pairPotential.C

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/*---------------------------------------------------------------------------*\
  =========                 |
  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
   \\    /   O peration     |
    \\  /    A nd           | Copyright (C) 2011-2015 OpenFOAM Foundation
     \\/     M anipulation  |
-------------------------------------------------------------------------------
License
    This file is part of OpenFOAM.
 
    OpenFOAM is free software: you can redistribute it and/or modify it
    under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.
 
    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
    for more details.
 
    You should have received a copy of the GNU General Public License
    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
 
\*---------------------------------------------------------------------------*/
 
#include "pairPotential.H"
#include "energyScalingFunction.H"
 
// * * * * * * * * * * * * * * Static Data Members * * * * * * * * * * * * * //
 
namespace Foam
{
    defineTypeNameAndDebug(pairPotential, 0);
    defineRunTimeSelectionTable(pairPotential, dictionary);
}
 
 
// * * * * * * * * * * * * * Private Member Functions  * * * * * * * * * * * //
 
 
void Foam::pairPotential::scaleEnergy(scalar& e, const scalar r) const
{
    if (!esfPtr_)
    {
        esfPtr_ = energyScalingFunction::New
        (
            name_, pairPotentialProperties_, *this
        ).ptr();
    }
 
    esfPtr_->scaleEnergy(e, r);
}
 
 
// * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
 
Foam::pairPotential::pairPotential
(
    const word& name,
    const dictionary& pairPotentialProperties
)
:
    name_(name),
    pairPotentialProperties_(pairPotentialProperties),
    rCut_(readScalar(pairPotentialProperties_.lookup("rCut"))),
    rCutSqr_(rCut_*rCut_),
    rMin_(readScalar(pairPotentialProperties_.lookup("rMin"))),
    dr_(readScalar(pairPotentialProperties_.lookup("dr"))),
    forceLookup_(0),
    energyLookup_(0),
    esfPtr_(NULL),
    writeTables_(Switch(pairPotentialProperties_.lookup("writeTables")))
{}
 
 
// * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * * //
 
void Foam::pairPotential::setLookupTables()
{
    label N = label((rCut_ - rMin_)/dr_) + 1;
 
    forceLookup_.setSize(N);
 
    energyLookup_.setSize(N);
 
    forAll(forceLookup_, k)
    {
        energyLookup_[k] = scaledEnergy(k*dr_ + rMin_);
 
        forceLookup_[k] = -energyDerivative((k*dr_ + rMin_), true);
    }
}
 
 
Foam::scalar Foam::pairPotential::force(const scalar r) const
{
    scalar k_rIJ = (r - rMin_)/dr_;
 
    label k = label(k_rIJ);
 
    if (k < 0)
    {
        FatalErrorInFunction
            << "r less than rMin in pair potential " << name_ << nl
            << abort(FatalError);
    }
 
    scalar f =
        (k_rIJ - k)*forceLookup_[k+1]
      + (k + 1 - k_rIJ)*forceLookup_[k];
 
    return f;
}
 
 
Foam::List< Foam::Pair< Foam::scalar > >
Foam::pairPotential::forceTable() const
{
    List<Pair<scalar> > forceTab(forceLookup_.size());
 
    forAll(forceLookup_,k)
    {
        forceTab[k].first() = rMin_ + k*dr_;
 
        forceTab[k].second() = forceLookup_[k];
    }
 
    return forceTab;
}
 
 
Foam::scalar Foam::pairPotential::energy(const scalar r) const
{
    scalar k_rIJ = (r - rMin_)/dr_;
 
    label k = label(k_rIJ);
 
    if (k < 0)
    {
        FatalErrorInFunction
            << "r less than rMin in pair potential " << name_ << nl
            << abort(FatalError);
    }
 
    scalar e =
        (k_rIJ - k)*energyLookup_[k+1]
      + (k + 1 - k_rIJ)*energyLookup_[k];
 
    return e;
}
 
 
Foam::List< Foam::Pair< Foam::scalar > >
    Foam::pairPotential::energyTable() const
{
    List<Pair<scalar> > energyTab(energyLookup_.size());
 
    forAll(energyLookup_,k)
    {
        energyTab[k].first() = rMin_ + k*dr_;
 
        energyTab[k].second() = energyLookup_[k];
    }
 
    return energyTab;
}
 
 
Foam::scalar Foam::pairPotential::scaledEnergy(const scalar r) const
{
    scalar e = unscaledEnergy(r);
 
    scaleEnergy(e, r);
 
    return e;
}
 
 
Foam::scalar Foam::pairPotential::energyDerivative
(
    const scalar r,
    const bool scaledEnergyDerivative
) const
{
    // Local quadratic fit to energy: E = a0 + a1*r + a2*r^2
    // Differentiate to give f = -dE/dr = -a1 - 2*a2*r
 
    scalar ra = r - dr_;
    scalar rf = r;
    scalar rb = r + dr_;
 
    scalar Ea, Ef, Eb;
 
    if (scaledEnergyDerivative)
    {
        Ea = scaledEnergy(ra);
        Ef = scaledEnergy(rf);
        Eb = scaledEnergy(rb);
    }
    else
    {
        Ea = unscaledEnergy(ra);
        Ef = unscaledEnergy(rf);
        Eb = unscaledEnergy(rb);
    }
 
    scalar denominator = (ra - rf)*(ra - rb)*(rf - rb);
 
    scalar a1 =
    (
        rb*rb*(Ea - Ef) + ra*ra*(Ef - Eb) + rf*rf*(Eb - Ea)
    ) / denominator;
 
    scalar a2 =
    (
        rb*(Ef - Ea) + rf*(Ea - Eb) + ra*(Eb - Ef)
    ) / denominator;
 
    return a1 + 2.0*a2*r;
}
 
 
bool Foam::pairPotential::read(const dictionary& pairPotentialProperties)
{
    pairPotentialProperties_ = pairPotentialProperties;
 
    return true;
}
 
 
// ************************************************************************* //