[lammps-users] Some issues in LAMMPS while performing Granular simulations

Dear Steve,

I am studying segregation of granular particles under external excitations. I have written my own Fortran code for that.
I wanted to check the accuracy of my code using LAMMPS. But, in this process, I found some disagreement between my code’s results
and LAMMPS result for the same set of simulation parameters. When I checked the source code of LAMMPS for granular particles, I found that
there is no restriction on the normal force when it becomes negative, which is undesirable in case of dry granular particles (because, only repulsive forces act between them).
This fact is beautifully explained in the book “Computational Granular Dynamics” by Poschel and Schwager.

Second, I was checking my code for a simple mechanics problem of a sphere rolling down an inclined plane. In this case also, acceleration of rolling sphere do not change (in LAMMPS) from pure rolling acceleration to sliding acceleration,
when we reduce the coefficient of friction below its limiting value (at which pure rolling starts).

I would be happy if we can make suitable corrections in the LAMMPS.


With best wishes,

Ashish Bhateja

I'm open to enhancements, but you'd have to be more precise. I.e. what
formula is incorrect/incomplete on what line of the code. I believe LAMMPS
does implement correctly the granular model/force-field it claims to. But
there are many granular models. I don't know what you
mean by negative normal forces, as the normal force is a repulsive spring.