Numerical evaluation of the action on a pile-moored fish cage forced by a storm sea state in different configurations

The conservation and reuse of the foundation of offshore platforms, at times, can be more ecologically sustainable than their complete removal, which can result in the loss of biodiversity. In our work we consider fish-farming as possible reuse of offshore depleted oil and gas mono-pile infrastructures, being the role of aquaculture in fish-food supply continuously increasing in the last decades. Offshore fish-farm cages are exposed to strong actions and knowing the dynamical response of the cage to different marine forcing is fundamental for the design of the structure. Hence, the dynamics of cylindrical pile-moored fish cages has been studied numerically with a net-truss model, including the screen model for the viscous forces proposed by Kristiansen and Faltinsen (2012) and the elasticity of the net trusses (Zitti et al.,2020, 2022). The model simulates a cylindrical cage fixed to a top ring and a bottom ring, which are moored to the central tubular pillar, whose net is characterized by solidity ratio Sn=0.087, material density pnet=1140 kg/m3, and Young modulus E =81Ί06 N/m2. The grouping method with G=10 is included in the model, for the reduction of the computational cost of the simulations. The cage net is forced with a flow derived by a linear superposition of the flows associated to linear waves, based on a JONSWAP spectrum representative a storm sea state typical of the Adriatic sea, on the Italian East coast, where a number of mono-pile oil and gas infrastructures are located. Different configurations of the cage are simulated and the resulting actions on the support system are compared.