"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

gran rolling_friction epsd :h3

[Syntax:]

rolling_friction epsd :pre

[LIGGGHTS vs. LAMMPS Info:]

This part of "pair gran"_pair_gran.html and 
"fix wall/gran"_fix_wall_gran.html
is not availabe in LAMMPS.

[Description:]

This model can be used as part of "pair gran"_pair_gran.html and 
"fix wall/gran"_fix_wall_gran.html

The elastic-plastic spring-dashpot (EPSD) model (see Ai et al.) adds an additional 
torque contribution, equal to

:c,image(Eqs/pair_gran_hooke_eqEpsd1.gif)

where the torque due to the spring M_rk is calculated as

:c,image(Eqs/pair_gran_hooke_eqEpsd2.gif)

Here k_r denotes the rolling stiffness and dtheta_r is the incremental relative 
rotation between the particles. The spring torque is limited by the full mobilisation 
torque M_rm that is determined by the normal force F_n and the coefficient of rolling 
friction (rmu) (compare the "CDT model"_gran_rolling_friction_cdt.html).

The viscous damping torque M_rd is implemented as

:c,image(Eqs/pair_gran_hooke_eqEpsd3.gif)

where in the current implementation the damping is disabled in case of full mobilisation 
(f = 0). The damping coefficient C_r may be expressed as:

:c,image(Eqs/pair_gran_hooke_eqEpsd4.gif)

Here I_i/j is the moment of inertia and m_i/j is the mass of the particles i and j, 
respectively. 

The coefficient of rolling friction (rmu) must be defined as

fix id all property/global coefficientRollingFriction peratomtypepair n_atomtypes value_11 value_12 .. value_21 value_22 .. .
    (value_ij=value for the coefficient of rolling friction between atom type i and j; n_atomtypes is the number of atom types you want to use in your simulation)

This coefficient rmu is equal to the rmu as defined in the "CDT model"_gran_rolling_friction_cdt.html.
In addition to rmu, eta_r is the required material property that must be defined as

fix id all property/global coefficientRollingViscousDamping peratomtypepair n_atomtypes value_11 value_12 .. value_21 value_22 .. .
    (value_ij=value for the coefficient of rolling friction between atom type i and j; n_atomtypes is the number of atom types you want to use in your simulation) :pre

IMPORTANT NOTE: You have to use atom styles beginning from 1, e.g. 1,2,3,...

[(Ai)] Jun Ai, Jian-Fei Chen, J. Michael Rotter, Jin Y. Ooi, Powder Technology, 206 (3), p 269-282 (2011).
