Dynamic Analysis of a Vessel-shaped Fish Farm for Open Sea

Master's thesis in Offshore Technology : Marine and Subsea TechnologyIn recent years, aquaculture has been the fastest-growing animal food producing industry in the world. However, the absence of suitable production areas might potentially become the most limiting factor for future production growth. This motivates and necessitates the development of open sea fish farming. Design of offshore aquaculture systems is a novel and unique engineering challenge, which will depend on numerical tools that can simulate and predict the structural response in open sea conditions. In this master thesis, a vessel-shaped fish farm concept for offshore fish farming is studied. The vessel uses a turret mooring system for station keeping and is designed to break incoming waves and reduce environmental loads on the system. Dynamic analyses have been carried out using numerical simulation programs, with the aim to analyse vessel motions, mooring lines, fish nets, and coupled motions of the system. For studies of the hydrodynamic properties of the vessel, different panel models were created using the design analysis tool GeniE. The RAOs in heave, roll, and pitch were obtained from frequency domain analyses of the vessel hull, using the potential flow solver Wadam. Hydrodynamic data acquired from frequency domain analyses were exported from Wadam to SIMO, the program used for quasi-static time domain analysis of the vessel and simplified mooring system. Based on the mooring lines performance in SIMO, new mooring line parameters were established for the fully coupled time domain simulations in SIMO-Riflex, where fully coupled time domain analyses of the vessel-shaped fish farm was carried out. A sensitivity study was carried out from the fully coupled time domain simulations by comparing three different fish net models; rigid model, flexible model, and flexible model with no reduction factor. It was found that the simplified models overestimate the drag forces on the system, and it is recommended that neither of the simplified models should be used for future dynamic analyses of aquaculture systems. Development of tension in the foremost and rearmost fish nets was studied in steady current conditions, and with a conjunction of regular waves and steady currents. A mutual dependency between the forces on the net and its deformations was found. Motions of the coupled fish farm system and the efficiency of mooring lines were studied in time domain simulations with regular waves and steady currents