Stochastic sediment transport: anomalous diffusions and random movement
Journal
Stochastic Environmental Research and Risk Assessment
Journal Volume
34
Journal Issue
2
Pages
397-413
Date Issued
2020
Author(s)
Abstract
A sediment particle in a flow not only follows the flow direction but also randomly diffuses through the surrounding fluid, because of the turbulence in the flow. In this study, particle movement is regarded as a stochastic process. The stochastic-diffusion particle tracking model is able to simulate the random characteristics of particle trajectories based on stochastic methodologies and physical mechanisms. This study proposes a state-of-the-art two-particle stochastic-diffusion particle tracking model, which considers particle correlation. The spatial correlation depends on the distance between paired particles. Particles are highly correlated and have similar random movement because of large-scale eddies when paired particles are located in the immediate vicinity of each other. The model is applied to open-channel flows, and simulation results of ensemble means and variances of particle positions are examined. Concentration results can be expressed as time-varying probability density functions. The proposed models are validated against the experimental data through ensemble mean velocities and sediment concentrations. This study also examines whether movements of sediment particles in open-channel flow follow the Fickian law. Simulation results of ensemble variances of particle displacements in longitudinal and vertical directions reveal a deviation from the Fickian hypothesis. The influence of the resuspension mechanism on the observed anomalous diffusions is discussed.
Type
journal article