96 lines
3.5 KiB
HTML
96 lines
3.5 KiB
HTML
<HTML>
|
|
<CENTER><A HREF = "http://www.cfdem.com">LIGGGHTS WWW Site</A> - <A HREF = "http://lammps.sandia.gov">LAMMPS WWW Site</A> - <A HREF = "Manual.html">LIGGGHTS Documentation</A> - <A HREF = "Section_commands.html#comm">LIGGGHTS Commands</A>
|
|
</CENTER>
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
<HR>
|
|
|
|
<H3>fix ave/euler command
|
|
</H3>
|
|
<P><B>Syntax:</B>
|
|
</P>
|
|
<PRE>fix ID group-ID ave/euler nevery N cell_size_relative c
|
|
</PRE>
|
|
<UL><LI>ID, group-ID are documented in <A HREF = "fix.html">fix</A> command
|
|
|
|
<LI>ave/euler = style name of this fix command
|
|
|
|
<LI>nevery = obligatory keyword
|
|
|
|
<LI>n = calculate average values every this many timesteps
|
|
|
|
<LI>cell_size_relative = obligatory keyword
|
|
|
|
<LI>c = cell size in multiples of max cutoff
|
|
|
|
|
|
</UL>
|
|
<P><B>Examples:</B>
|
|
</P>
|
|
<PRE>fix 1 all ave/euler nevery 100 cell_size_relative 4.5
|
|
</PRE>
|
|
<P><B>Description:</B>
|
|
</P>
|
|
<P>Calculate cell-based averages of velocity, radius, volume fraction,
|
|
and pressure (-1/3 * trace of the stress tensor) every few timesteps,
|
|
as specified by the <I>nevery</I> keyword. The size of the cells is calculated
|
|
as multiple of the maximum cutoff, via the <I>cell_size_relative</I>.
|
|
Note that at least a relative cell size of 3 is required.
|
|
</P>
|
|
<P>Note that velocity is favre (mass) averaged, whereas radius is arithmetically
|
|
averaged. To calculate the stress, this command internally uses a
|
|
<A HREF = "compute_stress_atom.html">compute stress/atom</A> . It includes the convective
|
|
term correctly for granular particles with non-zero average velocity
|
|
(which is not included in <A HREF = "compute_stress_atom.html">compute stress/atom</A>).
|
|
However, it does not include bond, angle, diahedral or kspace contributions
|
|
so that the stress tensor finally reads
|
|
</P>
|
|
<CENTER><IMG SRC = "Eqs/stress_tensor_granular.png">
|
|
</CENTER>
|
|
<P>where vave is the (cell-based) average velocity.
|
|
The first term is a kinetic energy contribution for atom <I>I</I>. The
|
|
second term is a pairwise energy contribution where <I>n</I> loops over the
|
|
<I>Np</I> neighbors of atom <I>I</I>, <I>r1</I> and <I>r2</I> are the positions of the 2
|
|
atoms in the pairwise interaction, and <I>F1</I> and <I>F2</I> are the forces on
|
|
the 2 atoms resulting from the pairwise interaction.
|
|
</P>
|
|
<HR>
|
|
|
|
<P><B>Restart, fix_modify, output, run start/stop, minimize info:</B>
|
|
</P>
|
|
<P>No information about this fix is written to <A HREF = "restart.html">binary restart
|
|
files</A>. None of the <A HREF = "fix_modify.html">fix_modify</A> options
|
|
are relevant to this fix.
|
|
</P>
|
|
<P>This fix computes the above-mentioned quantities for output via a
|
|
<A HREF = "dump.html">dump euler/vtk</A> command. The values can
|
|
only be accessed on timesteps that are multiples of <I>nevery</I> since that
|
|
is when calculations are performed.
|
|
</P>
|
|
<P>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>.
|
|
</P>
|
|
<P><B>Restrictions:</B>
|
|
</P>
|
|
<P>Volume fractions and stresses are calculated based on the assumption
|
|
of a structured (equidistant regular) grid, so volume fractions and
|
|
stresses near walls that are not alligned with the grid will be
|
|
incorrect.
|
|
</P>
|
|
<P><B>Related commands:</B>
|
|
</P>
|
|
<P><A HREF = "compute.html">compute</A>, <A HREF = "compute_stress_atom.html">compute stress/atom</A>,
|
|
<A HREF = "fix_ave_atom.html">fix ave/atom</A>, <A HREF = "fix_ave_histo.html">fix ave/histo</A>,
|
|
<A HREF = "fix_ave_time.html">fix ave/time</A>, <A HREF = "fix_ave_spatial.html">fix ave/spatial</A>,
|
|
</P>
|
|
<P><B>Default:</B> none
|
|
</P>
|
|
</HTML>
|