Pål Lader

Exposed Aquaculture in Norway

Farming of Atlantic salmon in exposed areas poses unique challenges to operations, structures and equipment due to severe and irregular wind, wave and current conditions, and sheer remoteness. Many of the operational challenges seen at present sheltered sites are likely to be amplified when moving production to more exposed locations. There is, however, a strong Norwegian industrial interest in utilizing such areas. A new research center, the Exposed Aquaculture Operations center has been initialized to develop competence and technology to address the challenges. Six core research areas are identified that will be crucial to address the challenges with exposed farming, with a focus on the industrial status in Norway. Four areas target technological innovations that will enable safe and reliable exposed aquaculture operations: 1) Autonomous systems and technologies for remote operations, 2) Monitoring and operational decision support, 3) Structures for exposed locations and 4) Vessel design for exposed operations. Two areas represent core requirements for sustainable production: 5) Safety and risk management and 6) Fish behavior and welfare. This paper describes the research needs and the research strategy planned for the Exposed Aquaculture Operations center.

Drag Forces on, and Deformation of, Closed Flexible Bags

The use of closed flexible bags is among the suggestions considered as a potential way to expand the salmon production in Norway. Few ocean structures exist with large, heavily compliant submerged components, and there is presently limited existing knowledge about how aquaculture systems with flexible closed cages will respond to external sea loads. The flexibility and deformation of the bag are coupled to the hydrodynamic forces, and the forces and deformation will be dependent on the filling level of the bag. In order to get a better understanding of the drag forces on, and deformation of, such bags, experiments were conducted with a series of closed flexible bags. The bags were towed in a towing tank in order to simulate uniform current. Four different geometries were investigated, cylindrical, cubical, conical, and pyramidal, and the filling levels were varied between 70% and 120%. The main findings from the experiments were that the drag force was highly dependent on the filling level, and that the drag force increases with decreasing filling level. Comparing the drag force on a deflated bag with an inflated one showed an increase of up to 2.5 times.

Modelling of Drag Forces on a Closed Flexible Fish Cage

Abstract To cope with ecological challenges in the aquaculture industry, Closed Flexible Fish Cages (CFC) are proposed used in the sea. However, the existing knowledge about how the CFC will respond to external sea loads are limited. More knowledge is needed to understand the response of the cage if this technology is to be utilized in an industrial scale. In this paper a new method for mathematical modelling of the increase in drag, for decreasing filling level of a CFC is proposed. A model for a filling-level-dependent drag coefficient is presented. Experimental data are analysed related to forces and deformations on the bag for different filling levels. The analysed bag showed an increased tendency to deform for decreasing filling levels, leading to an increase in drag coefficient.

Wave Crest Kinematics of Deep Water Breaking Waves

Measurements of the kinematics of three cases of breaking waves have been conducted using the Particle Image Velocimetry (PIV) method. A set of four parameters are used do describe the kinematics, and the development of the waves as they approach breaking is studied using these parameters. The parameters reveal significant features in the temporal development of the internal kinematics of steep, asymmetric transient waves. Introduction Knowledge of the mechanisms leading to the generation of breaking waves in deep water is still not fully understood, and breaking of waves can not be defined uniquely by any parameter at present. A breaking criterion is of fundamental importance, and also enters in practical applications, e.g. in estimating the probability of occurrence of breaking waves at sea. Several criteria have been suggested, but none have proven to give a unique definition of the inception of breaking (Tulin and Li, 1992). In this paper we present measurements of the crest kinematics in three different cases of breaking waves: A plunging breaker, a spilling breaker, and an intermediate breaker (see Figure 1). The intermediate breaker is a breaker that is initiated by a microscale plunging event, and evolves further as a spilling breaker. The classification of breakers follows Kjeldsen and Myrhaug (1978). The plunging and intermediate breakers were generated by using the method of phase focusing (see e.g. LonguetHiggins, 1974 and Kjeldsen and Myrhaug, 1979). The spilling breaker was generated 1. Research Scientist, SINTEF Fisheries and Aquaculture, N-7465 Trondheim, Norway, Phone: +47 73 59 76 92, fax: +47 73 59 56 60, e-mail: Pal.Lader@fish.sintef.no 2. Professor, Department of Marine Hydrodynamics, Norwegian University of Science and Technology. 3. Professor, Department of Marine Hydrodynamics, Norwegian University of Science and Technology.

