Experimental study on bubble pulse features under different circumstances

Underwater explosion bubbles do severe damage to warshipstructures, and the particularity of underwater explosion and the quality ofwater bring great difficulties to get a clear picture. So lots oflaboratories all around the world make use of discharge or laser to generatebubbles to replace real underwater explosion experiments.Based on the designation from Turangan et al and Abdolranman Dadvand, anelectric circuit with a relatively low voltage 200V and three shunt-wound2200\muF capacitances is used to generate bubbles by discharge ina 500mm\times500mm\times500mm water tank to study underwater bubbledynamics. The experiment setup is safe, stable, low in costs and simple tofix. It can generate bubbles with radius up to 12~15mm.A device generating bubble by a relatively low voltage is designed to studybubble dynamics in detail under various boundary conditions in this paper.Main conclusions are obtained below by comparison and analysis:(1) A voltage of 200 V is adopted to generate bubble by discharge in water inthis paper. The voltage is fairly low yet the bubble generated is relativelylarge in size. The pictures shot are pretty clear as well.(2) There are copper wires burning inside the bubble throughout theexpansion process, causing the temperature inside bubble to rise apparentlyhigher and result in the small calculated value of bubble pulsing period. Sop_v within the bubble is actually very large and the calculated p_v ofa single bubble pulsing in free field is 5.8\times 10^4 Pa.(3) Bubble's second pulsing energy is merely 5\%\sim 15\% of the firstpulsing energy and the pulsing energy after the second pulse can be ignored.(4) \gamma , the dimensionless standoff is defined betweenbubble and boundary. When \gamma \ge 2.8, the influence of the wall tobubble can be neglected. When 1.95 \le \gamma \le 2.8, no jet is formedduring the first cycle of bubble pulse. When \gamma \le 1.53, jet is formedduring the first cycle of bubble pulse, and the smaller \gamma is, thelarger bubble migration distance and the more fiercely the jet would be.(5) The bubble jetting velocity is minimum when the dimensionless standoff\gamma is around 0.8.(6) Bubble will interact strongly with boundaries when it moves near theshipboard and the free surface. It can be seen from the experiments that thebubble may produce jets that are towards two different directions whencollapsing near the free surface and the shipboard, and this will certainlylead to the weakening effect of bubble attack to the shipboard.