층적분된 3차원 해빈류 수치모형의 개발과 적용

Abstract

Models that predict the fluid motion in the nearshore and surf zones on beaches are necessary in the effort to understand nearshore processes. The phenomenon of wave breaking is relevant to the coastal processes such as the wave decay, the change of mean water level, and the development of alongshore currents in the surf zone. The movement of sediment and the associated shoreline change are caused by the action of waves and current over time. Therefore the understandings of them are very important in nearshore and surf zones on beaches. In this thesis we examine the effect of longshore varying topographies on the nearshore and alongshore currents. The governing equations are derived form the conservation of mass and momentum principles, integrated over the depth and turbulent motions. This new model includes nonlinear correction terms in the radiation stress and energy flux that become important in very shallow water. The turbulent Reynolds stresses are modeled using the eddy viscosity concept, which provides a simple closure to determine analytical profiles for the vertical variation of the horizontal currents. The short-wave quantities are given by an external wave model and thus the wave-induced forcing is assumed known. The coupling between the depth-varying and the depth-integrated equations forms the Thee-dimensional model system considered here. The model equations are solved numerically using a finite difference scheme. A moving boundary condition is incorporated at the shoreline to account for wave run-up. An absorbing-generating boundary is incorporated offshore. The boundary treatments are tested using analytical and numerical results. The three-dimensional mathematical model has been applied to the numerical simulation of wave-induced current. We compare the solution of the present numerical model with that of a simplified. The computed longshore current velocities are compared with measurements obtained from laboratory experiments and numerical models for wave induced current over the plane profile and the barred beach. This comparison provides an analysis of the limitations of the simplified model, which thus out to be grossly inaccurate for a barred beach with a small rip-channel. The model is tested against other numerical model and experimental data. Good agreement has been achieved. The results are pending further study and comparison with field and laboratory measurements.