Study Of Wave Radiation Stress And Its Effect On The Surf Beat In The Nearshore Zone

Wave radiation stress was proposed first by Longuet-Higgins and Stewart,which has been defined as the excess flux of momentum due to the presence of waves.In the past decades. many researches have been done and found that the radiation stress plays an important role in a variety of oceanographic phenomena,for example the wave set-up and set-down;the interaction of waves with steady currents;the generation of surf beat and so on.Usually,the method of Longuet-Higgins and Stewart is used to calculate the radiation stress.It's dependent on the velocity of water particle,wave height and incidence angle.A method of calculating the wave radiation stress is proposed based on the Boussinesq equations in this thesis.The method has been effectively solved.The method has been used to simulate the variation of radiation stress on a horizontal bottom and a sloping bottom.In the comparison of surface elevations,root-mean-squared wave heights and radiation stress,the numerical results agree well with the analytical results and the experimental data with high accuracy.Therefore it may be concluded that the proposed method is accurate and reliable.Low-frequency wave,surf beat is an important hydrodynamic wave motion in the nearshore zone,which is believed to have significant effect on the sediment transport, tranquility in the harbor and the vibration of moored ships.The present method of calculating radiation stress is used to simulate and analyze the surf beat and the effect of radiation stress on it.On a horizontal bottom,the results show that modulation rate is an important factor to distinguish the structure of surf beat.Over a sloping bottom in a physical model,the surface elevations,amplitudes at primary frequencies,amplitude at low frequency and radiation stress are compared in the breaking and nonbreaking cases.The results show that wave radiation stress changes according to the variation of wave groups,which has a sharp fall where the wave break and low-frequency waves grow simultaneously.The relationships among them are caused by nonlinear energy transfer among the different wave components.