Karl Gunnar Aarsæther

Modelling of Roll Damping Effects for a Fishing Vessel With Forward Speed

Vessels in the ocean-going fishing fleet are in general operating in almost all weather conditions. This includes operation in high sea-states which may lead to large amplitude ship motions, depending on the seakeeping characteristics of the vessel. Wave-induced ship motions are important factors for the safety and well-being of fishermen at work. Generally, potential flow theory overpredicts wave-induced roll motion amplitudes for conventional ship hulls. This is due to the presence of viscous damping effects in reality. Large amplitude roll motion of ships can be a real problem if no anti-rolling devices (e.g. bilge keels, anti-rolling tanks or roll-damping fins) are installed, as the roll damping coefficient of a ship is the limiting factor for the resonant roll motion amplitudes. The different components of roll damping for a ship at forward speed were investigated by Ikeda et al. [1], [2] and [3] and updated guidelines for numerical estimation of roll damping have been presented by the International Towing Tank Conference [4], where a component discrete type method for estimation of the damping is suggested. The different roll-damping components of Ikeda et al. has been complemented by skeg damping for smooth hulls [5]. This paper presents comparison between model experiments and the numerical results obtained from the guidelines [4] where the effects of bilge-keels and skeg are isolated.Copyright

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

The Physical Behaviour of Seine Ropes for Evaluating Demersal Seine Fishing

Demersal seining is an active bottom fishing method, which apply seine ropes and a seine net. The seine ropes and net are laid out on the fishing ground with the seine ropes encircling an aggregation of fish on the seabed. The area on the seabed encircled by the seine ropes is typical much larger than the swept area that will be covered by the seine net during the fishing process. Therefore, the catching performance of a demersal seine depends on the efficiency by which the seine ropes are able to herd the fish into and maintain them in the path of the net until they are overtaken by it in the late stages of the fishing process. This article describes flume tank experiments to validate a numerical model. This model simulates the physical behaviour of seine ropes during the fishing process. The experiments are conducted for varying physical properties of the ropes and for different layout patterns. The seine ropes are hauled back at different speeds. A motion tracking system, based on stereo vision, is applied to record the gradual change in the area encircled by the ropes. The experimental results from the flume tank are compared with data obtained using the simulation model. Finally, the validated simulation model is applied for predictions.Copyright

Predicting the effect of seine rope layout pattern and haul-in procedure on the effectiveness of demersal seine fishing: a computer simulation-based approach

Demersal Seining is an active fishing method applying two long seine ropes and a seine net. Demersal seining relies on fish responding to the seine rope as it moves during the fishing process. The seine ropes and net are deployed in a specific pattern encircling an area on the seabed. In some variants of demersal seining the haul-in procedure includes a towing phase where the fishing vessel moves forward before starting to winch in the seine ropes. The initial seine rope encircled area, the gradual change in it during the haul-in process and the fishs reaction to the moving seine ropes play an important role in the catch performance of demersal seine fishing. The current study investigates this subject by applying computer simulation models for demersal seine fishing. The demersal seine fishing is dynamic in nature and therefore a dynamic model, SeineSolver is applied for simulating the physical behaviour of the seine ropes during the fishing process. Information about the seine rope behaviour is used as input to another simulation tool, SeineFish that predicts the catch performance of the demersal seine fishing process. SeineFish implements a simple model for how fish at the seabed reacts to an approaching seine rope. Here, the SeineSolver and SeineFish tools are applied to investigate catching performance for a Norwegian demersal seine fishery targeting cod (Gadus morhua) in the coastal zone. The effect of seine rope layout pattern and the duration of the towing phase are investigated. Among the four different layout patterns investigated, the square layout pattern was predicted to perform best; catching 69%-86% more fish than would be obtained with the rectangular layout pattern. Inclusion of a towing phase in the fishing process was found to increase the catch performance for all layout patterns. For the square layout pattern, inclusion of a towing phase of 15 or 35 minutes increased the catch performance by respectively 37% and 48% compared to fishing without a towing phase. These results highlights the importance of the selected seine rope layout pattern and the duration of the towing phase when fishermen try to maximize the catch performance of their fishery. To our knowledge this is the first time the combination of models for the physical behaviour of seine ropes and for fish behaviour in response to seine rope movements have been applied to predict catch performance for demersal seining.

