Hydrodynamic behaviors of rotatable horizontal aquaculture cage groups

Abstract

To enhance the safety of aquaculture cages under extreme marine conditions and address the issue of netting biofouling, this study innovatively designed a horizontal aquaculture cage structure capable of floating, submerging, and rotating. A combined theoretical and experimental approach was adopted to investigate the hydrodynamic behavior of such cage groups under different layouts and marine conditions. Firstly, a dynamic model of the cage group was established based on the lumped mass method and Morison equation, and the rotatable performance of the cage and the reliability of the numerical model were verified through underwater tests on the physical model. Subsequently, taking the 1 × 4 layout cage group as the research object, the time-domain analysis method was used to analyze the effects of wave height and the ratio of cage spacing (L) to wavelength (λ) on hydrodynamic responses and mooring tension. Finally, the nonlinear dynamic response characteristics of the 1 × 4 and 2 × 2 layout cage groups under combined wave-current action were studied. The results show that the surge, heave, and pitch motions of horizontal cage groups in floating and submerged states are significantly affected by wave height and the ratio of L/λ. The submerged state can effectively suppress the pitch amplitude and reduce mooring tension. In layout design, cage spacing should be avoided to be close to the wavelength to prevent resonance and reduce the risk of extreme loads. Compared to the 1 × 4 layout, the 2 × 2 layout reduces the average standard deviation of mooring tension by 6.06 % with more uniform tension distribution. However, positive incidence of wave-current significantly increases the pitch amplitude of the rear cages in the 2 × 2 layout.