Structural Analysis of Aquaculture Nets: Comparison and Validation of Different Numerical Modelling Approaches

The performance of three different numerical methods were compared and evaluated against data from physical model tests. A parameter study of a simplified net cage model subjected to a steady flow was performed by all methods, varying the net solidity and the flow velocity. The three numerical methods applied models based on springs, trusses or triangular finite elements. Hydrodynamic load calculations were based on the drag term in Morison’s equation and the cross-flow principle. Different approaches to account for wake effects were applied. In general, the presented numerical methods should be able to calculate loads and deformations within acceptable tolerance limits for low to intermediate current flow velocities and net solidities, while numerical analyses of high solidity nets subjected to high current velocities tend to overpredict the drag loads acting on the structure. To accurately estimate hydrodynamic loads and structural response of net structures with high projected solidity, new knowledge and methods are needed.Copyright

Wave Response of Closed Flexible Bags

Recent environmental considerations, as salmon lice, escape of farmed fish and release of nutrients, have prompted the aquaculture industry to consider the use of closed fish production systems. The use of such systems is considered as one potential way of expanding the salmon production in Norway. To better understand the response in waves of such bags, experiments were conducted with a series of 1:30 scaled models of closed flexible bags. The bags and floater were moored in a wave tank and subjected to series of regular waves (wave period between 0.5 and 1.5s and wave

Simulation and Validation of a Numerical Model of a Full Aquaculture Net-Cage System

Numerical simulation models are useful tools for the design and capacity analyses of cage-based fish farm systems. To ensure that such tools produce realistic estimates on forces and deformations experienced by fish farms, it is important to validate the models through comparison with experiments. A recent experiment investigated the response of a scaled model of a full aquaculture net cage placed in a mooring system when exposed to waves and current. In this study, a numerical model of this system containing the main components used in the physical experiments was set up and simulated. After simulations the tension in anchor lines, bridles and buoys were compared to the corresponding data series obtained in the experiments. The comparison indicated that FhSim was able to reproduce the main dynamics and responses of the physical model when exposed to currents and waves. Furthermore, a sensitivity analysis was conducted, aimed at investigating how much model output is affected by variations in the stiffness of the mooring system.Copyright

Environmental Description in the Design of Fish Farms at Exposed Locations

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 uncer-

Classification of Aquaculture Locations in Norway With Respect to Wind Wave Exposure

In Norway there are a total of 1070 registered sites for salmon farming all along the coast. Trends in the aquaculture industry in the recent decade are that salmon farming sites tend to gradually relocate to more wave and current exposed locations. This trend is mainly motivated by the good water quality found in more exposed areas, as well as a lack of available sheltered locations. On the other hand, the increased exposure puts higher loads on the structures and this needs to be addressed by the development of more robust technology. The first step in order to address an increased exposure is to quantify the level of exposure of waves and current, and in this paper a method to easily estimate the level of wind wave exposure on a large number of sites are presented, and subsequently used to analyse all Norwegian sites.The method can be called fetch analysis, and use long term wind data connected with the fetch length in order to estimate wind wave conditions. The method is divided into four steps: 1) Fetch analysis, 2) Wind data, 3) Estimating wave parameters Hs and Tp and 4) Wave statistics. Significant wave height Hs with return period 1 year and 50 years are estimated for each site. Hs 50 year is often used for design, and the analysis shows that for 38% of the sites Hs 50 year exceeds 1 meter, for 17% of the sites Hs 50 year exceeds 1.5 meter, while 1.4% of the sites have Hs 50 year larger than 2.5 meter. The most exposed site has a Hs 50 year of 2.9 meter. Thus there are large differences in Hs 50 year in the various coastal regions of Norway.Copyright