Vessel-shaped fish cages are a new type of large aquaculture structure consisting of a floating body, steel frames, net system, and mooring system. The diffraction and radiation waves induced by the floating body can disturb the velocity field and induce additional changes to the hydrodynamic loads on the nets. In this paper, the velocity transfer functions around the nets induced by the diffraction and radiation waves are obtained and the effects of floating body on the forces of the nets are calculated by the Morison equation. By performing the iterations between the motion of floating body and loads on the nets, the fully coupled dynamic response of motion-disturbing velocity field-net loads is realized. Finally, the effects of diffraction and radiation waves on motion response, tension in the net twine, volume reduction, and connector loads are investigated. The results show that the influences of disturbing velocity field on cage motion response and volume reduction are not obvious, but they can lead to a significant increase in the tension in net twine and connector loads, which can provide helpful reference for the structural strength analysis and safety design of vessel-shaped fish cages.
Keywords：vessel-shaped fish cage;
diffraction and radiation waves;
cage motion;
tension in net twine;
volume reduction;
connector load
WANG Yihou, FU Shixiao, XU Yuwang, LI Shuai, FU Qiang, LIU Fuxiang. Dynamic Response of a Vessel-Shaped Fish Cage Considering Coupling Effect Among Body Motion, Disturbed Velocity Field, and Net Loads[J]. Journal of Shanghai Jiaotong University, 2024, 58(2): 147-155 doi:10.16183/j.cnki.jsjtu.2022.404
The operation of a deep-sea cage in the open sea is affected by extreme and severe sea conditions. An effective and reliable mooring system is the key to ensuring the excellent seakeeping of the cage and good aquaculture benefits. In this paper, the hydrodynamic numerical model of a single point mooring ship-type truss cage was established. And then the model was verified by comparison between numerical calculation results and physical experiment results. On this basis, two mooring types, "—" and "Y", were presented and their characteristics were compared by analyzing the dynamic response of the cage, mooring tension of the anchor chain, and minimum lying length of the chain under multiple wave conditions. After that, the mooring influencing parametric analysis was implemented from two aspects: anchor chain length and weight of clump weight. The results show that the "Y" mooring system is better than the "—" mooring system and different anchor chain lengths and clump weights have little effect on the motion response of the cage, but the increase of anchor chain length and weight of clump weight can effectively reduce the peak mooring tension and extend the length of lying chain. This research can provide the basis for the mooring analysis and optimization design of truss cages.<br>
WANGY, FUS, XUY, et al.
Loads on a vessel-shaped fish cage steel structures, nets and connectors considering the effects of diffraction and radiation waves
Deep sea aquaculture is an important way to expand new space for aquaculture development, and reduce the pressure on offshore ecological environment. It is of great significance to improve the quality and efficiency of aquaculture, to modernize fisheries, to ensure world food security and to sustainable development of aquaculture. However, the equipment and technology of deep sea aquaculture are the key to support and realize the development and growth of deep sea aquaculture. This paper briefly introduces the research and application status of deep sea aquaculture vessels and deep sea aquaculture cages, and points out that there is still a big gap between China's deep-sea aquaculture and foreign fishery developed countries in the automation and intelligence of mechanical equipment. This paper discusses the current main problems and future research and development directions of deep sea aquaculture vessels and deep sea aquaculture cages, and makes corresponding discussions and thoughts on the future development of deep sea aquaculture, especially planning objectives, function expansion, scientific and technological support of deep sea aquaculture. This study is expected to provide reference for the research and development of deep sea aquaculture equipment and technology and future marine construction in China.<br>
There are excellent conditions for developing aquaculture in deep sea waters including the high quality water, suitable regional or current water temperature, and very few terrigenous pollution & disease, etc.. The support of safe & reliable engineering equipment and guarantee system for marine operation is significant for developing deep sea aquaculture and realizing "deep blue fishery". Large-scale fish farming ships and cages facilities are the core equipment of deep sea aquaculture engineering, and also the leading R&D technology over the world. Based on the analysis of deep sea engineering equipment research progress, this paper proposed the strategic conception and pointed out the key tasks of boosting the scientific and technological progress in China's deep sea aquaculture engineering equipment and "deep blue fishery".<br>
The aquaculture industry is aiming to move fish farms from nearshore areas to open seas because of many attractive advantages in the open water. However, one major challenge is to design the structure to withstand the environmental loads due to wind, waves, and currents. The purpose of this paper is to study a vessel-shaped fish farm concept for open sea applications. The structure includes a vessel-shaped hull, a mooring system, and fish cages. The shape of the hull minimizes the wave loads coming from the bow, and the single-point mooring system is connected to the turret at the vessel bow. Such a system allows the whole fish farm to rotate freely about the turret, reduces the environmental loads on the structure and increases the spread area of fish wastes. A basic geometry of the vessel hull was considered and the hydrodynamic properties were obtained from the frequency-domain (FD) analysis. A mooring system with six mooring lines was designed to avoid possible interactions with the fish cages. Time-domain (TD) simulations were performed by coupling the hull with the mooring system. A simplified rigid model of the fish cages was considered. The global responses of the system and the mooring line loads were compared under various wave and current conditions. The effects due to misalignment of wave and current directions on the responses were discussed. Finally, the responses using flexible and rigid net models were compared under steady current conditions.
LIL, JIANGZ, ONGM C, et al.
Design optimization of mooring system: An application to a vessel-shaped offshore fish farm
The aquaculture industry is aiming to move fish farms from nearshore areas to open seas because of many attractive advantages in the open water. However, one major challenge is to design the structure to withstand the environmental loads due to wind, waves, and currents. The purpose of this paper is to study a vessel-shaped fish farm concept for open sea applications. The structure includes a vessel-shaped hull, a mooring system, and fish cages. The shape of the hull minimizes the wave loads coming from the bow, and the single-point mooring system is connected to the turret at the vessel bow. Such a system allows the whole fish farm to rotate freely about the turret, reduces the environmental loads on the structure and increases the spread area of fish wastes. A basic geometry of the vessel hull was considered and the hydrodynamic properties were obtained from the frequency-domain (FD) analysis. A mooring system with six mooring lines was designed to avoid possible interactions with the fish cages. Time-domain (TD) simulations were performed by coupling the hull with the mooring system. A simplified rigid model of the fish cages was considered. The global responses of the system and the mooring line loads were compared under various wave and current conditions. The effects due to misalignment of wave and current directions on the responses were discussed. Finally, the responses using flexible and rigid net models were compared under steady current conditions.
OTTERSENP A. Structural assessment of an offshore ship-shaped fish farm[D]. Lyngby, Denmark: Technical University of Denmark, 2017.
