1,721,014 research outputs found
In situ results from a new energy scavenging system for an autonomous underwater vehicle
No full textA probabilistic method to evaluate bow foils for realistic seas and shipping routes
No full textTo improve ship efficiency and reduce CO
2 emissions, the use of renewable based energy saving devices is an emerging field. By harnessing the ambient wave energy, ship bow mounted foils can serve as an energy saving device (ESD), reducing the added resistance in waves and generating an additional thrust. This paper presents a methodology to predict the efficiency of bow foils over various regions, seasons and ship routes. The results show that ship length significantly influences the effectiveness of bow foils with respect to differing regions worldwide. The percentage foil retraction is also shown to be a significant factor in operating bow foils with a large variation depending on ship heading and encountered sea state. The presented method, which could be implemented for the assessment of future bow foil designs, provides a holistic approach to evaluate bow foils for route and ship specific energy savings.
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Self powered Autonomous Underwater Vehicles (AUVs): Results from a gyroscopic energy scavenging prototype
No full textThis paper describes and presents preliminary experimental results from a novel prototype energy scavenging system installed in a model 2m cylindrical Autonomous Underwater Vehicle (AUV). The system, which is based on control moment gyroscope (CMG) principles, utilises the gyroscopic response of a gimballed flywheel mounted within an AUV body to generate energy from the wave induced rotational motions of the vehicle. This method, of using the reaction of a spinning wheel under an input torque to provide an output torque of greater magnitude, orthogonal to the input torque axis and the spin axis provides a means to harvest energy in-situ, without external appendages and additional hydrodynamic drag. The system promises to extend AUV mission durations indefinitely and reduce support vessel time currently required for periodical recharging and redeployment. A description of the system operation, design and experimental results from a series of regular wave tests conducted at zero speed in a towing tank are presented in this paper. The results show that the system can harvest energy, with greatest power generation around resonance, tailing off as the frequency increases and typically nonlinear in nature. The results show that the system could provide additional hotel load or power specific systems on an AUV and potentially any rotationally excited platform, e.g., Autonomous Surface Vessels (ASVs), Buoys or Boats
Control strategies for marine gyrostabilizers
No full textThis paper examines various control strategies for a marine gyrostabilizer system, including passive and derivative-based control methods and proposes two new marine gyrostabilizer control strategies: reaction wheel and unrestricted gimbal control. A numerical model is developed, and simulations of a 20-m monohull boat, in irregular beam waves, is presented, based on the control objective of minimizing the resultant excitation moments on the vessel. With limited literature on the subject of marine gyrostabilizers, this paper is intended to convey the state of the art, presenting the governing equations of motions, in addition to presenting new marine gyrostabilizer control strategies, which may be able to further improve their performance
Feasibility study of a new energy scavenging system for an autonomous underwater vehicle
No full textAutonomous underwater vehicles (AUV) can only operate for hours or days at a time between battery charges. Alternative power systems or in-situ charging strategies are required to extend missions. This paper presents the feasibility of a new gyroscopic wave-energy scavenging system. The energy scavenging system promises to; reduce AUV battery requirements negating the necessity to carry sufficient energy reserves (size and weight) for entire missions, reduce costs by freeing support vessel time (a major cost component in AUV deployment) and enable AUVs to be remotely and renewably recharged at sea, indefinitely extending missions. A theoretical description of the system and simulation results for a range of geometrically scaled torpedo style AUVs are presented. The results show that the generated power is sufficient to provide power for a range of AUV sensors and comparable to equivalent solar panel and wind turbine devices
A gyroscopic wave energy recovery system for marine vessels
No full textIn this paper, a wave energy capture system for marine vessels is described. The system uses gyroscopic precession to create a relative motion within a vessel to generate power from the wave-induced roll and pitch motions. The governing equations of motion and a numerical model of the system are described in this paper and the behaviour and performance of the system is identified. The system has several significant advantages over existing wave energy devices. For marine craft that operate in waves, the system could be very useful, providing a means to recover wave energy, reducing environmental impact, and improving operational effectivenes
