Abstract: Offshore aquaculture has developed rapidly in recent decades. As the most common aquaculture equipment, fish cages are widely used in the world. In order to further adapt to the harsh environment and improve the efficiency of aquaculture, a variety of large scale aquaculture cages combined with traditional marine engineering structures have also emerged. Vessel-shaped fish cage is a new type of large aquaculture structure, composed of steel floating body, net, steel frames and mooring lines, etc. Different from the conventional platform and fish cage, vessel-shaped fish cage has a large number of nets, which will affect fish cage motion and mooring response, furthermore increase economic and ecological risks. In this study, a time-domain coupling analysis method is developed to calculate the dynamic response of large floating cages in waves. Firstly, the three-dimensional potential flow theory is employed to determine the hydrodynamic coefficients of floating body, including added mass, potential damping coefficients and first order wave excitation force RAO. Subsequently the state space method is used to simulate the radiation load of floating body, the Morison equation is used to solve the hydrodynamic loads on slender structures (including steel frame, mooring line and net). Then, the coupled whole cage motion equation is established in time domain. By numerical method, influence of 3 different net models (no net, rigid net, flexible net) and net solidity ratios on motion and mooring responses were studied respectively. The results show that net increases the surge motion with 26%, but the heave and pitch motion are weakened due to the net damping effect. Additional, damping effect of flexible net is more obvious than that of rigid net. An increase of mooring line tension due to the net influence is also observed. This study can provide engineering reference and design basis for large fish cage in the concept and basic design stage.

Key words: vessel-shaped fish cage, net force, solidity ratio, hydrodynamic response, numerical method

摘要： 船型网箱是一种新型的大型海洋养殖网箱，由大型浮体、网衣、钢架和系泊缆等组成。不同于传统海洋平台，船型网箱的大量网衣会影响其在波浪中的运动和系泊响应。该研究建立了一种时域耦合方法用于波浪中浮式网箱的响应分析，首先利用三维势流理论计算网箱浮体的水动力系数，然后利用状态空间法模拟浮体辐射力，并通过莫里森方程求解钢架及网衣等的水动力，建立网箱整体运动方程，研究了无网衣、刚性网衣、柔性网衣3种模型以及不同网衣密实度的网箱运动和系泊响应。结果显示，网衣使网箱纵荡增幅超26%，由于网衣的阻尼效应，垂荡和纵摇响应会减弱。柔性网衣比刚性网衣的阻尼效应更明显。该研究结果可为大型网箱在前期设计阶段提供工程借鉴和设计依据。

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