Abstract
Recently, the concept of a vessel-shaped fish farm was proposed for open sea applications. The fish farm comprises a vessel-shaped floater, five fish cages, and a single-point mooring system. Such a system weathervanes, and this feature increases the spread area of fish waste. Still, the downstream cages may experience decreased exchange of water flow when the vessel heading is aligned with the current direction, and fish welfare may be jeopardized. To ameliorate the flow conditions, a dynamic positioning (DP) system may be required, and its power consumption should relate to the heading misalignment. This paper proposes an integrated method for predicting the heading misalignment between the vessel-shaped fish farm and the currents under combined waves and currents. A numerical model is first established for the fish farm system with flexible nets. Current reduction factors are included to address the reduction in flow velocity between net panels. The vessel heading is obtained by finding the equilibrium condition of the whole system under each combined wave and current condition. Then, the Kriging metamodel is applied to capture the relation between the misalignment angle and environmental variables, and the probability distribution of this misalignment angle is estimated for a reference site. Finally, the requirement for the DP system to improve the flow condition in the fish cages is discussed.
Highlights
Many benefits attract the installation of fish farms in exposed seas, including ample space for expansion, tremendous carrying capacity of sea water, reduced conflict with many user groups, lower exposure to human sources of pollution and the potential to reduce negative environmental impacts
We focus on the waves and currents, and the variables include significant wave height (Hs), wave spectral peak period, Tp, mean current velocity, Uc, and the directional difference between the waves and current, ∆θ
This paper presents a numerical study to predict the misalignment angle between the heading of the vessel-shaped offshore fish farm and the incoming currents
Summary
Many benefits attract the installation of fish farms in exposed seas, including ample space for expansion, tremendous carrying capacity of sea water, reduced conflict with many user groups, lower exposure to human sources of pollution and the potential to reduce negative environmental impacts. The Norwegian aquaculture industry has recently proposed several new and potential fish farm concepts for open seas. The semi-submersible fish farm ‘Ocean Farm 1’ developed by Ocean Farming AS, is the world’s largest fish farm to be installed in exposed offshore areas [2]. This design combines technology from both the aquaculture industry and the offshore oil and gas industry. Norway Royal Salmon AS and Aker Solutions ASA proposed another semi-submersible fish farm, and the global response analysis of a similar structure under waves has been carried out in both frequency and time domains [4]
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