波流作用下深水网箱流固耦合特性研究

Open sea aquaculture has been initiated due to overfishing and environmental concern at near-shore waters. As typical marine structures to grow fish, aquaculture cages deployed in open sea are often exposed to wind, wave and current. The harsh environment in open sea can affect the growth of marine organisms and the stability of structures. Thus, understanding the interaction of aquaculture cages and their surrounding fluids is becoming vitally important. In this project, interactions between open aquaculture cages and the severe oceanic environment will be investigated. Through analytical studies, numerical implementations and laboratory model tests, a list of hydrodynamic problems is demonstrated, which are, the analytical solution to three-dimensional hydroelastic responses of the floating collar exposed to waves; hydrodynamic performance and deformation of biofouling nets under non-uniform flow; the investigation on impact loads of a three-dimensional net induced by relative motion between the floating collar and sinkers; dynamic responses of and the flow field around aquaculture cage under waves and current with fish inside. Great achievements could be obtained with respect to three items, the horizontal hydroelastic response of the floating collar exposed to waves, three-dimensional impact loads acting on the net under waves combined with current, and the effect of fish locomotion on the dynamic response and flow field of the cage under joint waves and current. Which provide solid evidences to industrial design and engineering applications.

深水网箱是深水养殖的主要装备，其在风、浪、流联合作用下的安全性直接影响了整个深水养殖的成败。网箱结构形式完全不同于船舶、海洋平台等常见的海工结构物，必须对其水动力学特性进行有针对性的研究。本项目拟以深水网箱为对象，研究其在离岸深水区恶劣海况条件下的相关水动力问题。以数值模拟、模型试验和理论分析为研究手段，通过对浮架结构在波浪作用下的三维水弹性响应解析解的推导；非均匀流作用下有生物附着物网衣动态变形及水动力性能研究；浮架与沉子间相对运动引起的三维网衣冲击载荷研究；含鱼群网箱在波-流共同作用下整体动力响应及网箱周围流场研究，解决波浪诱导下浮架结构的水平方向水弹性响应；网衣在波流作用下承受三维冲击载荷；鱼群运动对网箱在波-流作用下整体动力响应及网箱周围流场影响三个关键科学问题，深化对波流联合作用下深水网箱水动力特性的研究，为深水抗风浪网箱工程设计提供科学依据。

深水网箱是深水养殖的主要装备，其在风、浪、流联合作用下的水动力响应直接影响了整个深水养殖的成败。本项目推导了波浪与浮圈系统垂荡运动之间的传递函数及浮圈垂荡运动响应谱，证实了不同波浪谱对浮圈垂荡运动的不同影响；扩展了计算浮圈上最可几最大归一化弯曲应力分布的圆频率值，修正了原有的计算方法；提出了沿界面施加流体的Dirichlet边界条件和结构的Neumann边界条件的一种柔性网衣的分区流固耦合计算方法；给出了首个生物附着网衣的数值模型，定义了生物附着程度的控制标准，得到了生物附着网衣的阻力和流场特性；建立了重力式网箱、半潜式深海养殖渔场的物理模型并进行了试验，获得了沿框架五个不同位置的稳态无量纲一阶和二阶谐波加速度及系泊张力，评估了自由表面效应，填补了极端海况产生的非线性因素对深水网箱影响的研究空白。