Nonlinear dynamics of an aquaculture cage array under oblique wave attack

Abstract

Nonlinear interactions of an oblique wave with an aquaculture cage array containing 16 net cages in a 2 × 8 configuration is studied in this paper. Our objective is to understand the nonlinear dynamics of the cage array induced by different hydrodynamic forcing mechanisms under oblique wave attack. To this end, we use an efficient numerical scheme with a robust implicit finite-element method for the nonlinear wave-structure interactions. The nonlinear and non-stationary data is decomposed by the empirical mode decomposition method, allowing for identification of different hydrodynamic forcing mechanisms. Then, physical model tests of a cage array in the 1 × 3 configuration under the low-frequency wave are conducted to verify the present numerical model. The harmonic responses of the surge and heave between numerical simulations and experimental tests are close to each other; indicating that the present numerical model is feasible to predict the dynamic response of the cage array in waves. The results highlight that the flexible cage with lower elastic modulus shows larger excursion in the weather side of the cage array, and the flexible cage has a better ability to absorb energy from incident waves. However, the elastic modulus of the floating collar has little effect on the surge and heave motions. Under the oblique wave attack, the nonlinear responses of a representative mooring are identified to be wave-frequency and low-frequency driven, and the nonlinear sway responses are found to be dominant by low-frequency excitations.