[lammps-users] units for granular flow simulation

Hello All,

I have three questions about LAMMPS:
First of all, the units used in LAMMPS for granular flow: it is unit mass
or unit density?

In the code, it reads density, then calculate mass and gravity. The data
format in the data file is as follows: granular atom-ID atom-type diameter
density x y z.
For pour command: the default is "The option defaults are diam = 1.0 1.0,
dens = 1.0 1.0, vol = 0.25 50, rate = 0.0, vel = 0.0 0.0 0.0 0.0 0.0. "

Second, Why is there "*PI/6.0" in the follow line?

In the subroutine of fix_gran_diag, we have:

for (m = 0; m < nmax; m++)
      fprintf(fpden,"%d %g %g\n",m+1,(m+1)*stepz+boxzlo,dendens[m]*PI/6.0);

Last but not the least, anybody simulate the granular system with liquid
using lattice boltzman method or some other method?

Thank you so much.


It's neither unit mass or density. You input the diameter and density of
each particle explicitly. The code computes a mass. So the mass and density
of every particle is set by the input.

I think the PI/6 comes from the the volume of a particle with unit diameter.
So densdens (what the code is printing out) is like a density per volume where
the volume is of the z-layer it was binned over.

You can contact Jeremy Lechman (jblechm at sandia.gov) for info on
current work on coupling LAMMPS to fluid solvers.