Study On Hydrodynamic Characteristics Of Deepwater Long-line Rope Aquaculture Facility

Raft culture system was one of the important methods of seawater aquaculture. It was widely used in economical seawater cultured products such as algae, shellfish, abalone, oysters, crabs, etc. In recent years, as a result of capacity saturation and environmental deterioration in the breeding. Beeding at offshore became a important trend. The development of raft culture system to the deepwater also became inevitable. There was no effective protection of islands at the offshore waters, and especially the wind and waves caused by the typhoon had important influence on facilities security, it was the key factors that breeding is success or failure. Therefore, in this paper, the force and movement of deepwater long-line rope aquaculture facility in waves were studied on. Deepwater long-line rope aquaculture facility is made up by anchor rope, anchor, longline, Bouy, float rope, lifting lug, lifting rope. Anchor rope and anchor are for anchoring system. Bouy and floating rope are for buoyancy system. Lifting lug and lifting rope are for farming system. Longline rope is the main part.Bouy is widely used in the raft culture facilities, as the party which provides the main buoyancy in fishery production. In this paper, the horizontal forces of three typical aquaculture floating balls were obtained through experimental tests. The Morison equation was modified in order to get a better fitting result of the forces in time series. The effect of the parameters KH, KT and Reynolds number Re, on the hydro-coefficients CD and CM were discussed. It was found that the inertia force accounted for the main part of the total force on the spherical structures in waves. The results showed that the wave parameters and the Reynolds number had significant influence on the values of the hydro-coefficients:The values decreased as the wave height KH increased with a powered fitted function. However, the relationship with KT and Re was discrete. The values decreased apparently as KT and KH increased. The Reynolds number Re, seemed to have little influence on the inertia force coefficient. Based on the results achieved, the authors also gave the empirical formulas for calculating the hydro-coefficients CD and Cm for practical use.In this paper, method of numerical simulation and model test were used for studying the force and movement of deepwater long-line rope aquaculture facility in waves. It was found wave height and period to have effect on the deepwater long-line rope aquaculture facility's force and movement. But the impact of methods are different. Wave height had main effect on the maximum force of facility. Wave period had main effect on the stress distribution characteristics of facility. It showed positive correlation between wave height and the maximum force of each part of facility. The maximum force increased as wave height increased. Vertical movement amplitude of each node on longline increased as wave height and period increases. Both ends of the longline nodes were bounded by the anchor rope, trajectory became slim. Middle node trajectory became slim as wave period increasd, the horizontal motion amplitude decreased as wave period increased. The maximum force of floating ball line mainly appears in the back wave side, but may be change as the wave period and facility structure changed.freeweight and system angle have an effect on long-line rope aquaculture facility. Long-line displacement are negatively related with freeweight. The displacement of longline decreased as freeweight increased. The force of longline,back anchor rope, float ball rope and lifting rope increased as freeweight increased. But the force of front anchor rope decreased as freeweight increased. Float ball pattern had little impact on the system's movement and force. Anchor rope force,the displacement of long-line were positively correlated relationship with system angle at 0° to 60°. They increased as the angle increased. Anchor rope force, the displacement of long-line were negative correlated relationship with Angle at 60° to 90°. They decreased as the system angle increased. The force of longline, float ball rope, the lifting rope affected by the system angle is small. When doing the design of raft culture system,we should avoid to 60° Angle with wave direction, as far as possible to parallel with wave direction.Deepwater long-line rope aquaculture facility belongs to the typical flexible multi degree of freedom offshore structures, this research results can provide the reference for designing deepwater long-line rope aquaculture facility and safety evaluationt. But the hydrodynamic characteristics of r deepwater long-line rope aquaculture facility are related to its structure and environmental factors, therefore we need specific conditions and specific analysis in the raft system designing and safety assessment.