forked from lijiext/lammps
104 lines
4.2 KiB
Plaintext
104 lines
4.2 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,Commands_all.html)
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:line
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fix wall/body/polyhedron command :h3
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[Syntax:]
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fix ID group-ID wall/body/polyhedron k_n c_n c_t wallstyle args keyword values ... :pre
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ID, group-ID are documented in "fix"_fix.html command :ulb,l
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wall/body/polyhedron = style name of this fix command :l
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k_n = normal repulsion strength (force/distance units or pressure units - see discussion below) :l
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c_n = normal damping coefficient (force/distance units or pressure units - see discussion below) :l
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c_t = tangential damping coefficient (force/distance units or pressure units - see discussion below) :l
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wallstyle = {xplane} or {yplane} or {zplane} or {zcylinder} :l
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args = list of arguments for a particular style :l
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{xplane} or {yplane} args = lo hi
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lo,hi = position of lower and upper plane (distance units), either can be NULL)
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{zcylinder} args = radius
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radius = cylinder radius (distance units) :pre
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zero or more keyword/value pairs may be appended to args :l
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keyword = {wiggle} :l
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{wiggle} values = dim amplitude period
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dim = {x} or {y} or {z}
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amplitude = size of oscillation (distance units)
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period = time of oscillation (time units) :pre
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:ule
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[Examples:]
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fix 1 all wall/body/polyhedron 1000.0 20.0 5.0 xplane -10.0 10.0
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[Description:]
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This fix is for use with 3d models of body particles of style
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{rounded/polyhedron}. It bounds the simulation domain with wall(s).
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All particles in the group interact with the wall when they are close
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enough to touch it. The nature of the interaction between the wall
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and the polygon particles is the same as that between the polygon
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particles themselves, which is similar to a Hookean potential. See
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the "Howto body"_Howto_body.html doc page for more details on using
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body particles.
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The parameters {k_n}, {c_n}, {c_t} have the same meaning and units as
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those specified with the "pair_style
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body/rounded/polyhedron"_pair_body_rounded_polyhedron.html command.
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The {wallstyle} can be planar or cylindrical. The 3 planar options
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specify a pair of walls in a dimension. Wall positions are given by
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{lo} and {hi}. Either of the values can be specified as NULL if a
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single wall is desired. For a {zcylinder} wallstyle, the cylinder's
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axis is at x = y = 0.0, and the radius of the cylinder is specified.
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Optionally, the wall can be moving, if the {wiggle} keyword is appended.
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For the {wiggle} keyword, the wall oscillates sinusoidally, similar to
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the oscillations of particles which can be specified by the "fix
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move"_fix_move.html command. This is useful in packing simulations of
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particles. The arguments to the {wiggle} keyword specify a dimension
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for the motion, as well as it's {amplitude} and {period}. Note that
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if the dimension is in the plane of the wall, this is effectively a
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shearing motion. If the dimension is perpendicular to the wall, it is
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more of a shaking motion. A {zcylinder} wall can only be wiggled in
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the z dimension.
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Each timestep, the position of a wiggled wall in the appropriate {dim}
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is set according to this equation:
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position = coord + A - A cos (omega * delta) :pre
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where {coord} is the specified initial position of the wall, {A} is
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the {amplitude}, {omega} is 2 PI / {period}, and {delta} is the time
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elapsed since the fix was specified. The velocity of the wall is set
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to the derivative of this expression.
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[Restart, fix_modify, output, run start/stop, minimize info:]
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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"_Howto_output.html. No parameter
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of this fix can be used with the {start/stop} keywords of the
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"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 BODY package. It is only enabled if LAMMPS
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was built with that package. See the "Build
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package"_Build_package.html doc page for more info.
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Any dimension (xyz) that has a wall must be non-periodic.
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[Related commands:]
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"atom_style body"_atom_style.html, "pair_style
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body/rounded/polyhedron"_pair_body_rounded_polyhedron.html
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[Default:] none
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