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### gran rolling_friction epsd2

Syntax:

    rolling_friction epsd2

Description:

This model can be used as part of pair gran and fix wall/gran

The alternative elastic-plastic spring-dashpot (EPSD2) model (see Iwashita and Oda) adds an additional torque contribution. It is similar to the EPSD model, but in contrast to the original model the rolling stiffness k_r is defined as

where k_t is the abovementioned tangential stiffness. Furthermore, the viscous damping torque M_rd is disabled at all.

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.

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).