forked from lijiext/lammps
152 lines
6.4 KiB
HTML
152 lines
6.4 KiB
HTML
<HTML>
|
|
<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>
|
|
|
|
|
|
|
|
|
|
|
|
|
|
<HR>
|
|
|
|
<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>
|
|
</HTML>
|