222 lines
11 KiB
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222 lines
11 KiB
HTML
<HTML>
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<CENTER><A HREF = "http://www.cfdem.com">LIGGGHTS WWW Site</A> - <A HREF = "http://lammps.sandia.gov">LAMMPS WWW Site</A> - <A HREF = "Manual.html">LIGGGHTS Documentation</A> - <A HREF = "Section_commands.html#comm">LIGGGHTS Commands</A>
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</CENTER>
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<HR>
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<H3>fix insert/rate/region command
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</H3>
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<P><B>Syntax:</B>
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</P>
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<PRE>fix ID group-ID insert/rate/region seed seed_value distributiontemplate dist-ID general_keywords general_values insert_rate_keywords insert_rate_values
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</PRE>
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<UL><LI>ID, group-ID are documented in <A HREF = "fix.html">fix</A> command
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<LI>insert/pack and insert/stream = style names of these fix commands
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<LI>seed = obligatory keyword
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<LI>seed_value = random # seed (positive integer)
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<LI>distributiontemplate = obligatory keyword
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<LI>dist-ID = ID of a <A HREF = "fix_particledistribution_discrete.html">fix_particledistribution_discrete</A> to be used for particle insertion
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<LI>one or more general keyword/value pairs can be appended
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<LI>general_keywords = <I>verbose</I> or <I>maxattampt</I> or <I>nparticles</I> or <I>mass</I> or <I>particlerate</I> or <I>massrate</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>
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<PRE> <I>verbose</I> = yes or no
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<I>maxattempt</I> value = ma
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ma = max # of insertion attempts per atom (positive integer)
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<I>nparticles</I> values = np or INF
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np = number of particles to insert (positive integer)
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INF = insert as many particles as possible
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<I>mass</I> values = mp
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mp = mass of particles to be inserted (positive float)
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INF = insert as many particles as possible
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<I>particlerate</I> values = pr
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pr = particle inseration rate (particles/time units)
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<I>massrate</I> values = mr
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mr = mass inseration rate (mass/time units)
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<I>insert_every</I> value = once or ie
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once = value to signalise that isertion takes place only once (the step after the fix is issued)
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ie = every how many time-steps particles are inserted - insertion happens periodically (positive integer)
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<I>start</I> value = ts
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ts = time-step at which insertion should start (positive integer larger than current time-step)
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<I>overlapcheck</I> value = yes or no
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<I>all_in</I> value = yes or no
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<I>random_distribute</I> value = exact or uncorrelated
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<I>vel constant</I> values = vx vy vz
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vx = x-velocity at insertion (velocity units)
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vy = y-velocity at insertion (velocity units)
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vz = z-velocity at insertion (velocity units)
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<I>vel uniform</I> values = vx vy vz vFluctx vFlucty vFluctz
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vx = mean x-velocity at insertion (velocity units)
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vy = mean y-velocity at insertion (velocity units)
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vz = mean z-velocity at insertion (velocity units)
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vFluctx = amplitude of uniform x-velocity fluctuation at insertion (velocity units)
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vFlucty = amplitude of uniform y-velocity fluctuation at insertion (velocity units)
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vFluctz = amplitude of uniform z-velocity fluctuation at insertion (velocity units)
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<I>vel gaussian</I> values = vx vy vz vFluctx vFlucty vFluctz
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vx = mean x-velocity at insertion (velocity units)
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vy = mean y-velocity at insertion (velocity units)
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vz = mean z-velocity at insertion (velocity units)
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vFluctx = standard deviation of Gaussian x-velocity fluctuation at insertion (velocity units)
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vFlucty = standard deviation of Gaussian y-velocity fluctuation at insertion (velocity units)
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vFluctz = standard deviation of Gaussian z-velocity fluctuation at insertion (velocity units)
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<I>orientation</I> values = random or template
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random = randomize rotational orientation
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template = use orientation from particle template
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<I>omega</I> values = constant omegax omegay omegaz
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constant = obligatory word
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omegax = x-comonent of angular velocity (1/time units)
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omegay = y-comonent of angular velocity (1/time units)
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omegaz = z-comonent of angular velocity (1/time units)
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</PRE>
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<LI>following the general keyword/value section, one or more rate_region keyword/value pairs can be appended for the fix insert/rate/region command
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<LI>rate_region keywords = <I>region</I> or <I>ntry_mc</I>
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<PRE> <I>region</I> value = region-ID
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region-ID = ID of the region where the particles will be generated (positive integer)
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<I>ntry_mc</I> values = n
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n = number of Monte-Carlo steps for calculating the region's volume (positive integer)
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</PRE>
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</UL>
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<P><B>Examples:</B>
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</P>
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<PRE>fix ins all insert/rate/region seed 1001 distributiontemplate pdd1 nparticles 1000 particlerate 5000 insert_every 1000 overlapcheck yes region mysphere ntry_mc 10000
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</PRE>
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<P><B>General description:</B>
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</P>
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<P>Insert particles into a granular run every few timesteps
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within a specified region at a specified rate.
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</P>
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<P>The <I>verbose</I> keyword controlls whether statistics about particle
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insertion is output to the screen each time particles are inserted.
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</P>
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<P>This command must use the <I>region</I> keyword to define an insertion
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volume. The specified region must have been previously defined with a
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<A HREF = "region.html">region</A> command. Dynamic regions are not supported as
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insertion region. Each timestep particles are inserted, they are
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placed randomly inside the insertion volume.
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</P>
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<P>To specify the number of particles to be inserted, you must use either
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the <I>nparticles</I> or the <I>mass</I> keyword (but not both). In the latter
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case, the number of particles to be inserted is calculated from the
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mass expectancy given by the particle distribution.
