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<HTML>
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<HR>
<H3>fix insert/pack command
</H3>
<P><B>Syntax:</B>
</P>
<PRE>fix ID group-ID insert/pack seed seed_value distributiontemplate dist-ID general_keywords general_values pack_keywords pack_values ...
</PRE>
<UL><LI>ID, group-ID are documented in <A HREF = "fix.html">fix</A> command
<LI>insert/pack = style names of this fix command
<LI>seed = obligatory keyword
<LI>seed_value = random # seed (positive integer)
<LI>distributiontemplate = obligatory keyword
<LI>dist-ID = ID of a <A HREF = "fix_particledistribution_discrete.html">fix_particledistribution_discrete</A> to be used for particle insertion
<LI>one or more general keyword/value pairs can be appended
<LI>general_keywords = <I>verbose</I> or <I>maxattampt</I> or <I>insert_every</I> or <I>overlapcheck</I> or <I>all_in</I> or <I>random_distribute</I> or <I>vel constant</I> or <I>vel uniform</I> or <I>vel gaussian</I> or <I>orientation</I> or <I>omega</I>
<PRE> <I>verbose</I> = yes or no
<I>maxattempt</I> value = ma
ma = max # of insertion attempts per atom (positive integer)
<I>insert_every</I> value = once or ie
once = value to signalise that isertion takes place only once (the step after the fix is issued)
ie = every how many time-steps particles are inserted - insertion happens periodically (positive integer)
<I>start</I> value = ts
ts = time-step at which insertion should start (positive integer larger than current time-step)
<I>overlapcheck</I> value = yes or no
<I>all_in</I> value = yes or no
<I>random_distribute</I> value = exact or uncorrelated
<I>vel constant</I> values = vx vy vz
vx = x-velocity at insertion (velocity units)
vy = y-velocity at insertion (velocity units)
vz = z-velocity at insertion (velocity units)
<I>vel uniform</I> values = vx vy vz vFluctx vFlucty vFluctz
vx = mean x-velocity at insertion (velocity units)
vy = mean y-velocity at insertion (velocity units)
vz = mean z-velocity at insertion (velocity units)
vFluctx = amplitude of uniform x-velocity fluctuation at insertion (velocity units)
vFlucty = amplitude of uniform y-velocity fluctuation at insertion (velocity units)
vFluctz = amplitude of uniform z-velocity fluctuation at insertion (velocity units)
<I>vel gaussian</I> values = vx vy vz vFluctx vFlucty vFluctz
vx = mean x-velocity at insertion (velocity units)
vy = mean y-velocity at insertion (velocity units)
vz = mean z-velocity at insertion (velocity units)
vFluctx = standard deviation of Gaussian x-velocity fluctuation at insertion (velocity units)
vFlucty = standard deviation of Gaussian y-velocity fluctuation at insertion (velocity units)
vFluctz = standard deviation of Gaussian z-velocity fluctuation at insertion (velocity units)
<I>orientation</I> values = random or template
random = randomize rotational orientation
template = use orientation from particle template
<I>omega</I> values = constant omegax omegay omegaz
constant = obligatory word
omegax = x-comonent of angular velocity (1/time units)
omegay = y-comonent of angular velocity (1/time units)
omegaz = z-comonent of angular velocity (1/time units)
</PRE>
<LI>following the general keyword/value section, one or more pack keyword/value pairs can be appended for the fix insert/pack command
<LI>pack_keywords = <I>region</I> or <I>volumefraction_region</I> or <I>particles_in_region</I> or <I>mass_in_region</I> or <I>ntry_mc</I>
<PRE>pack_keywords = where exactly one out of <I>volumefraction_region</I> or <I>particles_in_region</I> or <I>mass_in_region</I> has to be defined:l
<I>region</I> value = region-ID
region-ID = ID of the region where the particles will be generated (positive integer)
<I>volumefraction_region</I> values = vol
vol = desired volume fraction for the region (positive float, 0 < vol < 1)
<I>particles_in_region</I> values = np
np = desired number of particles in the region (positive integer)
<I>mass_in_region</I> values = m
m = desired mass in the region (positive float, m > 0)
<I>ntry_mc</I> values = n
n = number of Monte-Carlo steps for calculating the region's volume (positive integer)
</PRE>
</UL>
<P><B>Examples:</B>
</P>
<PRE>fix ins all insert/pack seed 1001 distributiontemplate pdd1 insert_every once overlapcheck yes volumefraction_region 0.3 region mysphere ntry_mc 10000
</PRE>
<P><B>Description:</B>
</P>
<P>Insert particles into a granular run either once or every few timesteps
within the specified region, as defined via the <I>region</I> keyword.
</P>
<P>The <I>verbose</I> keyword controlls whether statistics about particle
insertion is output to the screen each time particles are inserted.
</P>
<P>This command must use the distributiontemplate keyword to refer to a
<A HREF = "fix_particledistribution_discrete.html">fix_particledistribution_discrete</A> (defined by dist-fix-ID) that defines the properties of the
inserted particles.
