fix insert/fragments command

Syntax

fix ID group-ID insert/fragments seed seed_value distributiontemplate dist-ID general_keywords general_values fragment_keywords fragment_values ...
  • ID, group-ID are documented in fix command
  • insert/fragments = style names of this fix command
  • seed = obligatory keyword
  • seed_value = random # seed (prime number greater than 10000)
  • distributiontemplate = obligatory keyword
  • dist-ID = ID of a fix_particledistribution_discrete to be used for particle insertion
  • one or more general keyword/value pairs can be appended
  • general_keywords = every or verbose
every value = ev
  once = value to signalise that isertion takes place only once (the step after the fix is issued)
  ev = every how many time-steps eligible particles are replaced by fragments
verbose = yes or no
  • following the general keyword/value section, one or more fragment keyword/value pairs can be appended for the fix insert/fragments command
  • fragment_keywords = region or type_replace or check_bound_sphere
region value = region-ID
  region-ID = ID of the region where the particles will be generated (positive integer)
type_replace values = vol
  vol =  atom type (material type) of the particles to be replaced
check_bound_sphere values = yes or no
  yes =  do check if the bounding sphere of the fragment is < 1 (length units)
  no =  do check  the bounding sphere of the fragment

Examples

region  replacereg block -0.1 0.1 -0.1 0.1 0. 0.1 units box
fix     replace all insert/fragments seed 123457 distributiontemplate pdfragments every 1 region ins type_replace 1

Description

Replace granular particles every few timesteps by a predefined set of fragment particles. A particle is eligible to be replaced if it is within the specified region, as defined via the region keyword and if it is of the atom type specified via the type_replace keyword.

The verbose keyword controls whether statistics about particle insertion is output to the screen each time particles are inserted.

This command must use the distributiontemplate keyword to refer to a fix_particledistribution_discrete (defined by dist-fix-ID) that defines the properties of the inserted particles. This fix_particledistribution_discrete must hold exactly one particle template of type fix_particletemplate_multiplespheres that has a bounding radius of <= 1. It is required to use the relative = yes option as described in fix_particletemplate_sphere

The frequency of the insertion/replacement can be controlled via the every keyword. At each insertion step, fix insert/fragments replaces all eligible particles. Note that in general the particles to be replaced have different radii, so the fragment defined by the fix_particletemplate_multiplespheres is scaled down with the particle radius.

Inserted particles are assigned the atom type specified by the particledistribution defined via the fix_particledistribution_discrete and are assigned to 4 groups: the default group “all” and the group specified in the fix insert command, as well as the groups specified in the fix_particledistribution_discrete and fix_particletemplate_sphere command (all of which can also be “all”).

As all particles should be inserted within the hull of existing particles, no overlapcheck is performed.

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

Information about this fix is written to binary restart files. This means you can restart a simulation while inserting particles, when the restart file was written during the insertion operation.

None of the fix_modify options are relevant to this fix. A global vector is stored by this fix for access by various output commands. The first component of the vector is the number of particles already inserted, the second component is the mass of particles already inserted. 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

The overlapcheck = ‘yes’ option performs an inherently serial operation and will thus not scale well in parallel. For this reason, if you want to generate large systems, you are advised to turn overlapcheck off and let the packing relax afterwards to generate a valid packing.

Option all_in = ‘yes’ will not work if the region used is a tet mesh region.

Keywords duration and extrude_length can not be used together.

Currently all_in yes is not yet supported for all types of insertion.

Dynamic regions are not supported as insertion region.