Dynamic Analysis of a Floating Fish Cage with Feeding Systems

Abstract

Aquaculture is one of the fastest growing industries in Norway, and one of the fastest growing food production industries in the world. Limited access to available locations along the coast is gradually forcing aquacultural operations into exposed locations offshore. It is of interest to explore loading effects and the behaviors of fish farms exposed to considerable hydrodynamic loads. Furthermore, there has been limited analysis of feeding systems and load characteristics. Understanding these characteristics will be beneficial for the industry in learning how to establish and maintain sustainable longterm operations in harsh environments. A numerical model of a fish farm is developed using a combination of software programs. The numerical model is comprised of a feed barge, a mooring system, and a feeding tube. The feed barge model is established using GeniE, while response amplitude operators and damping coefficients are determined using Wadam. The fish cage, feeding tubes, and mooring lines are created using the programming language Python in conjuncture with the OrcaFlex Application Programming Interface (API). The fish cage net equivalence is determined, and dynamic analyses of the fish farm are subsequently presented. Three fish cage models of varying mesh density are developed, and a convergence study is conducted for different current velocities to compare volume reduction and mooring line tension. Time domain simulations for the numerical model of the fish farm have been conducted for different environmental parameters, solidity ratios, and feeding tube lengths. The focus of the thesis is on the response of mooring lines and feeding tubes, as they represent the loading and behavior of the system for various environmental conditions. The findings suggest that for operational environmental conditions, oscillations in the feeding tube may induce snap loads. For extreme conditions, the mooring system tensions increased considerably. Increasing the fish cage solidity ratio contributes to increased drag force, hence also increasing mooring line tension, and fish cage volume deformation. Furthermore, increasing feeding tube length resulted in a decrease in tension for the feeding tube in extreme conditions due to improved elastic characteristics. Similar trends are seen for the bending moment, but for extreme conditions, bend stiffeners can be used to reduce bending moment at connection points. In this study, the findings suggest that operational and extreme environmental conditions cause significant tension in the feeding tube that may cause snap loads and ruptures.