/** Calculate the local fluid fields.
* The calculation is implemented explicitly for the special case of D3Q19.
*
* @param index Index of the local lattice site.
* @param rho local fluid density
* @param j local fluid speed
* @param pi local fluid pressure
*/
inline void lb_calc_local_fields(index_t index, double *rho, double *j, double *pi) {
if (!(lattice_switch & LATTICE_LB)) {
ostringstream msg;
msg <<"Error in lb_calc_local_fields in " << __FILE__ << __LINE__ << ": CPU LB not switched on.";
runtimeError(msg);
*rho=0; j[0]=j[1]=j[2]=0; pi[0]=pi[1]=pi[2]=pi[3]=pi[4]=pi[5]=0;
return;
}
#ifndef D3Q19
#error Only D3Q19 is implemened!
#endif
if (!(lattice_switch & LATTICE_LB)) {
ostringstream msg;
msg <<"Error in lb_calc_local_pi in " << __FILE__ << __LINE__ << ": CPU LB not switched on.";
runtimeError(msg);
j[0] = j[1] = j[2] = 0;
return;
}
#ifdef LB_BOUNDARIES
if ( lbfields[index].boundary ) {
*rho = lbpar.rho[0]*lbpar.agrid*lbpar.agrid*lbpar.agrid;
j[0] = 0.; j[1] = 0.; j[2] = 0.;
if (pi) {pi[0] = 0.; pi[1] = 0.; pi[2] = 0.; pi[3] = 0.; pi[4] = 0.; pi[5] = 0.;}
return;
}
#endif
double mode[19];
double modes_from_pi_eq[6];
lb_calc_modes(index, mode);
*rho = mode[0] + lbpar.rho[0]*lbpar.agrid*lbpar.agrid*lbpar.agrid;
j[0] = mode[1];
j[1] = mode[2];
j[2] = mode[3];
#ifndef EXTERNAL_FORCES
if (lbfields[index].has_force)
#endif
{
j[0] += 0.5*lbfields[index].force[0];
j[1] += 0.5*lbfields[index].force[1];
j[2] += 0.5*lbfields[index].force[2];
}
if (!pi)
return;
/* equilibrium part of the stress modes */
modes_from_pi_eq[0] = scalar(j,j)/ *rho;
modes_from_pi_eq[1] = (SQR(j[0])-SQR(j[1]))/ *rho;
modes_from_pi_eq[2] = (scalar(j,j) - 3.0*SQR(j[2]))/ *rho;
modes_from_pi_eq[3] = j[0]*j[1]/ *rho;
modes_from_pi_eq[4] = j[0]*j[2]/ *rho;
modes_from_pi_eq[5] = j[1]*j[2]/ *rho;
/* Now we must predict the outcome of the next collision */
/* We immediately average pre- and post-collision. */
mode[4] = modes_from_pi_eq[0] + (0.5+0.5*gamma_bulk )*(mode[4] - modes_from_pi_eq[0]);
mode[5] = modes_from_pi_eq[1] + (0.5+0.5*gamma_shear)*(mode[5] - modes_from_pi_eq[1]);
mode[6] = modes_from_pi_eq[2] + (0.5+0.5*gamma_shear)*(mode[6] - modes_from_pi_eq[2]);
mode[7] = modes_from_pi_eq[3] + (0.5+0.5*gamma_shear)*(mode[7] - modes_from_pi_eq[3]);
mode[8] = modes_from_pi_eq[4] + (0.5+0.5*gamma_shear)*(mode[8] - modes_from_pi_eq[4]);
mode[9] = modes_from_pi_eq[5] + (0.5+0.5*gamma_shear)*(mode[9] - modes_from_pi_eq[5]);
// Transform the stress tensor components according to the modes that
// correspond to those used by U. Schiller. In terms of populations this
// expression then corresponds exactly to those in Eqs. 116 - 121 in the
// Duenweg and Ladd paper, when these are written out in populations.
