Abstract:
Abstract: The deepwater long-line rope aquaculture facility (the raft system) belongs to a raft mariculture method which is mainly composed of buoys, main rope, aquaculture net cages, mooring ropes and anchor stakes embedded into seabed. The buoys are connected with the main rope by rope, the main rope is connected to stake anchor by mooring rope, and the aquaculture net cage is hung on the main rope. The buoyancy of raft system is provided by buoys and the structure stability is ensured by the mooring force from anchor stakes embedded into seabed. The facility stays in deep-open waters with winds, waves, urgent flow, and is influenced by complex sea environment. The raft system will move and deform in the action of environmental load. When the tension force is over the strength of mooring rope or the maximum mooring anchorage force provided by the anchor stake, or the transversal displacement of the main rope is oversize, the raft system will become less stable. The safety and stability of the aquaculture facility will directly affect the success or failure of the whole aquaculture production. Therefore, it's certainly worth researching on the force and motion of the raft system considering the effect of ocean waves and current for structure design, and furthermore analyzing the raft system's wind resistance ability to provide reference for the parameter design of the raft system. In this paper, based on the finite element method, the stress characteristic and deforming of deepwater long-line rope aquaculture facility system were analyzed to establish finite element model equation. For the components in the raft system (buoy, cage, rope) belong to small scale marine structures, the fluent loads were calculated by Morison method, in which in order to calculate different grades of wave, the large wave height should be considered and the nonlinear wave force cannot be ignored, and the two order Stokes wave theory was employed to calculate the speed and acceleration of water particle. Broyden iteration method was used to solve the finite element equation of aquaculture facility system, and then the maximum tensions of the mooring rope in the system in different heights (1-14 m) of sea wave were calculated and compared to its break strength and mooring force of anchoring pile for evaluating wind resistance ability of the aquaculture facility system. As an instance, the wind resistance abilities of deepwater long-line rope aquaculture facilities erected in 30-meter deep sea waters of Zhangzidao aquaculture sea area were analyzed. The result showed that maximum tension of mooring rope was 78.8 kN, the maximum transverse displacement of the raft system was 18.5 m and the wind resistance abilities were at 6-7 level of sea wave (6 m wave height) with 1.5 m/s current. Respectively the actual measured data were 72.7 kN and 16.9 m. By comparison, the values of calculation are well consistent with actual measured ones. By further experimental verification, the analysis model and method can be referenced for practical engineering design of deepwater long-line rope aquaculture facility.