Design development of porous collar barrier for offshore floating fish cage against wave action,debris and predators |
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| Affiliation: | 1. College of Ocean Engineering, Guangdong Ocean University, Guangdong 524088, China;2. College of Civil Engineering and Architecture, Zhejiang University, Hangzhou 310058, China;3. Centre for Marine Technology and Ocean Engineering (CENTEC), Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal;1. Cetaqua, Centro Tecnológico del Agua, Los Pozos, 7340, Santiago, Chile;2. Salmones Blumar S.A., Puerto Montt, Chile;1. National Marine Hazard Mitigation Service, Ministry of Natural Resources, Beijing, China, 100000;2. Marine Monitoring and Forecasting Center of Zhejiang, Hangzhou, China, 310000;3. Dalian University of Technology, Dalian, China, 116000;4. Ningbo Research Institute of Dalian University of Technology, China;1. Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro, Tokyo, 1538505, Japan;2. College of Marine Sciences, Shanghai Ocean University, Shanghai, 201306, China;3. Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo, 1138656, Japan;4. School of Fisheries, Zhejiang Ocean University, Zhejiang, 316022, China |
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| Abstract: | This paper presents a design concept of a porous collar barrier for a novel floating open-net fish cage that is integrated with a floating spar wind turbine (referred to as COSPAR fish cage). The COSPAR fish cage has an octagonal shape with each side length of 30m. The collar barrier, having an array of rectangular cut-outs with round corners, is installed at the top portion of the cage to attenuate wave transmission inside the cage as well as to protect fish from external predators and debris. Single and double collar barrier designs corresponding to single net and double net cages are studied. The wave transmission, reflection and energy-loss coefficients of barriers are determined from numerical analysis based on the linear potential wave theory and the eigenfunction expansion method. Various underwater heights (2m ≤ h ≤ 8m) and porosity (0.25≤ ε ≤ 0.75) of the collar barriers are examined with the view to obtaining the barrier design for minimal transmission coefficient and energy-loss coefficient. Without a collar barrier, the single net and double net cage can only provide average wave transmission coefficients of 0.9 and 0.8, respectively. This study finds that the transmission coefficient could be reduced below 0.4 by having a single collar barrier with h = 4m and ε = 0.25. On the other hand, the transmission coefficient could be further reduced below 0.3 by a double collar barrier with the same h and ε. In addition, the double collar barrier gives lower energy-loss coefficient and better proofing against fish escape, biosecurity and predator intrusion than the single collar barrier. A double collar barrier design with porosity combination of ε1 = 0.25, ε2 = 0.5 is recommended for the COSPAR fish cage as it yields competitive wave scattering performances and saves collar material by 25 % when compared with the best performing porosity combination of ε1 = ε2 = 0.25. |
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| Keywords: | Offshore fish farm Floating fish cage Porous collar barrier Wave transmission Wave reflection Energy-loss |
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