fix nve/cfd_cn/sphere command

Purpose

Integrator for coupled CFD-DEM simulations for spherical particles.

Syntax

fix ID group-ID nve/cfd_cn/sphere

  • ID, group-ID are documented in fix command

  • nve/cfd_cn/sphere = style name of this fix command

  • zero or more keyword/value pairs may be appended

  • keyword = update

update value = dipole
  dipole = update orientation of dipole moment during integration
CrankNicolson value = CNalpha
  CNalpha = Crank-Nicolson coefficient for hybrid explicit-implicit velocity
  integration
momentOfInertiaFactor
  scaling factor for the moment of inertia of particles

Examples

fix 1 all nve/cfd_cn/sphere
fix 1 all nve/cfd_cn/sphere update dipole

Description

Perform constant NVE integration to update position, velocity, and angular velocity for finite-size spherical particles in the group each timestep in the presence of fluid. V is volume; E is energy. This creates a system trajectory consistent with the microcanonical ensemble.

This fix is similar to the fix nve/sphere command, which assumes point particles and only updates their position and velocity. However, depending on the varying particle velocity (and thus relative velocity between fluid and particles) the drag force on the particles is calculated at every DEM time step until new data is obtained in the next coupling time step.

If the Crank-Nicolson keyword is present, Crank-Nicolson integration scheme with given CNalpha is applied, otherwise the default value is chosen.

When the CAddRhoFluid keyword is active, couple/cfd/force will consider added mass, where CAddRhoFluid = rhoFluid / rhoParticle.

If the update keyword is used with the dipole value, then the orientation of the dipole moment of each particle is also updated during the time integration. This option should be used for models where a dipole moment is assigned to particles via use of the atom_style dipole command.

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

No information about this fix is written to binary restart files. None of the fix_modify options are relevant to this fix. No global 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. This fix is not invoked during energy minimization.

Restrictions

This command is only valid in coupled simulations.

This fix requires that atoms store torque and angular velocity (omega) and a radius as defined by the atom_style sphere command. If the dipole keyword is used, then they must also store a dipole moment as defined by the atom_style dipole command.

All particles in the group must be finite-size spheres. They cannot be point particles.

Default

CrankNicolson 0.5 momentOfInertiaFactor 0.4