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Old   August 15, 2011, 13:10
Default viewfactor
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javad
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thanks for your attention
I can't understand the file named viewFactorDict.
I want to know that what the below parameters mean.
writeViewFactorMatrix true;
writeFacesAgglomeration true;
writePatchViewFactors false;
nFacesInCoarsestLevel 24;
featureAngle 10;
thease are from the tutorials ,sample multiRegionHeaterRadiation.
below is the hole file:

/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: 2.0.0 |
| \\ / A nd | Web: www.OpenFOAM.com |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
object viewFactorsDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //


writeViewFactorMatrix true;
writeFacesAgglomeration true;
writePatchViewFactors false;

topAir_to_heater
{
nFacesInCoarsestLevel 24;
featureAngle 10;
}

topAir_to_leftSolid
{
nFacesInCoarsestLevel 20;
featureAngle 10;
}

topAir_to_rightSolid
{
nFacesInCoarsestLevel 20;
featureAngle 10;
}

minX
{
nFacesInCoarsestLevel 10;
featureAngle 10;
}

maxY
{
nFacesInCoarsestLevel 40;
featureAngle 10;
}

minZ
{
nFacesInCoarsestLevel 20;
featureAngle 10;
}

maxX
{
nFacesInCoarsestLevel 10;
featureAngle 10;
}

maxZ
{
nFacesInCoarsestLevel 20;
featureAngle 10;
}


// ************************************************** *********************** //
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Old   August 15, 2011, 14:48
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Mirko Vukovic
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Quote:
Originally Posted by javad814 View Post
thanks for your attention
I can't understand the file named viewFactorDict.
I want to know that what the below parameters mean.
writeViewFactorMatrix true;
writeFacesAgglomeration true;
writePatchViewFactors false;
nFacesInCoarsestLevel 24;
featureAngle 10;
thease are from the tutorials ,sample multiRegionHeaterRadiation.
below is the hole file:

... stuff deleted
Unfortunately you will have to hit the books, as at least some of the stuff has to do with the numerical method.

As I recall from Fluent, faceAgglomeration has to do with merging multiple face elements. So for example if the body has a surface mesh with 10,000 elements, when you agglomerate them, you may end up with a 1000 elements. This reduces the size of the ViewFactor matrix.

Other than the need to reduce the computational load, agglomeration may have to do with the fact that radiation and conduction/convection are very different problems, and that the mesh necessary for one may be too fine for the other. But I am only guessing.

I need to dig through the code more to understand better where agglomeration is happening (looks like somewhere in faceAgglomerate.C)

Mirko
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Old   August 18, 2011, 05:24
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javad
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below is more information:
path(openFoam 2.0.0): tutorial/heatTransfer/chtMultiRegionSimpleFoam/multiRegionHeaterRadiation/constant/bottomAir/viewFactorsDict
in this sample a new radiation model is used and i must understand how it works and which files are necessary for this model.
to see the results in paraview you must type each region seperatly for example:
paraFoam -region heater
then you can see other regions in paraview as follows:
File>Open
now you can select any region you want,like
multiRegionHeaterRadiation{bottomAir}.OpenFOAM
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Old   June 3, 2016, 07:57
Default viewFactor
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I see that it is an old topic. That's a pity to find only one tutorial on the use of viewFactor radiation model!

I used javad814's advices to plot the geometry but I still don't understand how to specify the "nFacesInCoarsestLevel 24" in viewFactorDict... Why 24 for topAir_to_heater?
Please find attached a picture of the geometry. Maybe one can understand what nFacesInCoarsestLevel means?


bottomAIr
heater
leftSolid
rightSolid
topAir
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