[LuckyTran]

I'm trying to output the centroid of several fields, Temperature in this example. This seems doable using the weightedVolAverage function object and doing a position weighted volume average. But what field name should I set for the weight field to get the x,y,z coordinates? Or conversely, average the coordinates and weight it by the T field.

T.x
    {
          functionObjectLibs ("libfieldFunctionObjects.so");
          type                  cellSource;
          source                all;
          weightField        banana; // <<< x coordinate of T field
          fields                 ( T );
          operation             volAverage;
    }

I'm using OF 2.4 which only has the operation volAverage instead of weightedVolAverage (but supports weighting anyway). weightedVolIntegral would be nice, but I can't seem to find it.

Or maybe it is not possible with built-in function opbjects? swak4Foam, defining the new field in createFields, or a coded function object comes to mind.

[Taataa]

The weightedVolAverage doesn't give the centroid only the value of average, you need to use the coded directive in the functions and write a code that calculates the centroid. For example:

const volScalarField& T = mesh().lookupObject<volScalarField>("T");
const volVectorField& centers = mesh().C();
const scalarField& vols = mesh().V();
const objectRegistry& db = mesh().thisDb();
scalar ts = db.time().value();

scalar sumX = 0;
scalar sumY = 0;
scalar sumTV = 0;
scalar sumV = 0;

forAll(centers, I)
{
    sumX    += T[I]*vols[I]*centers[I].x();
    sumY    += T[I]*vols[I]*centers[I].y();
    sumTV   += T[I]*vols[I];
    sumV    += vols[I];
}
reduce(sumX , sumOp<scalar>());
reduce(sumY , sumOp<scalar>());
reduce(sumTV, sumOp<scalar>());
reduce(sumV , sumOp<scalar>());

if (Pstream::master())
{
    scalar cX = sumX/max(sumTV, SMALL);
    scalar cY = sumY/max(sumTV, SMALL);
    scalar Ta = sumTV/max(sumV, SMALL);
    
    const fileName& outputFile = "TCentroids";
    OFstream os
    (
        outputFile,
        IOstream::ASCII,
        IOstream::currentVersion,
        IOstream::UNCOMPRESSED,
        true
    );
    
    Info<< "Writing temperature field centroid" << endl;
    os  << ts << "  " << Ta << "  " << cX << "  " << cY << endl;
}

I haven't tested it but it should work. Also, since you're using version 2 you may have to change the syntax, for example instead of mesh() I think you need to use mesh. I am not sure though.

[LuckyTran]

With minor tinkering to suit my purpose it works except for appending to an open file. In particular,

        OFstream os
        (
        outputFile,
        IOstream::ASCII,
        IOstream::currentVersion,
        IOstream::UNCOMPRESSED
        true
        );

This seems to work for only OpenFOAM-dev. OFstream does not have a constructor to take the append argument for 2.4, 4.0, and not even 5.0. Is there are workaround that doesn't involve recompiling the main source code? I'm okay with recompiling my custom solver, but I'd like to leave the main OF source alone.

[Taataa]

Originally Posted by LuckyTran

With minor tinkering it works except for appending to an open file. In particular,

        OFstream os
        (
        outputFile,
        ios_base::app,
        IOstream::ASCII,
        IOstream::currentVersion,
        IOstream::UNCOMPRESSED
        true
        );

This seems to work for only OpenFOAM-dev. OFstream does not have a constructor to take the append argument for 2.4, 4.0, and not even 5.0. Is there are workaround that doesn't involve recompiling the main source code? I'm okay with recompiling my custom solver, but I'd like to leave the main OF source alone.

It was added in version 5 (here). I remember when I was looking for a way to append a file this was the only way to use OF classes the rest was using C++ standard libraries. You can find a discussion here.

[LuckyTran]

So std :: ofstream writes to file but formatting is required and need to include iomanip (not the IOmanip.H in openfoam). Since OFstream is not used, it's no longer necessary to include OFstream.H. And std :: ofstream does not need any include.

#include <iomanip>
std::ofstream os;
    os.open ("Centroid", std::ofstream::out | std::ofstream::app);
    os <<std::setPrecision(9)<< ts << "  " << Ta << "  " << cX << "  " << cY << "  " << cZ << nl << endl;
    os.close();