cundall_damping command

Warning

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

Syntax

cundall_damping id ID particle-group group-ID damping_factor damp

cundall_damping = name of this command
id, ID = optional keyword/value pair to identify this command
particle-group, group-ID = optional keyword/value pair to apply the effects of this command only to a particular particle group
damping_factor = mandatory keyword
damp = damping factor

Examples

cundall_damping damping_factor 0.03
cundall_damping id damp particle-group damped_particles damping_factor 0.1

Description

This fix reduces the forces acting on all particles by the specified damping factor damp. The exact formula reads

$F_{damped} = F (1 - damp\,sgn(F \cdot v)),$

where $F$ and $v$ are the particle force and velocity, respectively. Equivalently for the torque:

$T_{damped} = T (1 - damp\,sgn(T \cdot \omega)),$

where $T$ and $\omega$ are the particle torque and angular velocity, respectively. Note, that sgn represents the signum function and has a value of either -1 or 1.

Restart, fix_modify, output, run start/stop

No information about this fix is written to binary restart files.

This fix computes a global scalar which can be accessed by various output commands. This scalar gives the total energy dissipated by this damping fix.

Restrictions

none