WallSpringSliderDashpot.C

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    Copyright (C) 2019 OpenCFD Ltd.
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#include "WallSpringSliderDashpot.H"
 
// * * * * * * * * * * * * * Private Member Functions  * * * * * * * * * * * //
 
template<class CloudType>
void Foam::WallSpringSliderDashpot<CloudType>::findMinMaxProperties
(
    scalar& rMin,
    scalar& rhoMax,
    scalar& UMagMax
) const
{
    rMin = VGREAT;
    rhoMax = -VGREAT;
    UMagMax = -VGREAT;
 
    for (const typename CloudType::parcelType& p : this->owner())
    {
        // Finding minimum diameter to avoid excessive arithmetic
 
        scalar dEff = p.d();
 
        if (useEquivalentSize_)
        {
            dEff *= cbrt(p.nParticle()*volumeFactor_);
        }
 
        rMin = min(dEff, rMin);
 
        rhoMax = max(p.rho(), rhoMax);
 
        UMagMax = max
        (
            mag(p.U()) + mag(p.omega())*dEff/2,
            UMagMax
        );
    }
 
    // Transform the minimum diameter into minimum radius
    //     rMin = dMin/2
 
    rMin /= 2.0;
}
 
 
template<class CloudType>
void Foam::WallSpringSliderDashpot<CloudType>::evaluateWall
(
    typename CloudType::parcelType& p,
    const point& site,
    const WallSiteData<vector>& data,
    scalar pREff,
    scalar kN,
    bool cohesion
) const
{
    vector r_PW = p.position() - site;
 
    vector U_PW = p.U() - data.wallData();
 
    scalar r_PW_mag = mag(r_PW);
 
    scalar normalOverlapMag = max(pREff - r_PW_mag, 0.0);
 
    vector rHat_PW = r_PW/(r_PW_mag + VSMALL);
 
    scalar etaN = alpha_*sqrt(p.mass()*kN)*pow025(normalOverlapMag);
 
    vector fN_PW =
        rHat_PW
       *(kN*pow(normalOverlapMag, b_) - etaN*(U_PW & rHat_PW));
 
    // Cohesion force, energy density multiplied by the area of wall/particle
    // overlap
    if (cohesion)
    {
        fN_PW +=
           -cohesionEnergyDensity_
           *mathematical::pi*(sqr(pREff) - sqr(r_PW_mag))
           *rHat_PW;
    }
 
    p.f() += fN_PW;
 
    vector USlip_PW =
        U_PW - (U_PW & rHat_PW)*rHat_PW
      + (p.omega() ^ (pREff*-rHat_PW));
 
    scalar deltaT = this->owner().mesh().time().deltaTValue();
 
    vector& tangentialOverlap_PW =
        p.collisionRecords().matchWallRecord(-r_PW, pREff).collisionData();
 
    tangentialOverlap_PW += USlip_PW*deltaT;
 
    scalar tangentialOverlapMag = mag(tangentialOverlap_PW);
 
    if (tangentialOverlapMag > VSMALL)
    {
        scalar kT = 8.0*sqrt(pREff*normalOverlapMag)*Gstar_;
 
        scalar etaT = etaN;
 
        // Tangential force
        vector fT_PW;
 
        if (kT*tangentialOverlapMag > mu_*mag(fN_PW))
        {
            // Tangential force greater than sliding friction,
            // particle slips
 
            fT_PW = -mu_*mag(fN_PW)*USlip_PW/mag(USlip_PW);
 
            tangentialOverlap_PW = Zero;
        }
        else
        {
            fT_PW = - kT*tangentialOverlap_PW - etaT*USlip_PW;
        }
 
        p.f() += fT_PW;
 
