forked from lijiext/lammps
265 lines
13 KiB
Plaintext
265 lines
13 KiB
Plaintext
"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
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:link(lws,http://lammps.sandia.gov)
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:link(ld,Manual.html)
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:link(lc,Section_commands.html#comm)
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:line
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fix pour command :h3
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[Syntax:]
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fix ID group-ID pour N type seed keyword values ... :pre
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ID, group-ID are documented in "fix"_fix.html command :ulb,l
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pour = style name of this fix command :l
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N = # of particles to insert :l
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type = atom type to assign to inserted particles (offset for molecule insertion) :l
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seed = random # seed (positive integer) :l
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one or more keyword/value pairs may be appended to args :l
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keyword = {region} or {diam} or {vol} or {rate} or {dens} or {vel} or {mol} or {rigid} or {shake} or {ignore} :l
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{region} value = region-ID
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region-ID = ID of region to use as insertion volume
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{diam} values = dstyle args
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dstyle = {one} or {range} or {poly}
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{one} args = D
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D = single diameter for inserted particles (distance units)
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{range} args = Dlo Dhi
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Dlo,Dhi = range of diameters for inserted particles (distance units)
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{poly} args = Npoly D1 P1 D2 P2 ...
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Npoly = # of (D,P) pairs
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D1,D2,... = diameter for subset of inserted particles (distance units)
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P1,P2,... = percentage of inserted particles with this diameter (0-1)
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{id} values = idflag
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idflag = {max} or {next} = how to choose IDs for inserted particles and molecules
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{vol} values = fraction Nattempt
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fraction = desired volume fraction for filling insertion volume
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Nattempt = max # of insertion attempts per particle
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{rate} value = V
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V = z velocity (3d) or y velocity (2d) at which
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insertion volume moves (velocity units)
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{dens} values = Rholo Rhohi
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Rholo,Rhohi = range of densities for inserted particles (mass/volume units)
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{vel} values (3d) = vxlo vxhi vylo vyhi vz
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{vel} values (2d) = vxlo vxhi vy
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vxlo,vxhi = range of x velocities for inserted particles (velocity units)
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vylo,vyhi = range of y velocities for inserted particles (velocity units)
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vz = z velocity (3d) assigned to inserted particles (velocity units)
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vy = y velocity (2d) assigned to inserted particles (velocity units)
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{mol} value = template-ID
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template-ID = ID of molecule template specified in a separate "molecule"_molecule.html command
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{molfrac} values = f1 f2 ... fN
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f1 to fN = relative probability of creating each of N molecules in template-ID
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{rigid} value = fix-ID
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fix-ID = ID of "fix rigid/small"_fix_rigid.html command
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{shake} value = fix-ID
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fix-ID = ID of "fix shake"_fix_shake.html command
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{ignore} value = none
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skip any line or triangle particles when detecting possible
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overlaps with inserted particles :pre
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:ule
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[Examples:]
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fix 3 all pour 1000 2 29494 region myblock
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fix 2 all pour 10000 1 19985583 region disk vol 0.33 100 rate 1.0 diam range 0.9 1.1
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fix 2 all pour 10000 1 19985583 region disk diam poly 2 0.7 0.4 1.5 0.6
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fix ins all pour 500 1 4767548 vol 0.8 10 region slab mol object rigid myRigid :pre
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[Description:]
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Insert finite-size particles or molecules into the simulation box
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every few timesteps within a specified region until N particles or
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molecules have been inserted. This is typically used to model the
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pouring of granular particles into a container under the influence of
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gravity. For the remainder of this doc page, a single inserted atom
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or molecule is referred to as a "particle".
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If inserted particles are individual atoms, they are assigned the
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specified atom type. If they are molecules, the type of each atom in
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the inserted molecule is specified in the file read by the
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"molecule"_molecule.html command, and those values are added to the
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specified atom type. E.g. if the file specifies atom types 1,2,3, and
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those are the atom types you want for inserted molecules, then specify
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{type} = 0. If you specify {type} = 2, the in the inserted molecule
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will have atom types 3,4,5.
