"LIGGGHTS WWW Site"_liws - "LAMMPS WWW Site"_lws - "LIGGGHTS Documentation"_ld - "LIGGGHTS Commands"_lc :c

:link(liws,http://www.cfdem.com)
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Section_commands.html#comm)

:line

fix ave/euler command :h3

[Syntax:]

fix ID group-ID ave/euler nevery N cell_size_relative c :pre

ID, group-ID are documented in "fix"_fix.html command :ulb,l
ave/euler = style name of this fix command :l
nevery = obligatory keyword :l
n = calculate average values every this many timesteps :l
cell_size_relative = obligatory keyword :l
c = cell size in multiples of max cutoff :l 
:ule

[Examples:]

fix 1 all ave/euler nevery 100 cell_size_relative 4.5 :pre

[Description:]

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 {nevery} keyword. The size of the cells is calculated
as multiple of the maximum cutoff, via the {cell_size_relative}.
Note that at least a relative cell size of 3 is required.

Note that velocity is favre (mass) averaged, whereas radius is arithmetically
averaged. To calculate the stress, this command internally uses a 
"compute stress/atom"_compute_stress_atom.html . It includes the convective 
term correctly for granular particles with non-zero average velocity 
(which is not included  in "compute stress/atom"_compute_stress_atom.html).
However, it does not include bond, angle, diahedral or kspace contributions 
so that the stress tensor finally reads

:c,image(Eqs/stress_tensor_granular.png)

where vave is the (cell-based) average velocity. 
The first term is a kinetic energy contribution for atom {I}.  The
second term is a pairwise energy contribution where {n} loops over the
{Np} neighbors of atom {I}, {r1} and {r2} are the positions of the 2
atoms in the pairwise interaction, and {F1} and {F2} are the forces on
the 2 atoms resulting from the pairwise interaction.

:line

[Restart, fix_modify, output, run start/stop, minimize info:]

No information about this fix is written to "binary restart
files"_restart.html.  None of the "fix_modify"_fix_modify.html options
are relevant to this fix.

This fix computes the above-mentioned quantities for output via a 
"dump euler/vtk"_dump.html command.  The values can
only be accessed on timesteps that are multiples of {nevery} since that
is when calculations are performed. 

No parameter of this fix can be used with the {start/stop} keywords of
the "run"_run.html command.  This fix is not invoked during "energy
minimization"_minimize.html.

[Restrictions:]

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.

[Related commands:]

"compute"_compute.html, "compute stress/atom"_compute_stress_atom.html,
"fix ave/atom"_fix_ave_atom.html, "fix ave/histo"_fix_ave_histo.html, 
"fix ave/time"_fix_ave_time.html, "fix ave/spatial"_fix_ave_spatial.html,

[Default:] none
