Evolution characteristics and quantization of wave period variation for breaking waves.

The wave parameters (the wave height and period) are important environmental factors in the ocean engineering design. General numerical wave models, such as SWAN and WAVEWATCH, are widely employed to simulate the wave conditions. However, significant differences were observed between the measurement and the simulation for both the wave height and period, which asks for wave model improvements. The differences are mainly due to the uncertainty of parameterizing various physical processes, including the wave breaking. The energy transfer and loss during the wave breaking involves an important physical mechanism, and the energy dissipation and the period changes are not well studied. This paper studies the deep and shallow water wave breaking using the wave focusing and the slope platform random wave experiments. The characteristics of the wave periods under different conditions are studied in detail, including the period variation. The results show that the periods change during the wave propagation and breaking processes. The energy transfer caused by the strongly nonlinear interaction between the wave components, as well as the energy loss caused by the wave breaking, are the primary causes. The corresponding relationships are established by fitting the data. For the deep water breaking waves induced by the wave focusing, the spectrally averaged period (SAP) increases, and a positive correlation between the rate of change and the wave steepness is found. In the shallow water, the nonlinear interactions are stronger than in the deep water, the wave periods are significantly reduced, and a negative correlation between the rate of change and a nonlinear parameter is found. The inherent mechanism of the period variation is analyzed based on the energy spectrum distribution variations. The contributions of the nonlinear interactions and the wave breaking to the SAP evolution are discussed. [ABSTRACT FROM AUTHOR]