Abstract:At present, China's leading offshore aquaculture cages are enormous high-density polyethylene gravity deep water cages, generally composed of floating frame systems, netting systems, counterweight systems, and mooring systems. The cage culture space is formed by the counterweight system and the netting system, therefore, it will be significantly reduced when the environmental load is large, which will affect the expected growth of the fish, even causing extrusion and other problems. This makes the cage generally choose to be installed in the coastal areas with a slight wind and wave environmental loads, such as ports and coasts, and adopt the intensive development model. In the past 20 years, this industry has provided many high-quality animal proteins to the Chinese people, alleviated the pressure of food supply to some extent, and has indispensable importance for China's marine fisheries and economic development. However, with the rapid development of science, technology, and the economy in China in recent years, the cage industry has gradually improved. The cost of cage manufacturing has decreased annually, and an increasing number of anglers have joined. Due to the lack of space and unreasonable layout of offshore aquaculture, environmental deterioration and frequent diseases are becoming increasingly severe, greatly influencing the quality and safety of aquatic products. To obtain a vast water space and high-quality environmental conditions, developing a method to explore deep-sea aquaculture vigorously is essential. Traditional gravity cages are difficult to adapt to the harsh environment of the deep sea and cannot be placed offshore for aquaculture. As one of the critical aquaculture equipment for the development of deep-sea fishery, the deep-sea cage has integrated aquaculture management with a larger main structure. Its large-scale and intelligent characteristics can significantly reduce the cost of aquaculture and improve the interests of anglers in aquaculture. However, it should be noted that the environment faced by cages operating in the deep sea is more complex and harsher than offshore cages. In particular, the East China Sea and the South China Sea are in typhoon-prone areas. They often encounter strong wind jets, causing irreversible damage to the cages. Therefore, for this new type of large-scale intelligent aquaculture equipment, we need to understand its hydrodynamic parameters in the marine environment to provide primary theoretical guidance data for the construction, site selection, and operation of the cage and ensure the safe operation and stable output of the cage. The research object of this study is development of a new type of anti-wind wave cage with a single-point mooring system. The main body of the cage is a hybrid structure consisting of a ship truss and a floating body. The overall floating and diving off the mainframe of the cage are realized through the front and rear floating ballast water to meet the operational requirements of the aquaculture process. The single-point mooring system can adapt the cage to adjust its position during typhoons and big waves and significantly reduce the impact of wind and waves on the cage. It has the characteristics of high safety and structural stability. The research was mainly conducted through physical model tests with a model scale of 1:40. The cage's hydrodynamic characteristics (including mooring force, heave, pitch, and roll) under the wave and current were analyzed and compared. The purpose was to determine the dynamic response characteristics of the cage under the action of waves and currents and the wave resistance after diving. The cage is in a floating state during regular operation and only adjusts to a diving state when encountering strong waves and current. Therefore, three groups of tests were conducted: 1. Dynamic response characteristics of cages in floating state (7.5~12.5 cm) under general wave conditions. 2. The cage's performance in the high wave (15.0 and 17.5 cm) after diving. 3. Effect of current on the wave resistance performance of the cage under the combined action of waves and currents. The results show that under the condition of 7.5~12.5 cm wave height, the floating cage's mooring force and motion response are small, proving that it has good safety and stability and can meet aquaculture requirements under these conditions. Under severe conditions, that is, under a wave height of 15.0 and 17.5 cm in this experiment, the cage showed good wave resistance by increasing draught, in which the mooring force was reduced by more than 70%, and the motion components such as heave, pitch, and roll were also reduced by 20%~60%. In the wave combined with the current test, the current has a particular influence on the wave resistance of the cage. However, generally, it still has good wave resistance. In this study, the dynamic response characteristics of cages under wave currents were understood. The research results can provide a theoretical basis and data reference for the safe operation and daily management of single-point mooring diving cages and help the innovation of deep-sea aquaculture equipment in China to promote the development of marine fisheries.
