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fix insert/pack command

fix insert/stream command

Syntax:

fix ID group-ID insert/pack   seed seed_value distributiontemplate dist-ID general_keywords general_values pack_keywords pack_values ... 
fix ID group-ID insert/stream seed seed_value distributiontemplate dist-ID general_keywords general_values stream_keywords stream_values ... 

Examples:

fix ins all insert/stream seed 1001 distributiontemplate pdd1 nparticles 5000 vel constant 0. -0.5 -2. particlerate 1000 overlapcheck yes insertion_face ins_mesh extrude_length 0.6 
fix ins all insert/pack seed 1001 distributiontemplate pdd1 insert_every once overlapcheck yes volumefraction 0.3 region mysphere ntry_mc 10000 

General description:

Insert particles into a granular run either once or every few timesteps within a specified region until either np particles have been inserted or the desired particle mass (mp) has been reached.

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.

To specify the numbe of particles to be inserted, you must use either the nparticles or the mass keyword (but not both). In the latter case, the number of particles to be inserted is calculated from the mass expectancy given by the particle distribution. The start keyword can be used to set the time-step at which the insertion should start,

Likewise, you can use the particlerate or the massrate keyword (but not both) to control the insertion rate. Particles are not inserted continuously, but in packets (for efficiency reasons). The frequency of the particle insertion can be controlled by the keyword insert_every, which defines the number of time-steps between two insertions. Alternatively, by specifying insert_every once, particles are inserted only once (only applicable to fix insert/pack). The number of particles to be inserted at each insertion event is calculated from the insertion rate and insert_every.

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").

The keyword overlapcheck controls if overlap is checked for at insertion, both within the inserted particle package and with other existig particles. If this option is turned off, insertion will scale very well in parallel, otherwise not. Be aware that in case of no overlap check, highly overlapping configurations will be produced, so you will have to relax these configurations.

If overlapcheck if performed, the number of insertion attempts per particle can be specified via the maxattempt keyword. Each timestep particles are inserted, the command will make up to a total of M tries to insert the new particles without overlaps, where M = # of inserted particles * ma. If unsuccessful at completing all insertions, a warning will be printed.

The all_in flag determines if the particle is completely contained in the insertion region (all_in yes) or only the particle center (all_in no). Currently all_in yes is not yet supported for all types of insertion.

The initial velocity and rotational velocity can be controlled via the vel and omega keywords.

Description for fix insert/pack:

This command must use the region keyword to define an insertion volume. The specified region must have been previously defined with a region command. Each timestep particles are inserted, they are placed randomly inside the insertion volume.

The volumefraction option specifies what volume fraction of the insertion volume will be filled with particles. The higher the value, the more particles are inserted each timestep. Since inserted particles should not overlap, the maximum volume fraction should be no higher than about 0.6.

To determine the volume of the insertion region, a Monte Carlo approach might be used for some cases where the volume is difficult to calculate or where the volume calculation is simply not implemented by the region. The ntry_mc keyword is used to control the number of MC tries that are used for the volume calculation.

Description for fix insert/stream:

Each timestep particles are inserted, they are placed randomly inside the insertion volume so as to mimic a stream of poured particles. The insertion volume is generated by extruding the insertion face as specified via insertion_face in the direction of the face normal.

The amount of extrusion is either calculated from the insertion frequency (keyword insert_every) or specified directly via keyword extrude_length. In case the former case, you have the possibility to define the duration of each insertion via the duration keyword. duration < insert_every will generate a "pulsed" stream as opposed to a continuous stream. Example: Setting insert_every = 1000 and duration = 600 will produce a stream that pour material for 600 time-steps, will pause for 400 time-steps, pour for another 600 time-steps etc. duration and extrude_length cannot be used together.

Particles are inserted again after enough time has elapsed that the previously inserted particles have left the insertion volume. Until the time these particles reach the insertion face, no other forces affect the particles (pair forces, gravity etc.). Fix insert/stream internally issues a special integrator to take care of this. This procedure guarantees that the specified velocity, omega etc. values are perfectly met at the specified insertion face.

The larger the volume, the more particles that can be inserted at one insertion step. Insertions will continue until the desired # of particles has been inserted.

NOTE: The insertion face must be a planar face, and the insertion velocity projected on the face normal must be non-zero.

NOTE: Keywords insert_every and extrude_length may not be used together

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 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. 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:

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.

Keywords duration and extrude_length can not be used together.

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

Related commands:

fix_deposit, fix_gravity, region, fix_pour_dev, fix_pour

Default:

The defaults are maxattempt = 50, all_in = no, overlapcheck = yes vel = 0.0 0.0 0.0, omega = 0.0 0.0 0.0, start = next time-step, duration = insert_every

For fix insert/pack, defaults are ntry_mc = 100000

For fix insert/stream, no further defaults apply