# gran rolling_friction cdt model

## Syntax

    rolling_friction cdt [other model_type/model_name pairs as described here ] keyword values

- zero or more keyword/value pairs may be appended to the end (after all models are specified)

    torsionTorque values = 'on' or 'off'
      on = also the normal, relative rotation (torsion) contributes to the resulting torque
      off = only the tangential, relative rotation contributes to the resulting torque

## Description

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

The constant directional torque (CDT) model adds an additional torque contribution, equal to

torque_rf = rmu*k_n*delta_n*w_r_shear/mag(w_r_shear)*(R*).

w_r_shear is the projection of w_r into the shear plane, where w_r = w1-w2

If the rolling friction model is activated, 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)

Warning

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

Torque information:

By default the relative, normal rotation (torsion) is subtracted and does not contribute to the resulting torque. By setting the torsionTorque keyword to ‘on’, the full relative rotation contributes to the rolling friciton torque.

Coarse-graining information:

Using `coarsegraining` in combination with this command might lead to different dynamics or system state and thus to inconsistancies.

Note

`Coarsegraining` may or may not be available in LIGGGHTS(R)-PUBLIC.

## Default

torsionTorque = ‘off’

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