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All atoms in the inserted particle are assigned to two groups: the
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default group "all" and the group specified in the fix pour command
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(which can also be "all").
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This command must use the {region} keyword to define an insertion
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volume. The specified region must have been previously defined with a
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"region"_region.html command. It must be of type {block} or a z-axis
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{cylinder} and must be defined with side = {in}. The cylinder style
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of region can only be used with 3d simulations.
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Individual atoms are inserted, unless the {mol} keyword is used. It
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specifies a {template-ID} previously defined using the
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"molecule"_molecule.html command, which reads a file that defines the
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molecule. The coordinates, atom types, center-of-mass, moments of
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inertia, etc, as well as any bond/angle/etc and special neighbor
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information for the molecule can be specified in the molecule file.
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See the "molecule"_molecule.html command for details. The only
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settings required to be in this file are the coordinates and types of
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atoms in the molecule.
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If the molecule template contains more than one molecule, the relative
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probability of depositing each molecule can be specified by the
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{molfrac} keyword. N relative probablities, each from 0.0 to 1.0, are
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specified, where N is the number of molecules in the template. Each
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time a molecule is inserted, a random number is used to sample from
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the list of relative probabilities. The N values must sum to 1.0.
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If you wish to insert molecules via the {mol} keyword, that will be
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treated as rigid bodies, use the {rigid} keyword, specifying as its
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value the ID of a separate "fix rigid/small"_fix_rigid_small.html
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command which also appears in your input script.
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If you wish to insert molecules via the {mol} keyword, that will have
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their bonds or angles constrained via SHAKE, use the {shake} keyword,
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specifying as its value the ID of a separate "fix
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shake"_fix_shake.html command which also appears in your input script.
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Each timestep particles are inserted, they are placed randomly inside
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the insertion volume so as to mimic a stream of poured particles. If
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they are molecules they are also oriented randomly. Each atom in the
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particle is tested for overlaps with existing particles, including
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effects due to periodic boundary conditions if applicable. If an
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overlap is detected, another random insertion attempt is made; see the
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{vol} keyword discussion below. The larger the volume of the
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insertion region, the more particles that can be inserted at any one
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timestep. Particles are inserted again after enough time has elapsed
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that the previously inserted particles fall out of the insertion
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volume under the influence of gravity. Insertions continue every so
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many timesteps until the desired # of particles has been inserted.
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NOTE: If you are monitoring the temperature of a system where the
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particle count is changing due to adding particles, you typically
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should use the "compute_modify dynamic yes"_compute_modify.html
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command for the temperature compute you are using.
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:line
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All other keywords are optional with defaults as shown below.
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The {diam} option is only used when inserting atoms and specifes the
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diameters of inserted particles. There are 3 styles: {one}, {range},
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or {poly}. For {one}, all particles will have diameter {D}. For
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{range}, the diameter of each particle will be chosen randomly and
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uniformly between the specified {Dlo} and {Dhi} bounds. For {poly}, a
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series of {Npoly} diameters is specified. For each diameter a
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percentage value from 0.0 to 1.0 is also specified. The {Npoly}
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percentages must sum to 1.0. For the example shown above with "diam 2
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0.7 0.4 1.5 0.6", all inserted particles will have a diameter of 0.7
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or 1.5. 40% of the particles will be small; 60% will be large.
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Note that for molecule insertion, the diameters of individual atoms in
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the molecule can be specified in the file read by the
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"molecule"_molecule.html command. If not specified, the diameter of
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each atom in the molecule has a default diameter of 1.0.
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The {id} option has two settings which are used to determine the atom
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or molecule IDs to assign to inserted particles/molecules. In both
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cases a check is done of the current system to find the maximum
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current atom and molecule ID of any existing particle. Newly inserted
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particles and molecules are assigned IDs that increment those max
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values. For the {max} setting, which is the default, this check is
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done at every insertion step, which allows for particles to leave the
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system, and their IDs to potentially be re-used. For the {next}
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setting this check is done only once when the fix is specified, which
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can be more efficient if you are sure particles will not be added in
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some other way.
