自由落体入水的非定常水动力载荷研究

Water entry of objects is an important phenomenon in ship and ocean engineering, for instance water entry of freefall lifeboats, water entry of air-to-sea projectiles and impact between ship bow and water surface. During the water entry of a freefall object, impulse loads can be formed on the impact side of the object causing a rapid change of acceleration of the object and a large acceleration, which can damage the object and/or injure occupants. After water flow is separated from the body surface, an open cavity is formed on the top of the object. Before the closure of the cavity, the cavity significantly influences the evolution of the transient hydrodynamic loads acting on the object. After the closure of the cavity, the compressibility of air plays an importance role causing the oscillation of the water-body-cavity system. Good understanding and accurate models of such phenomenon are therefore important for the effective design of air-to-sea projectiles. In the proposed research project, new experimental, numerical and theoretical methods are to be developed for investigating the water entry of freefall cones. The research work will focus on the evolution of transient hydrodynamic loads, formation of the cavity and oscillation of the water-body-cavity system, and influence of governing parameters such as the mass of the object, initial entry speed, geometry of the object and Euler number on the evolution of the transient hydrodynamic loads and cavity.

物体入水是船舶与海洋工程中重要的物理现象，如自由坠落救生艇的入水，空对海武器的入水，船首与水面的抨击等。针对目前自由落体入水过程水动力影响机制不明的问题(如流动分离后非定常水动力的变化规律和气泡闭合后物-水-气泡系统的振动规律),本项目拟采用模型实验，数值方法和理论分析三个途径研究圆锥垂直自由入水的水动力特性。发展新的实验方法对入水物体的运动和载荷(位移，加速度和气泡压强)进行高保真的测量，考察物体质量、初始入水速度和几何形状对入水过程中水动力载荷和伴生气泡形成的影响；结合数值模拟分析无因次参数如欧拉数等对气泡闭合过程和闭合后振动过程的影响。建立完善的自由落体物体入水的理论模型，揭示气泡闭合前水动力载荷的变化规律和气泡闭合后物-水-气泡系统的振动规律，为船舶海洋工程装备的研发提供理论依据。

物体入水是船舶与海洋工程中重要的物理现象，如自由坠落救生艇的入水，空对海武器的入水，船首与水面的抨击等。本项目采用了模型实验，数值方法和理论分析三个途径研究物体垂直自由入水的水动力特性。发展了新的实验方法对入水物体的运动和载荷(位移，加速度和气泡压强)进行高保真的测量，考察物体质量、初始入水速度和几何形状对入水过程中水动力载荷和伴生气泡形成的影响。建立了自由落体物体入水的理论模型和数值模型，阐明了带气泡物体垂直入水的非定常水动力载荷的演化机理，透切分析了这个大约一个世纪以来物理学家都没能完全理解的重要物理现象。初步揭示了气泡闭合后物-水-气泡系统的振动规律。