LONG-TERM GOALS

The primary goal of the research project is to contribute to a better understanding of the basic mechanisms controlling sediment transport in the nearshore regions. In particular, the structure of flow in the bottom boundary layer is studied along with its interaction with sediment dynamics and bottom morphology. Attention is also devoted to the steady streamings generated both within the bottom boundary layer and throughout the water column up to the free surface. OBJECTIVES The dynamics of the coherent vortex structures are being studied which are generated by waves at the bottom by 1) the instability of the laminar boundary layer and the development of turbulence, 2) the nonlinear interaction of the oscillatory boundary layer with a wavy bed of small amplitude and with a sloping bottom, and 3) the separation of the boundary layer at the crests of 2-D ripples of large amplitude. Moreover, we want to investigate the steady streaming induced both close to the sea bed and far from it. The resulting velocity fields are used to study sediment dynamics and the processes, which lead to the formation of small and medium scale bedforms. APPROACH The investigation is based on analytical approaches, numerical simulations of momentum (Navier-Stokes) and continuity equations and the analysis of field data. Analytical solutions describing the flow field generated by a propagating wave close to the sea bottom are obtained to interpret selected field measurements and to study how the flow in the bottom boundary layer affects small and large scale morphodynamic phenomena. The numerical codes consider the full 3-D problem and simulate coherent vortex structures and turbulence. Field data are used to test the analytical results and the numerical findings