There are four types of oyster aquaculture such as oyster plug rod, horizontal hanging scaffold, pontoon-style longline, and floating raft system. This study is to investigate the mooring tension of an oyster floating raft system under environmental loadings. According to the hydrodynamic experimental test, the horizontal fluid velocity has a retarded phenomenon when encountering the front part of structure, and then gradually reduces to a stable situation after the second floating rod. The phenomenon is identified as shielding effect for the raft system and has been used as a shielding coefficient to modify the fluid velocity in the computation program. The dynamic analysis of floating raft system under random wave interaction is investigated numerically and experimentally. The lumped mass method is applied to divide the structure into many nodes and elements. A modified Morison equation dealing with moving structure components is used to calculate the environmental forces on the elements. Further, the forces on elements are divided equally into neighboring nodes to form the equation of motion based on Newton¡¦s second law. Finally, the 4th-order Runge-Kutta (RK4) method is used as a time marching scheme to predict the displacement and velocity of nodes for the next time step. The results of time series and spectrum analysis of mooring tension show good agreement between numerical predictions and experimental data. This paper has further expanded to predict the field oyster raft system in an open sea, and offers some useful information to the oyster farmers in terms of improving the structure safety.

Abstract This research is to develop a new compound cage system that not only has the benefit of the traditional cage system but also has a series of oyster containers hanged on the circumference of the floating collar to add economic value to the cage aquaculture industry. The purpose of this study is to investigate the cage net deformation rate and the maximum mooring tension at the anchor under three types of Liuchiu sea states. The results of numerical simulation could be used as valuable guide for fish farmers and aquacultural cage designers. The developed numerical method is based on a lumped-mass approach to build a system of motion equations, and then utilizes the fourth order Runge-Kutta method to solve the motion equations. The numerical results reveal that under regular wave conditions, the cage net deformation rate for the compound cage system is slightly less than that of the traditional cage system, but the maximum mooring tension has reversed effect, i.e., the compound cage system has higher mooring tension than that of traditional one. As for the cases of irregular waves, the numerical results indicate that the cage net deformed so seriously that the fish can¡¦t survived at the sea condition of typhoon 50-year return period. To overcome this net shrinkage problem, an improved scheme is necessary to be implemented before a real compound cage system is installed in the open sea.