# Normal and tangential force on a structure

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May 7, 2020, 06:16
Normal and tangential force on a structure
#1
New Member

Constance Clément
Join Date: Nov 2018
Location: Paris
Posts: 6
Rep Power: 6
Hi everyone,

I am looking for a way to determine the normal and tangential force to a structure in OF. With libforces, one can get Fx, Fy, Fz (pressure and viscous components) in the coordinate system of the mesh. I want to determine the forces in the coordinate system of the structure (a cylinder).

These forces are thus normal and tangential to the cylinder. I saw that in the code forces.C, the normal and tangential components are computed. Unfortunately, I am not sure to understand what "forcedensity" refers to.

Quote:
 void Foam::functionObjects::forces::calcForcesMoment() { initialise(); resetFields(); if (directForceDensity_) { const volVectorField& fD = lookupObject(fDName_); const surfaceVectorField::Boundary& Sfb = mesh_.Sf().boundaryField(); for (const label patchi : patchSet_) { 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] ) ); // Tangential force (total force minus normal fN) vectorField fT(sA*fD.boundaryField()[patchi] - fN); // Porous force vectorField fP(Md.size(), Zero); addToFields(patchi, Md, fN, fT, fP); applyBins(Md, fN, fT, fP, mesh_.C().boundaryField()[patchi]); } }
Thanks a lot for your help,

Constance

 May 9, 2020, 12:46 #2 Senior Member     Herpes Free Engineer Join Date: Sep 2019 Location: The Home Under The Ground with the Lost Boys Posts: 932 Rep Power: 11 Hi, >> I am looking for a way to determine the normal and tangential force to a structure in OF. With libforces, one can get Fx, Fy, Fz (pressure and viscous components) in the coordinate system of the mesh. I want to determine the forces in the coordinate system of the structure (a cylinder). You can change the default coordinate system to a local coordinate system for a given force function object without modifying the code itself. Having said that I can't write a set of settings out of my head. So, please do search for the forum for an example (a doc: https://www.openfoam.com/documentati...es-forces.html). Hope it helps. __________________ The OpenFOAM community is the biggest contributor to OpenFOAM: User guide/Wiki-1/Wiki-2/Code guide/Code Wiki/Journal Nilsson/Guerrero/Holzinger/Holzmann/Nagy/Santos/Nozaki/Jasak/Primer Governance Bugs/Features: OpenFOAM (ESI-OpenCFD-Trademark) Bugs/Features: FOAM-Extend (Wikki-FSB) Bugs: OpenFOAM.org How to create a MWE New: Forkable OpenFOAM mirror

 May 11, 2020, 03:05 #3 New Member   Constance Clément Join Date: Nov 2018 Location: Paris Posts: 6 Rep Power: 6 Hi, Thanks a lot for your reply, it helped me a lot. Constance

 May 11, 2020, 18:33 #4 Senior Member     Herpes Free Engineer Join Date: Sep 2019 Location: The Home Under The Ground with the Lost Boys Posts: 932 Rep Power: 11 pleasure - and good luck! __________________ The OpenFOAM community is the biggest contributor to OpenFOAM: User guide/Wiki-1/Wiki-2/Code guide/Code Wiki/Journal Nilsson/Guerrero/Holzinger/Holzmann/Nagy/Santos/Nozaki/Jasak/Primer Governance Bugs/Features: OpenFOAM (ESI-OpenCFD-Trademark) Bugs/Features: FOAM-Extend (Wikki-FSB) Bugs: OpenFOAM.org How to create a MWE New: Forkable OpenFOAM mirror

 Tags forcedensity, forces, normal, openfoam, tangential