Numerical And Experimental Study On Interaction Between Underwater Explosion Bubble And Flexible Structure

Bubble dynamics has played a significant role in the field of naval architecture and ocean engineering,such as seabed geophysical exploration,underwater explosion and microbubble drag reduction.However,the research of bubble dynamics involves complex gas-liquid multiphase flows,transient fluid-structure interaction,strongly nonlinear mechanical interaction and so on,thus bubble dynamics has been the hot and difficult research area.Recently,a large number of flexible structures have been widely applied in the area of naval architecture and marine engineering with the development of deep-sea resources.When underwater explosion(UNDEX)occurs near flexible structures,dynamic responses between bubble and flexible structures involve a series of key factors,such as material nonlinearities and geometric nonlinearities of flexible structures.At present,the relevant researches on the coupling between bubble and flexible structure are deficient,especially the deformation response of structures,the oscillating and jet features of bubbles.The load characteristics of UNDEX are introduced,then the research progresses and shortcomings of traditional numerical methods in simulating bubble motions and its coupling characteristics with structures are clarified.In order to solve complex fluid-structure interactions between bubble and flexible structure,the arbitrary Euler-Lagrange(ALE)numerical method is adopted to simulate the bubble dynamics by LS-DYNA program.Moreover,the corresponding spark-generated bubble experiments are carried out to reveal the coupling characteristics between flexible structures and oscillating bubble.Firstly,the free field underwater explosion and its load characteristics are analyzed.The continuous processes of underwater explosion,including shock wave propagation and bubble motions,are simulated with ALE method in LS-DYNA program.At the same time,the numerical results are quite consistent with empirical formulas and experimental results,which presents the reliability and accuracy of ALE method in dealing with underwater explosion problems.As for the UNDEX generated near free surface,the effective simulation of shock wave propagation,bubble evolutions and water spike by the initial explosive model is verified compared with experimental results.Moreover,the influences of different dimensionless distance parameters on bubble behaviors and water spike are analyzed.Secondly,the coupling characteristics between UNDEX bubble and flexible structure are discussed.Based on the initial explosive model of ALE method,and the phenomenological Ogden model is adopted to calculate behaviors of the hyperplastic rubber plate.The differences between bubble interacting with flexible plate or rigid plate are discussed.Then,a series of numerical researches on distance and thickness parameters of bubble subjected to flexible plates are performed.Moreover,the bubble motion,pulsating pressure loads and deformation responses of the flexible plate have been specifically analyzed.Finally,based on spark-generated bubble and high-speed photography technology,the different bubble dynamic behaviors are compared when bubble is generated near rigid or flexible boundary.Then,the coupling characteristics of bubble and flexible structure boundary are studied by a series of experiments,especially for the typical flexible plate and flexible pipe boundaries.Distance parameters play a significant part in determining the bubble oscillating features,and jet directions on interaction between bubble and flexible boundary,as well as the deformation mechanisms of flexible structures.