A hydrodynamic particle tracking algorithm for simulating settling of sediment

The transport of sediment is an aggregated phenomenon reflecting the response of individual sediment particles to the surrounding fluid flow. Traditional modelling of sediment transport has concentrated on conceptualisations of either the overall behaviour (analogous to the thermodynamic approach to atomic modelling) or simplifications of the movement of individual particles that assume that the motion of a particle is the same as that of the surrounding fluid (analogous to a simplification of the particle dynamics approach to atomic modelling). This paper describes a numerical technique that models the hydrodynamics of individual sediment particles in a turbulent flow field, tracking the path of the particle under the action of a mean velocity field and superimposed random fluctuations, thus inferring data about the aggregate transport. The movement of individual sediment particles is modelled by analysing the drag forces acting on a particle under the action of a turbulent flow field and calculating its motion from a force balance. Particles never move with exactly the same motion as the surrounding fluid, they lag behind it generating the drag force that drives the particle's motion. In an example, it is shown that turbulence has a significant effect on settling velocity of particles compared with the still water case. Settling velocities increase or decrease depending on the turbulence applied.