Theoretical study of bubble pulsation characteristics in underwater contact explosions
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摘要: 为揭示水下接触爆炸气泡脉动特性的变化规律,弥补现有理论对接触爆炸工况研究的不足,基于不可压缩无粘流体假设,建立了刚性壁面接触爆炸的半球形气泡动力学模型,推导了气泡最大半径、初始半径以及脉动周期与自由场参数的定量关系。理论分析表明,接触爆炸气泡最大半径、初始半径及脉动周期为自由场工况的1.26倍(理论比例系数)。通过LS-DYNA软件对0.300、0.233和5.000 g TNT装药在不同水深条件下的水下爆炸进行数值模拟,结果表明接触爆炸气泡最大半径和脉动周期的模拟值分别为自由场气泡的1.22~1.24倍和1.20~1.21倍,与理论预测误差小于5%。进一步通过水箱实验验证,接触爆炸气泡最大半径与周期分别为自由场的1.10倍和1.06倍,实际工况因流体可压缩性、气泡不稳定变形等因素影响,实际比例系数略低于理论比例系数。Abstract: Contact explosion is an important condition in the damage and protection of underwater structures, and the pulsating bubbles generated by explosive underwater explosion are an important damage source. The current research on underwater explosion bubbles mainly focuses on the pulsating characteristics of spherical bubbles under free-field and typical boundary conditions, while there is a notable lack of research on non-spherical bubbles under contact explosion conditions. The pulsation characteristics of underwater contact explosion bubbles were systematically investigated through theoretical modeling, numerical simulations, and experiments. To address the theoretical gap in contact explosion dynamics, a hemispherical bubble dynamics model under rigid wall contact conditions was established based on incompressible and inviscid fluid assumptions. By comparing present model with the spherical bubble pulsation model in an incompressible flow field, quantitative relationships between parameters such as the maximum bubble radius, initial radius, pulsation period were obtained. Theoretical analysis reveals that the maximum radius, initial radius, and pulsation period of contact explosion bubbles are 1.26 (theoretical scaling factor) times those of free-field conditions. An error analysis was conducted to account for factors such as fluid compressibility, unstable bubble deformation, and energy dissipation induced by bubble-rigid wall interactions. Numerical simulations using LS-DYNA for underwater explosions with 0.3 g, 0.233 g, and 5 g TNT charges under varying water depths reveal that the scaling factors for maximum radius and pulsation period under contact explosion conditions range from 1.22 to 1.24 and 1.20 to 1.21 times those of free-field results, respectively, with simulation errors below 5% compared to theoretical predictions. Experimental validation in a water tank shows that the maximum radius and period of contact explosion bubbles are 1.10 and 1.06 times those of free-field conditions. During the experiments, plate vibrations were observed upon explosion, which significantly contributed to experimental errors. This work addresses the theoretical gap in contact explosion bubble dynamics, enhances the understanding of boundary effects in underwater explosion phenomena.
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表 1 不同边界条件下工况下气泡脉动特性关系
Table 1. Relationship of bubble pulsation characteristics under two different boundary conditions
特性 关系 气泡最大半径 Rh,m = 21/3Rm 气泡初始半径 Rh,0 = 21/3R0 第1次脉动周期 Th = 21/3T 表 2 不同边界条件下气泡脉动特性实际关系
Table 2. The actual relationship of bubble pulsation characteristics under two different boundary conditions
脉动特性 实际关系 气泡最大半径 Rh,m < 21/3Rm 气泡初始半径 Rh,0 < 21/3R0 第1次脉动周期 Th < 21/3T 表 3 不同边界条件下气泡脉动特性模拟结果与理论结果的对比
Table 3. Comparison of simulation and theoretical results of bubble pulsation characteristics under two different boundary conditions
工况 最大半径/cm 周期/ms 自由场 接触爆炸 自由场 接触爆炸 1 10.3 12.6 4.3 5.3 2 12.6 21.0 2.5 3.0 3 6.5 7.9 12.9 15.5 表 4 接触爆炸与自由场爆炸中相同气泡脉动特性之间的比例系数
Table 4. Scaling factors for bubble pulsation characteristics between contact and free-field explosions
工况 最大半径比例系数 周期比例系数 理论 数值模拟 相对误差/% 理论 数值模拟 相对误差/% 1 1.26 1.22 −3.2 1.26 1.20 −4.7 2 1.26 1.24 −1.6 1.26 1.21 −4.0 3 1.26 1.22 −3.2 1.26 1.20 −4.7 表 5 气泡脉动特性试验结果
Table 5. Experimental results of bubble pulsation characteristics
实验 边界条件 气泡最大半径/cm 脉动周期/ms 1 自由场 9.58 15.9 2 自由场 9.94 15.9 3 自由场 9.24 16.1 平均值 9.59 15.97 4 接触爆炸 10.58 17.0 5 接触爆炸 10.54 16.9 6 接触爆炸 10.67 17.0 平均值 10.60 16.97 -
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