forked from lijiext/lammps
65 lines
2.3 KiB
HTML
65 lines
2.3 KiB
HTML
<HTML>
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<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>
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</CENTER>
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<HR>
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<H3>fix wiggle command
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</H3>
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<P><B>Syntax:</B>
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</P>
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<PRE>fix ID group-ID wiggle dim amplitude period
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</PRE>
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<UL><LI>ID, group-ID are documented in <A HREF = "fix.html">fix</A> command
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<LI>wiggle = style name of this fix command
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<LI>dim = <I>x</I> or <I>y</I> or <I>z</I>
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<LI>amplitude = size of oscillation (distance units)
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<LI>period = time of oscillation (time units)
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</UL>
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<P><B>Examples:</B>
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</P>
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<PRE>fix 1 frozen wiggle y 3.0 0.5
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</PRE>
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<P><B>Description:</B>
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</P>
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<P>Move a group of atoms in a sinusoidal oscillation. This is useful in
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granular simulations when boundary atoms are wiggled to induce packing
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of the dynamic atoms. The dimension <I>dim</I> of movement is specified as
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is the <I>amplitude</I> and <I>period</I> of the oscillations. Each timestep
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the <I>dim</I> coordinate of each atom is set to
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</P>
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<PRE>coord = coord0 + A - A cos (omega * delta)
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</PRE>
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<P>where <I>coord0</I> is the coordinate at the time the fix was specified,
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<I>A</I> is the <I>amplitude</I>, <I>omega</I> is 2 PI / <I>period</I>, and <I>delta</I> is the
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elapsed time since the fix was specified. The velocity of the atom is
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set to the derivative of this expression.
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</P>
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<P>Note that if a value of A > 0 is specified, each wiggling atom does
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not oscillate around its initial position, but moves entirely in the
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positive direction relative to its initial position. This is so that
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its initial velocity will be 0.0.
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</P>
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<P><B>Restart, fix_modify, output, run start/stop, minimize info:</B>
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</P>
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<P>No information about this fix is written to <A HREF = "restart.html">binary restart
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files</A>. None of the <A HREF = "fix_modify.html">fix_modify</A> options
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are relevant to this fix. No global scalar or vector or per-atom
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quantities are stored by this fix for access by various <A HREF = "Section_howto.html#4_15">output
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commands</A>. No parameter of this fix can be
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used with the <I>start/stop</I> keywords of the <A HREF = "run.html">run</A> command.
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This fix is not invoked during <A HREF = "minimize.html">energy minimization</A>.
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</P>
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<P><B>Restrictions:</B> none
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</P>
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<P><B>Related commands:</B> none
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</P>
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<P><B>Default:</B> none
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</P>
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</HTML>
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