含气泡卷入的破碎波砰击浮体耦合动力特性研究

When a breaking wave hits a floating body, an air bubble will be trapped. The large fluid load, generated by the impact from the breaking wave and air bubble, would pose a great threat to the safety of floating bodies. Previous work was mainly focused on the exclusive study about the impact pressure features or air bubble effect, while rare attention was paid to the mutual dependence of fluid loading, the body motion and bubble deformation. In such a case, the following four aspects of work will be undertaken. First, the problem of the breaking wave impacting on a floating body with air bubble effect is modelled based on the incompressible velocity potential theory, to investigate the coupled process of the wave, floating body and air bubble. Second, based on the previous numerical work, a linear dynamic equation for an elastic plate is provided, and the effect of hydroelasticity is studied. Third, a local compressible numerical procedure is proposed to study the effect of compressibility, to be in detail, the compressibility theory is used to the impact zone while incompressible theory is applied to the other zone, and two zones will be combined through a coupled procedure. Finally, the experiment of a breaking wave impacting on floating bodies is carried out in a water tank to test the validity of numerical procedure, and the spatial and temporal distribution characteristics and impact factors for the fluid loading in the process of breaking wave impact will be discussed.

破碎波砰击浮体时，一部分空气会被卷入到波浪中，以气泡形式与破碎波一起冲击物面，产生的巨大流体载荷，将对海洋浮体的安全造成极大的威胁。过去研究多集中在冲击压力特性和气泡效应的独立研究，对浮体运动、流体载荷和气泡效应的耦合作用研究得十分匮乏。为此，本项目拟开展四个方面的研究，首先基于不可压缩势流理论，建立考虑气泡效应的破碎波砰击刚性浮体模型，研究破碎波、浮体与气泡的耦合作用；第二，在破碎波、浮体和气泡相互作用数值计算结果基础上，建立弹性平板动力学方程，研究水弹性对砰击过程的影响；第三，建立局部不可压缩势流理论模型，即在砰击区域建立可压缩模型，在非砰击区域采用不可压缩模型，然后将两者耦合，研究流体可压缩性对波峰砰击的影响。最后，在波浪水槽中进行破碎波砰击浮体实验，将实验与数值结果对比分析，验证数值计算程序的有效性，旨在揭示破碎波冲击浮体过程中流体载荷的时空分布特征和影响因素。

破碎波在涌向浮体时，波峰发生翻卷，一部分空气被卷入到流体中，以气泡形式与波浪一起冲击物面。从波峰顶端触碰物面开始，流场内将经历极其复杂的力学变化过程。翻卷波峰的强烈砰击、卷入气泡的膨胀和收缩、气液掺混、结构弹性变形等物理现象，将极大地影响和改变浮体的水动力性能。为此，本项目以破碎波砰击刚性浮体和柔性浮体为研究对象，采用数值模拟和模型试验研究手段，综合考虑可压缩性、弹性效应、气泡效应，研究含气泡卷入的破碎波砰击浮体过程。.本课题首先采用基于势流理论的拉普拉斯方程建立翻卷波峰砰击刚性浮体模块，采用双重坐标系技术处理波峰砰击时初始湿面积极小所带来的数值困难，研究发现在砰击早期阶段，砰击区域湿面积极小，砰击压力极大，气泡脉动对砰击力有着非常显著的影响。然后，基于波动方程和弹性平板动力学方程建立考虑可压缩性的柔性浮体数值计算模块，研究发现在砰击早期，平板中心的变形最大，随着时间的增加，变形逐步向四周传递。最后进行翻卷波浪作用于浮体的模型试验，实验数据与数值计算结果吻合良好，验证了数值模型的有效性。.本项目通过数值模型和模型试验研究手段，研究了破碎波与浮式结构物相互作用时复杂流场内的力学变化过程，为极端波浪下海洋结构物砰击载荷预报和极限强度评估提供理论基础和数值工具。