NUMERICAL SIMULATION OF FINE SEDIMENT TRANSPORT IN WAVE BOUNDARY LAYER

Abstract

Wave-induced sediment transport is recognized as one of the main mechanisms that play part in the morphodynamics and sediment source to sink. In this study, we identify and quantify the role of turbulence-sediment interactions in determining the diverse bed state using turbulence-resolving numerical simulations of fine sediment transport in a oscillatory bottom boundary layer. The formation and the dynamics of lutocline waves observe at muddy shelves, sediment burst events observed during flow reversal in sandy nearshore and at muddy shelves, and relaminarization of wave boundary layer due to concentrated fluid mud are the few examples that are well captured in a series of simulations in this study. The laminarization process is often assumed in two-layer (or multi-layer) models for wave-mud interactions. However, the criteria for laminarization in a wave boundary layer as a function of Reynolds number, settling velocity and sediment concentration have not yet been established. In addition, the accuracy of the waveresolving Reynolds-averaged (RANS) wave boundary layer sediment transport models in predicting the state of the muddy seabed under the influence of variable parameters has not yet been evaluated. It is demonstrated here that RANS model can predict the formation of lutocline from low to moderately concentration condition. However, when sediment concentration is further increased, sediment burst events and laminarization of the wave boundary layer cannot be reproduced without further modification to the conventional turbulence closure.