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 (integer value)

• 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 scale scalefactor
  option 2 = 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

  mass value = mass assigned to this particle template
  inertia_tensor values = Ixx Ixy Ixz Iyy Iyz Izz
    Ixx Ixy Ixz Iyy Iyz Izz = 6 independent 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')

Examples¶

fix pts1 all particletemplate/multisphere 57461 atom_type 1 density constant 2500 nspheres 3 ntry 1000000 spheres 0. 0. 0. 0.005   0.005 0. 0. 0.005   0.01 0. 0. 0.005 type 1
fix pts2 all particletemplate/multisphere 31967 atom_type 1 density constant 2500 nspheres 30 ntry 1000000 spheres file spherefile.txt scale 1.0 type 1

LIGGGHTS vs. LAMMPS Info:

This command is not available in LAMMPS.

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. When a file is used for defining the multi-sphere template, the keyword scale must 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.

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 independent. Thus, you are offered two options when mass and inertia_tensor are used: (a) if keyword use_volume is specified, LIGGGHTS 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 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-dependent drag for CFD-DEM simulations in the future.

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