Micro Scale Sediment - Fluid Interactions

Abstract

This thesis was inspired by the inherent limitations in the quantification of the physical parameters (e.g. flow speed, grain size and density) controlling sediment-fluid interactions in the direct vicinity of the sediment water interface of a seabed. For this, the transport behaviour of layered - and mixed sediment beds consisting of a simplified two-grain fraction distribution (silt and sand) was tested in an analogue laboratory-based annular flume. The results showed that the sediment bed stabilized with increasing silt composition. To investigate this effect in more detail, a high resolution 3D numerical model was designed for the simulation of sediment transport by a fluid by coupling two numerical techniques i.e., Finite Difference Method (FDM) and the Distinct Element Method (DEM). It verified that in the case of the deposition of fine particles on top of, or mixed into, a coarse matrix, the bed stability increased significantly. The model was also used to examine the role of grain density variations on the threshold conditions and erosion behavior of sediment beds. The experiments showed that bed stability increased when the heavy mineral concentrations were increased, which validated the process of heavy mineral enrichment.