FLUID-STRUCTURE INTERACTION BETWEEN A HIGH-PRESSURE PULSATING BUBBLE AND A FLOATING STRUCTURE

This paper experimentally and numerically investigates the fluid-structure interaction between a spark-induced bubble and a floating structure. The boundary integral method is adopted to simulate the bubble dynamic behaviors and the auxiliary function method is used to improve the computational accuracy of the nonlinear fluid-structure interaction. The double-node method is employed to maintain the computational stability of the gas-liquid-solid interaction line. Besides, we use the underwater electric discharge technique to generate bubbles and the high-speed photography to record the bubble dynamics and the structural responses. Firstly, we compare the numerical result with the experimental data and favorable agreement is achieved which validates this numerical model. Through parametric study with respect to the dimensionless distance \gamma _s from the initial bubble center to the floating structure (the reference length is the maximum bubble radius), we then find that (1) as \gamma_s increases from 0.2 to 2, five types of jetting pattern such as necking together with annular jet (0.2\leqslant \gamma_s \leqslant 0.3), contacting jet (0.4\leqslant \gamma_s \leqslant 0.6), non-contacting jet (0.7\leqslant \gamma_s \leqslant 1), collision of a jet directed towards the floating body and a counter-jet (1.1\leqslant \gamma_s \leqslant 1.3) and individual counter-jet (1.4\leqslant \gamma_s \leqslant 2) can be formed; (2) it is also found that the velocity of the jet directed towards the structure first increases, then decreases and finally increases again as \gamma_s increases; additionally, it may be in the order of \sim1000m/s when \gamma _s varies from 0.7 to 0.9; as \gamma_s increases, the counter-jet velocity increases; (3) under the conditions of the presented experiments, the bubble migrates towards the floating structure when \gamma_s <\mbox1.5 due to the stronger Bjerknes attraction of the floating structure than the Bjerknes repellence of the free surface on the bubble during the collapsing phase. When \gamma_s \geqslant \mbox1.5, however, the free surface has stronger effects on the migratory behavior of the bubble than the floating structure which causes the bubble to migrate away from the free surface at the collapse stage.