sixDoFRigidBodyMotion.C

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  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
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    \\  /    A nd           | Copyright (C) 2011-2018 OpenFOAM Foundation
     \\/     M anipulation  |
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License
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    under the terms of the GNU General Public License as published by
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#include "sixDoFRigidBodyMotion.H"
#include "sixDoFSolver.H"
#include "septernion.H"

// * * * * * * * * * * * * * Private Member Functions  * * * * * * * * * * * //

void Foam::sixDoFRigidBodyMotion::applyRestraints()
{
    if (restraints_.empty())
    {
        return;
    }

    if (Pstream::master())
    {
        forAll(restraints_, rI)
        {
            if (report_)
            {
                Info<< "Restraint " << restraints_[rI].name() << ": ";
            }

            // Restraint position
            point rP = Zero;

            // Restraint force
            vector rF = Zero;

            // Restraint moment
            vector rM = Zero;

            // Accumulate the restraints
            restraints_[rI].restrain(*this, rP, rF, rM);

            // Update the acceleration
            a() += rF/mass_;

            // Moments are returned in global axes, transforming to
            // body local to add to torque.
            tau() += Q().T() & (rM + ((rP - centreOfRotation()) ^ rF));
        }
    }
}


// * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //

Foam::sixDoFRigidBodyMotion::sixDoFRigidBodyMotion()
:
    motionState_(),
    motionState0_(),
    restraints_(),
    constraints_(),
    tConstraints_(tensor::I),
    rConstraints_(tensor::I),
    initialCentreOfMass_(Zero),
    initialCentreOfRotation_(Zero),
    initialQ_(I),
    mass_(vSmall),
    momentOfInertia_(diagTensor::one*vSmall),
    aRelax_(1.0),
    aDamp_(1.0),
    report_(false),
    solver_(nullptr)
{}


Foam::sixDoFRigidBodyMotion::sixDoFRigidBodyMotion
(
    const dictionary& dict,
    const dictionary& stateDict
)
:
    motionState_(stateDict),
    motionState0_(),
    restraints_(),
    constraints_(),
    tConstraints_(tensor::I),
    rConstraints_(tensor::I),
    initialCentreOfMass_
    (
        dict.lookupOrDefault
        (
            "initialCentreOfMass",
            vector(dict.lookup("centreOfMass"))
        )
    ),
    initialCentreOfRotation_(initialCentreOfMass_),
    initialQ_
    (
        dict.lookupOrDefault
        (
            "initialOrientation",
            dict.lookupOrDefault("orientation", tensor::I)
        )
    ),
    mass_(readScalar(dict.lookup("mass"))),
    momentOfInertia_(dict.lookup("momentOfInertia")),
    aRelax_(dict.lookupOrDefault<scalar>("accelerationRelaxation", 1.0)),
    aDamp_(dict.lookupOrDefault<scalar>("accelerationDamping", 1.0)),
    report_(dict.lookupOrDefault<Switch>("report", false)),
    solver_(sixDoFSolver::New(dict.subDict("solver"), *this))
{
    addRestraints(dict);

    // Set constraints and initial centre of rotation
    // if different to the centre of mass
    addConstraints(dict);

    // If the centres of mass and rotation are different ...
    vector R(initialCentreOfMass_ - initialCentreOfRotation_);
    if (magSqr(R) > vSmall)
    {
        // ... correct the moment of inertia tensor using parallel axes theorem
        momentOfInertia_ += mass_*diag(I*magSqr(R) - sqr(R));

        // ... and if the centre of rotation is not specified for motion state
        // update it
        if (!stateDict.found("centreOfRotation"))
        {
            motionState_.centreOfRotation() = initialCentreOfRotation_;
        }
    }

    // Save the old-time motion state
    motionState0_ = motionState_;
}


Foam::sixDoFRigidBodyMotion::sixDoFRigidBodyMotion
(
    const sixDoFRigidBodyMotion& sDoFRBM
)
:
    motionState_(sDoFRBM.motionState_),
    motionState0_(sDoFRBM.motionState0_),
    restraints_(sDoFRBM.restraints_),
    constraints_(sDoFRBM.constraints_),
    tConstraints_(sDoFRBM.tConstraints_),
    rConstraints_(sDoFRBM.rConstraints_),
    initialCentreOfMass_(sDoFRBM.initialCentreOfMass_),
    initialCentreOfRotation_(sDoFRBM.initialCentreOfRotation_),
    initialQ_(sDoFRBM.initialQ_),
    mass_(sDoFRBM.mass_),
    momentOfInertia_(sDoFRBM.momentOfInertia_),
    aRelax_(sDoFRBM.aRelax_),
    aDamp_(sDoFRBM.aDamp_),
    report_(sDoFRBM.report_)
{}


