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#===========================================================================#
# System of 2 pairs of rigid particles moving towards one another. #
# At each timestep, the hydrodynamic force acting on one of these four #
# rigid particles is printed to the screen. #
# #
# Here, gamma (used in the calculation of the particle-fluid interaction #
# force) is set by the user (gamma = 3.303 for this simulation...this #
# value has been calibrated a priori through simulations of the drag #
# force acting on a single particle of the same radius). #
# #
# Sample output from this run can be found in the file: #
# 'fourspheres_velocity0d0001_setgamma.out' #
#===========================================================================#
units micro
dimension 3
boundary p p p
atom_style atomic
#----------------------------------------------------------------------------
# Need a neighbor bin size smaller than the lattice-Boltzmann grid spacing
# to ensure that the particles belonging to a given processor remain inside
# that processors lattice-Boltzmann grid.
# The arguments for neigh_modify have been set to "delay 0 every 1", again
# to ensure that the particles belonging to a given processor remain inside
# that processors lattice-Boltzmann grid. However, these values can likely
# be somewhat increased without issue. If a problem does arise (a particle
# is outside of its processors LB grid) an error message is printed and
# the simulation is terminated.
#----------------------------------------------------------------------------
neighbor 1.0 bin
neigh_modify delay 0 every 1 exclude type 1 1
read_data data.four
#----------------------------------------------------------------------------
# None of the particles interact with one another.
#----------------------------------------------------------------------------
pair_style lj/cut 2.45
pair_coeff * * 0.0 0.0 2.45
mass * 1.0
timestep 4.0
group sphere1 id <> 1 320
group sphere2 id <> 321 640
group sphere3 id <> 641 960
group sphere4 id <> 961 1280
velocity sphere1 set 0.0 0.0001 0.0 units box
velocity sphere2 set 0.0 -0.0001 0.0 units box
velocity sphere3 set 0.0 0.0001 0.0 units box
velocity sphere4 set 0.0 -0.0001 0.0 units box
#---------------------------------------------------------------------------
# Create a lattice-Boltzmann fluid covering the simulation domain.
# All of the particles in the simulation apply a force to the fluid.
# Use the LB integration scheme of Ollila et. al. (for stability reasons,
# this integration scheme should be used when a large user set value for
# gamma is specified), a fluid density = 1.0, fluid viscosity = 1.0, value
# for gamma=3.303, lattice spacing dx=4.0, and mass unit, dm=10.0.
# Print the force and torque acting on one of the spherical colloidal objects
# to the screen at each timestep.
#----------------------------------------------------------------------------
fix 1 all lb/fluid 1 2 1.0 1.0 setGamma 3.303 dx 4.0 dm 10.0 calcforce 20 sphere1
#---------------------------------------------------------------------------
# For this simulation the colloidal particles move at a constant velocity
# through the fluid. As such, we do not wish to apply the force from
# the fluid back onto these objects. Therefore, we do not use any of the
# viscous_lb, rigid_pc_sphere, or pc fixes, and simply integrate the
# particle motions using one of the built-in LAMMPS integrators.
#---------------------------------------------------------------------------
fix 2 all nve
run 300000
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