Source code for espressomd.swimmer_helpers

# Copyright (C) 2023 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
# 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 <>.

import numpy as np
from . import code_features
from .math import calc_quaternions_from_angles

[docs]def add_dipole_particle(system, particle, dipole_length, dipole_particle_type, mode="pusher"): """ Add a virtual particle pointing opposite of the swimmer particle either in front of (mode="puller") or behind (mode="pusher") the swimmer. The virtual particle is set up to exert the swimming force of the swimmer particle on a fluid in the opposite direction. Parameters ---------- system : :obj:`~espressomd.system.System` The system that the particle belongs to. particle : :obj:`~espressomd.particle_data.ParticleHandle` The swimmer particle that will be paired with the virtual dipole particle. Must have the ``swimming`` attribute already set up to get the correct value for ``f_swim``. dipole_length : :obj:`float` The distance between the swimmer and the virtual dipole particle. dipole_particle_type : :obj:`int` The type of the virtual dipole particle. mode : :obj:`str` Allowed values: "pusher" (default) and "puller". Determines whether the virtual dipole particle will be placed in front of or behind the swimmer. Returns ------- dipole_particle : :obj:`~espressomd.particle_data.ParticleHandle` The newly created particle. """ if mode == "pusher": dip_sign = -1 elif mode == "puller": dip_sign = 1 else: raise ValueError(f"'mode' must be 'pusher' or 'puller', got '{mode}'") if dipole_length < 0: raise ValueError("'dipole_length' must be >= 0.") code_features.assert_features(["ENGINE", "VIRTUAL_SITES_RELATIVE"]) p = system.part.add( pos=particle.pos + dip_sign * dipole_length * particle.director, type=dipole_particle_type, swimming={ "f_swim": particle.swimming["f_swim"], "is_engine_force_on_fluid": True, }) p.vs_auto_relate_to(particle, couple_to_lb=True) p.vs_quat = calc_quaternions_from_angles(np.pi, 0.) return p