// But to ensure this, the expression in Schiller's modes has to be different!
pi[0] = ( 2.0*(mode[0] + mode[4]) + mode[6] + 3.0*mode[5] )/6.0; // xx
pi[1] = mode[7]; // xy
pi[2] = ( 2.0*(mode[0] + mode[4]) + mode[6] - 3.0*mode[5] )/6.0; // yy
pi[3] = mode[8]; // xz
pi[4] = mode[9]; // yz
pi[5] = ( mode[0] + mode[4] - mode[6] )/3.0; // zz
}
void lb_bounce_back() {
#ifdef D3Q19
#ifndef PULL
int k,i,l;
int yperiod = lblattice.halo_grid[0];
int zperiod = lblattice.halo_grid[0]*lblattice.halo_grid[1];
int next[19];
int x,y,z;
double population_shift;
double modes[19];
next[0] = 0; // ( 0, 0, 0) =
next[1] = 1; // ( 1, 0, 0) +
next[2] = - 1; // (-1, 0, 0)
next[3] = yperiod; // ( 0, 1, 0) +
next[4] = - yperiod; // ( 0,-1, 0)
next[5] = zperiod; // ( 0, 0, 1) +
next[6] = - zperiod; // ( 0, 0,-1)
next[7] = (1+yperiod); // ( 1, 1, 0) +
next[8] = - (1+yperiod); // (-1,-1, 0)
next[9] = (1-yperiod); // ( 1,-1, 0)
next[10] = - (1-yperiod); // (-1, 1, 0) +
next[11] = (1+zperiod); // ( 1, 0, 1) +
next[12] = - (1+zperiod); // (-1, 0,-1)
next[13] = (1-zperiod); // ( 1, 0,-1)
next[14] = - (1-zperiod); // (-1, 0, 1) +
next[15] = (yperiod+zperiod); // ( 0, 1, 1) +
next[16] = - (yperiod+zperiod); // ( 0,-1,-1)
next[17] = (yperiod-zperiod); // ( 0, 1,-1)
next[18] = - (yperiod-zperiod); // ( 0,-1, 1) +
int reverse[] = { 0, 2, 1, 4, 3, 6, 5, 8, 7, 10, 9, 12, 11, 14, 13, 16, 15, 18, 17 };
/* bottom-up sweep */
// for (k=lblattice.halo_offset;k<lblattice.halo_grid_volume;k++) {
for (z=0; z<lblattice.grid[2]+2; z++) {
for (y=0; y<lblattice.grid[1]+2; y++) {
for (x=0; x<lblattice.grid[0]+2; x++) {
k= get_linear_index(x,y,z,lblattice.halo_grid);
if (lbfields[k].boundary) {
lb_calc_modes(k, modes);
for (i=0; i<19; i++) {
population_shift=0;
for (l=0; l<3; l++) {
population_shift-=lbpar.agrid*lbpar.agrid*lbpar.agrid*lbpar.agrid*lbpar.agrid*lbpar.rho[0]*2*lbmodel.c[i][l]*lbmodel.w[i]*lb_boundaries[lbfields[k].boundary-1].velocity[l]/lbmodel.c_sound_sq;
}
if ( x-lbmodel.c[i][0] > 0 && x -lbmodel.c[i][0] < lblattice.grid[0]+1 &&
y-lbmodel.c[i][1] > 0 && y -lbmodel.c[i][1] < lblattice.grid[1]+1 &&
z-lbmodel.c[i][2] > 0 && z -lbmodel.c[i][2] < lblattice.grid[2]+1) {
if ( !lbfields[k-next[i]].boundary ) {
for (l=0; l<3; l++) {
lb_boundaries[lbfields[k].boundary-1].force[l]+=(2*lbfluid[1][i][k]+population_shift)*lbmodel.c[i][l];
}
lbfluid[1][reverse[i]][k-next[i]] = lbfluid[1][i][k]+ population_shift;
}
else {
lbfluid[1][reverse[i]][k-next[i]] = lbfluid[1][i][k] = 0.0;
}
}
}
}
}
}
}
#else
#error Bounce back boundary conditions are only implemented for PUSH scheme!
#endif
#else
#error Bounce back boundary conditions are only implemented for D3Q19!
#endif
}
