normal model hertz/vel_dependent

Purpose

Implement the normal contact model Hertz with user-defined velocity-dependent coefficient of restitution.

Syntax

model hertz/vel_dependent [other model_type/model_name pairs as described here ] settings keyword values

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

limitForce values = 'on' or 'off'
  on = ensures that the normal force is never attractive (an artefact that can occur at the end of a collision).
  off = standard implementation that might lead to attractive forces.
tangential_damping values = 'on' or 'off'
  on = activates tangential damping
  off = no tangential damping
heating_normal_hertz values = 'on' or 'off'
  on = model contributes to surface heating in the frame of enable_surface_heating
  off = model does not contribute to surface heating
disableNormalWhenBonded values = 'on' or 'off'
  on = if the cohesion bond model is used, then the normal force is only added if the two particles are not bonded
  of = the normal force is always added if two particles overlap
computeDissipatedEnergy values = 'on' or 'off'
  on = the normal model saves the dissipated energy for each contact for the
  use in fix calculate/dissipated_energy
  of = no values are saved
computeElasticPotential values = 'on' or 'off'
  on = the normal model saves the current elastic potential for each contact
  for the use in fix calculate/normal_elastic_energy
  off = no values are saved

Associated material properties

Material properties

youngsModulus ( $Y$ ): Youngs Modulus of the material [pressure]
poissonsRatio ( $\nu$ ): Poisson’s ratio of the material [ $\cdot$ ]

Material interaction properties

cor_lookup ( $e$ ): coefficient of restitution [ $\cdot$ ]. It is expressed as a function of the initial impact velocity of a contact and provided via lookup table.

Description

This model extends the normal contact model Hertz by allowing a coefficient of restitution which depends on the the initial impact velocity. The discrete function between coefficient of restitution and initial impact velocity must be provided via lookup table (see material_properties command for more information).

Warning

The user must ensure that stability criteria are fulfilled for all possible values of the coefficient of restitution.

Restrictions

If using SI units, $Y$ must be bigger than 5e6. If using CGS units, $Y$ must be bigger than 5e5. When using the limitForce, the specified coefficient of restitution is only approximate. This might become problematic for low coefficients of restitution as shown in Schwager and Poschel.

Coarse-graining information

Using coarsegraining in combination with this command should lead to statistically equivalent dynamics and system state.

Default

tangential_damping = ‘on’, limitForce = ‘off’, heating_normal_hertz = ‘off’