Numerical Study On2-D Suspended Sediment Transport Under Waves And Tidal Currents At The Sea Area Of Changxing Island

Study of the near-shore ocean phenomena such as waves, storm surges, circulation, tides, sediment transport and morphology has an important significance on environmental protection and marine engineering.So many studies have shown that these phenomena are not isolated but there are interactions between them. Most of the papers that have been reported are based on structured grid. In the area with regular boundaries, the structured grid is accepted, while in the coastal boundaries characterized by barrier island and tidal creek complexes, unstructured grid used can improve computational accuracy. Until now, most of the study on near-shore water Dynamics are always focused on waves or tidal currents alone, or one-way or using structured grid. So it is important to creat a model that is two-way, using unstructured grid,coupled with waves and tidal currents.In order to calculate2-D suspended sediment transport under waves and currents in the sea area of Changxing island of Dalian, a numerical model system is developed. Five models, a2-D compound fluid model including wind, waves and tides, a SWAN wave model, a wave-current bottom boundary layer model, a2-D suspended sediment transport model, and a morphology model.First history and current study of wave current interaction are summarized, including the model and theoretical study. Then two ideal experiments are carried out to verify the model, including a tidal inlet and Li Mengguo’s mathematical model experiment. The first experiment is to investigate the interactions in the coupled model, and to verify the main coupling mechanism and discuss the wave-current-sediment interaction system; the second experiment is to study the influence of radiation stress on the hydrodynamic model. The basic coupling mechanisms is fully tested after these two experiment. A practical case is introduced to study the wave, current, sediment interaction, and fully explain the results.The inlet case mainly told us in the sea area where flow velocity is large, when considered the influence of current, the wave can change obviously. And in Li Mengguo’s mathematical model experiment, the results is in the process of propagating of wave from shallow water to deep water, the wave can become break because of the water become shallow, and the wave factors can change greatly, especially in the near shore, can form wave-induced set-up and current. I n the simulation of the sea area of Changxing Island, the wave is important for the re-suspension of the sediment, in the weather of high winds, the wave can greatly increase the bottom shear stress, and can influence the flow velocity also, we concluded that introducing waves can make sediment concentration increased by many times in deep water, and in shallow water, the concentration can increased by40%to100%. So, the influence of waves should be considered when simulating sediment. The waves can show the same cyclical change when influenced by tidal current. Generally, when they are in the same direction, the wave height can be smaller, when they are in the opposite direction, the wave height can be larger. The trend of the drive function of wave to tidal, no matter to the radiation but also to the bottom friction stress, is through flow velocity, when they are in the same direction, the flow velocity can be smaller, when they are in the opposite direction, the flow velocity can be larger.