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The {vol} option specifies what volume fraction of the insertion
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volume will be filled with particles. For particles with a size
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specified by the {diam range} keyword, they are assumed to all be of
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maximum diamter {Dhi} for purposes of computing their contribution to
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the volume fraction.
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The higher the volume fraction value, the more particles are inserted
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each timestep. Since inserted particles cannot overlap, the maximum
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volume fraction should be no higher than about 0.6. Each timestep
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particles are inserted, LAMMPS will make up to a total of M tries to
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insert the new particles without overlaps, where M = # of inserted
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particles * Nattempt. If LAMMPS is unsuccessful at completing all
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insertions, it prints a warning.
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The {dens} and {vel} options enable inserted particles to have a range
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of densities or xy velocities. The specific values for a particular
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inserted particle will be chosen randomly and uniformly between the
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specified bounds. Internally, the density value for a particle is
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converted to a mass, based on the radius (volume) of the particle.
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The {vz} or {vy} value for option {vel} assigns a z-velocity (3d) or
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y-velocity (2d) to each inserted particle.
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The {rate} option moves the insertion volume in the z direction (3d)
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or y direction (2d). This enables pouring particles from a
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successively higher height over time.
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The {ignore} option is useful when running a simulation that used line
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segment (2d) or triangle (3d) particles, typically to define
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boundaries for spherical granular particles to interact with. See the
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"atom_style line or tri"_atom_style.html command for details. Lines
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and triangles store their size, and if the size is large it may
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overlap (in a spherical sense) with the insertion region, even if the
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line/triangle is oriented such that there is no actual overlap. This
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can prevent particles from being inserted. The {ignore} keyword
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causes the overlap check to skip any line or triangle particles.
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Obviously you should only use it if there is in fact no overlap of the
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line or triangle particles with the insertion region.
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:line
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[Restart, fix_modify, output, run start/stop, minimize info:]
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No information about this fix is written to "binary restart
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files"_restart.html. This means you must be careful when restarting a
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pouring simulation, when the restart file was written in the middle of
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the pouring operation. Specifically, you should use a new fix pour
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command in the input script for the restarted simulation that
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continues the operation. You will need to adjust the arguments of the
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original fix pour command to do this.
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Also note that because the state of the random number generator is not
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saved in restart files, you cannot do "exact" restarts with this fix,
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where the simulation continues on the same as if no restart had taken
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place. However, in a statistical sense, a restarted simulation should
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produce the same behavior if you adjust the fix pour parameters
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appropriately.
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None of the "fix_modify"_fix_modify.html options are relevant to this
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fix. No global or per-atom quantities are stored by this fix for
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access by various "output commands"_Section_howto.html#howto_15. No
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parameter of this fix can be used with the {start/stop} keywords of
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the "run"_run.html command. This fix is not invoked during "energy
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minimization"_minimize.html.
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[Restrictions:]
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This fix is part of the GRANULAR package. It is only enabled if
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LAMMPS was built with that package. See the "Making
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LAMMPS"_Section_start.html#start_3 section for more info.
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For 3d simulations, a gravity fix in the -z direction must be defined
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for use in conjunction with this fix. For 2d simulations, gravity
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must be defined in the -y direction.
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The specified insertion region cannot be a "dynamic" region, as
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defined by the "region"_region.html command.
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[Related commands:]
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"fix_deposit"_fix_deposit.html, "fix_gravity"_fix_gravity.html,
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"region"_region.html
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[Default:]
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Insertions are performed for individual particles, i.e. no {mol}
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setting is defined. If the {mol} keyword is used, the default for
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{molfrac} is an equal probabilities for all molecules in the template.
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Additional option defaults are diam = one 1.0, dens = 1.0 1.0, vol =
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0.25 50, rate = 0.0, vel = 0.0 0.0 0.0 0.0 0.0 (for 3d), vel = 0.0 0.0 0.0
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(for 2d), and id = max.
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