fix scale/diameter command

Syntax

fix ID group-ID scale/diameter N keyword value ...

  • ID, group-ID are documented in fix command

  • scale/diameter = style name of this fix command

  • N = scale diameter every this many timesteps

  • region = obligatory keyword

  • region_value = ID of a spherical or cylindrical region where the particles will be scaled

  • scale = obligatory keyword

  • scale_value = scaling factor for change in diameter at region center

  • scale_width = outer fraction of radius to be used for actual scaling 0;1

Examples

fix scale all scale/diameter 10 region scale_region scale 0.5 0.5

Description

Change particle diameter over time as a simulation runs.

If N is specified as 0, the particle diameters are only changed once, before a simulation run begins. This is all that is needed if the diameter is not time-dependent. If N > 0, then changes are made every N steps during the simulation.

The scale value describes the relative change in diameter when particles reach the center of the specified region.

If the per-atom mass is defined for particles (e.g. atom_style granular), then the mass of each particle is also changed when the diameter changes (density is assumed to stay constant).

For example, these commands would shrink the diameter of all granular particles in the “center” group from 100% to 10% in a linear fashion while advancing towards the region center and increase the diameter again while diverging from the center:

region scale_region sphere 0.0 0.0 0.0 0.5 units box
fix scale center scale/diameter 10 region scale_region scale 0.1

Restart, fix_modify, output, run start/stop, minimize info:

This fix writes the original radius of the particles to binary restart files. None of the fix_modify options are relevant to this fix. The per-atom radius is stored by an internal fix and can be accessed by various output commands. No parameter of this fix can be used with the start/stop keywords of the run command. This fix is not invoked during energy minimization.

Restrictions

none

Default

scale = 1.0.