Numerical Study of Mooring Force and Motion Response in Closed Fish Cage Systems for Marine Aquaculture

Abstract The marine aquaculture industry faces significant challenges with traditional flexible open-net cage systems. While closed fish cage systems offer promising solutions to these issues, their complex interactions with marine forces present new technical challenges. A critical knowledge gap exists in translating scaled-model experimental results to full-scale applications, particularly regarding the hydrodynamic behavior of these novel systems. This study presents a comprehensive numerical investigation by employing a two-phase validation approach. Initially, we validated our numerical scheme against two-dimensional experimental data from Rognebakke and Faltinsen (2003), focusing on hull sections with empty and water-filled tank configurations under regular wave excitation. Subsequently, we conducted simulations to replicate the cylinder-shaped closed fish cage experiments reported by Zhao et al. (2023), analyzing pitch motions and mooring forces. Simulations accurately captured general trends, with discrepancies in pitch motion observed for wave periods between 0.8 and 1.0 s, attributed to the influence of secondary motion components isolated in simulations. Mooring forces were well-predicted under long-period waves, but short-period results indicated the need for further refinement by including all degrees of freedom. Additionally, flow pattern analysis revealed asymmetry, and possibly, swirling under long-period waves, contrasting previous findings of symmetry during forced oscillations. These results highlight the framework’s potential to enhance understanding of fish cage hydrodynamics, despite areas requiring further investigation.