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<CENTER><A HREF = "http://lammps.sandia.gov">LAMMPS WWW Site</A> - <A HREF = "Manual.html">LAMMPS Documentation</A> - <A HREF = "Section_commands.html#comm">LAMMPS Commands</A>
</CENTER>
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<H3>fix pour command
</H3>
<P><B>Syntax:</B>
</P>
<PRE>fix ID group-ID pour N type seed keyword values ...
</PRE>
<UL><LI>ID, group-ID are documented in <A HREF = "fix.html">fix</A> command
<LI>pour = style name of this fix command
<LI>N = # of atoms to insert
<LI>type = atom type to assign to inserted atoms
<LI>seed = random # seed (positive integer)
<LI>one or more keyword/value pairs may be appended to args
<LI>keyword = <I>region</I> or <I>diam</I> or <I>dens</I> or <I>vol</I> or <I>rate</I> or <I>vel</I>
<PRE> <I>region</I> value = region-ID
region-ID = ID of region to use as insertion volume
<I>diam</I> values = lo hi
lo,hi = range of diameters for inserted particles (distance units)
<I>dens</I> values = lo hi
lo,hi = range of densities for inserted particles
<I>vol</I> values = fraction Nattempt
fraction = desired volume fraction for filling insertion volume
Nattempt = max # of insertion attempts per atom
<I>rate</I> value = V
V = z velocity (3d) or y velocity (2d) at which
insertion volume moves (velocity units)
<I>vel</I> values (3d) = vxlo vxhi vylo vyhi vz
<I>vel</I> values (2d) = vxlo vxhi vy
vxlo,vxhi = range of x velocities for inserted particles (velocity units)
vylo,vyhi = range of y velocities for inserted particles (velocity units)
vz = z velocity (3d) assigned to inserted particles (velocity units)
vy = y velocity (2d) assigned to inserted particles (velocity units)
</PRE>
</UL>
<P><B>Examples:</B>
</P>
<PRE>fix 3 all pour 1000 2 29494 region myblock
fix 2 all pour 10000 1 19985583 region disk vol 0.33 100 rate 1.0 diam 0.9 1.1
</PRE>
<P><B>Description:</B>
</P>
<P>Insert particles into a granular run every few timesteps within a
specified region until N particles have been inserted. This is useful
for simulating the pouring of particles into a container under the
influence of gravity.
</P>
<P>Inserted particles are assigned the specified atom type and are
assigned to two groups: the default group "all" and the group
specified in the fix pour command (which can also be "all").
</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. It must be of type <I>block</I> or a z-axis
<I>cylinder</I> and must be defined with side = <I>in</I>. The cylinder style
of region can only be used with 3d simulations.
</P>
<P>Each timestep particles are inserted, they are placed randomly inside
the insertion volume so as to mimic a stream of poured particles. The
larger the volume, the more particles that can be inserted at any one
timestep. Particles are inserted again after enough time has elapsed
that the previously inserted particles fall out of the insertion
volume under the influence of gravity. Insertions continue every so
many timesteps until the desired # of particles has been inserted.
</P>
<P>All other keywords are optional with defaults as shown below. The
<I>diam</I>, <I>dens</I>, and <I>vel</I> options enable inserted particles to have a
range of diameters or densities or xy velocities. The specific values
for a particular inserted particle will be chosen randomly and
uniformly between the specified bounds. The <I>vz</I> or <I>vy</I> value for
option <I>vel</I> assigns a z-velocity (3d) or y-velocity (2d) to each
inserted particle.
</P>
<P>The <I>vol</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 cannot
overlap, the maximum volume fraction should be no higher than about
0.6. Each timestep particles are inserted, LAMMPS will make up to a
total of M tries to insert the new particles without overlaps, where M
= # of inserted particles * Nattempt. If LAMMPS is unsuccessful at
completing all insertions, it prints a warning.
</P>
<P>The <I>rate</I> option moves the insertion volume in the z direction (3d)
or y direction (2d). This enables pouring particles from a
successively higher height over time.
</P>
<P><B>Restart, fix_modify, output, run start/stop, minimize info:</B>
</P>
<P>No information about this fix is written to <A HREF = "restart.html">binary restart
files</A>. This means you must be careful when restarting a
pouring simulation, when the restart file was written in the middle of
the pouring operation. Specifically, you should use a new fix pour
command in the input script for the restarted simulation that
continues the operation. You will need to adjust the arguments of the
original fix pour command to do this.
</P>
<P>Also note that because the state of the random number generator is not
saved in restart files, you cannot do "exact" restarts with this fix,
where the simulation continues on the same as if no restart had taken
place. However, in a statistical sense, a restarted simulation should
produce the same behavior if you adjust the fix pour parameters
appropriately.
</P>
<P>None of the <A HREF = "fix_modify.html">fix_modify</A> options are relevant to this
fix. No global or per-atom quantities are stored by this fix for
access by various <A HREF = "Section_howto.html#howto_15">output commands</A>. 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>This fix is part of the "granular" package. It is only enabled if
LAMMPS was built with that package. See the <A HREF = "Section_start.html#start_3">Making
LAMMPS</A> section for more info.
</P>
<P>For 3d simulations, a gravity fix in the -z direction must be defined
for use in conjunction with this fix. For 2d simulations, gravity
must be defined in the -y direction.
</P>
<P>The specified insertion region cannot be a "dynamic" region, as
defined by the <A HREF = "region.html">region</A> command.
</P>
<P><B>Related commands:</B>
</P>
<P><A HREF = "fix_deposit.html">fix_deposit</A>, <A HREF = "fix_gravity.html">fix_gravity</A>,
<A HREF = "region.html">region</A>
</P>
<P><B>Default:</B>
</P>
<P>The option defaults are diam = 1.0 1.0, dens = 1.0 1.0, vol = 0.25 50,
rate = 0.0, vel = 0.0 0.0 0.0 0.0 0.0.
</P>
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