gran cohesion sjkr2 model — LIGGGHTS v3.X documentation

# gran cohesion sjkr2 model

## Syntax

    cohesion sjkr2

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

    tangential_reduce values = 'on' or 'off'
      on = tangential model does not see normal force computed by this model
      off = tangential model does see normal force computed by this model

## Description

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

The modified simplified JKR - Johnson-Kendall-Roberts (SJKR2) model adds an additional normal force contribution. If two particle are in contact, it adds an additional normal force tending to maintain the contact, which writes

F = k A,

where A is the particle contact area and k is the cohesion energy density in J/m3. For sjkr2, the sphere-sphere contact area is calculated as

A = 2*Pi * delta_n * (2R*)

If you are using the SJKR2 model, you must also define the cohesion energy density:

    fix id all property/global cohesionEnergyDensity peratomtypepair n_atomtypes value_11 value_12 .. value_21 value_22 .. .
        (value_ij=value for the cohesion energy density (in Energy/Length3 units) between atom type i and j; n_atomtypes is the number of atom types you want to use in your simulation)

Warning

The cohesion model has been derived for the Hertzian Style, it may note be appropriate for the Hookean styles.

Warning

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

The optional keyword tangential_reduce defines if the tangential force model should “see” the additional normal force excerted by this model. If it is ‘off’ (which is default) then the tangential force model will be able to transmit a larger amount of tangential force If tangential_reduce = ‘on’ then the tangential model will not take the normal force from this model into account, typically leading to a lower value of tangential force (via the Coulomb friction limit)

## Restrictions

The cohesion model has been derived for the Hertzian Style, it may note be appropriate for the Hookean styles.

It is not available for atom_style superquadric

Coarse-graining information:

Using `coarsegraining` in combination with this command might lead to statistically different dynamics and system state. To the best knowledge of the developers, the cross-influence between this command and coarse-graining is unknown.

Note

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

## Default

tangential_reduce = ‘off’