Three-Dimensional Numerical Simulation Of Nearshore Current

In coastal area, it is very important to predict nearshore current accurately for investigation of sediment transport, coastal evolution and environmental problems. However, the nearshore current is affected greatly by various factors, e.g., the role of waves must be described reasonablely when the wave is relatively strong. The previous studies on the impact of waves, such as wave radiation stress, the surface stress generated by wave rolling due to wave breaking and the bottom shear stress due to combined waves and current, are mostly obtained by a number of simplifying assumptions or not fully taking into account the avove factors. Thus it is of great significance to develop a three-dimensional nearshore hydrodynamic model on the basis of considering wave impact reasonably and comprehensively, and to investigate the nearshore current field due to waves.Firstly, the expressions for vertical distributions of radiation stresses were dirived based on the second-order Stokes waves and the second-order cnoidal wave theory respectively; and the vertical profiles of radiation stresses are discussed. Secondly, after the introduction of three-dimensional ELCIRC hydrodynamic model and REFDIF wave model, the vertical profile of radiation stresses of non-linear waves, the shear stress of wave roller under wave breaking and the bottom shear stress due to combined waves and current were incoorpated into the ELCIRC model, which leads to a three-dimensional nearshore hydrodynamic model with the function of describing the complex system of wave-induced nearshore current. The newly developd model was verified by the experimental data of wave setup and setdown, undertow and longshore current.Using the three-dimensional nearshore hydrodynamic model metioned above, the longshore current and rip current are studied in detail. The numerical simulation results of longshore current show that the distribution of longshore current is affected by the wave height, wave direction and beach slope. The distribution laws are as follows: the greater the incident wave height is, the greater the longshore current velocity and the influence area are; when the wave incident angle comes to 45 degrees, the longshore current velocity reaches maximum; the influence area of the longshore current on the gentle slope is greater than that on the the steep slope, and the flow distribution is relatively concentrated on the steep terrain. The results of the rip current show that the distribution of rip current flow is affeccted by the incident wave height, incident wave angle and hump height. The distribution laws are as follows: the greater the incident wave height is, the greater of the rip current velocity and the influence range are; On the sinusoidal topography, the oblique incident wave can produce longshore current and nearshore circulation; the greater the amplitude of the sinusoidal topography(hump height) is, the greater the rip current velocity generated at the ditch of the rip current is.