Development And Application Of A Three-dimensional Unstructured Fully Coupled Wave-current Model

Recognizing the important role of wave-current interaction played in hydrodynamic and water environment, scientists have become increasingly interested in establishing a regional predicting system that could couple three-dimensional ocean models with wave models. Using unstructured meshes provides an accurate fitting of the irregular coastal boundary, with refined grid resolution in regions of interest and not elsewhere. In this study, an unstructured three-dimensional fully coupled wave-current model is developed. Several applications are presented to evaluate the developed model.A parallel, unstructured grid, parametric wind-wave model is firstly developed with the intention of coupling to three-dimensional unstructured grid ocean circulation models. The model is derived from a conservation of energy flux formulations. In the model, the shoaling, refraction, and wave dissipation, as well as exchange of current and stokes drift momentum effects are considered. Then, the existing Finite-Volume Coastal Ocean Model is modified to couple with the wave module. The couple procedure includes depth dependent wave radiation stress terms, Stokes drift, vertical transfer of wave-generated pressure transfer to the mean momentum equation, wave dissipation as a source term in the turbulence kinetic energy equation, and mean current advection and refraction of wave energy. Several applications are presented to evaluate the developed model. In particular the wind and wave-induced storm surge generated by hurricane Katrina is investigated. The obtained results have been compared to the in situ measurements with respect to the wave heights and water level elevations revealing good accuracy of the model in reproduction of the investigated events. Several runs were carried out to analyze the effects of waves. The experiments show that among the processes that represent wave effects, radiation stress and wave-induced surface stress are more important than wave-induced bottom stress in affecting the water level. The hurricane Katrina simulations showed the importance of the inclusion of the wave effects for the hindcast of the water levels during the storm surge.Seasonal circulation of the Bohai Sea (BS) in 1992 was investigated using Lagrangian particle tracking method. The transport of particles has three-dimensional (3D) structure in the BS. Compared with central Bohai and Bohai Strait, the differences of particles'transportation between surface and bottom layer in three bays are small. The circulation in the summer is stronger than that in the winter, with the average residual velocity in the surface layer being about 3.7 cm/s during the summer while only 1.8 cm/s during the winter. Using the same model, several well-designed numerical experiments were performed to investigate the effect of oceanic tide, river discharge, wind stress and thermal stratification on the circulation. It is shown that winds play an important role in the circulation of the BS during both the winter and the summer. Density circulation is important during the summer; however, it is negligible during the winter. River runoff only affects the area around the river mouth. Compared with wind and thermohaline effect, the contribution of tides is small during the summer, and the circulation under only M2 tidal constituent could not reflect the actual circulation of the BS.A three-dimensional integrated model is developed for simulating transport and fate of oil spills in seas. The model contains two main modules, flow and transport-fate modules. The flow module uses an unstructured finite-volume wave-ocean coupling model. In the transport-fate module the oil dispersion is solved using a particle-tracking method. The model simulates the most significant processes that affect the motion of oil particles, such as advection, surface spreading, evaporation, dissolution, emulsification and turbulent diffusion as well as the interaction of the oil particles with the shoreline, sedimentation and the temporal variations of oil viscosity, density and surface tension. This model has been applied to simulate the oil-spill accident in the BS.A three-dimensional hydro-eutrophication model was implemented to compute average residence time, water age and water quality in the Dahuofang Reservoir, China. Residence time estimations yield a broad range of values depending on the position. The average residence time for a tracer placed at the head of the reservoir under high-, mean-, and low flow conditions was found to be about 125,236 and 521 days, respectively. The age simulation reveals that the age distribution is a function of the freshwater discharge. In the vertical, the age of the surface layers is larger than that of the bottom layers and age difference between the surface and bottom layers decreases further downstream. The density-induced circulation plays an important role in the circulation in the reservoir, and can generate vertical age distribution in the reservoir. Sensitive of the parameters has been analyzed to decide which process would affect the water quality in the simulation. Water quality verification suggested the model successfully computed the temporal cycles and spatial distributions of key water quality components. The model could be used as a tool to guide physico-biological engineering design or management strategies for Dahuofang Reservoir.