Kinematics and Transformation of New Type Wave Front Breaker over Submerged Breakwater

This study presents the discovery of a new type of wave breaking over a submerged breakwater. Our findings were made through laboratory experiments. In this new type, wave breaking first occurs at a wave's front part, not at the top of the wave crest. Next, the wave crest passes over the breakwater's crown without breaking. In this study, we call this wave breaker a wave front breaker, and the process of wave transformation and the conditions for the wave front breaker to occur are clarified. The wave kinematics of the wave front breaker is also investigated by PIV and LDV measurements. Consequently, it is shown that the occurrence of the wave front breaker strongly depends on the incident wave length, and the wave transmission coefficients of the wave front breaker become larger. It is also found that an inverse layer of the mass transport velocity exists near the seabed against the main region of the mass transport velocity. Furthermore, the direction of the mass transport velocity near the toe in the inverse layer is onshore, while that of the maximum acceleration is offshore and the value of the acceleration increases as the measuring points get closer to the seabed and away from the toe.