6b7dd8160d
triangle, from: http://en.wikipedia.org/wiki/Inertia_tensor_of_triangle Adding the ability to calculate the inertia tensor of a polygon face by summing the triangle inertias. Added a test application to draw a test face with its principal axes and moments of inertia.
113 lines
3.1 KiB
C
113 lines
3.1 KiB
C
/*---------------------------------------------------------------------------*\
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========= |
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\\ / F ield | OpenFOAM: The Open Source CFD Toolbox
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\\ / O peration |
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\\ / A nd | Copyright (C) 2009-2009 OpenCFD Ltd.
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\\/ M anipulation |
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-------------------------------------------------------------------------------
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License
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This file is part of OpenFOAM.
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OpenFOAM is free software; you can redistribute it and/or modify it
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under the terms of the GNU General Public License as published by the
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Free Software Foundation; either version 2 of the License, or (at your
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option) any later version.
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OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
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ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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for more details.
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You should have received a copy of the GNU General Public License
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along with OpenFOAM; if not, write to the Free Software Foundation,
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Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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Application
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momentOfInertiaTest
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Description
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Calculates the inertia tensor and principal axes and moments of a
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test face.
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\*---------------------------------------------------------------------------*/
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#include "ListOps.H"
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#include "face.H"
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#include "OFstream.H"
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#include "meshTools.H"
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// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
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using namespace Foam;
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int main(int argc, char *argv[])
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{
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label nPts = 6;
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pointField pts(nPts);
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pts[0] = point(4.495, 3.717, -4.112);
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pts[1] = point(4.421, 3.932, -4.112);
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pts[2] = point(4.379, 4.053, -4.112);
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pts[3] = point(4.301, 4.026, -4.300);
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pts[4] = point(4.294, 4.024, -4.317);
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pts[5] = point(4.409, 3.687, -4.317);
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scalar density = 1.0;
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face f(identity(nPts));
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point Cf = f.centre(pts);
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tensor J = tensor::zero;
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J = f.inertia(pts, Cf, density);
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vector eVal = eigenValues(J);
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tensor eVec = eigenVectors(J);
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Info<< nl << "Inertia tensor of test face " << J << nl
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<< "eigenValues (principal moments) " << eVal << nl
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<< "eigenVectors (principal axes) " << eVec
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<< endl;
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OFstream str("momentOfInertiaTest.obj");
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Info<< nl << "Writing test face and scaled principal axes to "
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<< str.name() << endl;
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forAll(pts, ptI)
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{
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meshTools::writeOBJ(str, pts[ptI]);
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}
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str << "l";
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forAll(f, fI)
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{
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str << ' ' << fI + 1;
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}
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str << " 1" << endl;
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scalar scale = mag(Cf - pts[f[0]])/eVal.component(findMin(eVal));
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meshTools::writeOBJ(str, Cf);
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meshTools::writeOBJ(str, Cf + scale*eVal.x()*eVec.x());
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meshTools::writeOBJ(str, Cf + scale*eVal.y()*eVec.y());
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meshTools::writeOBJ(str, Cf + scale*eVal.z()*eVec.z());
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for (label i = nPts + 1; i < nPts + 4; i++)
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{
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str << "l " << nPts + 1 << ' ' << i + 1 << endl;
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}
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Info<< nl << "End" << nl << endl;
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return 0;
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}
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// ************************************************************************* //
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