The present paper addresses the seakeeping behavior of a rigid type of floating closed fish cages, with focus on effects of sloshing on the coupled motions and mooring loads. Closed cages have gained much attention recently as a strategy to avoid sea-lice infections in farming of Atlantic salmon. However, closed cages are novel structures and more knowledge is needed on the wave induced motions and coupling effects with sloshing for development of reliable closed cage structures to reduce risk for failure and possible escape of fish. In this paper, dedicated scaled model tests of closed cages in waves are presented and compared with numerical simulations using linear potential theory in frequency domain. The results shows that the influence of sloshing on the rigid body motion is significant. A nonlinear effect of sloshing was observed for a small region of excitation frequencies, where the surge amplitude increased with increasing wave steepness. Mean wave loads were also affected by sloshing. Hence, coupled motions with sloshing is important to consider in design of floating closed rigid fish cages and their mooring system.

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This paper addresses the description of exposure from waves and currents in coastal regions for design of marine fish farms. Representative descriptions of environmental conditions are important inputs to the design and dimensioning of reliable fish farm structures. A trend with moving production to more exposed sites and introduction of new and novel fish farm structures increase the need for more precise descriptions of the marine environment to keep control of uncertainties in design. Dedicated field measurements at two exposed aquaculture sites from February to December 2016 are presented. Results from statistical analyses of the measurement data demonstrate that common practice for characterization of exposure in design of fish farms has several deficiencies that should be improved to reduce uncertainties in design.

First-year sea ice ridges are a major concern for structures operating in the Arctic offshore and will in many cases give the design mooring load. In this paper, the response of a moored conical floater, somewhat similar to the well-known Kulluk, is studied in first-year ridges. The study is based on model tests performed at Hamburg Ship Model Basin (HSVA) in several ridges with different properties. Mooring forces and floater response, resulting from interaction with different ridges, were compared with respect to ridge properties, ridge behavior, and simulated ice management. Clearance of accumulated rubble upstream the structure was the dominating physical process in the ridge–structure interaction. Accumulation of rubble caused large mooring forces. The amount of accumulated rubble depended on the ridge cross-sectional area, thus the mooring forces increased with ridge cross-sectional area. Large mooring forces were also experienced after the ridge was passed by the structure due to difficulties with clearing of accumulated rubble.

First-year sea ice ridges are a major concern for structures operating in the Arctic and will in many cases give the design mooring load. In this paper, a moored conical floater, somewhat similar to the well-known Kulluk, is studied in first-year ridges. The study is based on model tests performed at HSVA in several ridges with different properties. Mooring forces and floater response resulting from interaction with different ridges were compared with respect to ridge properties, ridge behaviour and simulated ice management. Clearance of accumulated rubble upstream the structure was the dominating physical process in the ridge-structure interaction. Accumulation of rubble caused large mooring forces. The amount of accumulated rubble depended on the ridge cross-sectional area, thus the mooring forces increased with ridge cross-sectional area. Large mooring forces were also experienced after the initial position of the ridge was passed due to difficulties with clearing of accumulated rubble.