// * * * * * * * * * * * * * * * * Destructor  * * * * * * * * * * * * * * * //

Foam::sixDoFRigidBodyMotion::~sixDoFRigidBodyMotion()
{}


// * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * * //

void Foam::sixDoFRigidBodyMotion::addRestraints
(
    const dictionary& dict
)
{
    if (dict.found("restraints"))
    {
        const dictionary& restraintDict = dict.subDict("restraints");

        label i = 0;

        restraints_.setSize(restraintDict.size());

        forAllConstIter(IDLList<entry>, restraintDict, iter)
        {
            if (iter().isDict())
            {
                restraints_.set
                (
                    i++,
                    sixDoFRigidBodyMotionRestraint::New
                    (
                        iter().keyword(),
                        iter().dict()
                    )
                );
            }
        }

        restraints_.setSize(i);
    }
}


void Foam::sixDoFRigidBodyMotion::addConstraints
(
    const dictionary& dict
)
{
    if (dict.found("constraints"))
    {
        const dictionary& constraintDict = dict.subDict("constraints");

        label i = 0;

        constraints_.setSize(constraintDict.size());

        pointConstraint pct;
        pointConstraint pcr;

        forAllConstIter(IDLList<entry>, constraintDict, iter)
        {
            if (iter().isDict())
            {
                constraints_.set
                (
                    i,
                    sixDoFRigidBodyMotionConstraint::New
                    (
                        iter().keyword(),
                        iter().dict(),
                        *this
                    )
                );

                constraints_[i].setCentreOfRotation(initialCentreOfRotation_);
                constraints_[i].constrainTranslation(pct);
                constraints_[i].constrainRotation(pcr);

                i++;
            }
        }

        constraints_.setSize(i);

        tConstraints_ = pct.constraintTransformation();
        rConstraints_ = pcr.constraintTransformation();

        Info<< "Translational constraint tensor " << tConstraints_ << nl
            << "Rotational constraint tensor " << rConstraints_ << endl;
    }
}


void Foam::sixDoFRigidBodyMotion::updateAcceleration
(
    const vector& fGlobal,
    const vector& tauGlobal
)
{
    static bool first = true;

    // Save the previous iteration accelerations for relaxation
    vector aPrevIter = a();
    vector tauPrevIter = tau();

    // Calculate new accelerations
    a() = fGlobal/mass_;
    tau() = (Q().T() & tauGlobal);
    applyRestraints();

    // Relax accelerations on all but first iteration
    if (!first)
    {
        a() = aRelax_*a() + (1 - aRelax_)*aPrevIter;
        tau() = aRelax_*tau() + (1 - aRelax_)*tauPrevIter;
    }
    else
    {
        first = false;
    }
}


void Foam::sixDoFRigidBodyMotion::update
(
    bool firstIter,
    const vector& fGlobal,
    const vector& tauGlobal,
    scalar deltaT,
    scalar deltaT0
)
{
    if (Pstream::master())
    {
        solver_->solve(firstIter, fGlobal, tauGlobal, deltaT, deltaT0);

        if (report_)
        {
            status();
        }
    }

    Pstream::scatter(motionState_);
}


void Foam::sixDoFRigidBodyMotion::status() const
{
    Info<< "6-DoF rigid body motion" << nl
        << "    Centre of rotation: " << centreOfRotation() << nl
        << "    Centre of mass: " << centreOfMass() << nl
        << "    Orientation: " << orientation() << nl
        << "    Linear velocity: " << v() << nl
        << "    Angular velocity: " << omega()
        << endl;
}


Foam::tmp<Foam::pointField> Foam::sixDoFRigidBodyMotion::transform
(
    const pointField& initialPoints
) const
{
    return
    (
        centreOfRotation()
      + (Q() & initialQ_.T() & (initialPoints - initialCentreOfRotation_))
    );
}


Foam::tmp<Foam::pointField> Foam::sixDoFRigidBodyMotion::transform
(
    const pointField& initialPoints,
    const scalarField& scale
) const
{
    // Calculate the transformation septerion from the initial state
    septernion s
    (
        centreOfRotation() - initialCentreOfRotation(),
        quaternion(Q().T() & initialQ())
    );

    tmp<pointField> tpoints(new pointField(initialPoints));
    pointField& points = tpoints.ref();

    forAll(points, pointi)
    {
        // Move non-stationary points
        if (scale[pointi] > small)
        {
            // Use solid-body motion where scale = 1
            if (scale[pointi] > 1 - small)
            {
                points[pointi] = transform(initialPoints[pointi]);
            }
            // Slerp septernion interpolation
            else
            {
                septernion ss(slerp(septernion::I, s, scale[pointi]));

                points[pointi] =
                    initialCentreOfRotation()
                  + ss.invTransformPoint
                    (
                        initialPoints[pointi]
                      - initialCentreOfRotation()
                    );
            }
        }
    }

    return tpoints;
}


// ************************************************************************* //