data/src/rigidBodyMotion/rigidBodyDynamics/restraints/linearAxialAngularSpring/linearAxialAngularSpring.C

/*---------------------------------------------------------------------------*\
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License
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    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
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#include "linearAxialAngularSpring.H"
#include "rigidBodyModel.H"
#include "addToRunTimeSelectionTable.H"

// * * * * * * * * * * * * * * Static Data Members * * * * * * * * * * * * * //

namespace Foam
{
namespace RBD
{
namespace restraints
{
    defineTypeNameAndDebug(linearAxialAngularSpring, 0);

    addToRunTimeSelectionTable
    (
        restraint,
        linearAxialAngularSpring,
        dictionary
    );
}
}
}


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

Foam::RBD::restraints::linearAxialAngularSpring::linearAxialAngularSpring
(
    const word& name,
    const dictionary& dict,
    const rigidBodyModel& model
)
:
    restraint(name, dict, model)
{
    read(dict);
}


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

Foam::RBD::restraints::linearAxialAngularSpring::~linearAxialAngularSpring()
{}


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

void Foam::RBD::restraints::linearAxialAngularSpring::restrain
(
    scalarField& tau,
    Field<spatialVector>& fx,
    const rigidBodyModelState& state
) const
{
    vector refDir = rotationTensor(vector(1, 0, 0), axis_) & vector(0, 1, 0);

    vector oldDir = refQ_ & refDir;
    vector newDir = model_.X0(masterBodyIndex_).E() & refDir;

    if (mag(oldDir & axis_) > 0.95 || mag(newDir & axis_) > 0.95)
    {
        // Directions close to the axis, changing reference
        refDir = rotationTensor(vector(1, 0, 0), axis_) & vector(0, 0, 1);
        oldDir = refQ_ & refDir;
        newDir = model_.X0(masterBodyIndex_).E() & refDir;
    }

    // Removing axis component from oldDir and newDir and normalising
    oldDir -= (axis_ & oldDir)*axis_;
    oldDir /= (mag(oldDir) + vSmall);

    newDir -= (axis_ & newDir)*axis_;
    newDir /= (mag(newDir) + vSmall);

    scalar theta = mag(acos(min(oldDir & newDir, 1.0)));

    // Temporary axis with sign information
    vector a = (oldDir ^ newDir);

    // Ensure a is in direction of axis
    a = (a & axis_)*axis_;

    scalar magA = mag(a);

    if (magA > vSmall)
    {
        a /= magA;
    }
    else
    {
        a = Zero;
    }

    // Damping of along axis angular velocity only
    vector moment
    (
        -(
            stiffness_*theta
          + damping_*(model_.v(masterBodyIndex_).w() & a)
         )*a
    );

    if (model_.debug)
    {
        Info<< " angle " << theta*sign(a & axis_)
            << " moment " << moment
            << endl;
    }

    // Accumulate the force for the restrained body
    fx[masterBodyIndex_] +=
        model_.X0(masterBodyIndex_).T()
      & spatialVector(moment, Zero);
}


bool Foam::RBD::restraints::linearAxialAngularSpring::read
(
    const dictionary& dict
)
{
    restraint::read(dict);

    refQ_ = coeffs_.lookupOrDefault<tensor>("referenceOrientation", I);

    if (mag(mag(refQ_) - sqrt(3.0)) > 1e-9)
    {
        FatalErrorInFunction
            << "referenceOrientation " << refQ_ << " is not a rotation tensor. "
            << "mag(referenceOrientation) - sqrt(3) = "
            << mag(refQ_) - sqrt(3.0) << nl
            << exit(FatalError);
    }

    axis_ = coeffs_.lookup("axis");

    scalar magAxis(mag(axis_));

    if (magAxis > vSmall)
    {
        axis_ /= magAxis;
    }
    else
    {
        FatalErrorInFunction
            << "axis has zero length"
            << abort(FatalError);
    }

    coeffs_.lookup("stiffness") >> stiffness_;
    coeffs_.lookup("damping") >> damping_;

    return true;
}


void Foam::RBD::restraints::linearAxialAngularSpring::write
(
    Ostream& os
) const
{
    restraint::write(os);

    writeEntry(os, "referenceOrientation", refQ_);

    writeEntry(os, "axis", axis_);

    writeEntry(os, "stiffness", stiffness_);

    writeEntry(os, "damping", damping_);
}


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