![]() ![]() So, the pressure loading, generated by a near-field underwater explosion, on the surface consists of a shock wave loading and a series of continuous bubble-jet loadings. Here, the pressure loading due to the jet and the bubble collapse is called as bubble-jet loading (B-J loading). Then, the bubble will rebound its second cycle. As the bubble continuously shrinks, it will reach its minimum volume, releasing a high-pressure wave. This water jet will traverse the whole bubble at a very high velocity and impact on the surface of the structure, acting another pressure loading on the surface. In the case that the charge is detonated near the surface of a structure, a high-speed water jet will develop with the help of the Bjerknes effect, the inertia and the influence of gravity. Then, the bubble stops expanding and begins to collapse. The overexpansion leads to the pressure inside the bubble to become lower than that of the surrounding water. Due to the inertia, the bubble will continuously expand when the pressure inside the bubble is equal to that of the surrounding water. With the expansion of the bubble, the pressure inside the bubble decreases and the pressure of the surrounding water increases. As a result, the bubble will expand fast. The pressure inside the gas bubble is much higher than that of the surrounding water after the detonation. Here, the pressure loading due to the shock wave is called as shock wave loading (SWL). When the shock wave gets at a structure, a high-pressure loading will act at the surface of the structure. The shock wave propagates in the water at a very high speed. Immediately after the explosive charge is detonated, a strong shock wave will appear, and massive product gas is released, forming a high-pressure gas bubble in the water. Underwater explosion is an extremely complex procedure. Also, the accurate pressure loading information is of great help to some other interesting problems, such as the ice breaking. The accurate assessment of the wall pressure loading generated by the near-field underwater explosion is an extremely important basis to design ship structures of high quality and save lives in conflicts or sea wars. The loading generated by the near-field underwater explosion acting on the hull is extremely high and can cause serious damage to the structure of the ship and great casualties. With the development and improvement of the underwater guidance technology, the probability of ships subjected to the near-field underwater explosion rises rapidly, which contributes to much more attention received in the quantification of the wall pressure loading and structure protection subjected to the near-field underwater explosion. Especially, the peak pressure of the shock wave is captured. Part of the pressure loading of the experiment at stand-off distance is recorded, which is still of great help and significance for engineers. From the recorded pressure-time profiles coupled with the underwater explosion evolution images captured by the HSV camera, the shock wave pressure loading and bubble-jet pressure loadings are captured in detail at, ,, stand-off distances. ![]() To verify the capability of this improved methodology and experimental system, a series of minicharge underwater explosion experiments are conducted. Based on the assumption that the shock wave pressure profiles at the two points on the two plates which are symmetrical to each other about the middle plane of symmetry are the same, it was found that the pressure obtained by the HPB was in excellent agreement with pressure transducer measurements, thus validating the proposed technique. To validate the pressure measurement technique based on the HPB, an underwater explosion between two parallelly mounted circular target plates is used as the validating system. The second one is a hard rubber cylinder placed at the distal end, and a pair of ropes taped on the HPB is used to pull the HPB against the cylinder hard to ensure the HPB’s end face flushes with loaded face of the target plate during the bubble collapse. The first one is some waterproof units added to make it suitable for the underwater environment. Furthermore, two improvements have been made on this methodology to measure the wall pressure loading from a near-field underwater explosion. ![]() In the methodology, a Hopkinson bar (HPB), used as the sensing element, is inserted through the hole drilled on the target plate and the bar’s end face lies flush with the loaded face of the target plate to detect and record the pressure loading. In this article, an improved methodology and a lab-scale experimental system are proposed and manufactured to assess the wall pressure loading. ![]() Direct measurement of the wall pressure loading subjected to the near-field underwater explosion is of great difficulty. ![]()
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