        p.torque() += (pREff*-rHat_PW) ^ fT_PW;
    }
}
 
 
// * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
 
template<class CloudType>
Foam::WallSpringSliderDashpot<CloudType>::WallSpringSliderDashpot
(
    const dictionary& dict,
    CloudType& cloud
)
:
    WallModel<CloudType>(dict, cloud, typeName),
    Estar_(),
    Gstar_(),
    alpha_(this->coeffDict().getScalar("alpha")),
    b_(this->coeffDict().getScalar("b")),
    mu_(this->coeffDict().getScalar("mu")),
    cohesionEnergyDensity_
    (
        this->coeffDict().getScalar("cohesionEnergyDensity")
    ),
    cohesion_(false),
    collisionResolutionSteps_
    (
        this->coeffDict().getScalar("collisionResolutionSteps")
    ),
    volumeFactor_(1.0),
    useEquivalentSize_(Switch(this->coeffDict().lookup("useEquivalentSize")))
{
    if (useEquivalentSize_)
    {
        this->coeffDict().readEntry("volumeFactor", volumeFactor_);
    }
 
    scalar nu = this->coeffDict().getScalar("poissonsRatio");
 
    scalar E = this->coeffDict().getScalar("youngsModulus");
 
    scalar pNu = this->owner().constProps().poissonsRatio();
 
    scalar pE = this->owner().constProps().youngsModulus();
 
    Estar_ = 1/((1 - sqr(pNu))/pE + (1 - sqr(nu))/E);
 
    Gstar_ = 1/(2*((2 + pNu - sqr(pNu))/pE + (2 + nu - sqr(nu))/E));
 
    cohesion_ = (mag(cohesionEnergyDensity_) > VSMALL);
}
 
 
// * * * * * * * * * * * * * * * * Destructor  * * * * * * * * * * * * * * * //
 
template<class CloudType>
Foam::WallSpringSliderDashpot<CloudType>::~WallSpringSliderDashpot()
{}
 
 
// * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
 
template<class CloudType>
Foam::scalar Foam::WallSpringSliderDashpot<CloudType>::pREff
(
    const typename CloudType::parcelType& p
) const
{
    if (useEquivalentSize_)
    {
        return p.d()/2*cbrt(p.nParticle()*volumeFactor_);
    }
 
    return p.d()/2;
}
 
 
template<class CloudType>
bool Foam::WallSpringSliderDashpot<CloudType>::controlsTimestep() const
{
    return true;
}
 
 
template<class CloudType>
Foam::label Foam::WallSpringSliderDashpot<CloudType>::nSubCycles() const
{
    if (!(this->owner().size()))
    {
        return 1;
    }
 
    scalar rMin;
    scalar rhoMax;
    scalar UMagMax;
 
    findMinMaxProperties(rMin, rhoMax, UMagMax);
 
    // Note:  pi^(7/5)*(5/4)^(2/5) = 5.429675
    scalar minCollisionDeltaT =
        5.429675
       *rMin
       *pow(rhoMax/(Estar_*sqrt(UMagMax) + VSMALL), 0.4)
       /collisionResolutionSteps_;
 
    return ceil(this->owner().time().deltaTValue()/minCollisionDeltaT);
}
 
 
template<class CloudType>
void Foam::WallSpringSliderDashpot<CloudType>::evaluateWall
(
    typename CloudType::parcelType& p,
    const List<point>& flatSitePoints,
    const List<WallSiteData<vector>>& flatSiteData,
    const List<point>& sharpSitePoints,
    const List<WallSiteData<vector>>& sharpSiteData
) const
{
    scalar pREff = this->pREff(p);
 
    scalar kN = (4.0/3.0)*sqrt(pREff)*Estar_;
 
    forAll(flatSitePoints, siteI)
    {
        evaluateWall
        (
            p,
            flatSitePoints[siteI],
            flatSiteData[siteI],
            pREff,
            kN,
            cohesion_
        );
    }
 
    forAll(sharpSitePoints, siteI)
    {
        // Treating sharp sites like flat sites, except suppress cohesion
 
        evaluateWall
        (
            p,
            sharpSitePoints[siteI],
            sharpSiteData[siteI],
            pREff,
            kN,
            false
        );
    }
}
 
 
// ************************************************************************* //