advectiondiffusionlbhelpers.h

open lattice boltzmann project www.openlb.org

/*  This file is part of the OpenLB library
 *
 *  Copyright (C) 2008 Orestis Malaspinas, Andrea Parmigiani
 *  Address: EPFL-STI-LIN Station 9, 1015 Lausanne
 *  E-mail: [e-mail]
 *
 *  This program 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 2
 *  of the License, or (at your option) any later version.
 *
 *  This program 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 this program; if not, write to the Free 
 *  Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
 *  Boston, MA  02110-1301, USA.
*/

/** \file
 * Helper functions for the implementation of LB dynamics. This file is all
 * about efficiency. The generic template code is specialized for commonly
 * used Lattices, so that a maximum performance can be taken out of each
 * case.
 */
#ifndef ADVECTION_DIFFUSION_LB_HELPERS_H
#define ADVECTION_DIFFUSION_LB_HELPERS_H

#include "advectionDiffusionLatticeDescriptors.h"
#include "core/lbHelpers.h"
#include "core/util.h"


namespace olb {

template<typename T, class Descriptor> struct adLbDynamicsHelpers;

/// All helper functions are inside this structure
template<typename T, template<typename U> class Lattice>
struct advectionDiffusionLbHelpers {
    
    static T equilibrium(int iPop, T rho, const T u[Lattice<T>::d]) {
        return adLbDynamicsHelpers<T,typename Lattice<T>::BaseDescriptor>
            ::equilibrium(iPop, rho, u);
    }
    
    static T rlbCollision(Cell<T,Lattice>& cell, T rho, const T u[Lattice<T>::d], T omega)
    {
        return adLbDynamicsHelpers<T,typename Lattice<T>::BaseDescriptor>
            ::rlbCollision(&cell[0], rho, u, omega);
    }

    static T bgkCollision(Cell<T,Lattice>& cell, T rho, const T u[Lattice<T>::d], T omega)
    {
        return adLbDynamicsHelpers<T,typename Lattice<T>::BaseDescriptor>
            ::bgkCollision(&cell[0], rho, u, omega);
    }
};
    
/// All helper functions are inside this structure
template<typename T, class Descriptor>
struct adLbDynamicsHelpers {
    /// equilibrium distribution
    static T equilibrium( int iPop, T rho, const T u[Descriptor::d])
    {
        T c_u = T();
        for (int iD=0; iD < Descriptor::d; ++iD)
        {
            c_u += (T)Descriptor::c[iPop][iD] * u[iD];
        }
        return rho*Descriptor::t[iPop]*((T)1 + c_u*Descriptor::invCs2)-Descriptor::t[iPop];
    }

    /// RLB advection diffusion collision step
    static T rlbCollision( T* cell,
                           T rho, const T u[Descriptor::d],
                           T omega)
    {
        const T uSqr = util::normSqr<T,Descriptor::d>(u);
        // First-order moment for the regularization
        T j1[Descriptor::d];
        for (int iD=0; iD<Descriptor::d; ++iD) 
        {
            j1[iD] = T();
        }
    
        T fEq[Descriptor::q];
        for (int iPop=0; iPop<Descriptor::q; ++iPop) 
        {
            fEq[iPop] = adLbDynamicsHelpers<T,Descriptor>::equilibrium(iPop, rho, u);
            for (int iD=0; iD<Descriptor::d; ++iD) {
                j1[iD] += Descriptor::c[iPop][iD]*(cell[iPop]-fEq[iPop]);
            }
        }

        // Collision step
    	for (int iPop=0; iPop<Descriptor::q; ++iPop) 
	    {
    		T fNeq = T();
    		for (int iD=0; iD<Descriptor::d; ++iD) 
	    	{
    	        fNeq += Descriptor::c[iPop][iD]*j1[iD];
        	}
	        fNeq *= Descriptor::t[iPop] * Descriptor::invCs2;
    	    cell[iPop] = fEq[iPop] + ((T)1-omega)*fNeq;
    	}
        return uSqr;
    }
    
    /// BGK advection diffusion collision step
    static T bgkCollision( T* cell,
                                  T rho, const T u[Descriptor::d],
                                  T omega)
    {
        const T uSqr = util::normSqr<T,Descriptor::d>(u);
        for (int iPop=0; iPop < Descriptor::q; ++iPop)
        {
            cell[iPop] *= (T)1-omega;
            cell[iPop] += omega * adLbDynamicsHelpers<T,Descriptor>::equilibrium (
                    iPop, rho, u); // uses linear equilibrium
        }
        return uSqr;
    }

};

} // namespace olb

#include "advectionDiffusionLbHelpers2D.h"
#include "advectionDiffusionLbHelpers3D.h"

#endif