近场水下爆炸气泡脉动及水射流的实验与数值模拟研究

海上作战时，近场水下爆炸形成的水射流能造成水面舰船结构的严重局部毁伤。为了研究近场爆炸时舰船底部水射流的形成机理及规律，开展了TNT当量2.5 g的炸药在固支方板底部不同爆距下起爆的水下爆炸实验。结果表明，气泡坍塌形成水射流的过程随着爆距的增加由吸附式向非吸附式转化。接着，基于ABAQUS软件采用CEL方法开展了系列数值模拟，结果表明:爆距在0.821～0.867倍最大气泡半径时，存在吸附式射流向非吸附式射流转化的临界点；固支方板加快了气泡坍塌的进程，炸药与钢板间的距离越小则射流形成的时间越早；射流形成过程中最大速度和射流击中钢板时速度均随着爆距的增大先增大后减小，并在临界点附近达到最大值，射流速度最大可达621 m/s，射流击中钢板时速度最大可达269 m/s。最后，给出了射流开始形成时间、射流最大速度、射流最大速度出现时间、射流击中钢板速度和射流击中钢板时间与距离参数的函数关系式。

Experimental study and numerical simulation on bubble pulsation and water jet in near-field underwater explosion

In marine warfare, the water jets formed by near-field underwater explosions can cause serious local damage to ship structures. With more knowledge on near-field underwater explosions, the phenomenon of water jet has become a hot research topic in recent years. To study the formation mechanism of water jet during near-field explosion under the bottom of a ship, an underwater explosion experiment was carried out, in which 2.5 g of TNT was detonated under the bottom of a clamped square plate at different explosion distances. A high-speed camera was used to record the evolution of the bubble jet. At the same time, a free-field underwater pressure sensor was used to measure the pressure field in the water tank. The experimental results show that with the increase of the burst distance, the process of bubbles evolving to form jets at the bottom of the square plate can be divided into two types; that is, the adsorption type and non-adsorption type. Then, by employing ABAQUS software andusing the CEL method, a series of numerical simulations were carried out for the experiment. The numerical simulation results show that the critical point for the conversion from the adsorption jet to the non-adsorption jet is between 0.821 times the maximum bubble radius and 0.867 times the maximum bubble radius. Because the upper part of the bubble is difficult to expand freely under the barrier of the steel plate, the corresponding burst distance when the bubble is adsorbed is smaller than the maximum bubble radius. By analyzing the velocity cloud diagram at the jet being formed, it is found that with the increase of the burst distance, because the clamped square plate accelerates the process of bubble collapse, the time of jet formation is advanced. The maximum velocity during the formation process of water jet and the velocity when water jet hits the steel plate both increase first and then decrease with the increase of the burst distance, reaching the maximum near the critical point. The maximum jet velocity can reach 621 m/s, the maximum jet velocity when jet hits the steel plate can reach 269 m/s. Because the larger the burst distance, the later the bubble collapses, and the more concentrated the energy in the bubble, which makes the jet velocity larger, but when the burst distance is too large, the Bjerknes effect of the steel plate on the bubble will be weakened, which will reduce the jet velocity. Consequently, a critical point of the burst distance exists, at which the jet velocity renders a maximum.