Design evaluation of a fish cage mooring system with different bridle line connections using model experiments and simulations

Abstract

Because fish cage systems are strongly influenced by various marine environmental conditions such as currents and waves, structural safety design is of crucial importance during their installation. It is particularly important to design a technical solution for a mooring system. In this study, we designed four types of fish cage systems with different bridle connection arrangements (two single-rope and two multiple-rope connection methods) to evaluate the structural safety of fish cage systems based on the bridle connection arrangement and to propose an efficient design direction. The level of the structural safety of the fish cage system in terms of the resistance force, shape, and inside volume reduction ratio was found to vary according to the position of the frame lines connected to the bridle lines, the number of bridle lines, and the angle between the frame line and the direction of currents and waves. Improved structural safety was observed when the bridle lines were connected to the midpoints of the frame lines compared to those connected to the vertices, and the multiple-rope connection method was found to provide higher structural safety than the single-rope connection method. Increased fish cage system structural safety was also confirmed when the frame line orientation was 90° to the direction of currents and waves compared to that at 45°. From these findings, it can be concluded that the structural safety of a fish cage system can be improved by using multiple bridle lines to disperse the tension of the mooring lines connected to the frame lines and by installing the fish cage with the frame lines aligned at an angle that minimizes the projected area exposed to currents and waves. Moreover, the simulation technique presented in this study is expected to contribute to the efficient evaluation of the structural safety of various fish cage mooring systems designed using multiple-rope connection methods, accounting for the number and position of bridle lines connected on a frame line.