# [lammps-users] lj units for granular material

Dear lammps users,
In lj units, dimensionless time is t* = t (epsilon / m / sigma^2)^1/2.
But in granular materials, there is no epsilon kind of thing. So, what
is the dimensionless time in granular materials.
Thanking you

Shantanu

I think it's the same - you can just assume eps = 1.
See the granular papers by Grest on the LAMMPS pub
page - they discuss LJ units for granular materials.

Steve

Hi Shantanu,
As far I understand the \sqrt{d/g} and 1/shear rate, can form the dimensionless time in granular matter. The first one (\sqrt{d/g}) is for simulations having gravity and later one (1/shear rate) is for shearing simulation without gravity. At least Campbell’s work on granular material show that. So one can form the non dimensional time as t*=t/ \sqrt{d/g} or t*=\gamma*t, where d is particle diameter, g is acceleration due to gravity and \gamma is the applied shear rate.

Regards,
Vidya