Multisphere problem

This is a sample script that simulates the tumbling of tablets in a rotating drum. Air resistance is accounted for using a viscous force proporational to the tablet velocity. The input script is found in the pygran examples/scripts/multisphere directory. The input files are available here.

Stage 1: data structure creation

First, a python dictionary (params) defining the simulation parameters is created as shown below:

In [ ]:
from pygran import simulation
from pygran.params import organic

# Create a dictionary of physical parameters
params = {

    # Define the system
    'boundary': ('f','f','f'), # fixed BCs
    'box':  (-1, 1, -1 , 1, -1, 1), # simulation box size

    # Define component(s)
    'species': ({'material': organic, 'style': 'multisphere/tablet', 'radius': 2e-2, 'nspheres': 12, 'length': 1e-1},

    # Set skin distance to be 1/4 particle diameter
    'nns_skin': 5e-3,

    # Timestep
    'dt': 2e-7,
    # Apply gravitional force in the negative direction along the z-axis
    'gravity': (9.81, 0, 0, -1),

    # Setup I/O
    'traj': {'pfile': 'particles*.vtk', 'mfile': 'tumbler*.vtk'},
    # Stage runs [optional]
    'stages': {'insertion': 1e6, 'rotation': 1e6},

    # Define mesh for rotating mesh (tumbler)
    'mesh': {
              'tumbler': {'file': 'mesh/tumbler.stl', 'mtype': 'mesh/surface/stress', 'material': organic, \
                          'args': {'scale': 1e-3}},

Stage 2: simulation

The params dictionary is then used to create a pygran.DEM class and run the simulation.

In [ ]:
# Create an instance of the DEM class
sim = simulation.DEM(**params)

# Insert 800 particles once in a cylinder
insert = sim.insert(species=1, value=800, region=('cylinder', 'y', 0, 0, 0.7, -0.4, 0.4), \
                    args={'orientation': 'random'})

# Add dissipative force proprtional to tablet velocity
air_resistance = sim.addViscous(species=1, gamma=0.1)

# Run insertion stage['stages']['insertion'], params['dt'])

# Delete insertion fix

# Rotate mesh (tumbler) along the xoz plane
sim.moveMesh(name='tumbler', rotate=('origin', 0, 0, 0), axis=(0, 1, 0), period=5e-1)

# Run rotation stage['stages']['rotation'], params['dt'])


In [4]:
# Play video
import io
import base64
from IPython.display import HTML

video ='movie/tumbler.mp4', 'r+b').read()