def check_for_matching_equilibrium(method_name, stencil, compressibility):
omega = sp.Symbol("omega")
if method_name == Method.SRT:
method = create_srt(stencil,
omega,
compressible=compressibility,
equilibrium_order=2)
elif method_name == Method.TRT:
method = create_trt(stencil,
omega,
omega,
compressible=compressibility,
equilibrium_order=2)
elif method_name == Method.MRT:
method = create_mrt_orthogonal(stencil, [omega] * stencil.Q,
weighted=False,
compressible=compressibility,
equilibrium_order=2)
else:
raise ValueError("Unknown method")
reference_equilibrium = discrete_maxwellian_equilibrium(
stencil,
order=2,
c_s_sq=sp.Rational(1, 3),
compressible=compressibility)
equilibrium = method.get_equilibrium()
equilibrium = equilibrium.new_without_subexpressions(
subexpressions_to_keep=sp.symbols("rho u_0 u_1 u_2"))
diff = sp.Matrix(reference_equilibrium) - sp.Matrix(
[eq.rhs for eq in equilibrium.main_assignments])
diff = sp.simplify(diff)
assert sum(diff).is_zero
def test_weights(stencil_name):
stencil = LBStencil(stencil_name)
cumulant_method = create_with_default_polynomial_cumulants(stencil, [1])
moment_method = create_srt(stencil,
1,
compressible=True,
maxwellian_moments=True)
assert cumulant_method.weights == moment_method.weights
def test_simplifications_srt_d2q9_compressible():
omega = sp.symbols('omega')
method = create_srt(LBStencil(Stencil.D2Q9),
omega,
compressible=True,
equilibrium_order=2,
moment_transform_class=None)
check_method(method, [53, 58, 1], [53, 42, 1])
def create_lb_method(lbm_config=None, **params):
"""Creates a LB method, defined by moments/cumulants for collision space, equilibrium and relaxation rates."""
lbm_config, _, _ = update_with_default_parameters(params, lbm_config=lbm_config)
relaxation_rates = lbm_config.relaxation_rates
dim = lbm_config.stencil.D
if isinstance(lbm_config.force, Field):
lbm_config.force = tuple(lbm_config.force(i) for i in range(dim))
common_params = {
'compressible': lbm_config.compressible,
'equilibrium_order': lbm_config.equilibrium_order,
'force_model': lbm_config.force_model,
'maxwellian_moments': lbm_config.maxwellian_moments,
'c_s_sq': lbm_config.c_s_sq,
'moment_transform_class': lbm_config.moment_transform_class,
'central_moment_transform_class': lbm_config.central_moment_transform_class,
}
cumulant_params = {
'equilibrium_order': lbm_config.equilibrium_order,
'force_model': lbm_config.force_model,
'c_s_sq': lbm_config.c_s_sq,
'galilean_correction': lbm_config.galilean_correction,
'central_moment_transform_class': lbm_config.central_moment_transform_class,
'cumulant_transform_class': lbm_config.cumulant_transform_class,
}
if lbm_config.method == Method.SRT:
assert len(relaxation_rates) >= 1, "Not enough relaxation rates"
method = create_srt(lbm_config.stencil, relaxation_rates[0], **common_params)
elif lbm_config.method == Method.TRT:
assert len(relaxation_rates) >= 2, "Not enough relaxation rates"
method = create_trt(lbm_config.stencil, relaxation_rates[0], relaxation_rates[1], **common_params)
elif lbm_config.method == Method.MRT:
method = create_mrt_orthogonal(lbm_config.stencil, relaxation_rates, weighted=lbm_config.weighted,
nested_moments=lbm_config.nested_moments, **common_params)
elif lbm_config.method == Method.CENTRAL_MOMENT:
method = create_central_moment(lbm_config.stencil, relaxation_rates,
nested_moments=lbm_config.nested_moments, **common_params)
elif lbm_config.method == Method.MRT_RAW:
method = create_mrt_raw(lbm_config.stencil, relaxation_rates, **common_params)
elif lbm_config.method in [Method.TRT_KBC_N1, Method.TRT_KBC_N2, Method.TRT_KBC_N3, Method.TRT_KBC_N4]:
if lbm_config.stencil.D == 2 and lbm_config.stencil.Q == 9:
dim = 2
elif lbm_config.stencil.D == 3 and lbm_config.stencil.Q == 27:
dim = 3
else:
raise NotImplementedError("KBC type TRT methods can only be constructed for D2Q9 and D3Q27 stencils")
method_nr = lbm_config.method.name[-1]
method = create_trt_kbc(dim, relaxation_rates[0], relaxation_rates[1], 'KBC-N' + method_nr, **common_params)
elif lbm_config.method == Method.ENTROPIC_SRT:
method = create_srt_entropic(lbm_config.stencil, relaxation_rates[0], lbm_config.force_model,
lbm_config.compressible)
elif lbm_config.method == Method.CUMULANT:
if lbm_config.nested_moments is not None:
method = create_with_polynomial_cumulants(
lbm_config.stencil, relaxation_rates, lbm_config.nested_moments, **cumulant_params)
else:
method = create_with_default_polynomial_cumulants(lbm_config.stencil, relaxation_rates, **cumulant_params)
elif lbm_config.method == Method.MONOMIAL_CUMULANT:
method = create_with_monomial_cumulants(lbm_config.stencil, relaxation_rates, **cumulant_params)
else:
raise ValueError("Failed to create LB method. Please use lbmpy.enums.Method for the creation")
# >>Entropic methods can only be created for methods with two relaxation rates One free relaxation rate
# determining the viscosity and one to be determined by the entropy condition<<
# Thus we fix the conserved quantities to one of the relaxation rates because zero would be recognised as
# a third relaxation rate here.
if lbm_config.entropic:
method.set_conserved_moments_relaxation_rate(relaxation_rates[0])
return method