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rLAMMPS lammps
fix_wall_gran.html
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<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
lo, hi = position of lower and upper plane (either can be NULL)
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
<PRE>
keyword =
<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)
</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>
<P>
Optionally, a wall can be oscillated, 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.
If the keyword
<I>
wiggle
</I>
is appended to the argument list, then a
dimension for the motion, as well as it's
<I>
amplitude
</I>
and
<I>
period
</I>
is
specified. Each timestep, the position of the wall in the appropriate
<I>
dim
</I>
is set according to this equation:
</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
also set to the derivative of this expression.
</P>
<P><B>
Restrictions:
</B>
</P>
<P>
Any dimension (xyz) that has a granular wall must be non-periodic.
</P>
<P>
This fix can only be used if LAMMPS was built with the "granular"
package and with atom_style granular. A zcylinder wall can only be
oscillated in the z dimension.
</P>
<P><B>
Related commands:
</B>
</P>
<P><A
HREF =
"fix_wiggle.html"
>
fix_wiggle
</A>
</P>
<P><B>
Default:
</B>
none
</P>
</HTML>
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