近场水下爆炸气泡坍塌后期撕裂行为及其对结构的损伤机理研究

The destructive bubble jet has features of high directivity and high energy density, and the impact pressure is one of the most important loads during the final stage of bubble collapse in near-field underwater explosion. As suggested by many experimental studies, the bubble transforms into a toroidal bubble after the jet impact, and the toroidal bubble usually splits into two parts afterwards. However, the mechanisms of toroidal bubble splitting and the subsequent bubble loads are still not well understood. This project aims to establish a 3D numerical model to simulate toroidal bubble splitting using boundary integral method coupled with the vortex ring model. Then, the loads caused by the collapsing bubble can be obtained based on the auxiliary function method. On these bases, a fully coupled fluid-structure interaction model is established using elasticity and plasticity theory coupled with explicit finite element method. To validate the numerical model, experiments are intended to be carried out for a spark-generated bubble in a low-pressure tank. At last, the structural damages caused by the bubble pulsating pressure and the jet impact pressure are discussed systematically. The research results will provide theoretical reference and basic technical support for underwater explosion studies. Detailed research contents are as follows: 1) Modelling for toroidal bubble splitting and study on the pressure generated by a collapsing bubble; 2) Fully coupled fluid-structure interaction model for near-field underwater explosion bubble and the mechanisms of structural damage; 3) Experimental study on bubble splitting at the final collapse stage and the associated loads and the structural damages.

气泡射流载荷具有能量密度高、指向性强、破坏力大等特点，是近场水下爆炸气泡坍塌后期最重要的载荷形式之一。实验表明，射流砰击后常常会出现环状气泡撕裂行为，然而其背后的力学机理以及对气泡载荷的影响规律尚未揭示。鉴于此，本项目拟采用边界积分法和解析涡环理论，建立三维环状气泡撕裂动力学模型，实现气泡坍塌全过程的精细模拟，进而计算完整的气泡载荷。在此基础上，依据弹塑性动力学和瞬态流固耦合理论，建立计及材料弹塑性特征的气泡—结构“全耦合”计算方法，深入探索气泡脉动载荷与射流载荷对结构的损伤特性。最后，开展减压环境电火花气泡机理实验，验证数值模型的有效性，为舰船近场水下爆炸研究提供理论参考和基础性技术支撑。本项目的主要研究内容包括：1）环状气泡撕裂力学模型及气泡载荷特性研究；2）近场水下爆炸气泡—结构“全耦合”计算方法及结构损伤机理研究；3）气泡坍塌后期撕裂行为、载荷及结构损伤特性实验研究。

本课题以舰船水下爆炸抗冲击与水下武器毁伤效应为研究背景，重点研究大尺度水下爆炸气泡动力学行为及其与结构物非线性流固耦合特性，研究内容包括：（1）环状气泡撕裂力学模型及气泡载荷特性研究；（2）近场水下爆炸气泡-结构“全耦合”计算方法及结构损伤机理研究；（3）气泡坍塌后期撕裂行为、载荷及结构损伤特性实验研究。本项目首先提出了解析涡环理论，建立了环状气泡撕裂动力学模型，联合边界积分法实现了气泡坍塌全过程的精细模拟；其次，提出了气泡载荷分解的理论方法，将其分解为脉动载荷和射流载荷，并给出了这两种载荷的时空分布规律。在此基础上，依据固体力学和瞬态流固耦合理论，建立了超近边界气泡-结构强非线性瞬态“全耦合”计算方法（FCM），突破了距离参数对传统“松耦合”计算方法的限制，FCM相比LCM具有更高的计算精度和稳定性，发现在两种情况下LCM的计算精度会显著降低：（i）结构尺度小于最大气泡尺度；（ii）结构密度小于流体密度。本项目采用FCM深入系统的研究了不同边界条件下气泡与结构物的复杂耦合特性，得到了不同特征参数下气泡对结构物的攻击模式相图。在实验方面，本课题搭建了高重复性的电火花气泡和水下爆炸气泡实验台，开展了大量的气泡-结构耦合作用机理实验，发现了气泡对结构物的“弹射效应”、气泡环形射流及撕裂、气泡背离结构物迁移等许多新的物理现象，同时验证了数值模型的有效性，完善了本课题得到的相关结论。