Research On Characteristics Of Bubble Pulsation And Jetting Near Boundary Induced By Underwater Explosion

A lot of research and facts show that the damage of structures induced by an underwater explosion bubble can not be ignored. So numerical method is used to study the response of the structure in water under the effect of underwater explosion bubbles pulsation load and the jetting characteristics of bubble near boundaries, and model tests are carried out to research the motion characteristics of underwater bubble near the ship and submarine using an spark-generated bubble, which provides a great reference for the evaluation of damage of structures induced by underwater explosion bubble loading.Firstly, the stage of shock wave and bubble pulse are took into account integratively, the Geers and Hunter bubble mode is derived. Based on this model, the bubble pulsation and the load in the free field are calculated, the effect of the charge and explosive distance on the pulsating pressure is analysised, and the load characteristics of shock wave and bubble pulsation are also compared; Coupled acoustic-structural analysis method is adopted to calculate the response of structures in water under the underwater explosion bubble pulsating loads, simultaneity the scope of the method is given and the validity is verified; This method is used to calculate the response of cylindrical shells induced by an underwater explosion bubble pulsating load and the effect on the response of cylindrical shells of structural frequency and bubble frequency is derived.Secondly, the finite difference solver AUTODYN is used to calculate the jet of underwater explosion bubble near the boundaries. One-dimensional spherically symmetric and two-dimensional axisymmetric solvers are adopted to simulate the explosion of a small charge in large depth water and bubble in gravity field respectively. The contrast between the numerical results and experimental data shows that the solver can simulate the jet phenomenon of underwater explosion bubble near the boundaries successfully; Motion characteristics of bubble near free surface and a fixed wall is researched. The effect of distance parameter on the jet shape, maximum radius of bubble and the first pulsating period is discussed, and bubble jet velocity, jet impact time and pressure are derived espetially for the case of bublle near a fixed wall. Finally, the response of a clamped circular plate under the bubble jet is studied. Lastly, the scaling relations for bubbles induced by spark and underwater explosion are derived. A ship and a submarine model based on geometric similarity are built up and model tests are carried out to studiy the motion characteristics of an underwater explosion bubble near the structures using a spark-generated bubble. Thus, the interaction between the bubble and the ship structure is observed apparently.