis ...
shrinkMeshMedialDistance : Reduce layer thickness at 1242 nodes where thickness to medial axis distance is large
shrinkMeshDistance : Removing isolated regions ...
Number isolated points extrusion stopped : 1
shrinkMeshDistance : Smoothing field ...
Iteration 0 residual 0.301
shrinkMeshMedialDistance : Moving mesh ...
Iteration 0
Moving mesh using diplacement scaling : min:1 max:1
Checking faces in error :
non-orthogonality > 65 degrees : 0
faces with face pyramid volume < 1e-13 : 0
faces with concavity > 80 degrees : 0
faces with skewness > 4 (internal) or 20 (boundary) : 0
faces with interpolation weights (0..1) < 0.02 : 0
faces with volume ratio of neighbour cells < 0.01 : 0
faces with face twist < 0.02 : 0
faces on cells with determinant < 0.001 : 0
shrinkMeshMedialDistance : Successfully moved mesh
shrinkMeshMedialDistance : Finished moving mesh ...
Prevented extrusion on 0 coupled patch points during syncPatchDisplacement.
truncateDisplacement : Unextruded 0 faces due to non-consecutive vertices being extruded.

Setting up information for layer truncation ...
Killed

I am not able to figure out the problem. Can you help me out with this?

The layer part of my sHMDict file is given below:

/ Settings for the layer addition.
addLayersControls
{

relativeSizes true;

// Per final patch (so not geometry!) the layer information
layers
{
gondel
{
nSurfaceLayers 5;
}
}

// Expansion factor for layer mesh
expansionRatio 1.15;

finalLayerThickness 0.2;

//- 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.
finalLayerRatio 0.1;

//- 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 0.01;

//- 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 1;


// Advanced settings

//- When not to extrude surface. 0 is flat surface, 90 is when two faces
// make straight angle.
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
minMedianAxisAngle 130;

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

// Overall max number of layer addition iterations
nLayerIter 10;
}



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