Effects of mooring pattern on dynamic characteristics of a deep-water aquaculture cage

We established a numerical model for calculating the dynamic characteristics of a triangular high-density polyethylene (HDPE) deep-water aquaculture cage in waves and current based on the Finite Element Method. To verify the accuracy of the numerical model, we carried out a series of physical model tests on the single-point mooring (SPM) cage under the conditions of pure wave and combined wave-current, in which the model scale was set at 1∶15. The relative error between the numerical and experimental results was within 10%. Afterwards, considering the sea state of the prototype cage, the calculated parameters for waves and currents were as follows: wave height 4–6 m, period 9 s, current velocity 0.5–1.5 m·s⁻¹. We analyzed the deformation of the floating collar and the mooring force of the cage with single-point mooring (SPM) and multiple-point mooring (MPM). Besides, we discussed the effect of the mooring pattern on the motion characteristics of the cage. The results show that under the conditions of wave and current, the peak value of MPM force was higher than that of SPM force, and the difference became greater with the increase of velocity and wave height. Under the condition of severe waves and strong currents, the MPM system could reduce the deformation of the floating collar. However, the mooring pattern had little influence on the heave of the cage collar. For the MPM system, the x-axis displacement of the collar was greater than that of the SPM system, in which the difference was 25.64%. During a wave period, the xz plane profiles of the net deformation under sea conditions were almost the same for the two different mooring systems.