A hybrid empirical-numerical method for hydroelastic analysis of a floater-and-net system

Abstract

Because of scale effects and inappropriate hydrodynamic models, the nonlinear hydroelastic response of net cages used for fish farming cannot be analyzed precisely with traditional model testing or combinations of FEMs (finite element methods) and load models. In this study, an innovative hybrid method is proposed to determine the hydroelastic response of full-scale floater-and-net systems more accurately. In this method, the net for the fish cage was vertically and peripherally divided into similar interconnected sections with different hydrodynamic parameters, which were assumed to be uniformly distributed over each section. A model of a typical section was subjected to various towing velocities, oscillation periods and amplitudes in a towing tank to simulate the potential motions of all sections in the net under various currents, waves and floater movements. By analyzing the measured hydrodynamic force from this test section, a hydrodynamic force database for a typical net section under various currents, waves and floater motions was built. Finally, based on an FEM, the modified Morison equation and the hydrodynamic force database, the hydroelastic behavior of the full-scale fish cage was calculated with an iterative scheme. It is demonstrated that this hybrid method is able to produce correct hydroelastic response for both steady and oscillatory flows. The hydroelastic response of a 2D example of a full-length net panel with steady currents and floater oscillations was studied in detail.