升降式贝类筏架养殖系统流固耦合机理研究

Bivalve aquaculture conducted under localised conditions is generaly considered to have minimal negative environmetal impact. Marine raft culture is one of the main methods to bivalve aquaculture in China. Commercial suspended mussel culture is commonly conducted by growing mussels attached to ropes hung from rafts or long-lines. In confined areas such as bays and river estuaries, growing mussels on densely packed ropes suspended from rafts reduce interference with other marine users, reduce lease costs based on area fees, and provide convenient platforms for farming operations. At present, the narrow bay and near shore are the main concentration of the large-scale and intensive bivalve aquaculture. The inshore cultivation faces doubling restriction by resource and environment. One big problem is the carry capacity of coastal waters. With inshore development reaching saturation in terms of space, aesthetics and ecological carrying capacity, future expansion will be offshore. Considered that aquaculture production in a coastal bay, to develop offshore aquaculture and deep-sea aquaculture equipment technology are the strategic demand and future direction of the shellfish aquaculture development in China. There are advantages, however, in using this concept in more open exposed locations. Low suspended sediment, high plankton content water in open bays has been found to promote faster mussel growth and a higher meat-to-shell ration. Open water sites, however, subject rafts to extreme wave environment. .For the small inshore farms this influence is likely to be small compared to natural variability. However, the effect of large distributed structures like that of typical proposed offshore submersible raft farm may be significant. Mussel raft aquaculture structures cause flow disturbances over scales ranging individual structures to coastal systems. The complex nature of flow around rafts including eddying behind the structure and combined tide/wind effects should be identified. Studies focus on FSI (Fluid-structure interaction) in submersible raft structures. FSI is a multifiaceted physics problem occurring in a system where flow of a fluid causes deformation of a solid structure which, in turn, changes the boundary condition of the fluid problem. This research project is conducted at the non-linear dynamics of the submersible raft system for exposed marine environment and has some work in the refereed literature describing the influence of submersible raft farms on hydrodynamics. The numerical model of the submersible raft is established based on the finite element method and kinematics theory. Numerical simulations and model tank tests are carried out to study the hydrodynamic characteristics of the raft system, the mooring line tension, and the vibration characteristics of the raft platform in waves and currents. The influence of the different structure parameters such as, the diameter and length of the pontoons, the density of the suspended ropes, and submersible depth on the hydrodynamics and security of the submersible raft system are studied. The hydrodynamic characteristics of the different combinations of the rafts are also analyzed. This research not only enriches the hydrodynamic theory of the submersible raft system in deep sea, but also provides the theoretical guidance and valuable reference for improving the wave resistance and security of the submersible raft system.

海上筏式养殖是我国海水贝类养殖的主要方式之一，目前我国大规模贝类筏式养殖主要集中在海湾和近岸的狭窄区域，近海养殖面临的一个很大的问题是空间上的竞争。因此开拓离岸深远海养殖空间，发展大型基站式深远海贝类养殖装备技术，是我国贝类海水养殖发展的战略需求和未来走向。因此，本项目以升降式筏架养殖系统为研究对象，对筏架结构的流固耦合振动特性以及在水流、波浪等荷载作用下的水动力特性进行研究。基于有限元方法建立数学模型，通过水槽模型实验和数值模拟，研究升降式贝类筏架养殖系统在波流共同作用下的运动响应、锚绳力及筏架平台的振动特性。研究不同结构参数（如养殖绳密度、筏架平台浮管直径及长度、平台下潜深度等）和布设方式对升降式筏架养殖系统的水动力学特性和设施安全性的影响。深入开展水中柔性结构流固耦合振动特性以及在水流、波浪等荷载作用下的力学行为的研究，对提高水中柔性结构的安全运营具有十分重要的理论和现实意义。

海水养殖是人类主动、定向利用国土海域资源的重要途径，已经成为对食物安全、国民经济和贸易平衡作出重要贡献的产业。世界主要沿海发达国家高度重视海洋经济发展，把海洋开发作为国家战略加以实施。但随着经济社会的快速发展，近岸海域提供给海水养殖的空间受到严重挤压，导致海水养殖密度过大、环境恶化、病害频发等问题日益突出，传统养殖方式的弊端逐步凸显，而设施养殖相对于传统养殖具有生产力的先进性。海上筏式养殖作为我国海水贝类养殖的主要方式之一，由近海推向深远海，深远海养殖装备研发尚处在起步阶段，构建适宜深远海养殖的设施结构，需要考虑设施系统的适宜性、安全性和经济性等多个因素。本项目对升降式筏式养殖结构在波流联合作用下的水动力特性、筏架结构在极端海洋环境下的结构动力响应、不同结构参数（养殖绳索、下潜深度等）对筏式养殖系统的运动响应的影响展开了相关研究。（1）通过水槽实验研究筏式养殖结构在不同养殖绳索密度、下潜深度时结构运动响应和养殖网笼对水流的阻流效应；（2）基于有限单元法和Morison水动力模型建立筏式养殖系统水动力特性的数值模型，并基于势流理论研究筏架养殖结构的稳定性和安全性。研究结果表明下潜式筏式养殖系统能够减小养殖绳索和养殖网网笼的垂向运动，从而能够减弱海浪对结构的运动响应的影响。随着波流入射角的增加，锚绳张力逐渐增加。当波流入射角为90度时，锚绳张力达到最大值。浮筒中心距对结构的固有频率存在影响，随着距离的增加，纵摇和锚绳张力减小。因此若要提高结构的稳定性，需要适当降低浮筒间距。在极端波况下，浮筒间距的改变对结构的稳定性有着显著的影响。因此，基于本研究的试验结果能够对深远海筏式养殖设施系统的结构优化提供科学依据及参数指导。