2006-09-22 00:22:34 +08:00
|
|
|
<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 wall/gran command
|
|
|
|
|
</H3>
|
|
|
|
|
<P><B>Syntax:</B>
|
|
|
|
|
</P>
|
|
|
|
|
<PRE>fix ID group-ID wall/gran wallstyle args keyword values ...
|
|
|
|
|
</PRE>
|
|
|
|
|
<UL><LI>ID, group-ID are documented in <A HREF = "fix.html">fix</A> command
|
|
|
|
|
|
|
|
|
|
<LI>wall/gran = style name of this fix command
|
|
|
|
|
|
|
|
|
|
<LI>style = <I>xplane</I> or <I>yplane</I> or <I>zplane</I> or <I>zcylinder</I>
|
|
|
|
|
|
|
|
|
|
<LI>args = list of arguments for a particular style
|
|
|
|
|
|
|
|
|
|
<PRE> <I>xplane</I> or <I>yplane</I> or <I>zplane</I> args = lo hi gamma xmu
|
2008-04-10 01:29:51 +08:00
|
|
|
lo,hi = position of lower and upper plane (distance units), either can be NULL)
|
2006-09-22 00:22:34 +08:00
|
|
|
gamman = damping coeff for normal direction collisions with wall
|
|
|
|
|
xmu = friction coeff for the wall
|
|
|
|
|
<I>zcylinder</I> args = radius gamma xmu
|
|
|
|
|
radius = cylinder radius (distance units)
|
|
|
|
|
gamman = damping coeff for normal direction collisions with wall
|
|
|
|
|
xmu = friction coeff for the wall
|
|
|
|
|
</PRE>
|
|
|
|
|
<LI>zero or more keyword/value pairs may be appended to args
|
|
|
|
|
|
2008-04-10 01:29:51 +08:00
|
|
|
<LI>keyword = <I>wiggle</I> or <I>shear</I>
|
|
|
|
|
|
|
|
|
|
<PRE> <I>wiggle</I> values = dim amplitude period
|
|
|
|
|
dim = <I>x</I> or <I>y</I> or <I>z</I>
|
|
|
|
|
amplitude = size of oscillation (distance units)
|
|
|
|
|
period = time of oscillation (time units)
|
|
|
|
|
<I>shear</I> values = dim vshear
|
|
|
|
|
dim = <I>x</I> or <I>y</I> or <I>z</I>
|
|
|
|
|
vshear = magnitude of shear velocity (velocity units)
|
2006-09-22 00:22:34 +08:00
|
|
|
</PRE>
|
|
|
|
|
|
|
|
|
|
</UL>
|
|
|
|
|
<P><B>Examples:</B>
|
|
|
|
|
</P>
|
|
|
|
|
<PRE>fix 1 all wall/gran xplane -10.0 10.0 50.0 0.5
|
|
|
|
|
fix 2 all wall/gran zcylinder 15.0 50.0 0.5 wiggle z 3.0 2.0
|
|
|
|
|
fix 1 all wall/gran zplane 0.0 NULL 100.0 0.5
|
|
|
|
|
</PRE>
|
|
|
|
|
<P><B>Description:</B>
|
|
|
|
|
</P>
|
|
|
|
|
<P>Bound the simulation domain of a granular system with a frictional
|
|
|
|
|
wall. All particles in the group interact with the wall when they are
|
|
|
|
|
close enough to touch it.
|
|
|
|
|
</P>
|
|
|
|
|
<P>The <I>wallstyle</I> can be planar or cylindrical. The 3 planar options
|
|
|
|
|
specify a pair of walls in a dimension. Wall positions are given by
|
|
|
|
|
<I>lo</I> and <I>hi</I>. Either of the values can be specified as NULL if a
|
|
|
|
|
single wall is desired. For a <I>zcylinder</I> wallstyle, the cylinder's
|
|
|
|
|
axis is at x = y = 0.0, and the radius of the cylinder is specified.
|
|
|
|
|
For all wallstyles, a damping and friction coefficient for
|
|
|
|
|
particle-wall interactions are also specified.
|
|
|
|
|
</P>
|
2008-04-10 01:29:51 +08:00
|
|
|
<P>Optionally, the wall can be moving, if the <I>wiggle</I> or <I>shear</I>
|
|
|
|
|
keywords are appended. Both keywords cannot be used together.
