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# Copyright (c) 2022 NVIDIA CORPORATION.  All rights reserved.
# NVIDIA CORPORATION and its licensors retain all intellectual property
# and proprietary rights in and to this software, related documentation
# and any modifications thereto.  Any use, reproduction, disclosure or
# distribution of this software and related documentation without an express
# license agreement from NVIDIA CORPORATION is strictly prohibited.

import warp as wp
from .model import PARTICLE_FLAG_ACTIVE


@wp.func
def particle_force(n: wp.vec3, v: wp.vec3, c: float, k_n: float, k_d: float, k_f: float, k_mu: float):
    vn = wp.dot(n, v)
    jn = c * k_n
    jd = min(vn, 0.0) * k_d

    # contact force
    fn = jn + jd

    # friction force
    vt = v - n * vn
    vs = wp.length(vt)

    if vs > 0.0:
        vt = vt / vs

    # Coulomb condition
    ft = wp.min(vs * k_f, k_mu * wp.abs(fn))

    # total force
    return -n * fn - vt * ft


@wp.kernel
def eval_particle_forces_kernel(
    grid: wp.uint64,
    particle_x: wp.array(dtype=wp.vec3),
    particle_v: wp.array(dtype=wp.vec3),
    particle_radius: wp.array(dtype=float),
    particle_flags: wp.array(dtype=wp.uint32),
    k_contact: float,
    k_damp: float,
    k_friction: float,
    k_mu: float,
    k_cohesion: float,
    max_radius: float,
    # outputs
    particle_f: wp.array(dtype=wp.vec3),
):
    tid = wp.tid()

    # order threads by cell
    i = wp.hash_grid_point_id(grid, tid)
    if i == -1:
        # hash grid has not been built yet
        # if tid == 0:
        # print("hash grid has not been built yet")
        return
    if (particle_flags[i] & PARTICLE_FLAG_ACTIVE) == 0:
        return

    x = particle_x[i]
    v = particle_v[i]
    radius = particle_radius[i]

    f = wp.vec3()

    # particle contact
    query = wp.hash_grid_query(grid, x, radius + max_radius + k_cohesion)
    index = int(0)

    count = int(0)

    while wp.hash_grid_query_next(query, index):
        if (particle_flags[index] & PARTICLE_FLAG_ACTIVE) != 0 and index != i:
            # compute distance to point
            n = x - particle_x[index]
            d = wp.length(n)
            err = d - radius - particle_radius[index]

            count += 1

            if err <= k_cohesion:
                n = n / d
                vrel = v - particle_v[index]

                f = f + particle_force(n, vrel, err, k_contact, k_damp, k_friction, k_mu)

    particle_f[i] = f


def eval_particle_forces(model, state, forces):
    if model.particle_max_radius > 0.0:
        wp.launch(
            kernel=eval_particle_forces_kernel,
            dim=model.particle_count,
            inputs=[
                model.particle_grid.id,
                state.particle_q,
                state.particle_qd,
                model.particle_radius,
                model.particle_flags,
                model.particle_ke,
                model.particle_kd,
                model.particle_kf,
                model.particle_mu,
                model.particle_cohesion,
                model.particle_max_radius,
            ],
            outputs=[forces],
            device=model.device,
        )