limit_velocity command

Purpose

Command for limiting the (angular) velocity of the particles in a simulation.

Warning

GPU support for this command has not been tested and may not work as expected.

Syntax

limit_velocity id ID particle_group group-ID

limit_velocity = name of this command
ID, group-ID are documented in fix command
one or more keyword/value pairs may be appended
keywords = maximum_velocity or maximum_angular_velocity or mode

maximum_velocity value = max_vel
  max_vel = maximum velocity magnitude
maximum_angular_velocity value = max_omega
  max_omega = maximum angular velocity
mode value = absolute or relative
  absolute = maximum velocity is taken as absolute quantity [default]
  relative = maximum velocity is taken relative to the particle radius

Examples

limit_velocity maximum_velocity 10 maximum_angular_velocity 100
limit_velocity maximum_velocity 100 mode relative
limit_velocity maximum_angular_velocity 2

Description

If the maximum_velocity $v_{max}$ is set with a value then all particles in a simulation cannot move faster than this value. If mode is set to absolute this then this equivalent to

$\|v_p\| \leq v_{max} \qquad \forall p \in \mbox{Particles},$

if mode is set to relative then the maximum velocity is taken relative to the particle radius (bounding radius for superquadrics or convex), i.e.

$\|\frac{v_p}{r_p}\| \leq v_{max} \qquad \forall p \in \mbox{Particles}.$

If the maximum_angular_velocity keyword is set the angular velocity is limited to this value. Note, the mode keyword has no influence on this value as it is independent of distances.

Restrictions

This command cannot be used with multisphere or concave particles.

Defaults

mode = absolute