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</P>
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<P>Likewise, you can use the <I>particlerate</I> or the <I>massrate</I> keyword (but not both)
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to control the insertion rate.
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</P>
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<P>The frequency of the particle insertion is controlled by the
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keyword <I>insert_every</I>, which defines the number of time-steps
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between two insertions. The number of particles to be inserted
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at each insertion event is calculated from the insertion rate
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and <I>insert_every</I>. The <I>start</I> keyword can be used to set
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the time-step at which the insertion should start.
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</P>
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<P>This command must use the distributiontemplate keyword to refer to a
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<A HREF = "fix_particledistribution_discrete.html">fix_particledistribution_discrete</A> (defined by dist-fix-ID) that defines the properties of the
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inserted particles.
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</P>
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<P>Inserted particles are assigned the atom type specified by the
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particledistribution defined via the <A HREF = "fix_particledistribution_discrete.html">fix_particledistribution_discrete</A> and
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are assigned to 4 groups: the default group "all" and the group
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specified in the fix insert command, as well as the groups specified
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in the <A HREF = "fix_particledistribution_discrete.html">fix_particledistribution_discrete</A> and <A HREF = "fix_particletemplate_sphere.html">fix_particletemplate_sphere</A>
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command (all of which can also be "all").
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</P>
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<P>The keyword <I>overlapcheck</I> controls if overlap is checked for at insertion,
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both within the inserted particle package and with other existig particles.
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If this option is turned off, insertion will scale very well in parallel,
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otherwise not. Be aware that in case of no overlap check, highly overlapping
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configurations will be produced, so you will have to relax these configurations.
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</P>
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<P>If overlapcheck if performed, the number of insertion attempts per
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particle can be specified via the <I>maxattempt</I> keyword. Each timestep
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particles are inserted, the command will make up to a total of M tries
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to insert the new particles without overlaps, where
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M = # of inserted particles * ma. If unsuccessful at completing all
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insertions, a warning will be printed.
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</P>
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<P>The <I>all_in</I> flag determines if the particle is completely contained
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in the insertion region (<I>all_in yes</I>) or only the particle center
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(<I>all_in no</I>). Currently <I>all_in yes</I> is not yet supported for all
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types of insertion.
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</P>
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<P>Keyword <I>random_distribute</I> controls how the number of particles to
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be inserted is distributed among parallel processors and among the
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particle templates in the particle distribution. For style <I>exact</I>,
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the number of particles to be inserted each step is matched exactly.
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For style <I>uncorrelated</I>, the number of particles to be inserted
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for each particle template will be rounded in an uncorrelated way,
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so the total number of inserted particles may vary for each insertion
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step. However, statistically both ways should produce the same
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result. Style <I>uncorrelated</I> may be faster in parallel since it
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does not need global MPI operations.
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Please note that if the # of particles to be inserted is calculated
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e.g. from a particle mass to be inserted, the number of particles
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to be inserted each insertion step will vary by 1, irrespective of
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the <I>random_distribute</I> settings. This is because in this case the
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# of particles to insert in each step will be a floating point number,
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and applying a simple floor/ceil rounding operation would lead to a
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statistical bias.
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</P>
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<P>The initial velocity and rotational velocity can be controlled via the
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<I>vel</I> and <I>omega</I> keywords. <I>vel constant</I> simply patches a constant
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velocity to the inserted particles, <I>vel uniform</I> sets uniformly distributed
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velocities with mean and amplitude. <I>vel gaussian</I> sets Gaussian
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distributed particle velocities with mean and std. deviation.
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</P>
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<P><B>Restart, fix_modify, output, run start/stop, minimize info:</B>
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</P>
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<P>Information about this fix is written to <A HREF = "restart.html">binary restart
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files</A>. This means you can restart a simulation simulation
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while inserting particles, when the restart file was written during the
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insertion operation.
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</P>
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<P>None of the <A HREF = "fix_modify.html">fix_modify</A> options are relevant to this
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fix. A global vector is stored by this fix for access by various <A HREF = "Section_howto.html#4_15">output
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commands</A>. The first component of the vector is the
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number of particles already inserted, the second component is the mass
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of particles already inserted. No parameter of this fix can be
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used with the <I>start/stop</I> keywords of the <A HREF = "run.html">run</A> command.
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This fix is not invoked during <A HREF = "minimize.html">energy minimization</A>.
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</P>
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<P><B>Restrictions:</B>
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</P>
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<P>The <I>overlapcheck</I> = 'yes' option performs an inherently serial operation
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and will thus not scale well in parallel. For this reason, if you
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want to generate large systems, you are advised to turn <I>overlapcheck</I>
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off and let the packing relax afterwards to generate a valid packing.
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</P>
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<P>Keywords <I>duration</I> and <I>extrude_length</I> can not be used together.
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</P>
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<P>Currently <I>all_in yes</I> is not yet supported for all types of insertion.
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</P>
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<P>Dynamic regions are not supported as insertion region.
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</P>
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<P><B>Related commands:</B>
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</P>
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<P><A HREF = "fix_insert_stream.html">fix_insert_stream</A>, <A HREF = "fix_insert_pack.html">fix_insert_pack</A>,
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<A HREF = "fix_deposit.html">fix_deposit</A>, <A HREF = "fix_gravity.html">fix_gravity</A>,
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<A HREF = "region.html">region</A>, <A HREF = "fix_pour_dev.html">fix_pour_dev</A>, <A HREF = "fix_pour.html">fix_pour</A>
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</P>
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<P><B>Default:</B>
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</P>
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<P>The defaults are maxattempt = 50, all_in = no, overlapcheck = yes
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vel = 0.0 0.0 0.0, omega = 0.0 0.0 0.0, start = next time-step,
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duration = insert_every, ntry_mc = 100000, random_distribute = exact
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</P>
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</HTML>
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