axialAngularSpring.C

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#include "axialAngularSpring.H"
#include "addToRunTimeSelectionTable.H"
#include "sixDoFRigidBodyMotion.H"
#include "transform.H"
 
// * * * * * * * * * * * * * * Static Data Members * * * * * * * * * * * * * //
 
namespace Foam
{
namespace sixDoFRigidBodyMotionRestraints
{
    defineTypeNameAndDebug(axialAngularSpring, 0);
 
    addToRunTimeSelectionTable
    (
        sixDoFRigidBodyMotionRestraint,
        axialAngularSpring,
        dictionary
    );
}
}
 
 
// * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
 
Foam::sixDoFRigidBodyMotionRestraints::axialAngularSpring::axialAngularSpring
(
    const word& name,
    const dictionary& sDoFRBMRDict
)
:
    sixDoFRigidBodyMotionRestraint(name, sDoFRBMRDict),
    refQ_(),
    axis_(),
    moment_(),
    damping_()
{
    read(sDoFRBMRDict);
}
 
 
// * * * * * * * * * * * * * * * * Destructor  * * * * * * * * * * * * * * * //
 
Foam::sixDoFRigidBodyMotionRestraints::axialAngularSpring::~axialAngularSpring()
{}
 
 
// * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * * //
 
void Foam::sixDoFRigidBodyMotionRestraints::axialAngularSpring::restrain
(
    const sixDoFRigidBodyMotion& motion,
    vector& restraintPosition,
    vector& restraintForce,
    vector& restraintMoment
) const
{
    vector refDir = rotationTensor(vector(1, 0 ,0), axis_) & vector(0, 1, 0);
 
    vector oldDir = refQ_ & refDir;
 
    vector newDir = motion.orientation() & refDir;
 
    if (mag(oldDir & axis_) > 0.95 || mag(newDir & axis_) > 0.95)
    {
        // Directions getting close to the axis, change reference
 
        refDir = rotationTensor(vector(1, 0 ,0), axis_) & vector(0, 0, 1);
        oldDir = refQ_ & refDir;
        newDir = motion.orientation() & refDir;
    }
 
    // Removing any 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)));
 
    // Determining the sign of theta by comparing the cross product of
    // the direction vectors with the axis
    theta *= sign((oldDir ^ newDir) & axis_);
 
    const scalar moment = moment_->value(theta);
 
    // Damping of along axis angular velocity only
    restraintMoment = moment*axis_ - damping_*(motion.omega() & axis_)*axis_;
 
    restraintForce = Zero;
 
    // Not needed to be altered as restraintForce is zero, but set to
    // centreOfRotation to be sure of no spurious moment
    restraintPosition = motion.centreOfRotation();
 
    if (motion.report())
    {
        Info<< " angle " << theta
            << " moment " << restraintMoment
            << endl;
    }
}
 
 
bool Foam::sixDoFRigidBodyMotionRestraints::axialAngularSpring::read
(
    const dictionary& sDoFRBMRDict
)
{
    sixDoFRigidBodyMotionRestraint::read(sDoFRBMRDict);
 
    refQ_ = sDoFRBMRCoeffs_.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_ = sDoFRBMRCoeffs_.lookup("axis");
 
    scalar magAxis(mag(axis_));
 
    if (magAxis > vSmall)
    {
        axis_ /= magAxis;
    }
    else
    {
        FatalErrorInFunction
            << "axis has zero length"
            << abort(FatalError);
    }
 
    moment_ =
        Function1<scalar>::New
        (
            "moment",
            unitRadians,
            dimForce/dimLength,
            sDoFRBMRCoeffs_
        );
 
    if
    (
        sDoFRBMRCoeffs_.found("angleUnits")
     || sDoFRBMRCoeffs_.found("angleFormat")
    )
    {
        FatalIOErrorInFunction(sDoFRBMRCoeffs_)
            << "Angle units are no longer specified with 'angleUnits' or "
            << "'angleFormat' entries. Instead, parameters of the 'moment' "
            << "function can have their units specified directly."
            << exit(FatalIOError);
    }
 
    sDoFRBMRCoeffs_.lookup("damping") >> damping_;
 
    return true;
}
 
 
void Foam::sixDoFRigidBodyMotionRestraints::axialAngularSpring::write
(
    Ostream& os
) const
{
    writeEntry(os, "referenceOrientation", refQ_);
 
    writeEntry(os, "axis", axis_);
 
    writeEntry(os, moment_());
 
    writeEntry(os, "damping", damping_);
}
 
 
// ************************************************************************* //