Numerical Study on the Mooring Force in an Offshore Fish Cage Array

Abstract

The mooring force in a fish cage array subjected to currents and waves is investigated using the finite element method. Firstly, the numerical model of a fish cage array with six gravity cages is built by Ansys/APDL. Collars and bottom rings are simulated with pipe and beam elements while the rest structure is simulated with link elements, including the net and mooring cables. Thus, the weight and hydrodynamic load on the cables can be considered. The initial shape of the mooring ropes is calculated based on mooring dynamics. Since each component is a slender structure in the cage array, the Morison equation is used to calculate the hydrodynamic load. Secondly, the mooring forces are assessed for the system in different sea states. The locations of the maximum mooring force on different parts in the mooring system are found. The mean values and amplitudes of maximum mooring forces on different parts are calculated. The main ropes have the maximum mooring forces under all sea states. The mean values of the maximum mooring forces increase with the current velocity and wave height. When the attack angle is 0° and 90°, the two adjacent bridle ropes do not play the role of pulling the cage together. One is pulled tight and the other one is slack.