基于间断迦辽金法的近场水下爆炸载荷特性研究

With the accuracy and power rising of underwater weapons, warship structures have large probability to be damaged by near-field underwater explosion. In the near-field underwater explosion, there is the strongly coupling between shock wave,bubble and boundary. Structure will have large velocity in moment impacted by the shock wave and reflect the rarefaction wave to form cavitation.The existence of cavitation will change the characteristic impedance of medium near the structure and affect the load characteristics.And the bubble near discontinuous boundary formed by damaged structure will be broken and generate irregular jet.Thus the complex system with the coupling between gas,water and solid is formed bringing a serious of nonlinear problem including strong discontinuity,large deformation and so on. To solve these problem, the tranditional finite element method and boundary element method will meet great challenge.Therefore, based on the fluid-strcuture theory, the dynamics model of near-field underwater explosion is established and solved with discontinuous galerkin method combined with finite element method.With the model,nonlinear large deformation of bubble and influence of cavitation on the load characteristics is researched. And the interaction mechanism between shock wave, cavitation, bubble and various boundaries is explored.The main research contents of the project include: 1) three-dimensional near-field underwater explosion model based on discontinuous galerkin method; 2) the study on dynamics characteristics of bubble near discontinuous boundary; 3) the study on load law of near-field underwater explosion considering cavitation state characteristics; 4) experiment for influence of cavitation effect and bubble dynamics near discontinuous boundary.

随着水下兵器精准度及威力的提升，舰船结构遭受近场水下爆炸毁伤的概率增加。近场水下爆炸中存在冲击波、气泡与边界的强烈耦合。冲击波使结构瞬间拥有极大速度并反射稀疏波形成空穴，改变结构附近的介质特征阻抗比，影响载荷特性；而气泡在受损结构构成的不连续边界附近会发生破碎及不规则射流。由此形成气液固三相耦合的复杂系统，存在强间断、大变形等强非线性问题，传统有限元法、边界元法在求解该问题时均面临巨大挑战。为此，本项目基于流固耦合基本理论建立近场水下爆炸动力学模型，联合间断迦辽金法和有限元法进行求解，研究气泡非线性大变形及空穴对载荷特性的影响，探索冲击波、空穴、气泡与边界的相互作用机理。主要研究内容包括：1)基于间断迦辽金法的三维近场水下爆炸模型；2)不连续边界附近气泡动态特性研究；3)计入空穴物态特性影响的近场水下爆炸载荷规律研究；4)空穴效应及不连续边界附近气泡动态特性实验研究。

随着水下兵器精准度及威力的提升，舰船结构遭受近场水下爆炸毁伤的概率增加。近场水下爆炸中存在冲击波、气泡与边界的强烈耦合。冲击波使结构瞬间拥有极大速度并反射稀疏波形成空穴，改变结构附近的介质特征阻抗比，影响载荷特性；而气泡在受损结构构成的不连续边界附近会发生破碎及不规则射流。由此形成气液固三相耦合的复杂系统，存在强间断、大变形等强非线性问题，传统有限元法、边界元法在求解该问题时均面临巨大挑战。为此，本项目基于流固耦合基本理论建立近场水下爆炸动力学模型，联合间断迦辽金法和有限元法进行求解，研究气泡非线性大变形及空穴对载荷特性的影响，探索冲击波、空穴、气泡与边界的相互作用机理。主要的研究方法与成果如下。.首先，针对近场水下爆炸问题，基于非线性欧拉方程组，采用计及流场强可压缩性的高分辨率、高精度的近场水下爆炸RKDG数值计算模型。采用RKDG方法进行空间离散求解欧拉方程，捕捉流场中的强间断冲击波。同时，利用LSM捕捉运动界面，并将联合GFM解决强间断问题。基于上述理论和数值模拟结果，开展了近场水下爆炸模型和不连续边界附近气泡动态特性的研究。.其次，针对柱形装药近场水下爆炸冲击波载荷及其对弹塑性结构的冲击响应等瞬态流固耦合问题，本文基于高分辨率、高精度的RKDG数值方法，引入空化模型，建立RKDG水下近场爆炸模型，研究空化的产生以及溃灭过程。在此基础上，提出计及近边界空化效应的RKDG-FEM瞬态流固耦合数值计算方法，研究柱形装药近场水下冲击波载荷特性和冲击波在爆轰气体及自由液面或壁面边界间的传播规律及近边界处的空化载荷特性。.最后，针对强可压缩流场，以间断迦辽金法作为流场求解器,提出一种基于Level Set方法及Ghost Fluid方法且计入近边界空化效应的瞬态流固耦合数值计算方法，得到了考虑空穴效应及不连续边界附近气泡动态特性。.本项目为近场水下爆炸对舰船结构的毁伤机理研究提供理论参考和基础支持。

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