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Loop over face pressure values

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Old   November 18, 2019, 08:36
Default Loop over face pressure values
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David Andersson
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Hi all,

I am writing my own functionObject where I want to loop over each face in a specified patch and do some computations on the pressure values.

I generated a new file with foamNewFunctionObject. Then I found online the following code snippet that is almost doing what I want:

Code:
const polyBoundaryMesh& boundaryMesh = mesh.boundaryMesh();             // Boundary mesh

forAll(mesh.boundary(), patch)
{
    const word& patchName = mesh.boundary()[patch].name();              // Boundary patch name
    forAll(mesh.boundary()[patch], facei)
    {
        const label& face = boundaryMesh[patch].start() + facei;        // FaceID
    }
}
I would like to add a new variable myPressureField and extract the pressure value in the center of each face in the inner loop. Somthing like this:

Code:
const surfaceScalarField& myPressureField = p.boundaryMesh(); 


forAll(mesh.boundary()[patch], facei)
    {
        const scalar& faceP = myPressureField[patch][facei]
    }

I am new to programming in OpenFOAM so I am more or less guessing how I should do it based on what I can find online.

I would be thankful for some guidance with this.

Cheers,
David
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Old   November 19, 2019, 01:09
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Here's a bit of code I've used in the past for T values on a patch -- changing for p should be trivial.

Code:
    const volScalarField& Temp = mesh().lookupObject<volScalarField>("T");
    Foam::label patchLabel = mesh().boundaryMesh().findPatchID("myName");
    const Foam::fvPatch& patch = mesh().boundary()[patchLabel];

    forAll(currPatch,facei)
    {
        Foam::label faceCelli = currPatch.faceCells()[facei];
        Foam::scalar Tempi = Temp[faceCelli];
    }
Caelan
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Old   November 19, 2019, 03:21
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David Andersson
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Thank you Caelan for your answer!

Am I right when I say I should define this directly in my .C file?

At the moment I am just trying out the first row where I define my field, like this:

Code:
    const volScalarField& myPressure= mesh_.lookupObject<volScalarField>("p");
and it doesn't work. I also tried with volVectorFiled and "U" but the same problem.

Do I need to #include some special library(ies) to be able to access the fields?

//David
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Old   November 19, 2019, 11:40
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Yes, it'll go in the .C file for your function object.

Caelan
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Old   November 19, 2019, 11:56
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David Andersson
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I finally got it to work when I included "fvcGrad.H". Does that make sense? What is in that library?
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Old   November 19, 2019, 12:09
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Ultimately you'd need to link in something like fvCFD.H, which most function objects would do (I hope you didn't start from scratch, and copied an existing function object to work from!). That said, while the code I pasted doesn't need fvcGrad.H, it might need something that the .H file loops in. It is used to compute gradients of a volume field. Without seeing the compilation error it is hard to tell.

Caelan
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