Structual Damage Of Ships Subject To Underwater Explosion Loads In Waves

Studying underwater explosion does not only helps us to understand the damage mechanism of underwater explosion load on ship structures,but also guides anti-shock design of ships.Most of previous researches on the damage of ship structures subject to underwater explosions concentrated in still water conditions.Researches considering sea wave conditions are quite rare.The existence of waves changes the geometric feature of the free surface and the flow field properties beneath it,which must affect the characteristics of underwater explosion loads and cause changes in the loads acting on ships.The wave bending moment will also threaten the longitudinal strength of ships,so it is necessary to consider the effect of sea waves.Firstly,this dissertation starts with the basic phenomenon of the underwater explosion and systematically discusses the two typical methods in this field.As for underwater explosion,the fundamental theory of the acoustic-solid coupling method taking cavitation effect into account and the coupled Euler-Lagrangian method is explained.Then,these two methods are verified by calculating classic benchmark problems and comparing them with experimental or analytical solutions.Secondly,the acoustic-solid coupling method is used to calculate the shock wave and cavitation phenomenon of an underwater explosion in waves.The coupling mechanism of the shock wave and sea waves is explained.Then,the effects of different wave parameters(phase angle and wavelength)on cavitation and shock waves are studied.Aiming at the ship’s basic structural unit:plate grillage,the damage responses of a plate grillage with or without waves are analyzed.When the shock wave reaches a crest position of the sea waves,the reflected wave converges due to the curvature of the free surface.On the contrary,the shock wave reaches the trough position,the reflected wave diverges.The reflection characteristics near the free surface will also affect the evolution of the cavitation region.Thirdly,the interaction between an underwater explosion bubble and sea waves is studied.A small-scale wave-making device is designed in this paper.The spark discharge technology is used to generate a pulsating bubble which imitates the underwater explosion bubble,and the coupling experiments between it and the generated waves are implemented.The effects of different wave parameters on the dynamic characteristics of bubbles are analyzed in detail.Then,based on the coupled Euler-Lagrangian method,the interactions between the bubble and waves are simulated,and the coupling mechanism is further explained.Dynamic characteristics of underwater explosion bubbles with different wave parameters(phase angle and wavelength)are studied.The existence of waves changes the shape of free surfaces,and the velocity field caused by the waves leads the bubble generated by underwater explosion to expand non-spherically near the free surface.Besides,the waves have a certain effect on the bubble pulsation period,maximum radius,and jet angleFinally,a finite element model of a simplified box-ship is established in this dissertation.Based on the coupled Euler-Lagrangian method,the transient fluid-structure interaction between the box-ship and underwater explosion is simulated in waves,and the "whipping effect" of different conditions are compared.The research is intended to provide a reference for researches on underwater explosion and anti-shock design of ship structures.Due to the existence of wave bending moment,the longitudinal strength of the ship in waves is in a more dangerous situation.