The Investigation On Wave-Current Interaction In Shallow Water Based On A Non-hydrostatic Wave-Current Model

Waves will present strong nonlinear characteristics as they propagate from deep to shallow waters. Due to the nonlinear effect, the wave crests turn to sharpen and lean back or forward while the troughs turn to flatten. The ambient currents are one of the main factors which affect the intensity of nonlinear characteristics. When opposite currents reach to a critical value, waves will be blocked while wave energy cannot propagate forward at the blocking point. In this paper, we investigated the nonlinear parameterization of waves with ambient currents and the phenomenon of wave blocking over a submerged sill with a non-hydrostatic wave-current model.Physical model test was carried out to verify that the numerical model SWASH is reliable. Investigation of the current velocity and the current direction (following or opposite with waves propagation) effects on the nonlinear transformation of waves was carried out with SWASH. Each direction selects four current velocities. The nonlinear parameters (asymmetry, skewness and kurtosis) are estimated by using the wavelet-based bispectrum, and the empirical formulae regarding these nonlinear parameters as a function of the local Ursell number are derived based on the present data measured on each current velocity. In addition, the connections between the nonlinear parameters (asymmetry and skewness) and the local Ursell number of each current velocity are presented in this paper. In the shoaling area of submerged sill, the nonlinear characteristics of waves is most obvious when waves propagate in the same direction with currents. In the crest shallow area of submerged breakwater, the stronger current velocity, the more obvious the nonlinear characteristics of waves in the following current; while the nonlinear characteristics of waves grows when waves propagate in the weakening adverse current.The investigation of waves being blocked by strong opposing currents was carried out with SWASH. The conclusions are:high frequency waves turn to easier to be blocked compared with low frequency. As for regular waves, the waves with high wave steepness turn to more difficult to be totally blocked due to wave instability which cause the wave energy transmit form high frequency to low frequency. Supposing that the waves have not been broken at the blocking point, the energy of waves will be reflected instead of energy dissipation.