fix particletemplate/multisphere command

Syntax

fix ID group-ID particletemplate/multisphere seed keyword values nspheres nspheresvalue  ntry ntryvalue spheres values_spheres type mt opt_keyword opt_values

• ID, group-ID are documented in fix command
• particletemplate/multisphere = style name of this fix command
• seed = random number generator seed (prime number greater 10000)
• zero or more keyword/value pairs can be appended
• keyword, values are documented in fix particletemplate/sphere command
• nspheres = obligatory keyword
• nspheresvalue = number of spheres in the template (integer value)
• ntry = obligatory keyword
• ntryvalue: number of tries for Monte Carlo approach
• spheres = obligatory keyword
• values_spheres = one out of the following options

option 1 = file filename
option 2 = file filename scale scalefactor
option 3 = x1 y1 z1 r1 x2 y2 r2... where x/y/z are sphere positions and r are the radii

• type = obligatory keyword
• mt = multisphere type of the template
• opt_keyword = mass or inertia_tensor or use_volume or use_density or fflag or tflag

mass value = mass assigned to this particle template
inertia_tensor values = Ixx Ixy Ixz Iyy Iyz Izz
  Ixx Ixy Ixz Iyy Iyz Izz = 6 independant components of the inertia tensor
use_volume = particle density calculated from mass and volume (only if keyword 'mass' is used')
use_density = particle volume calculated from mass and density (only if keyword 'mass' is used')
fflag values = fflagx fflagy fflagz
  fflagx = on or off
  fflagy = on or off
  fflagz = on or off
tflag values = tflagx tflagy tflagz
  tflagx = on or off
  tflagy = on or off
  tflagz = on or off

Examples

fix pts1 all particletemplate/multisphere 123457 atom_type 1 density constant 2500 nspheres 50 ntry 1000000 spheres file data/stone1.multisphere scale 0.001 type 1
fix pts2 all particletemplate/multisphere 17903 atom_type 1 density constant 2500 nspheres 50 ntry 1000000 spheres 0. 0. 0. 0.005   0.005 0. 0. 0.005   0.01 0. 0. 0.005 scale 0.001 type 1

Description

Define a multisphere particle template that is used as input for a fix_particledistribution_discrete command. The particle parameters (positions, radii) are either defined manually as arguments to this command or via a text file, via the keyword file. The format of this text file is

x1 y1 z1 r1
x2 y2 z2 r2
...

and the number of lines in this file has to be equal to n_spheres as defined in this command. Comments can be made in this file via the ‘#’ character. Optionally, when a file is used for defining the multi-sphere template, keyword scale can be used to define a scalefactor to scale up or down the particle positions and radii.

After the spheres are read, a Monte Carlo procedure is used to assess everything that is needed for the motion integration: mass, center of mass, and the inertia tensor including its eigensystem. The values calculated are written to the logfile.

As an alternative, the body’s mass and inertia tensor can be specified directly via keywords mass and inertia_tensor. Note that you can use these keywords only together, i.e. defining only mass but not inertia_tensor will throw an error. Also note that only 2 out of the 3 variables density, mass and volume are independant. Thus, you are offered two options when mass and inertia_tensor are used: (a) if keyword use_volume is specified, LIGGGHTS(R)-PUBLIC will use the specified mass and volume_mc (the volume of the particle template calculated by the Monte Carlo procedure), and calculate the density from these two variables. (b) if keyword use_density is used, LIGGGHTS(R)-PUBLIC will use the specified mass and the specified density (see doc of fix particletemplate/sphere command), and the volume of the clump is then calculated from these two variables. Note you have to use either use_volume or use_density in case mass and inertia_tensor are used.

The multisphere type or shape type as defined via the type keyword must be unique integer given to each fix particletemplate/multisphere command by the user (starting with 1), the list of all multisphere types in the simulation must be consecutive. At the moment, the multisphere type is not used, but will be used to implement orientation-dependant drag for CFD-DEM simulations in the future.

The additional keywords fflag and tflag can be used to deactivate selected translational and rotational degrees of freedom of the bodies. For example fflag = on on off and tflag = off on on would mean that bodies will not move translationally in z-direction and will not rotate around the x-axis.

Warning

As opposed to the number-based distributions, this fix uses the more common distribution based on mass-% for the radius distribution (as does fix_particledistribution_discrete).

Restart, fix_modify, output, run start/stop, minimize info

Information about the random state in this fix is written to binary restart files so you can restart a simulation with the same particles being chosen for insertion. None of the fix_modify options are relevant to this fix. No global scalar or vector or per-atom quantities are stored by this fix for access by various output commands. No parameter of this fix can be used with the start/stop keywords of the run command. This fix is not invoked during energy minimization.

Restrictions

none

Related commands

fix_particletemplate_sphere

Default

radius = 1.0, density = 1.0, atom_type = 1, fflag = tflag = on on on