Mooring design of offshore aquaculture platform and its dynamic performance

Abstract

Floating offshore aquaculture platforms, or fish cages, are increasingly becoming popular in recent years in order to meet the world's growing demand for seafood products. These platforms are typically of frame type structures consisting of slender beams, buoyancy tanks and netting surrounding the frame. This unique structural feature leads to complex hydrodynamic properties, and consequently the dynamic performance assessment and mooring system design become more challenging. This paper reports numerical and experimental studies on the mooring system performance of an aquaculture platform under different environmental conditions, including wave and current, in floating operational condition and bottom-sitting survival condition. A method based on the conventional potential flow theory and Morison equation is proposed for the numerical assessment of the hydrodynamic loads on the aquaculture platforms including its frame and net. A mooring system for the position keeping of the platform was designed and its performance analyzed in time domain. A hybrid mooring composition consisting of steel chain and fiber rope in each line was adopted to increase the axial elasticity so that the extreme tension could be reduced. Wave basin model tests were also conducted to obtain the platform motions and mooring tensions, and the comparisons were made between the measured data and the numerical predictions. The results of this study show that the proposed numerical method could be applied to the prediction of the performance of the aquaculture platforms and the mooring system with a reasonable accuracy.