FVCOM-based Wave-Current-Sediment Model Coupling And Its Application

Study of the near-shore ocean phenomena such as tides, circulation, storm surges, waves, sediment transport and morphology has an important significance on marine engineering and environmental protection. Many studies have shown that these phenomena are not isolated while there are strong non-linear interactions between them, so studying them as a whole is quite necessary. Model has become an important tool to study physical oceanography. Most coupled models are two-dimensional or one-way or using structured grid. Due to the complex coastline and topography in near-shore, coupling between a set of unstructured grid models that can better resolve the coastline becomes important.Based on the finite volume method, triangular grid hydrodynamic model FVCOM, wave model FVCOM-SWAVE, sediment model FVCOM-SED, with the application of three-dimensional radiation stress, the waves-currents-sediment related bottom boundary model, sea surface stress model and morphology, a wave-current-sediment coupling system is set. First history and current study of wave current interaction are summarized, including the theoretical and model study. Then two ideal experiments are carried out to verify the model, including an incident wave with an angle on plane beach, and a tidal inlet. The first experiment is designed primarily to study the influence of radiation stress on the hydrodynamic model; the second experiment is to investigate the interactions in the coupled model, to verify the main coupling mechanism and discuss the wave-current-sediment inlet systems. After these two experiments, some basic coupling mechanisms and programming is fully tested. A storm surge case in the Yangtze River-Hangzhou Bay during is modeled to study wave, current, sediment interaction. As there were no observed data under storm surge for us to make the comparison, following this experiment, a simulation is made during a strong winter wind period in the Bohai Sea where there were observations on oil platforms. Thus we can test the model through observation.The inlet case mainly told us the flow field should be dramatically changed where there is a significant change in topography. In the Yangtze River-Hangzhou Bay simulation, we concluded that introducing waves can make sediment concentration one order larger in deeper water. Radiation stress can promote the water level in storm surge; the bottom boundary layer increased the water level also. In the Bohai Sea simulation, the water level are better after coupling; flows at the platform are quite weak and the interaction is small, but the modeled wave height varies with the tidal frequency due to the tides. Both the two applications show tide level change can influence wave only in shallow water. The current influence wave by Doppler shift and the its variability in time and space; generally speaking, wave height decreases when wave current are in the same direction and increases when their directions are opposite. The variation of water depth directly influences the calculation of wave speed and bottom friction which can change wave's propogation and disspition.