Multiscale air entrainment in wave-in-deck loads

Abstract

Since entrapped air directly affects the properties of wave impact loads, it has long been unclear whether an air cushioning or entrapped-air amplifying effect exists. Wave-in-deck impacts are innovatively divided into four types based on the air-entrapped scale and characteristics of loads, namely, direct impacts, wave impacts with large or small air pockets (several metres to dozens of metres), and wave impacts with minute bubble plumes (tens of microns to several millimetres). In this study, a systematic study of multiscale air entrapment when waves impact a flat deck is conducted. After volume averaging, the temporal and spatial closure terms are rationally modelled to develop a multiscale air-entrapped wave impact model that couples the compression and expansion properties of large air pockets with the mean hydrodynamic properties of unsteady, nonuniform bubble plumes at a single acceptable grid scale. The high aeration and disordered bubble plume field, which the model successfully captured, as well as the impulsive pressure, have been validated for the typical dam-break impact problem. The results demonstrate that the model is capable of simulating air cavities entrapped in the initial moment of wave impact on the deck and the minute bubble plumes formed by the subsequent breakup, which offers a plausible new explanation for the investigation of the complicated mechanism of multiscale air-entrapped impact.