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Layers in SHM and refineWallLayer

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Old   April 25, 2012, 05:21
Default Layers in SHM and refineWallLayer
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Daniele Vicario
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Hi,
This argument has been discussed several times but I haven't got a clear idea so far.

What is the difference between the addlayer step in SHM and the refineWallLayer utility ?

I've never been able to add layers in complex geometries with SHM but with rWL is simple. Unluckily the meshes obtained with the utility have usually severe non-orto and skewness problems.

I already tried following the advices in this threads:
snappyHexMesh: create boundary layer in a bent tube

SnappyHexMesh doesn't succeed in adding several layers

Boundary layers on an inlet/outlet for a pipe

But I couldn't get a clear general procedure... I don't think it's a problem related to my geometries, more probably to my brain

Has someone some hint ? Thanks.
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Old   April 30, 2012, 04:02
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Daniele Vicario
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I haven't completely solved my problem yet, but I found that is more simple, with SHM, to add one layer at time.

In the enclosed picture you can see 7 layers added to a simple pipe running SHM (guess...) 7 times.

finalLayerThickness is 0.9 in this case.

I don't know why but setting nSurfaceLayers=7 results in no layer added.

I still have to try on complex geometries.
Attached Images
File Type: jpg lay7.jpg (89.4 KB, 112 views)
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Old   April 30, 2012, 04:52
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If you post your snappyHexMesh dict I could have a look and see if I can find a reason why you don't get layers at once…
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Old   April 30, 2012, 05:32
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Daniele Vicario
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The reason is because I played too much with parameters... actually I can have 7 layers in one step if I choose the right values.

Here is my SHMDict for addlayer:

Code:
addLayersControls
{
    relativeSizes true;
 
    layers
    {
        walls
        {
            nSurfaceLayers 7;
        }
     }
 
    expansionRatio 1.1;
 
    finalLayerThickness 0.9;
 
    minThickness 0.000001;
 
    nGrow 0;
 
    featureAngle 30;
 
    nRelaxIter 5;
    nSmoothSurfaceNormals 1;
    nSmoothNormals 3;
    nSmoothThickness 10;
    maxFaceThicknessRatio 0.5;
    maxThicknessToMedialRatio 0.3;
    minMedianAxisAngle 90;
 
    nBufferCellsNoExtrude 0;
 
    nLayerIter 100;
}
With this expansionRatio and finalLayerThickness I am able to get the correct result.

Using my older values, expansionRatio=1.8 and finalLayerThickness=1, SHM is getting more than 100000 faces with zero volume and the results is no layer added.

I'll make some more tests.
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