The Laboratory Experiments Of Rip Currents Generated On Barred Beach And Numerical Prediction Model

Rip currents are an important part of the wave-induced currents in the nearshore region. Rip currents are shore normal, rapid and intense offshore-directed jets of water (up to2m/s) that originate within the surf zone and extend past the breaking region. It has been demonstrated that rip currents have great influence on sand or pollutants transportation, coastal morphology as well as public safety. This thesis mainly concerned on rip currents from two aspects:one is the experiment study of rip currents generated by rip channels in bar; the other is the developing phase-resolving type numerical model using the second-order fully nonlinear Boussinesq equations. The main content includes:1. Physical model experimentThe experiment investigates the wave-induced rip current pattern on a sand bar incised with a single channel. It was conducted in a flume for various normally-incident waves, including regular wave, irregular wave and wave group. Wave gage array and ADV array are respectively employed to obtain abundant data of surface elevations, mean-current field in1/3water depth and three-dimensional flow distribution. Wave height equipotential lines are plotted to learn about the wave propagation and transformation process over the bathymetry. Via analyzing the setup/setdown equipotential lines and horizontal mean flow pattern, the influence of the alongshore wave distribution variation on flow pattern is investigated. Further, the effect of wave condition, water depth and channel width on the flow pattern are analyzed. Great efforts are made to analyze the three dimensional characteristics of rip currents in the channel and nearby areas.2. Wave-induced current numerical modelA numerical model is set up based on the second order fully nonlinear Boussinesq equations to better understand the rip currents generated in nearshore region. The governing equations possess optimum linear characteristics and second order fully nonlinear properties in the medium water depth. To apply to the wave motions in nearshore region, the eddy viscosity method and slot method are respectively adapted to mimic the energy dissipation of wave breaking and moving shoreline boundary. The equations are numerically solved by finite difference method and a predictor-corrector ABM time integration scheme. The relaxation zone method is used to generate non-reflective and higher-order nonlinear waves. The developed model is used to simulate Haller’s rip currents experiment. Good agreements between the experiment data and numerical results show the applicability and accuracy of the model.Further, the investigations of the domain effects on the numerical results are conducted. Through comparison and analysis, the full scale simulation presents the best numerical results and has the superior performance than those using reduced spatial or time scales. At last, it is applied to preliminarily simulate the present rip current test and analysis the results.