import gstaichi as ti
import genesis as gs
from .elastic import Elastic
[docs]
@ti.data_oriented
class Muscle(Elastic):
"""
The muscle material class for MPM.
Parameters
----------
E: float, optional
Young's modulus. Default is 1e6.
nu: float, optional
Poisson ratio. Default is 0.2.
rho: float, optional
Density (kg/m^3). Default is 1000.
lam: float, optional
The first Lame's parameter. Default is None, computed by E and nu.
mu: float, optional
The second Lame's parameter. Default is None, computed by E and nu.
sampler: str, optional
Particle sampler ('pbs', 'regular', 'random'). Note that 'pbs' is only supported on Linux for now. Defaults to
'pbs' on supported platforms, 'random' otherwise.
model: str, optional
Stress model ('corotation', 'neohooken'). Default is 'corotation'.
n_groups: int, optional
Number of muscle group. Default is 1.
"""
def __init__(
self,
E=1e6,
nu=0.2,
rho=1000.0,
lam=None,
mu=None,
sampler=None,
model="neohooken",
n_groups=1, # number of muscle group
):
if sampler is None:
sampler = "pbs" if gs.platform == "Linux" else "random"
super().__init__(E, nu, rho, lam, mu, sampler, 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, U, S, V, F_tmp, F_new, J, Jp, actu, m_dir):
stress = self._update_stress_without_actuation(U, S, V, F_tmp, F_new, J, Jp, actu, m_dir)
# TODO: need to consider rotation in deformation gradient
AAt = m_dir.outer_product(m_dir)
stress += self._stiffness * actu * F_tmp @ AAt @ F_tmp.transpose()
return stress
@property
def stiffness(self):
"""Muscle stiffness."""
return self._stiffness
@property
def n_groups(self):
"""Number of muscle groups."""
return self._n_groups