|
|
|
|
|
</P>
|
|
|
|
|
<P>For the <I>wiggle</I> keyword, the wall oscillates sinusoidally, similar to
|
|
|
|
|
the oscillations of frozen particles specified by the
|
|
|
|
|
<A HREF = "fix_wiggle.html">fix_wiggle</A> command. This is useful in packing
|
|
|
|
|
simulations of granular particles. The arguments to the <I>wiggle</I>
|
|
|
|
|
keyword specify a dimension for the motion, as well as it's
|
|
|
|
|
<I>amplitude</I> and <I>period</I>. Note that if the dimension is in the plane
|
|
|
|
|
of the wall, this is effectively a shearing motion. If the dimension
|
|
|
|
|
is perpendicular to the wall, it is more of a shaking motion. A
|
|
|
|
|
<I>zcylinder</I> wall can only be wiggled in the z dimension.
|
|
|
|
|
</P>
|
|
|
|
|
<P>Each timestep, the position of a wiggled wall in the appropriate <I>dim</I>
|
|
|
|
|
is set according to this equation:
|
2006-09-22 00:22:34 +08:00
|
|
|
</P>
|
|
|
|
|
<PRE>position = pos0 + A - A cos (omega * delta)
|
|
|
|
|
</PRE>
|
|
|
|
|
<P>where <I>pos0</I> is the position at the time the fix was specified, <I>A</I> is
|
|
|
|
|
the <I>amplitude</I>, <I>omega</I> is 2 PI / <I>period</I>, and <I>delta</I> is the
|
|
|
|
|
elapsed time since the fix was specified. The velocity of the wall is
|
2008-04-10 01:29:51 +08:00
|
|
|
set to the derivative of this expression.
|
|
|
|
|
</P>
|
|
|
|
|
<P>For the <I>shear</I> keyword, the wall moves continuously in the specified
|
|
|
|
|
dimension with velocity <I>vshear</I>. The dimension must be tangential to
|
|
|
|
|
walls with a planar <I>wallstyle</I>, e.g. in the <I>y</I> or <I>z</I> directions for
|
|
|
|
|
an <I>xplane</I> wall. For <I>zcylinder</I> walls, a dimension of <I>z</I> means the
|
|
|
|
|
cylinder is moving in the z-direction along it's axis. A dimension of
|
|
|
|
|
<I>x</I> or <I>y</I> means the cylinder is spinning around the z-axis, either in
|
|
|
|
|
the clockwise direction for <I>vshear</I> > 0 or counter-clockwise for
|
|
|
|
|
<I>vshear</I> < 0. In this case, <I>vshear</I> is the tangential velocity of
|
|
|
|
|
the wall at whatever <I>radius</I> has been defined.
|
2006-09-22 00:22:34 +08:00
|
|
|
</P>
|
2007-10-11 06:28:11 +08:00
|
|
|
<P><B>Restart, fix_modify, output, run start/stop, minimize info:</B>
|
2007-06-26 08:03:39 +08:00
|
|
|
</P>
|
|
|
|
|
<P>This fix writes the shear friction state of atoms interacting with the
|
|
|
|
|
wall to <A HREF = "restart.html">binary restart files</A>, so that a simulation can
|
|
|
|
|
continue correctly if granular potentials with shear "history" effects
|
|
|
|
|
are being used. See the <A HREF = "read_restart.html">read_restart</A> command for
|
|
|
|
|
info on how to re-specify a fix in an input script that reads a
|
|
|
|
|
restart file, so that the operation of the fix continues in an
|
|
|
|
|
uninterrupted fashion.
|
|
|
|
|
</P>
|
|
|
|
|
<P>None of the <A HREF = "fix_modify.html">fix_modify</A> options are relevant to this
|
2007-10-11 06:28:11 +08:00
|
|
|
fix. No global scalar or vector or per-atom quantities are stored by
|
|
|
|
|
this fix for access by various <A HREF = "Section_howto.html#4_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>.
|
2007-06-26 08:03:39 +08:00
|
|
|
</P>
|
2006-09-22 00:22:34 +08:00
|
|
|
<P><B>Restrictions:</B>
|
|
|
|
|
</P>
|
2007-06-26 08:03:39 +08:00
|
|
|
<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#2_3">Making
|
|
|
|
|
LAMMPS</A> section for more info.
|
|
|
|
|
</P>
|
2007-03-08 09:01:08 +08:00
|
|
|
<P>Any dimension (xyz) that has a granular wall must be non-periodic.
|
|
|
|
|
</P>
|
2006-09-22 00:22:34 +08:00
|
|
|
<P><B>Related commands:</B>
|
|
|
|
|
</P>
|
|
|
|
|
<P><A HREF = "fix_wiggle.html">fix_wiggle</A>
|
|
|
|
|
</P>
|
|
|
|
|
<P><B>Default:</B> none
|
|
|
|
|
</P>
|
|
|
|
|
</HTML>
|
