SPH particle simulation fixes:

- Using correct frame to update particle system tree for SPH simulation (i.e. psys_update_particle_bvhtree(psys, cfra)).
 - Increased SPH neighbour count to 512 - this greatly reduces BVH tree search bias, and makes simulations more symmetrical.
Adaptive time step improvements:
 - Fix for relative velocities based on previous state (fixes fast-moving particle clusters).
 - Only reporting on element size once per time step. Prevents incorrect Courant number from being calculated when using multiple-step integration.
This commit is contained in:
Alex Fraser 2012-01-02 11:46:02 +00:00
parent 9a37e2682d
commit b6fb3d97f1

@ -2301,6 +2301,7 @@ static EdgeHash *sph_springhash_build(ParticleSystem *psys)
return springhash;
}
#define SPH_NEIGHBORS 512
typedef struct SPHNeighbor
{
ParticleSystem *psys;
@ -2308,7 +2309,7 @@ typedef struct SPHNeighbor
} SPHNeighbor;
typedef struct SPHRangeData
{
SPHNeighbor neighbors[128];
SPHNeighbor neighbors[SPH_NEIGHBORS];
int tot_neighbors;
float density, near_density;
@ -2319,10 +2320,6 @@ typedef struct SPHRangeData
float massfac;
int use_size;
/* Same as SPHData::element_size */
float element_size;
float flow[3];
} SPHRangeData;
typedef struct SPHData {
ParticleSystem *psys[10];
@ -2332,6 +2329,7 @@ typedef struct SPHData {
float *gravity;
/* Average distance to neighbours (other particles in the support domain),
for calculating the Courant number (adaptive time step). */
int pass;
float element_size;
float flow[3];
}SPHData;
@ -2345,11 +2343,13 @@ static void sph_density_accum_cb(void *userdata, int index, float squared_dist)
if(npa == pfr->pa || squared_dist < FLT_EPSILON)
return;
/* Ugh! One particle has over 128 neighbors! Really shouldn't happen,
* but even if it does it shouldn't do any terrible harm if all are
* not taken into account - jahka
/* Ugh! One particle has too many neighbors! If some aren't taken into
* account, the forces will be biased by the tree search order. This
* effectively adds enery to the system, and results in a churning motion.
* But, we have to stop somewhere, and it's not the end of the world.
* - jahka and z0r
*/
if(pfr->tot_neighbors >= 128)
if(pfr->tot_neighbors >= SPH_NEIGHBORS)
return;
pfr->neighbors[pfr->tot_neighbors].index = index;
@ -2359,15 +2359,38 @@ static void sph_density_accum_cb(void *userdata, int index, float squared_dist)
dist = sqrtf(squared_dist);
q = (1.f - dist/pfr->h) * pfr->massfac;
add_v3_v3(pfr->flow, npa->state.vel);
pfr->element_size += dist;
if(pfr->use_size)
q *= npa->size;
pfr->density += q*q;
pfr->near_density += q*q*q;
}
/*
* Find the Courant number for an SPH particle (used for adaptive time step).
*/
static void sph_particle_courant(SPHData *sphdata, SPHRangeData *pfr) {
ParticleData *pa, *npa;
int i;
float flow[3], offset[3], dist;
flow[0] = flow[1] = flow[2] = 0.0f;
dist = 0.0f;
if (pfr->tot_neighbors > 0) {
pa = pfr->pa;
for (i=0; i < pfr->tot_neighbors; i++) {
npa = pfr->neighbors[i].psys->particles + pfr->neighbors[i].index;
sub_v3_v3v3(offset, pa->prev_state.co, npa->prev_state.co);
dist += len_v3(offset);
add_v3_v3(flow, npa->prev_state.vel);
}
dist += sphdata->psys[0]->part->fluid->radius; // TODO: remove this? - z0r
sphdata->element_size = dist / pfr->tot_neighbors;
mul_v3_v3fl(sphdata->flow, flow, 1.0f / pfr->tot_neighbors);
} else {
sphdata->element_size = MAXFLOAT;
VECCOPY(sphdata->flow, flow);
}
}
static void sph_force_cb(void *sphdata_v, ParticleKey *state, float *force, float *UNUSED(impulse))
{
SPHData *sphdata = (SPHData *)sphdata_v;
@ -2408,8 +2431,6 @@ static void sph_force_cb(void *sphdata_v, ParticleKey *state, float *force, floa
pfr.density = pfr.near_density = 0.f;
pfr.h = h;
pfr.pa = pa;
pfr.element_size = fluid->radius;
pfr.flow[0] = pfr.flow[1] = pfr.flow[2] = 0.0f;
for(i=0; i<10 && psys[i]; i++) {
pfr.npsys = psys[i];
@ -2418,14 +2439,6 @@ static void sph_force_cb(void *sphdata_v, ParticleKey *state, float *force, floa
BLI_bvhtree_range_query(psys[i]->bvhtree, state->co, h, sph_density_accum_cb, &pfr);
}
if (pfr.tot_neighbors > 0) {
pfr.element_size /= pfr.tot_neighbors;
mul_v3_fl(pfr.flow, 1.0f / pfr.tot_neighbors);
} else {
pfr.element_size = MAXFLOAT;
}
sphdata->element_size = pfr.element_size;
copy_v3_v3(sphdata->flow, pfr.flow);
pressure = stiffness * (pfr.density - rest_density);
near_pressure = stiffness_near_fac * pfr.near_density;
@ -2490,6 +2503,10 @@ static void sph_force_cb(void *sphdata_v, ParticleKey *state, float *force, floa
/* Artificial buoyancy force in negative gravity direction */
if (fluid->buoyancy > 0.f && gravity)
madd_v3_v3fl(force, gravity, fluid->buoyancy * (pfr.density-rest_density));
if (sphdata->pass == 0 && psys[0]->part->time_flag & PART_TIME_AUTOSF)
sph_particle_courant(sphdata, &pfr);
sphdata->pass++;
}
static void sph_integrate(ParticleSimulationData *sim, ParticleData *pa, float dfra, float *gravity, EdgeHash *springhash, float *element_size, float flow[3])
@ -2513,6 +2530,7 @@ static void sph_integrate(ParticleSimulationData *sim, ParticleData *pa, float d
sphdata.gravity = gravity;
sphdata.mass = pa_mass;
sphdata.eh = springhash;
sphdata.pass = 0;
//sphdata.element_size and sphdata.flow are set in the callback.
/* restore previous state and treat gravity & effectors as external acceleration*/
@ -3628,7 +3646,7 @@ void update_courant_num(ParticleSimulationData *sim, ParticleData *pa,
float relative_vel[3];
float speed;
sub_v3_v3v3(relative_vel, pa->state.vel, flow);
sub_v3_v3v3(relative_vel, pa->prev_state.vel, flow);
speed = len_v3(relative_vel);
if (sim->courant_num < speed * dtime / element_size)
sim->courant_num = speed * dtime / element_size;
@ -3717,11 +3735,11 @@ static void dynamics_step(ParticleSimulationData *sim, float cfra)
case PART_PHYS_FLUID:
{
ParticleTarget *pt = psys->targets.first;
psys_update_particle_bvhtree(psys, psys->cfra);
psys_update_particle_bvhtree(psys, cfra);
for(; pt; pt=pt->next) { /* Updating others systems particle tree for fluid-fluid interaction */
if(pt->ob)
psys_update_particle_bvhtree(BLI_findlink(&pt->ob->particlesystem, pt->psys-1), psys->cfra);
psys_update_particle_bvhtree(BLI_findlink(&pt->ob->particlesystem, pt->psys-1), cfra);
}
break;
}