</P>
<P>At each insertion step, fix insert/pack tries inserts as many particles as
needed to reach a defined target, which can be either a region volume
fraction (keyword <I>volumefraction_region</I>), the total number of particles
in the region (keyword <I>particles_in_region</I>), or the total particle mass
in the region (keyword <I>mass_in_region</I>). Exactly one out of the keywords
<I>volumefraction_region</I>, <I>particles_in_region</I>, <I>mass_in_region</I> must
be defined.
</P>
<P>The frequency of the particle insertion can be controlled by the
keyword <I>insert_every</I>, which defines the number of time-steps between
two insertions. Alternatively, by specifying <I>insert_every once</I>,
particles are inserted only once.
</P>
<P>The <I>start</I> keyword can be used to set the time-step at which the insertion
should start.
</P>
<P>Inserted particles are assigned the atom type specified by the
particledistribution defined via the <A HREF = "fix_particledistribution_discrete.html">fix_particledistribution_discrete</A> 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 <A HREF = "fix_particledistribution_discrete.html">fix_particledistribution_discrete</A> and <A HREF = "fix_particletemplate_sphere.html">fix_particletemplate_sphere</A>
command (all of which can also be "all").
</P>
<P>The keyword <I>overlapcheck</I> 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.
</P>
<P>If overlapcheck if performed, the number of insertion attempts per
particle can be specified via the <I>maxattempt</I> 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.
</P>
<P>The <I>all_in</I> flag determines if the particle is completely contained
in the insertion region (<I>all_in yes</I>) or only the particle center
(<I>all_in no</I>). Currently <I>all_in yes</I> is not yet supported for all
types of insertion.
</P>
<P>Keyword <I>random_distribute</I> controls how the number of particles to
be inserted is distributed among parallel processors and among the
particle templates in the particle distribution. For style <I>exact</I>,
the number of particles to be inserted each step is matched exactly.
For style <I>uncorrelated</I>, the number of particles to be inserted
for each particle template will be rounded in an uncorrelated way,
so the total number of inserted particles may vary for each insertion
step. However, statistically both ways should produce the same
result. Style <I>uncorrelated</I> may be faster in parallel since it
does not need global MPI operations.
Please note that if the # of particles to be inserted is calculated
e.g. from a particle mass to be inserted, the number of particles
to be inserted each insertion step will vary by 1, irrespective of
the <I>random_distribute</I> settings. This is because in this case the
# of particles to insert in each step will be a floating point number,
and applying a simple floor/ceil rounding operation would lead to a
statistical bias.
</P>
<P>The initial velocity and rotational velocity can be controlled via the
<I>vel</I> and <I>omega</I> keywords. <I>vel constant</I> simply patches a constant
velocity to the inserted particles, <I>vel uniform</I> sets uniformly distributed
velocities with mean and amplitude. <I>vel gaussian</I> sets Gaussian
distributed particle velocities with mean and std. deviation.
</P>
<P><B>Description for fix insert/pack:</B>
</P>
<P>This command must use the <I>region</I> keyword to define an insertion
volume. The specified region must have been previously defined with a
<A HREF = "region.html">region</A> command. Dynamic regions are not supported as insertion region.
Each timestep particles are inserted, they are placed randomly inside the
insertion volume.
</P>
<P>The <I>volumefraction</I> 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.
</P>
<P>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 <I>ntry_mc</I> keyword is used to control the number of MC tries that
are used for the volume calculation.
</P>
<P><B>Restart, fix_modify, output, run start/stop, minimize info:</B>
</P>
<P>Information about this fix is written to <A HREF = "restart.html">binary restart
files</A>. This means you can restart a simulation
while inserting particles, when the restart file was written during the
insertion operation.
</P>
<P>None of the <A HREF = "fix_modify.html">fix_modify</A> options are relevant to this
fix. A global vector is stored by this fix for access by various <A HREF = "Section_howto.html#4_15">output
commands</A>. 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 <I>start/stop</I> keywords of the <A HREF = "run.html">run</A> command.
This fix is not invoked during <A HREF = "minimize.html">energy minimization</A>.
</P>
<P><B>Restrictions:</B>
</P>
<P>The <I>overlapcheck</I> = '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 <I>overlapcheck</I>
off and let the packing relax afterwards to generate a valid packing.
</P>
<P>Keywords <I>duration</I> and <I>extrude_length</I> can not be used together.
</P>
<P>Currently <I>all_in yes</I> is not yet supported for all types of insertion.
</P>
<P>Dynamic regions are not supported as insertion region.
</P>
<P><B>Related commands:</B>
</P>
<P><A HREF = "fix_insert_stream.html">fix_insert_stream</A>, <A HREF = "fix_insert_rate_region.html">fix_insert_rate_region</A>,
<A HREF = "fix_deposit.html">fix_deposit</A>, <A HREF = "region.html">region</A>,
<A HREF = "fix_pour.html">fix_pour</A>
</P>
<P><B>Default:</B>
</P>
<P>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, ntry_mc = 100000, random_distribute = exact
</P>
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