Numerical study of a well boat operating at a fish farm in current |
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| Institution: | 1. Centre for Autonomous Marine Operations and Systems (AMOS), Department of Marine Technology, NTNU, NO-7491 Trondheim, Norway;2. CNR-INSEAN Italian Ship Model Basin, Via di Vallerano 139, 00128 Roma, Italy;1. SINTEF Fisheries and Aquaculture, 7465 Trondheim, Norway;2. Fiskeaaling, Aquaculture Research Station of the Faroes, Við Áir, FO-430 3 Hvalvík, Faroe Islands;1. Department of Engineering Cybernetics, Norwegian University of Science and Technology (NTNU), O. S. Bragstads plass 2D, NO-7491 Trondheim, Norway;2. Nofima, Sjølsengvegen 22, NO-6600 Sunndalsøra, Norway;3. SINTEF Fisheries and Aquaculture, NO-7465 Trondheim, Norway;4. Nofima, NO-5828 Bergen, Norway;1. College of Engineering Science and Technology, Shanghai Ocean University, Shanghai 201306, China;2. National Distant-water Fisheries Engineering Research Center, Shanghai 201306, China;3. State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian 116024, China;1. Science Branch, Fisheries and Oceans Canada, P.O. Box 5667, St John’s, NL, A1C 5X1, Canada;2. Department of Biology, Memorial University of Newfoundland, St John’s, NL, A1B 3X9, Canada |
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| Abstract: | Dynamic response of a well boat operating at a fish farm in current is investigated numerically. An objective is to determine the operational conditions of the well boat. In terms of the fish farm, a realistic set-up (with single cage) is considered, including a floating collar, an elastic sinker tube, a flexible-closed net cage and a complex mooring system. A time-domain solution is used to find the steady configuration and response. Transverse viscous current loads are estimated using the cross-flow principle. The drag coefficients are obtained empirically by considering cross-sectional details, free surface and three-dimensional (3D) flow effects. The drag force is experimentally validated. The effect of the ship wake on the net loading is also assessed.The most critical scenario with the well boat placed at the weather side of the fish farm is analyzed in detail. Critical response variables for operational limits are the maximum anchor-line tensions and floater stresses. Numerical results show that the anchor loads will increase more than 40% in small current velocities and up to 90% in high current velocities due to the viscous current loads on the boat. There is also a strong increase of the floating collar deformations and stresses when the well boat is in contact with the floating collar.A sensitivity analysis has been carried out to identify the physical parameters affecting the anchor loads and the maximum stress in the floating collar. From our studies, the anchor loads are more sensitive to current direction, bottom weight system, sinker tube depth and mooring line properties (pretension load, anchor chain weight, etc.) and less sensitive to other parameters such as floating collar stiffness and cross-sectional drag coefficients of the well boat. The shading effect of the well boat on the fish-farm inflow has been examined and appeared not negligible with 4% to 10% reduction of the anchor loads for the studied current conditions. The maximum stress in the floating collar is sensitive to well-boat loads related parameters (current direction, cross-sectional drag coefficient) and pretension load in the anchor line; not so sensitive to net loading related parameters such as sinker tube depth and sinker tube weight.Lastly, the operational conditions of the well boat at the fish farm were discussed. Numerical results show that the maximum stresses in the floating collar should be of major concern. The loads in the mooring lines are moderate compared with the corresponding breaking limits. |
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| Keywords: | Fish farm Well boat Current Critical physical parameters Operational conditions |
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