genesis.engine.materials.FEM.muscle 源代码

import taichi as ti
import genesis as gs
from .elastic import Elastic


@ti.data_oriented
class Muscle(Elastic):
    def __init__(
        self,
        E=1e6,  # Young's modulus
        nu=0.2,  # Poisson's ratio
        rho=1000.0,  # density (kg/m^3)
        model="linear",
        n_groups=1,  # number of muscle group
    ):
        super().__init__(E, nu, rho, model)

        # inherit from Elastic
        self._update_stress_without_actuation = self.update_stress
        self.update_stress = self._update_stress_with_actuation

        self._stiffness = E  # NOTE: use Young's modulus as muscle stiffness
        self._n_groups = n_groups

    @ti.func
    def _update_stress_with_actuation(self, mu, lam, J, F, actu, m_dir):
        stress = self._update_stress_without_actuation(mu, lam, J, F, actu, m_dir)

        l = (F @ m_dir).norm(1e-12)
        mmT = m_dir.outer_product(m_dir)
        stress += self._stiffness * (actu / l) * F @ mmT

        return stress

    @property
    def stiffness(self):
        return self._stiffness

    @property
    def n_groups(self):
        return self._n_groups