Research on bubble jet of underwater explosion at the bottom of fixed square plate

Abstract

<p indent=0mm>The water jet formed after the collapse of the bubble in the near-field underwater explosion can cause serious damage to the local structure of the ship, and the formation of the jet is asymmetric, which makes it difficult to measure its data in the experiment. At present, studies on the pressure time history curves of the bubble jet in the underwater explosion are still relatively rare. In order to study the characteristics of the jet, the underwater explosion test of <sc>2.5 g</sc> TNT explosive at the bottom of fixed square plate at different detonation distances was carried out. First, the accuracy of the test data was verified by the underwater pressure sensor. Second, the image of the whole process from the explosive initiation to the bubble jet generated by the action of the bubble and the steel plate was obtained by high-speed camera. Finally, the time-history curve of water jet pressure was measured by the wall pressure sensor in the center of the steel plate, and another group of wall pressure sensors was set <sc>15 cm</sc> away from the center of the steel plate as a control group to ensure that the measured jet data were not clutter. The test data recorded by the underwater sensor show that the error between the shock wave overpressure, the maximum bubble radius of the bubble pulse period and the empirical formula is within 10%. The results recorded by the high-speed camera and wall pressure sensor show that three jets can be observed when the burst distance is <sc>28 cm,</sc> but the pressure time history curve is not measured due to the long burst distance. When the burst distances are <sc>15,</sc><sc> 17.5</sc> and <sc>20 cm,</sc> three jet pressure time history curves are measured. However, due to the short burst distance and the presence of a large number of bubbles between the steel plate and the water surface under the action of the shock wave, it is difficult to observe the test phenomenon with high-speed cameras. The pressure time history curve shows that three jets are generated after the first bubble pulse peak, and the jet pressure can reach 1/4 of the shock wave. The jet appears 1–3 ms after the first bubble pulse peak, and the time interval of each jet is between <sc>0.9</sc> and <sc>2.4 ms.</sc> The duration of jet load is between 4–27 μs, and it is greatly reduced as the distance increases.