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How to get forceDensity in OpenFOAM

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Old   March 27, 2014, 14:24
Default How to get forceDensity in OpenFOAM
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Ye Zhang
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Dear all,

I see the sorce code of force.C. There is forceDensity fD, my question is how to get this in OF??

Thank you!
Foam::forces::forcesMoments Foam::forces::calcForcesMoment() const
{
forcesMoments fm
(
pressureViscous(vector::zero, vector::zero),
pressureViscous(vector::zero, vector::zero)
);

if (directForceDensity_)
{
const volVectorField& fD = obr_.lookupObject<volVectorField>(fDName_);

const fvMesh& mesh = fD.mesh();

const surfaceVectorField::GeometricBoundaryField& Sfb =
mesh.Sf().boundaryField();

forAllConstIter(labelHashSet, patchSet_, iter)
{
label patchi = iter.key();

vectorField Md
(
mesh.C().boundaryField()[patchi] - coordSys_.origin()
);

scalarField sA(mag(Sfb[patchi]));

// Normal force = surfaceUnitNormal * (surfaceNormal & forceDensity)
vectorField fN
(
Sfb[patchi]/sA
*(
Sfb[patchi] & fD.boundaryField()[patchi]
)
);

fm.first().first() += sum(fN);
fm.second().first() += sum(Md ^ fN);

// Tangential force (total force minus normal fN)
vectorField fT(sA*fD.boundaryField()[patchi] - fN);
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Old   May 7, 2020, 06:05
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Constance Clément
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Hi kiddmax,

Did you find a solution to your problem ? I am also wondering what is this force density in OF. I want to determine the normal/tangential force on a structure but I need to give the name of this force density in controlDict when using the lib "libforces".

Thanks for your help,

Constance
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Old   May 12, 2020, 14:14
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HPE
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Hi,

- I think the force density in forces.C is a force field per unit area [N/m2].
- Some related notions can be deduced from https://en.wikipedia.org/wiki/Force_density , I think.

Hope it helps.
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