lammps/doc/fix_pour.txt

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fix pour command :h3

[Syntax:]

fix ID group-ID pour N type seed keyword values ... :pre

ID, group-ID are documented in "fix"_fix.html command :ulb,l
pour = style name of this fix command :l
N = # of atoms to insert :l
type = atom type to assign to inserted atoms :l
seed = random # seed (positive integer) :l
one or more keyword/value pairs may be appended to args :l
keyword = {region} or {mol} or {rigid} or {diam} or {dens} or {vol} or {rate} or {vel} :l
  {region} value = region-ID
    region-ID = ID of region to use as insertion volume
  {mol} value = template-ID
    template-ID = ID of molecule template specified in a separate "molecule"_molecule.html command
  {rigid} value = fix-ID
    fix-ID = ID of "fix rigid/small"_fix_rigid.html command
  {diam} values = dstyle args
    dstyle = {one} or {range} or {poly}
      {one} args = D
        D = single diameter for inserted particles (distance units)
      {range} args = Dlo Dhi
        Dlo,Dhi = range of diameters for inserted particles (distance units)
      {poly} args = Npoly D1 P1 D2 P2 ...
        Npoly = # of (D,P) pairs
        D1,D2,... = diameter for subset of inserted particles (distance units)
        P1,P2,... = percentage of inserted particles with this diameter (0-1)
  {vol} values = fraction Nattempt
    fraction = desired volume fraction for filling insertion volume
    Nattempt = max # of insertion attempts per atom
  {rate} value = V
    V = z velocity (3d) or y velocity (2d) at which
        insertion volume moves (velocity units)
  {vel} values (3d) = vxlo vxhi vylo vyhi vz
  {vel} 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
:ule

[Examples:]

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 range 0.9 1.1 
fix 2 all pour 10000 1 19985583 region disk diam poly 2 0.7 0.4 1.5 0.6
fix ins all pour 500 1 4767548 vol 0.8 10 region slab mol object rigid myRigid :pre

[Description:]

Insert finite-size particles or molecules into the simulation box
every few timesteps within a specified region until N particles or
molecules have been inserted.  This is typically used to model the
pouring of granular particles into a container under the influence of
gravity.  For the remainder of this doc page, a single inserted atom
or molecule is referred to as a "particle".

If inserted particles are individual atoms, they are assigned the
specified atom type.  For molecules the specified type is ignored, and
the type of each atom in the inserted molecule is specified in the
file read by the "molecule"_molecule.html command.

All atoms in the inserted particle are assigned to two groups: the
default group "all" and the group specified in the fix pour command
(which can also be "all").

This command must use the {region} keyword to define an insertion
volume.  The specified region must have been previously defined with a
"region"_region.html command.  It must be of type {block} or a z-axis
{cylinder} and must be defined with side = {in}.  The cylinder style
of region can only be used with 3d simulations.

Individual atoms are inserted, unless the {mol} keyword is used.  It
specifies a {template-ID} previously defined using the
"molecule"_molecule.html command, which reads a file that defines the
molecule.  The coordinates, atom types, center-of-mass, moments of
inertia, etc, as well as any bond/angle/etc information for the
molecule can be specified in the molecule file.  See the
"molecule"_molecule.html command for details.  The only settings
required to be in this file are the coordinates and types of atoms in
the molecule.

If you wish to insert molecules via the {mol} keyword, that will be
treated as rigid bodies, you can first specify a "fix
rigid/small"_fix_rigid.html command, and then use the {rigid} keyword
with this command, specifying the ID of the fix rigid/small command as
its value.

Each timestep particles are inserted, they are placed randomly inside
the insertion volume so as to mimic a stream of poured particles.  If
they are molecules they are also oriented randomly.  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.

All other keywords are optional with defaults as shown below.

The {diam} option is only used when inserting atoms and specifes the
diameters of inserted particles.  For molecule insertion, the
diameters of individual atoms in the molecule can be specified in the
file read by the "molecule"_molecule.html command.  There are 3
styles: {one}, {range}, or {poly}.  For {one}, all particles will have
diameter {D}.  For {range}, the diameter of each particle will be
chosen randomly and uniformly between the specified {Dlo} and {Dhi}
bounds.  For {poly}, a series of {Npoly} diameters is specified.  For
each diameter a percentage value from 0.0 to 1.0 is also specified.
The {Npoly} percentages must sum to 1.0.  For the example shown above
with "diam 2 0.7 0.4 1.5 0.6", all inserted particles will have a
diameter of 0.7 or 1.5.  40% of the particles will be small; 60% will
be large.

The {dens} and {vel} options enable inserted particles to have a range
of densities or xy velocities.  The specific values for a particular
inserted particle will be chosen randomly and uniformly between the
specified bounds.  The {vz} or {vy} value for option {vel} assigns a
z-velocity (3d) or y-velocity (2d) to each inserted particle.

The {vol} option specifies what volume fraction of the insertion
volume will be filled with particles.  For particles with a size
specified by the {diam range} keyword, they are assumed to all be of
maximum diamter {Dhi} for purposes of computing their contribution to
the volume fraction.

The higher the volume fraction 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.

The {rate} 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.

:line

[Restart, fix_modify, output, run start/stop, minimize info:]

No information about this fix is written to "binary restart
files"_restart.html.  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.

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.

None of the "fix_modify"_fix_modify.html options are relevant to this
fix.  No global or per-atom quantities are stored by this fix for
access by various "output commands"_Section_howto.html#howto_15.  No
parameter of this fix can be used with the {start/stop} keywords of
the "run"_run.html command.  This fix is not invoked during "energy
minimization"_minimize.html.

[Restrictions:]

This fix is part of the GRANULAR package.  It is only enabled if
LAMMPS was built with that package.  See the "Making
LAMMPS"_Section_start.html#start_3 section for more info.

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.

The specified insertion region cannot be a "dynamic" region, as
defined by the "region"_region.html command.

[Related commands:]

"fix_deposit"_fix_deposit.html, "fix_gravity"_fix_gravity.html,
"region"_region.html

[Default:]

The option defaults are diam = one 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.