//Basic first order semi-Lagrangian advection of velocities
void FluidSim::advect(float dt) {
temp_u.assign(0);
temp_v.assign(0);
temp_w.assign(0);
//semi-Lagrangian advection on u-component of velocity
for(int k = 0; k < nk; ++k) for(int j = 0; j < nj; ++j) for(int i = 0; i < ni+1; ++i) {
Vec3f pos(i*dx, (j+0.5f)*dx, (k+0.5f)*dx);
pos = trace_rk2(pos, -dt);
temp_u(i,j,k) = get_velocity(pos)[0];
}
//semi-Lagrangian advection on v-component of velocity
for(int k = 0; k < nk; ++k) for(int j = 0; j < nj+1; ++j) for(int i = 0; i < ni; ++i) {
Vec3f pos((i+0.5f)*dx, j*dx, (k+0.5f)*dx);
pos = trace_rk2(pos, -dt);
temp_v(i,j,k) = get_velocity(pos)[1];
}
//semi-Lagrangian advection on w-component of velocity
for(int k = 0; k < nk+1; ++k) for(int j = 0; j < nj; ++j) for(int i = 0; i < ni; ++i) {
Vec3f pos((i+0.5f)*dx, (j+0.5f)*dx, k*dx);
pos = trace_rk2(pos, -dt);
temp_w(i,j,k) = get_velocity(pos)[2];
}
//move update velocities into u/v vectors
u = temp_u;
v = temp_v;
w = temp_w;
}
//Basic first order semi-Lagrangian advection of velocities
void FluidSim::advect(float dt) {
//semi-Lagrangian advection on u-component of velocity
for(int j = 0; j < nj; ++j) for(int i = 0; i < ni+1; ++i) {
Vec2f pos(i*dx, (j+0.5f)*dx);
pos = trace_rk2(pos, -dt);
temp_u(i,j) = get_velocity(pos)[0];
}
//semi-Lagrangian advection on v-component of velocity
for(int j = 0; j < nj+1; ++j) for(int i = 0; i < ni; ++i) {
Vec2f pos((i+0.5f)*dx, j*dx);
pos = trace_rk2(pos, -dt);
temp_v(i,j) = get_velocity(pos)[1];
}
//move update velocities into u/v vectors
u = temp_u;
v = temp_v;
}
void FluidSim::advect_particles(float dt) {
for(unsigned int p = 0; p < particles.size(); ++p) {
particles[p] = trace_rk2(particles[p], dt);
//check boundaries and project exterior particles back in
float phi_val = interpolate_value(particles[p]/dx, nodal_solid_phi);
if(phi_val < 0) {
Vec3f grad;
interpolate_gradient(grad, particles[p]/dx, nodal_solid_phi);
if(mag(grad) > 0)
normalize(grad);
particles[p] -= phi_val * grad;
}
}
}
//Perform 2nd order Runge Kutta to move the particles in the fluid
void FluidSim::advect_particles(float dt) {
for(unsigned int p = 0; p < particles.size(); ++p) {
particles[p] = trace_rk2(particles[p], dt);
//Particles can still occasionally leave the domain due to truncation errors,
//interpolation error, or large timesteps, so we project them back in for good measure.
//Try commenting this section out to see the degree of accumulated error.
float phi_value = interpolate_value(particles[p]/dx, nodal_solid_phi);
if(phi_value < 0) {
Vec2f normal;
interpolate_gradient(normal, particles[p]/dx, nodal_solid_phi);
normalize(normal);
particles[p] -= phi_value*normal;
}
}
}
