forked from lijiext/lammps
121 lines
4.9 KiB
Plaintext
121 lines
4.9 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 wall/gran command :h3
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[Syntax:]
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fix ID group-ID wall/gran 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/gran = style name of this fix command :l
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style = {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} or {zplane} args = lo hi gamma xmu
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lo,hi = position of lower and upper plane (distance units), either can be NULL)
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gamman = damping coeff for normal direction collisions with wall
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xmu = friction coeff for the wall
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{zcylinder} args = radius gamma xmu
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radius = cylinder radius (distance units)
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gamman = damping coeff for normal direction collisions with wall
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xmu = friction coeff for the wall :pre
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zero or more keyword/value pairs may be appended to args :l
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keyword = {wiggle} or {shear} :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)
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{shear} values = dim vshear
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dim = {x} or {y} or {z}
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vshear = magnitude of shear velocity (velocity units) :pre
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:ule
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[Examples:]
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fix 1 all wall/gran xplane -10.0 10.0 50.0 0.5
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fix 2 all wall/gran zcylinder 15.0 50.0 0.5 wiggle z 3.0 2.0
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fix 1 all wall/gran zplane 0.0 NULL 100.0 0.5 :pre
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[Description:]
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Bound the simulation domain of a granular system with a frictional
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wall. All particles in the group interact with the wall when they are
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close enough to touch it.
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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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For all wallstyles, a damping and friction coefficient for
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particle-wall interactions are also specified.
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Optionally, the wall can be moving, if the {wiggle} or {shear}
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keywords are appended. Both keywords cannot be used together.
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For the {wiggle} keyword, the wall oscillates sinusoidally, similar to
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the oscillations of frozen particles specified by the
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"fix_wiggle"_fix_wiggle.html command. This is useful in packing
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simulations of granular particles. The arguments to the {wiggle}
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keyword specify a dimension for the motion, as well as it's
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{amplitude} and {period}. Note that if the dimension is in the plane
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of the wall, this is effectively a shearing motion. If the dimension
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is perpendicular to the wall, it is more of a shaking motion. A
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{zcylinder} wall can only be wiggled in 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 = pos0 + A - A cos (omega * delta) :pre
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where {pos0} is the position at the time the fix was specified, {A} is
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the {amplitude}, {omega} is 2 PI / {period}, and {delta} is the
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elapsed time since the fix was specified. The velocity of the wall is
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set to the derivative of this expression.
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For the {shear} keyword, the wall moves continuously in the specified
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dimension with velocity {vshear}. The dimension must be tangential to
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walls with a planar {wallstyle}, e.g. in the {y} or {z} directions for
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an {xplane} wall. For {zcylinder} walls, a dimension of {z} means the
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cylinder is moving in the z-direction along it's axis. A dimension of
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{x} or {y} means the cylinder is spinning around the z-axis, either in
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the clockwise direction for {vshear} > 0 or counter-clockwise for
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{vshear} < 0. In this case, {vshear} is the tangential velocity of
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the wall at whatever {radius} has been defined.
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[Restart, fix_modify, output, run start/stop, minimize info:]
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This fix writes the shear friction state of atoms interacting with the
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wall to "binary restart files"_restart.html, so that a simulation can
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continue correctly if granular potentials with shear "history" effects
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are being used. See the "read_restart"_read_restart.html command for
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info on how to re-specify a fix in an input script that reads a
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restart file, so that the operation of the fix continues in an
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uninterrupted fashion.
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None of the "fix_modify"_fix_modify.html options are relevant to this
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fix. No global scalar or vector or per-atom quantities are stored by
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this fix for access by various "output
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commands"_Section_howto.html#4_15. No parameter of this fix can be
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used with the {start/stop} keywords of the "run"_run.html command.
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This fix is not invoked during "energy 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#2_3 section for more info.
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Any dimension (xyz) that has a granular wall must be non-periodic.
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[Related commands:]
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"fix_wiggle"_fix_wiggle.html
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[Default:] none
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