Effects of mooring line breakage on dynamic responses of grid moored fish farms under pure current conditions

Abstract

Due to the lack of sheltered area, Norwegian fish farms are expanding to more exposed and remote sites. The severe environmental conditions in exposed sites can increase the risk of structural failure during aquaculture operations. In the present study, the program FhSim is employed to conduct time-domain simulations to investigate structural responses of a single-cage and 1 × 4 multi-cage fish farm due to breakages in mooring lines. The influences on the tension distribution in the mooring system and the displacement of the buoys due to breakage at different mooring lines are analysed in detail. Based on the analysis, a method to identify the broken mooring line and to predict the maximum tension increment in the remaining mooring lines is proposed. The results indicate that the breakage at one mooring line is unlikely to cause a progressive collapse of the fish farm immediately when the current velocity is less than 0.5 m/s. However, these breakages may cause structural collapses and fish escapes when the current and waves increase. In order to prevent fish escapes, suggestions to improve the mooring system design and recommendations for monitoring during operations are given.