Study On The Coupling Effect Between Underwater Explosion Bubbles And Structure Attached Air Bubble

The interaction between pulsating bubbles and surrounding boundaries is an important phenomenon in nature and industrial applications,It is widely used not only in traditional engineering field but also in many emerging fields,such as underwater explosion,hydro-mechanical cavitation,micro-bubbles in drag reduction technology,precision instrument cleaning,targeted therapy and so on.The bubble’s dynamic behavior and the pressure caused by the violent collapsing bubble in the above applications are the core problems.This paper mainly conducts experimental research on underwater explosive bubbles in the field of ship and Marine engineering,deeply explores the pulsation phenomenon of bubbles under various complex boundaries,and focuses on the characteristics of bubble jet load and the coupling law between bubbles and structures.The main contents of this paper are as follows:(1)The experimental study is adopted to reveal the bubble dynamics and the structural responses close to a rigid surface or a flexible structure.The experimental facilities are comprised of a low-voltage spark discharge and a high-speed camera.The bubble evolution close to various materials with different distance parameters are observed through the experimental devices.The major attentions are mainly focus on the transient response pattern of the flexible structure and special phenomenon of bubbles such as bubble splitting,the bubble jet direction property,the characteristic of bubble migration and the coupling response of the structure.A procedure is developed to transform a photograph to numerical data using MATLAB software.Through lots of experiments,it has been found that the bubble transforms to a“wooden club”shape or split into two small bubbles and water jets directed away from each other occur;the motion response of flexible materials in the whole bubble pulsation period is analyzed,the flexible plate takes on the one-order mode during the bubble expansion phase,while it changes to the third-order mode two displacement peaks transport phenomenon in the bubble collapse phase.(2)The interaction between a spark-generated bubble and a non-oscillating air bubble attached to a horizontal rigid plate is investigated using a low-voltage spark-discharge setup.In order to analyze the variation of the bubble shapes obtained through the high speed video.It is found that,under the combined influence of the cavitation and the structure,some complex phenomenon likes the direction variation of the bubble jet and migration,multi-direction jet and bubble tears are given rise to the spark bubble.The spark-generated bubble-air bubble-structure coupling phenomenon such as the bubble pulsation shapes,the bubble jet direction,volume variation tendency and the displacements of the points on the spark-generated bubble and attached bubble are discussed in detailed.The various motion tendencies of the volume variation of the spark bubble and cavitation bubble are summarize,and the effect of the distance parameter and volume ratio parameter on the motion tendencies are analyzed.(3)In order to consider the influence of the deformation effect of the flexible structure under bubble load on the dynamic characteristics of the bubble,the pulsation characteristics of the bubble near the flexible structure with attached single air bubble are experimentally studied.By observing the coupled pulsation phenomenon of bubble-cavity-flexible plate with different distance parameters under PVC plates with different thickness,the special morphology of bubble and cavity and the response characteristics of flexible plate are revealed.It is observed that the bubbles near the flexible boundary of attached cavitation tend to have mushroom-like annular jets,accompanied by a series of complex phenomena such as fusion rebound,deviation from the boundary and middle tearing.(4)The above research content is mainly aimed at the condition when attached cavitation is located directly above the bubble.In the following part,the coupling pulsation of the two bubbles when there is an inclination Angle between the bubbles and the fixed cavitation is studied.The research shows that the existence of the initial inclination Angle makes the efflux shape and direction of the bubble more diversified.This efflux complex phenomenon is mainly caused by the combination of the forces existing between the Bjerknes force of the cavitating bubbles and the suction force of the steel plate during the contraction phase.The displacement variation of two key measurement points of bubbles is analyzed emphatically and the response rule of attached cavitation when bubbles are pulsed is summarized.(5)The pulsation characteristics of bubbles near the rigid boundary with multiple cavitations in different spatial layouts are studied,and the coupling pulsation phenomenon between cavitation groups and bubbles is emphasized.The results show that the coupling pulsation is mainly affected by the dimensionless distance between the bubble and the boundary,the dimensionless distance between two air bubbles and the spatial arrangement.Compared with layout II,bubbles only produce off-axis migration and jet flow direction under layout I.For spatial layout I,when cavity spacingγ_L is fixed,the displacement of the cavity right above the bubble is proportional to the distance parameterγ_s.