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/* This file is part of the OpenLB library
*
* Copyright (C) 2006, 2007, 2013 Jonas Latt, Mathias J. Krause, Geng Liu
* E-mail contact: info@openlb.net
* The most recent release of OpenLB can be downloaded at
* <http://www.openlb.net/>
*
* 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 MRT_HELPERS_H
#define MRT_HELPERS_H
#include "lbHelpers.h"
#include "mrtLatticeDescriptors.h"
namespace olb {
/// All helper functions are inside this structure
template<typename T, typename DESCRIPTOR>
struct mrtHelpers {
static_assert(
std::is_same<typename DESCRIPTOR::category_tag, descriptors::tag::MRT>::value,
"DESCRIPTOR is tagged as MRT");
/// Computation of equilibrium distribution (in momenta space)
static T equilibrium( int iPop, T rho, const T u[DESCRIPTOR::d],
const T uSqr )
{
T equ = T();
for (int jPop = 0; jPop < DESCRIPTOR::q; ++jPop) {
equ += descriptors::m<T,DESCRIPTOR>(iPop,jPop) *
(lbHelpers<T,DESCRIPTOR>::equilibrium(jPop,rho,u,uSqr) +
descriptors::t<T,DESCRIPTOR>(jPop));
}
return equ;
}
/// Computation of all equilibrium distribution (in momenta space)
static void computeEquilibrium( T momentaEq[DESCRIPTOR::q],
T rho, const T u[DESCRIPTOR::d],
const T uSqr )
{
for (int iPop = 0; iPop < DESCRIPTOR::q; ++iPop) {
momentaEq[iPop] = T();
for (int jPop = 0; jPop < DESCRIPTOR::q; ++jPop) {
momentaEq[iPop] += descriptors::m<T,DESCRIPTOR>(iPop,jPop) *
(lbHelpers<T,DESCRIPTOR>::equilibrium(jPop,rho,u,uSqr) +
descriptors::t<T,DESCRIPTOR>(jPop));
}
}
}
static void computeMomenta(T momenta[DESCRIPTOR::q], Cell<T,DESCRIPTOR> &cell)
{
for (int iPop = 0; iPop < DESCRIPTOR::q; ++iPop) {
momenta[iPop] = T();
for (int jPop = 0; jPop < DESCRIPTOR::q; ++jPop) {
momenta[iPop] += descriptors::m<T,DESCRIPTOR>(iPop,jPop) *
(cell[jPop] + descriptors::t<T,DESCRIPTOR>(jPop));
}
}
}
/// MRT collision step
static T mrtCollision( Cell<T,DESCRIPTOR>& cell,
T rho, const T u[DESCRIPTOR::d],
T invM_S[DESCRIPTOR::q][DESCRIPTOR::q])
{
T uSqr = util::normSqr<T,DESCRIPTOR::d>(u);
T momenta[DESCRIPTOR::q];
T momentaEq[DESCRIPTOR::q];
computeMomenta(momenta,cell);
computeEquilibrium(momentaEq,rho,u,uSqr);
for (int iPop=0; iPop < DESCRIPTOR::q; ++iPop) {
T collisionTerm = T();
for (int jPop = 0; jPop < DESCRIPTOR::q; ++jPop) {
collisionTerm += invM_S[iPop][jPop] *
(momenta[jPop] - momentaEq[jPop]);
}
cell[iPop] -= collisionTerm;
}
return uSqr;
}
/// MRT SGS collision step
static T mrtSGSCollision( Cell<T,DESCRIPTOR>& cell,
T rho, const T u[DESCRIPTOR::d],
T omega,
T invM_S_SGS[DESCRIPTOR::q][DESCRIPTOR::q])
{
T uSqr = util::normSqr<T,DESCRIPTOR::d>(u);
T momenta[DESCRIPTOR::q];
T momentaEq[DESCRIPTOR::q];
computeMomenta(momenta,cell);
computeEquilibrium(momentaEq,rho,u,uSqr);
for (int iPop=0; iPop < DESCRIPTOR::q; ++iPop) {
T collisionTerm = T();
for (int jPop = 0; jPop < DESCRIPTOR::q; ++jPop) {
collisionTerm += invM_S_SGS[iPop][jPop] *
(momenta[jPop] - momentaEq[jPop]);
}
cell[iPop] -= collisionTerm;
}
return uSqr;
}
/// Ladd-Verberg-I body force model for MRT
/// A.Ladd, R. Verberg, DESCRIPTOR-Boltzmann simulations of particle-fluid suspensions, Journal of Statistical Physics 104(2001)
static void addExternalForce( Cell<T,DESCRIPTOR>& cell,
T rho,
const T u[DESCRIPTOR::d],
T invM_S[DESCRIPTOR::q][DESCRIPTOR::q])
{
T* force = cell.template getFieldPointer<descriptors::FORCE>();
T f_u = T();
for (int iD=0; iD < DESCRIPTOR::d; ++iD) {
f_u += force[iD]*u[iD];
}
for (int iPop=0; iPop < DESCRIPTOR::q; ++iPop) {
T c_u = T();
T c_f = T();
for (int iD=0; iD < DESCRIPTOR::d; ++iD) {
c_u += descriptors::c<DESCRIPTOR>(iPop,iD)*u[iD];
c_f += descriptors::c<DESCRIPTOR>(iPop,iD)*force[iD];
}
T f1 = descriptors::t<T,DESCRIPTOR>(iPop)*rho*c_f*descriptors::invCs2<T,DESCRIPTOR>();
T f2 = descriptors::t<T,DESCRIPTOR>(iPop)*rho*(c_u*c_f*descriptors::invCs2<T,DESCRIPTOR>()-f_u)*descriptors::invCs2<T,DESCRIPTOR>();
T invMsM = T();
for (int jPop=0; jPop < DESCRIPTOR::q; ++jPop) {
invMsM += invM_S[iPop][jPop]*descriptors::m<T,DESCRIPTOR>(jPop,iPop);
}
cell[iPop] += f1 + f2 - invMsM*f2/2.;
}
return;
}
}; // struct mrtHelpers
} // namespace olb
// The specialized code is directly included. That is because we never want
// it to be precompiled so that in both the precompiled and the
// "include-everything" version, the compiler can apply all the
// optimizations it wants.
#include "mrtHelpers2D.h"
#include "mrtHelpers3D.h"
#endif
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