# Source code for espressomd.lbboundaries

```
# Copyright (C) 2010-2022 The ESPResSo project
#
# This file is part of ESPResSo.
#
# ESPResSo is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# ESPResSo is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
from .script_interface import ScriptObjectList, ScriptInterfaceHelper, script_interface_register
from .__init__ import has_features
if any(has_features(i) for i in ["LB_BOUNDARIES", "LB_BOUNDARIES_GPU"]):
[docs] @script_interface_register
class LBBoundaries(ScriptObjectList):
"""
Creates a set of lattice-Boltzmann boundaries.
Methods
-------
size()
Get the number of active boundaries.
empty()
Return ``True`` if there are not active boundaries.
clear()
Clear the list of boundaries.
"""
_so_name = "LBBoundaries::LBBoundaries"
_so_bind_methods = ("size", "empty", "clear")
[docs] def add(self, *args, **kwargs):
"""
Adds a boundary to the set of boundaries.
Either pass a valid boundary as argument,
or a valid set of parameters to create a boundary.
"""
if len(args) == 1:
if isinstance(args[0], LBBoundary):
lbboundary = args[0]
else:
raise TypeError(
"Either a LBBoundary object or key-value pairs for the parameters of a LBBoundary object need to be passed.")
else:
lbboundary = LBBoundary(**kwargs)
self.call_method("add", object=lbboundary)
return lbboundary
[docs] def remove(self, lbboundary):
"""
Removes a boundary from the set.
Parameters
----------
lbboundary : :obj:`LBBoundary`
The boundary to be removed from the set.
"""
self.call_method("remove", object=lbboundary)
[docs] @script_interface_register
class LBBoundary(ScriptInterfaceHelper):
"""
Creates a LB boundary from a shape.
The fluid velocity is limited to :math:`v_{\\mathrm{max}} = 0.20`
(see *quasi-incompressible limit* in :cite:`kruger17a`,
chapter 7, page 272), which corresponds to Mach 0.35.
The relative error in the fluid density between a compressible fluid
and an incompressible fluid at Mach 0.30 is less than 5% (see
*constant density assumption* in :cite:`kundu01a` chapter 16, page
663). Since the speed of sound is :math:`c_s = 1 / \\sqrt{3}` in LB
velocity units in a D3Q19 lattice, the velocity limit at Mach 0.30
is :math:`v_{\\mathrm{max}} = 0.30 / \\sqrt{3} \\approx 0.17`.
At Mach 0.35 the relative error is around 6% and
:math:`v_{\\mathrm{max}} = 0.35 / \\sqrt{3} \\approx 0.20`.
Parameters
----------
shape : :obj:`espressomd.shapes.Shape`
The shape from which to build the boundary.
velocity : (3,) array_like of :obj:`float`, optional
The boundary slip velocity. By default, a velocity of zero is used
(no-slip boundary condition).
"""
_so_name = "LBBoundaries::LBBoundary"
_so_bind_methods = ("get_force",)
```