Evolution and Energy Transition of Focused Waves on Current

Abstract

Wave-current interaction is a common phenomenon in real sea, thus offshore structures are often exposed to combined wave and current actions. Focused wave is an unexpectedly large wave in ocean with large wave steepness and strong nonlinearity. The combined actions of focused wave and current threaten the safety of offshore structures. Due to the strong nonlinearity of the focused wave, viscous effect is important in the prediction of the flow patterns of waves which are interfered by current. The CFD method can obtain more accurate information of viscous flow field than the potential theory. Thus, RANS simulation is adopted to study the interaction between focused wave generated in a Circulating Water Channel (CWC) and current in this paper. The dynamic grid technique is adopted to simulate the motion of real wave maker in CWC while the VOF method is used to capture the free surface of wave. The transient water wave theory is used to generate deep water focused wave. Meanwhile, experiment was conducted to generate the focused wave with and without current in CWC and the numerical model is validated by the experimental data firstly. Then the effect of transient wave steepness on formation of rogue wave is studied. The effect of current on the propagation and breaking process of focused wave with special wave steepness is discussed in detail by analyzing the evolution of water surface. Accordingly, the kinetic energy of wave at different locations, the total wave energy dissipation rate and turbulent kinetic energy have been evaluated. The energy dissipation and transition in the focusing process are discussed in detail through the analyzed results of wavelet transform. From the results, wave energy has been concentrated remarkably when focused wave propagates in counter-current and the dissipation rate increase remarkably when wave breaking occurs. Wave energy transfers from low frequency to high frequency when the focused wave propagating on current.