linearAxialAngularSpring.C

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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(bodyID_).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(bodyID_).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(model_.master(bodyID_)).w() & a)
         )*a
    );
 
    if (model_.debug)
    {
        Info<< " angle " << theta*sign(a & axis_)
            << " moment " << moment
            << endl;
    }
 
    // Accumulate the force for the restrained body
    fx[bodyIndex_] += model_.X0(bodyID_).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_);
}
 
 
// ************************************************************************* //