Numerical modelling of copper alloy aquaculture net in currents with the Smoothed Particle Hydrodynamics method.

Abstract

Aquaculture in high-energy areas poses significant challenges to traditional engineering tools, as the strong non-linear loads exerted on structures often require more refined numerical models. In this work, we carry out the numerical modelling of an aquaculture net made of copper alloy interacting with current, employing a Computational Fluid Dynamic (CFD) method. The numerical approach used in this work allows for the simulation of the direct interaction between the net and the fluid, without the need to use hydrodynamic coefficients to model the net, unlike traditional numerical approaches. The methodology used was validated at current velocities typical of high energy sea states and gave satisfactory results in the majority of cases analysed. The methodology presented here allows the evaluation of hydrodynamic forces on the numerical net, its displacement and deformation, and the fluid velocity field surrounding the net. The proposed methodology is based on the application of the Smoothed Particle Hydrodynamics (SPH) method. The net is modelled as a set of fluid-driven elements with spherical geometry connected with dynamic mooring lines, where the boundary particles that make up the fluid-driven elements interact with the particles that make up the fluid, providing the fluid-structure interaction. The numerical modelling of the net is executed through the coupling of DualSPHysics and MoorDyn+. DualSPHysics is an open-source, fully Lagrangian, meshless code based on weakly compressible SPH that addresses the fluid-structure interaction. On the other hand, MoorDyn+ is a dynamic mooring library that uses a lumped-mass numerical model to resolve tensions in the mooring lines and allows the connections between fluid-driven elements. Two cases of analysis were carried out and validated against experimental data. For the first case, the net was modelled in a fixed frame in currents and the drag forces on the net were evaluated. In the second case, the setup comprises a floating fish cage (scale 1:15) with a copper alloy net moored to a fixed point, modelled in currents. In this latest study, the loads on the fish cage measured at the mooring were evaluated. The numerical results showed a satisfactory agreement.