Greenwater impacts on marine structures involve violent free-surface flows characterized by turbulence, high-speed jets, substantial aeration, and impulsive hydrodynamic loading. While plunging wave (PW) and plunging dam-break (PDB) impact types have been extensively investigated, the hydrodynamics of the hammer-fist (HF) type, in which a suspended water mass collapses vertically onto the deck, and the role of aeration in modulating these loads remains poorly understood. This study, as a continuation of W. L. Chuang “On the fluid kinematics of common types of greenwater events: An experimental study,” Appl. Ocean Res. 153, 104235 (2024), presents a comprehensive laboratory investigation of flow kinematics, impact pressures, and air-entrainment characteristics for PW, HF, and PDB greenwater events. Experiments were conducted in a wave flume using focused and regular wave generation techniques to ensure repeatability, with simultaneous measurements of impact pressure and local air fraction obtained via piezo-resistive transducers and fiber-optic reflectometry at 24 locations. The results reveal fundamental differences in loading mechanisms across the three event categories. The HF type produced the most severe local loading, with peak pressures reaching 27.10 kPa (11.41ρC2), substantially exceeding 15.87 kPa (8.86ρC2) for PW events and 4.82 kPa (2.12ρC2) for PDB events, despite comparable incident wave energy between PW and HF cases. Traditional impact coefficient formulations that neglect fluid density variations are shown to underestimate hydrodynamic loads. Incorporating the measured air fraction into the impact coefficient formulation increased coefficients by up to 29% for PW and PDB events and 102% for HF events. A pronounced negative correlation between peak pressure and aeration level further confirms a dominant cushioning effect.
Wei-Liang Chuang (Wed,) studied this question.