[lammps-users] units for granular flow simulation

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1

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.

Fuping

2

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.

Steve