fix concave command

fix concave/advanced command

Syntax

fix ID group-ID concave

fix ID group-ID concave/advanced

  • ID, group-ID are documented in fix command

  • concave or concave/advanced = style name of this fix command

  • zero or more keyword/value pairs may be appended

  • keyword = allow_group_and_set or allow_heatsource allow_group_and_set value = ‘yes’ or ‘no’ yes, no = determines if group and set command are allowed in the current simulation. allow_heatsource value = ‘yes’ or ‘no’ yes, no = determines if heatsources are allowed in the current simulation.

Examples

fix concave all concave

Description

Treat one or more sets of convex objects as independent rigid bodies. For style concave, this is done in a similar way that in fix multisphere . For style concave/advanced, there is a correction for the interaction forces for particle-particle and particle-wall collisions are re-scaled so that the coefficient of restitution is correctly reproduced (for details, please see fix multisphere/advanced)

A short introduction to concave particles can be found here. This means that each timestep the total force and torque on each rigid body is computed as the sum of the forces and torques on its constituent particles and the coordinates, velocities, and orientations of the atoms in each body are updated so that the body moves and rotates as a single entity. The integration that is performed by this command is equivalent to fix_rigid. However, the following implementation details are different:

(1) Body data held by this fix is distributed across all processes, yielding better parallel scalability.

(2) Bodies (particle clumps) can be added/inserted via fix_insert_stream, fix_insert_rate_region or fix_insert_pack and are automatically added to this fix.

(3) A body is removed from the simulation domain if any of it’s particles is removed from the simulation according to the boundary settings or by any command that deleted particles (e.g. delete_atoms).

(4) By using this fix, gravity (fix_gravity) will be handled correctly for overlapping particle clumps.

(5) This fix internally performs a neigh_modify exclude command so that particles belonging to the same rigid body are excluded from the neighborlist build.

Warning

You should not update the atoms in rigid bodies via other time-integration fixes (e.g. nve, nvt, npt), or you will be integrating their motion more than once each timestep.

Restart, fix_modify, output, run start/stop

Information about this fix is written to binary restart files. This means you can restart a simulation using concave particles.

fix_modify can be used to manipulate the fflag and tflag switches of concave bodies. They can be initially defined in the fix_particletemplate_concave command. The fix_modify manipulates all concave bodies, not only the initially defined f/tflags from the template.

E.g. fix_modify ms fflag on on off tflag on on off

No global scalar or vector or per-atom quantities are stored by this fix for access by various output commands. No parameter of this fix can be used with the start/stop keywords of the run command.

Restrictions

Fix concave does not work together with - fix deform - spherical particles - multisphere particles - heat transfer

Only one fix concave at a time is allowed. Heat transfer simulations are not possible when using this fix (e.g. fix heat/gran/conduction)

Warning

All fixes or computes gathering statistical output (such as e.g. compute com or fix ave/time operate on a per-convex particle basis rather than on a per-concave body basis.

Currently, using fix concave requires newton = off and dimension = 3.

Default

allow_group_and_set = ‘no’ allow_heatsource = ‘no’