Energy Savings in Coastal Fisheries: Use of a Serial Battery Hybrid Power System

Fuel effectivization and emission reductions have been on the forefront of research for marine power system solutions. The reduction in fuel use was originally motivated by savings on the principal operating cost of vessels. The need to reduce emissions, both CO2 for the global environment and nitrous oxides (NOx) and soot for the local environment, is on the agenda for the maritime industry. The introduction of shore power supply for ships in port and the NOx emission tax and reduction support scheme are examples of this in Norway. Another initiative that is intended to reduce emissions is the development of battery-based propulsion systems with electric power distribution. Unfortunately, the use of an electric power distribution system, with power conversions from a diesel generator and subsequent storage and retrieval from battery banks, will inevitably result in power losses. However, the actual operation of normal diesel-powered ships is seldom optimal, and only larger ocean-crossing vessels may hope to operate their prime mover and support power systems in an optimal fashion for prolonged periods of time. This article presents the application of a serial-diesel-battery hybrid power system installed onboard a Norwegian costal fisheries vessel, where the variation in power demand allows the batteries to replace the traditional diesel power used in fisheries. A power and propulsion system design is presented as well as energy and time use data for the vessels operation during one calendar year. The simple design of vessels, such as of the example vessels in this article, allows battery hybrid power systems to deliver energy savings due to the low-power demand of the diesel engine operation at idle power used during the operation of the fishing gear. The prime mover is used to supply limited propulsion power, which is mainly hydraulic and electric. The power system for the example vessel is designed as a serial hybrid where the diesel engine is exclusively used to supply electric power to the batteries, which has the added benefit of shielding the diesel engine from load variations on the propeller. The hybrid battery power system is expected to cut operating costs by minimizing fuel consumption during fishing, reducing the use of engine lubricants, diminishing maintenance costs by requiring fewer engine-running hours, and increasing the lifetime of the onboard diesel engine in calendar days due to decreased running time.

Development of a Simulator Training Platform for Fish Farm Operations

The Norwegian aquaculture industry is accident prone compared to other industries and employees report a high number of near-accidents. Furthermore, escape of fish is a challenge for the industry. There is a potential for increased safety for both humans and fish if operators can practice operations in a safe environment. Existing simulators are not suited for this context. This paper presents results from a research and development project aimed at developing a realistic simulator-based training platform for demanding fish farm operations. Three objectives guided the development process. First, a description of operations, aimed at identifying challenges and training needs, which formed the basis for selecting training scenarios well suited for aquaculture. Second, the development of mathematical models that could be used in the simulator were developed, and finally, a curriculum for training course modules to complete the platform. Platform thus points to the integration of the simulator and the practical and theoretical education of operators. In this article, the first and second part of the process are presented and discussed.

FHSIM — Time Domain Simulation of Marine Systems

Numerical time domain simulations have proven applicable for analysing marine systems and operations, but available tools often target specific sub-problems or applications associated with a system or an operation. Such tools are also often limited in terms of extensions and usage. This has motivated the development of FhSim at SINTEF Fisheries and Aquaculture (SFA). FhSim is a software framework aimed at simulating especially marine systems in the time domain, using models described as ordinary differential equations (ODEs).In this paper, we present the architecture and core functionality of the FhSim framework, including modelling, integration and 3D-visualisation. We also present a series of simulation cases which illustrate the different core properties of FhSim, including numerical simulations of aquaculture structures, model-based estimation of trawl nets and optimisation of energy systems in ships.Copyright