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The nonlinear dynamic response of an aquaculture cage array caused by wave-frequency and low-frequency excitations coupled with the nonlinearity of the mooring and the netting system is a complicated problem. So far, this problem still has not been completely understood. To address this issue, we consider the nonlinear interaction of an extreme wave with an aquaculture cage array containing 16 net cages in a 2 × 8 configuration. This paper aims to provide insight into understanding the nonlinear dynamics of an aquaculture cage array via time–frequency analysis. Time-domain analysis shows that the cage array exhibits weak nonlinearity in the surge and heave motions. On the contrary, there is strong nonlinearity in the sway motion under 45 ° and 90 ° wave attacks. Aside from this, the frequency-domain analysis indicates that nonlinearities exist in all three of these different responses (surge/sway/heave). Particularly, the low-frequency component has a predominant effect on the nonlinearity of the sway motion under 45 ° and 90 ° wave attacks. With this understanding, future aquaculture fish farms that contain multiple cages (i.e., cage array) can be potentially designed to withstand severe conditions in the open ocean. [ABSTRACT FROM AUTHOR]

The nonlinear dynamic response of an aquaculture cage array caused by wave-frequency and low-frequency excitations coupled with the nonlinearity of the mooring and the netting system is a complicated problem. So far, this problem still has not been completely understood. To address this issue, we consider the nonlinear interaction of an extreme wave with an aquaculture cage array containing 16 net cages in a 2 × 8 configuration. This paper aims to provide insight into understanding the nonlinear dynamics of an aquaculture cage array via time–frequency analysis. Time-domain analysis shows that the cage array exhibits weak nonlinearity in the surge and heave motions. On the contrary, there is strong nonlinearity in the sway motion under 45° and 90° wave attacks. Aside from this, the frequency-domain analysis indicates that nonlinearities exist in all three of these different responses (surge/sway/heave). Particularly, the low-frequency component has a predominant effect on the nonlinearity of the sway motion under 45° and 90° wave attacks. With this understanding, future aquaculture fish farms that contain multiple cages (i.e., cage array) can be potentially designed to withstand severe conditions in the open ocean.

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. • Nonlinear dynamics of an aquaculture cage array were examined under oblique wave attack. • Different nonlinearity components were distinguished via empirical mode decomposition. • The leading contributors for nonlinearity of mooring and motion responses were identified. • Suggestions for safety design of the fish farm were provided. [ABSTRACT FROM AUTHOR]

In this study, waves propagating through a square array of 16 net cages with different levels of biofouling are numerically studied using a three-dimensional computational fluid dynamics (CFD) model. A porous-media fluid model is adopted to simulate both clean and biofouled netting of a cage array in waves. A numerical wave tank is built, and the oscillating-boundary method is adopted to generate waves. The flow motion is solved by the Navier-Stokes equations, and the free water surface is captured using the volume of fluid (VOF) method. The numerical model is validated by comparing the numerical data with corresponding experimental measurements of a net-cage model with clean netting. To analyze wave attenuation, a numerical analysis of wave elevation both inside and around the cage arrays is presented, which considers the effect of biofouling. Based on the results of the present study, the effect of biofouling on wave elevation is noticeable; the damping effect of the cage array increases with increasing level of biofouling. Furthermore, the incident angle of waves has a noticeable effect on the wave field inside and around the cage array. [ABSTRACT FROM AUTHOR]

Computer simulations were conducted to understand the nonlinear dynamics of the cage array to establish an offshore fish farm capable of surviving the severe conditions. To that end, a large fish farm containing 16 net cages in a 2 × 8 configuration was modeled based on the lumped mass model. This numerical model was verified against the physical model tests regarding a single net cage and a net cage array. In particular, three different equivalent mesh groups were compared to each other to balance the numerical accuracy and the computational efficiency. Then, the candidate equivalent mesh group was used to separately model the rigid and the flexible cage arrays subjected to severe conditions. The results show that most trajectory patterns of mooring lines are not as elliptical as the water particle trajectories. This provides evidence to justify the perturbations about the equilibrium of the mooring grid for the full-scale aquaculture cage array system. Alongside this, flexible cages with lower bending stiffness have greater tension forces on the weather side. The bending stiffness has a predominant effect on the surge motion and is also the leading contributor to the nonlinearity of cage motion. The flexible cage with lower bending stiffness is appropriate for more exposed, open ocean fish farming applications, but the increased mooring tension should be taken into account for future design consideration. • Nonlinear dynamics of an aquaculture cage array were examined under severe conditions. • The nonlinear wave was considered by introducing the new Stoke wave solutions. • Flexible cages with lower bending stiffness exhibited greater tension forces on the weather side. • The bending stiffness contributed to the nonlinearity of cage motion had a predominant effect on the surge motion. [ABSTRACT FROM AUTHOR]