Particle Specification

PENKNIFE can use the NESO-Particles and NESO frameworks to allow users to use computational particles which interact with the fluid solver.

A Particle system is enabled using the <PARTICLES> field in the XML config file.

Global parameters for the particle system are specified in <PARAMETERS>

Particle information is specified on a per-species basis, within <SPECIES>

Each species must have mass and charge fields, as well as initial conditions, and may optionally have sources and sinks.

Initial Conditions

The species initial conditions are specified in the :code:`<INITIAL N=”num”>`field.

The density field can be specified by an analytic function for a probability distribution (everywhere between 0 and 1). During initialisation, num particles are created using adaptive rejection sampling over this distribution.

Sources

Sources are specified under a <SOURCE N="num"> field. Multiple sources can be created for each species. Here, num indicates the number of particles added at each timestep.

Sinks

Sinks are specified under a <SINK> field. Multiple sinks can be created for each species. The specified function indicates the probability that a particle is removed at each timestep. The probability function is evaluated at each particle’s position, which is then marked for removal with that probability.

Boundary Conditions

The particles may interact with the boundary regions by either reflecting, being absorbed, or taking part in a surface reaction.