[docs]
class PressureLessSPH(StruphyModel):
r"""Particle discretization of pressureless Euler flow with external forcing.
Parameters
----------
base_units : BaseUnits, optional
Reference units used to derive model normalization constants.
charge_number : int, optional
Species charge number (default is 1).
mass_number : float, optional
Species mass number (default is 1.0).
epsilon : float, optional
Scaling parameter for force field (default is None).
"""
@classmethod
def model_type(cls) -> LiteralOptions.ModelTypes:
return "Fluid"
## species
class ColdFluid(ParticleSpecies):
def __init__(
self,
charge_number: int = 1,
mass_number: float = 1.0,
epsilon: float = None,
):
self.var = SPHVariable()
self.init_variables(
charge_number=charge_number,
mass_number=mass_number,
epsilon=epsilon,
)
## propagators
class Propagators:
def __init__(self):
self.push_eta = PushEta()
self.push_v = PushVinEfield()
## abstract methods
def __init__(
self,
base_units: BaseUnits = BaseUnits(),
charge_number: int = 1,
mass_number: float = 1.0,
epsilon: float = None,
):
# 0. store input parameters
self.params = copy.deepcopy(locals())
# 1. instantiate all species
self.cold_fluid = self.ColdFluid(
charge_number=charge_number,
mass_number=mass_number,
epsilon=epsilon,
)
# 2. derive units (must be done after instantiating species to access charge and mass numbers)
self.setup_equation_params(base_units=base_units)
# 3. instantiate all propagators
self.propagators = self.Propagators()
# 4. assign variables to propagators
self.propagators.push_eta.variables.var = self.cold_fluid.var
self.propagators.push_v.variables.var = self.cold_fluid.var
# 5. define scalars to be tracked during simulation
self.scalars = Scalars(
en_kin=KineticEnergySPH(self.cold_fluid.var),
)
@property
def bulk_species(self):
return self.cold_fluid
@property
def velocity_scale(self):
return None
# @staticmethod
# def diagnostics_dct():
# dct = {}
# dct["projected_density"] = "L2"
# return dct
def allocate_helpers(self):
pass
## default parameters
def generate_default_parameter_file(self, path=None, prompt=True):
params_path = super().generate_default_parameter_file(path=path, prompt=prompt)
new_file = []
with open(params_path, "r") as f:
for line in f:
if "push_v.Options" in line:
new_file += ["phi = equil.p0\n"]
new_file += ["model.propagators.push_v.phi = phi\n"]
new_file += [line]
else:
new_file += [line]
with open(params_path, "w") as f:
for line in new_file:
f.write(line)
[docs]
@classmethod
def doc_pde(cls):
r"""**PDEs solved by model:**
Continuity:
.. math::
\partial_t \rho + \nabla \cdot (\rho \mathbf{u}) = 0
Momentum:
.. math::
\partial_t (\rho \mathbf{u}) + \nabla \cdot (\rho \mathbf{u} \otimes \mathbf{u}) = \mathbf{F}
where :math:`\mathbf{F}` is an external force.
"""
[docs]
@classmethod
def doc_normalization(cls):
r"""Velocity and field normalizations:
.. math::
\hat{u} = 1\,\textrm{m/s}, \qquad \hat{F} = \frac{m\hat{n}\hat{u}}{\hat{t}}\,.
"""
[docs]
@classmethod
def doc_scalar_quantities(cls):
r"""**The following scalars are tracked during simulation:**
- SPH kinetic energy: ``en_kin``"""
[docs]
@classmethod
def doc_discretization(cls):
"""Time integration is performed by the following propagators (in sequence):
1. :class:`~struphy.propagators.push_eta.PushEta`
2. :class:`~struphy.propagators.push_vin_efield.PushVinEfield`
"""
doc = rf"""**1. PushEta:**
{PushEta.__doc__}
**2. PushVinEfield:**
{PushVinEfield.__doc__}
"""
return doc
[docs]
@classmethod
def doc_long_description(cls):
r"""PressureLessSPH is a meshfree particle model for a pressureless fluid.
It is primarily useful as a simple SPH benchmark or as a reduced
particle transport model in a prescribed force field or potential."""
[docs]
@classmethod
def doc_examples(cls):
r"""Create and initialize a pressureless SPH model:
.. code-block:: python
from struphy.models import PressureLessSPH
model = PressureLessSPH()
model.cold_fluid.var
"""
[docs]
@classmethod
def doc_use_cases(cls):
r"""This model is appropriate for:
- meshfree pressureless-flow benchmarks
- straight-line particle transport with external forcing
- testing SPH particle loading and diagnostics"""
[docs]
@classmethod
def doc_cannot_be_used_for(cls):
r"""This model is not suitable for:
- compressible fluids with pressure forces
- FEEC-based grid discretizations
- electromagnetic plasma dynamics
- viscous or thermal closures"""
