Commit b7b3b0ca authored by Michael Kuron's avatar Michael Kuron
Browse files

Schiller force model

parent 8a3ac66b
......@@ -479,6 +479,7 @@ def force_model_from_string(force_model_name, force_values):
'buick': forcemodels.Buick,
'silva': forcemodels.Buick,
'edm': forcemodels.EDM,
'schiller': forcemodels.Schiller,
}
if force_model_name.lower() not in force_model_dict:
raise ValueError("Unknown force model %s" % (force_model_name,))
......
......@@ -88,7 +88,7 @@ second moment nonzero :class:`Luo` :class:`Guo`
import sympy as sp
from lbmpy.relaxationrates import get_shear_relaxation_rate
from lbmpy.relaxationrates import get_bulk_relaxation_rate, get_shear_relaxation_rate
class Simple:
......@@ -148,6 +148,7 @@ class Guo:
luo = Luo(self._force)
shear_relaxation_rate = get_shear_relaxation_rate(lb_method)
assert len(set(lb_method.relaxation_rates)) == 1, "Guo only works for SRT, use Schiller instead"
correction_factor = (1 - sp.Rational(1, 2) * shear_relaxation_rate)
return [correction_factor * t for t in luo(lb_method)]
......@@ -158,6 +159,35 @@ class Guo:
return default_velocity_shift(density, self._force)
class Schiller:
r"""
Force model by Schiller :cite:`schiller2008thermal`
Equivalent to Guo but not restricted to SRT.
"""
def __init__(self, force):
self._force = force
def __call__(self, lb_method):
u = sp.Matrix(lb_method.first_order_equilibrium_moment_symbols)
force = sp.Matrix(self._force)
uf = u.dot(force) * sp.eye(len(force))
omega = get_shear_relaxation_rate(lb_method)
omega_bulk = get_bulk_relaxation_rate(lb_method)
G = (u * force.transpose() + force * u.transpose() - uf * sp.Rational(2, 3)) * sp.Rational(1, 2) * \
(2 + omega) + uf * sp.Rational(1, 3) * (2 + omega_bulk)
result = []
for direction, w_i in zip(lb_method.stencil, lb_method.weights):
direction = sp.Matrix(direction)
tr = sp.trace(G * (direction * direction.transpose() - sp.Rational(1, 3) * sp.eye(len(force))))
result.append(3 * w_i * (force.dot(direction) + sp.Rational(3, 2) * tr))
return result
def macroscopic_velocity_shift(self, density):
return default_velocity_shift(density, self._force)
class Buick:
r"""
This force model :cite:`buick2000gravity` has a force term with zero second moment.
......
import sympy as sp
from lbmpy.moments import is_shear_moment
from lbmpy.moments import is_bulk_moment, is_shear_moment
def relaxation_rate_from_lattice_viscosity(nu):
......@@ -46,6 +46,18 @@ def get_shear_relaxation_rate(method):
"Can not determine their relaxation rate automatically")
def get_bulk_relaxation_rate(method):
"""
The bulk moment is x^2 + y^2 + z^2, plus a constant for orthogonalization.
If this moment does not exist, the bulk relaxation is part of the shear relaxation.
The bulk relaxation rate determines the bulk viscosity in hydrodynamic LBM schemes.
"""
for moment, relax_info in method.relaxation_info_dict.items():
if is_bulk_moment(moment, method.dim):
return relax_info.relaxation_rate
return get_shear_relaxation_rate(method)
def relaxation_rate_scaling(omega, level_scale_factor):
"""Computes adapted omega for refinement.
......
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