近场水下爆炸气泡与不完整边界的耦合效应研究

Underwater explosion of torpedo, mine and other underwater weapons will produce two major loads, namely shockwave and bubble, which will do great damage to warship structures, especially for near-field underwater explosion, it is of great significance to study the secondary damage after attacked. The initial crevasse will be produced under the impact of shockwave, i.e., the incomplete boundary is formed, and then a strong coupled effect will be taken between the bubble and the incomplete boundary, which will causes the secondary damage to structures. Due to the presence of strong nonlinear problems of discontinuity, large deformation, multiphase mixing, very close to boundary and so on, there are many challenges in solving these problems with a sole method,such as Finite Element Method (FEM), Boundary Element Method(BEM), Smothed Particle Hydrodynamics(SPH),etc. However,it is a good choice to take advantages of the above three methods to solve this difficult problem. Therefore, on the background of near-field underwater explosion, considering the shock damage of prophase, based on the first and second laws of thermodynamics, the compressible fluid dynamics theory and the fluid-structure interaction theory, etc., the coupled dynamics model of near-field underwater explosion bubble and incomplete boundary is established to be solved by the combination of SPH method, BEM method and FEM method. The stages of bubble formation and jet are simulated with SPH method, yet the pulsation stage with BEM method; the structural shock responses are resolved with SPH shell and FEM method. In addition, the model experiments are also conducted with the silent discharge equipment to verify the accuracy and effectiveness of the above method, meanwhile, the dynamic characteristics of bubble in decompression and normal pressure condition are also compared. On basis of these, the interaction mechanism of bubble and incomplete boundary will be investigated to provide a theroetical reference and technical support for the relevant researches on near-field underwater explosion of warship. The main research contents are as follows: 1) the underwater explosion bubble dynamics model in three dimensional compressible flow-field considering the effects of initial conditions; 2) the influences of "cavity suction phenomenon" of incomplete boundary on bubble jet; 3) the coupled effects between bubble and incomplete boundary considering structural elastoplasticity; 4) the model experiments of bubble near incomplete boundary in decompression condition.

鱼雷、水雷等武器近场水下爆炸对舰船结构造成严重毁伤，冲击波首先对舰船结构造成初始破口，形成不完整边界，接着水下爆炸气泡与具有初始破口的不完整边界产生强烈的耦合效应，对结构造成二次毁伤，由于此时存在超近边界、不连续、大变形等诸多强非线性问题，传统单一的有限元、边界元等方法在求解该问题时均存在着巨大的挑战。为此，本项目拟基于热力学第一、二定律、可压缩流体动力学理论以及流固耦合理论，建立近场水下爆炸气泡与不完整边界的耦合动力学模型，采用SPH方法与边界元方法、有限元方法联合求解该模型，并采用模型实验验证求解方法的正确性，在此基础上，探索气泡与不完整边界的相互作用机理。本项目的主要研究内容包括：1)计入初始条件影响的可压缩流场中气泡三维动力学模型；2)不完整边界的"腔吸现象"对气泡射流的影响规律；3)计入结构弹塑性特征的气泡与不完整边界的耦合效应；4)减压条件下不完整边界附近气泡运动模型实验研究。

水下爆炸包括两大部分载荷，冲击波和气泡，近场水下爆炸冲击波首先对舰船结构造成严重的局部损伤，使得结构产生初始破口，形成不完整边界。接下来水下爆炸形成高温高压的大尺度气泡，其与不完整边界产生强烈的耦合效应。在不完整边界条件下，气泡产生非对称射流、“腔吸”等现象，气泡的非线性运动产生的脉动和射流载荷对已破损的舰船结构造成二次损伤，严重威胁舰船的生命力。其中涉及近边界气泡运动、瞬态流固耦合等强非线性基础力学难题，前期研究人员已经进行了较多的研究，取得了较好的研究进展，但是由于问题的复杂性，仍有许多本质的基础力学问题有待深入研究。本项目按照计划任务书的研究内容和目标要求，依据流体动力学理论和流固耦合动力学理论，建立气泡与不完整边界的耦合模型与计算方法，并结合机理性实验，研究了不完整边界条件下气泡的运动与载荷特性，揭示了气泡与不完整边界的相互作用机理。主要完成的研究内容如下：.（1）依据流体动力学理论，建立了水下爆炸气泡与不完整边界耦合的三维动力学数值模型，并开发了相应的计算方法，并采用理论和实验值验证了计算方法的有效性。.（2）开展了不完整边界附近气泡运动与载荷特性的模型实验研究，研究了水下爆炸气泡与不完整边界耦合效应，得到了气泡的运动与载荷特性。.（3）研究了气泡与自由液面附近不完整边界的相互作用，探索了不完整边界对气泡运动的影响规律，揭示了不完整边界附近气泡的射流和“腔吸”现象的机理。.（4）研究了水下爆炸气泡后期载荷与破损船舶的流固耦合机制，给出了水下爆炸后期载荷对已破损船舶的作用规律。.（5）形成了水下气泡无声放电实验装置，开发了水下爆炸气泡与不完整边界相互作用计算软件。.在该国家自然科学基金的资助下，在《Physics of Fluids》、《Ocean Engineering》等期刊发表学术论文20篇，其中SCI检索19篇，EI检索19篇，高被引文章2篇，获得国防科学技术进步一等奖1项。

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