/*---------------------------------------------------------------------------*\
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    Copyright (C) 2019 OpenCFD Ltd.
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License
    This file is part of OpenFOAM.

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    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.

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    You should have received a copy of the GNU General Public License
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Class
    Foam::PairSpringSliderDashpot

Description
    Pair forces between particles colliding with a spring, slider, damper model

    Reference:
    \verbatim
        "Lagrangian numerical simulation of plug flow of cohesionless
         particles in a horizontal pipe"
        Tsuji, Y., Tanaka, T., Ishida, T.,
        Powder Technology
        Volume 73, Issue 3, September 1992, pp. 239-250
    \endverbatim

\*---------------------------------------------------------------------------*/

#ifndef PairSpringSliderDashpot_H
#define PairSpringSliderDashpot_H

#include "PairModel.H"
#include "CollisionRecordList.H"
#include "mathematicalConstants.H"

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

namespace Foam
{
/*---------------------------------------------------------------------------*\
                   Class PairSpringSliderDashpot Declaration
\*---------------------------------------------------------------------------*/

template<class CloudType>
class PairSpringSliderDashpot
:
    public PairModel<CloudType>
{
    // Private data

        //- Effective Young's modulus value, assuming both particles have
        //  the same E value
        scalar Estar_;

        //- Effective shear modulus value, assuming both particles have
        //  the same Poisson's ratio and Young's modulus
        scalar Gstar_;

        //- alpha-coefficient, related to coefficient of restitution
        scalar alpha_;

        //- Spring power (b = 1 for linear, b = 3/2 for Hertzian)
        scalar b_;

        //- Coefficient of friction in for tangential sliding
        scalar mu_;

        //- Cohesion energy density [J/m^3]
        scalar cohesionEnergyDensity_;

        //- Switch cohesion on and off
        bool cohesion_;

        //- The number of steps over which to resolve the minimum
        //  harmonic approximation of the collision period
        scalar collisionResolutionSteps_;

        //- Volume factor for determining the equivalent size of a
        //  parcel where nParticles is not 1.  The equivalent size of
        //  the parcel is
        //      parcelEquivVolume = volumeFactor*nParticles*p.volume()
        //  so
        //      parcelEquivD = cbrt(volumeFactor*nParticles)*p.d()
        //  + When volumeFactor = 1, the particles are compressed
        //    together so that the equivalent volume of the parcel is
        //    the sum of the constituent particles
        //  + When volumeFactor = 3*sqrt(2)/pi, the particles are
        //    close packed, but uncompressed.
        //  + When volumeFactor > 3*sqrt(2)/pi, the particles loosely
        //    grouped.
        // 3*sqrt(2)/pi = 1.350474 is the volume factor for close
        // packing, i.e pi/(3*sqrt(2)) is the maximum close packing
        // factor
        scalar volumeFactor_;

        //- Switch to control use of equivalent size particles.  Used
        //  because the calculation can be very expensive.
        bool useEquivalentSize_;


    // Private Member Functions

        //- Find the appropriate properties for determining the minimum
        //  allowable timestep
        void findMinMaxProperties
        (
            scalar& RMin,
            scalar& rhoMax,
            scalar& vMagMax
        ) const;

public:

    //- Runtime type information
    TypeName("pairSpringSliderDashpot");


    // Constructors

        //- Construct from dictionary
        PairSpringSliderDashpot(const dictionary& dict, CloudType& cloud);


    //- Destructor
    virtual ~PairSpringSliderDashpot() = default;


    // Member Functions

        //- Return the volumeFactor
        inline scalar volumeFactor() const
        {
            return volumeFactor_;
        }

        //- Return the area of overlap between two spheres of radii rA and rB,
        //  centres separated by a distance rAB.  Assumes rAB < (rA + rB).
        inline scalar overlapArea(scalar rA, scalar rB, scalar rAB) const
        {
            // Reference:
            // http://mathworld.wolfram.com/Sphere-SphereIntersection.html
            return
                mathematical::pi/4.0
               /sqr(rAB)
               *(
                    (-rAB + rA - rB)
                   *(-rAB - rA + rB)
                   *(-rAB + rA + rB)
                   *( rAB + rA + rB)
                );
        }

        //- Whether the PairModel has a timestep limit that will
        //  require subCycling
        virtual bool controlsTimestep() const;

        //- For PairModels that control the timestep, calculate the
        //  number of subCycles needed to satisfy the minimum
        //  allowable timestep
        virtual label nSubCycles() const;

        //- Calculate the pair interaction between parcels
        virtual void evaluatePair
        (
            typename CloudType::parcelType& pA,
            typename CloudType::parcelType& pB
        ) const;
};


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

} // End namespace Foam

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

#ifdef NoRepository
    #include "PairSpringSliderDashpot.C"
#endif

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

#endif

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