fix insert/pack/dense command

Syntax

fix ID group-ID insert/pack seed seed_value distributiontemplate dist-ID region region-id keywords

  • ID, group-ID are documented in fix command

  • insert/pack/dense = style names of this fix command

  • seed = obligatory keyword

  • seed_value = random # seed (positive integer)

  • distributiontemplate = obligatory keyword

  • dist-ID = ID of a fix_particledistribution_discrete to be used for particle insertion

  • region = obligatory keyword

  • region-id = id of the region to be used for insertion one or more keyword/value pairs can be appended

  • keywords = volumefraction_region or insert_every or target_variable

    volumefraction_region = the intended volume fraction in the region
insert_every = if specified, perform insertion every N time steps, otherwise only once
target_variable = name of a previously defined variable together with a target and a threshold value; insertion only if they match

Examples

fix ins_pack_dense all insert/pack/dense seed 123 region reg distributiontemplate pdd2 volumefraction_region 0.53

fix ins_pack_dense all insert/pack/dense seed 123 region reg distributiontemplate pdd2 volumefraction_region 0.53 insert_every 10000 target_variable fillLevel 0.0 0.1

Description

This fix creates a dense packing of particles in a region defined by the region keyword. The algorithm by Lozano et al. (Comput Math Appl 71 (2016), 1586-1601) is implemented.

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.

Insertion is always performed in the next timestep immediately after defining the fix. It is recommended to unfix the fix after insertion has happened, because it creates several data structures that might take up a lot of memory.

In the published form, the algorithm creates a packing as dense as possible. This implementation allows to create a lower volume fraction by internally scaling the radius of the particles by the third root of the ratio volumefraction_region/volumefraction_max where volumefraction_max is defined as 0.57. Depending on the region and the particle distribution, volumefraction_max can not always be reached, however in the limit of tiny, monodisperse particles in a giant region without complex geometrical features, 0.57 is a good estimate. If a value > 0.57 is given, the fix will ignore it and output a warning.

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”).

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

No information to restart files is written by this fix.

Restrictions

The insertion region can span several processors, but must be a single continuous volume. Regions consisting of several disconnected volumes will be filled incorrectly or not at all.

When running in parallel, the estimated number of particles is wrong when using a region of type mesh/tet.

Dynamic regions are not supported as insertion region.

Default

The default values are volumefraction_region = 0.57 (=volumefraction_max)