The performance of bow foils in irregular and oblique waves
No full textBow foils are an emerging energy saving device that utilise wave energy to improve the efficiency of ships operating in waves, through both a reduction in ship motions and the generation of additional thrust. To identify the performance of bow foils in oblique waves, this paper presents and compares experimental results from a series of free-running model tests, with and without a bow foil, with constant forward speed, in regular and irregular oblique waves. The experiments identify the effect of bow foils on the ship heave and pitch motions, shaft torque and revolutions and foil forces and motion, over a range of relative wave headings. The results, demonstrating the ITTC QNM method, show that the bow foil reduces the delivered power required to maintain a given speed in waves, and are effective across a range of heading angles, modal periods, and wave height once a threshold is reached. The results also verify the use of spectral approaches to predict the performance of bow foils in irregular waves using transfer functions and identify that the greatest power savings are achieved in head wave conditions. The presented results provide a holistic design methodology to predict and scale the performance of bow foils across a range of sea states
Modelling and analysis of a single gimbal gyroscopic energy harvester
No full textThis work investigates the non-linear dynamicsof a single gimbal gyroscopic energy harvester,excited by a harmonic moment about 1 and 2 axes simultaneously. The governing equations of motion arederived and a numerical model is developed to analysethe forced system response in all three rotationaldegrees of freedom. Simulations showing the effectof the harmonic forcing frequency and the gyroscopicdamping are presented. The results identify the characteristic motion responses and available power of asingle gimbal gyroscopic energy harvester includingthe development of the non-linear responses
Recharging autonomous underwater vehicles from ambient wave induced motions
No full textIn this paper a novel gyroscopic system capable of recharging an autonomous underwater vehicle (AUV) using wave energy is proposed. The system, which is based on control moment gyroscope (CMG) principles, utilises the gyroscopic response of a gimballed flywheel mounted within an AUV body to generate energy from the wave induced rotational motions of the vehicle. By utilising the wave induced rotational motions of an AUV and the relative motion/torque created by a precessing gimballed flywheel promises to enable AUVs to generate energy in-situ and from a renewable source. This novel approach has several advantages. As the system is housed internally it is not exposed to the harsh underwater environment, is not susceptible to bio-fouling and does not add any hydrodynamic drag. In addition, the system can be positioned anywhere within the AUV body and the technology has the potential to be developed into an integrated energy harvesting, storage and motion control system; whereby the wave induced gyroscopic precession of the flywheel can be used to generate energy, the flywheel kinetic energy (spin) can be utilised for energy storage (similar to Kinetic Energy Recovery Systems or KERS) and motion control can be provided by precession control of the flywheel (providing a stable platform for improved monitoring/recording capabilities). In this paper a theoretical description of the system is provided including a derivation of the governing equations of motion following a momentum (Newton-Euler) approach. A numerical model is also described and simulation results for a pitching 2m AUV system are presented. The results show that the system could be used to periodically recharge an AUV remotely, enabling longer AUV deployments at sea<br/
The effect of ship length scale on bow foil efficiency gains in waves
No full textFor a ship operating in waves, bow foils can significantly reduce the delivered power required to maintain a given speed in waves, saving fuel and reducing emissions. As a result, bow foils are receiving a significant interest as an innovative energy efficiency technology to reduce CO2 and comply with increasingly stringent regulations set by the International Maritime Organization (IMO). However, currently information on the suitability of bow foils for different ship types is limited. It remains unclear, which ship scales and areas of operation provide the greatest efficiency and emission savings. This paper assesses the efficiency of passive bow foils over a range of scales and sea states. Given that a ship’s seakeeping response relative to the incident wave directly affects the response of the bow foil, there exists an optimal wavelength to ship length ratio for optimal (passive) bow foil operation. This article uses an experimental dataset to demonstrate the effect of ship length scale on the bow efficiency gains achieved in different sea states. Using a range of ship length scales, the bow foil efficiency gain was determined for different irregular sea states at regular intervals of wave period. Combined with wave statistics, these results were employed to generate contour plots of optimal ship length for various oceans and seas. Since the wavelength and ship length are predefined parameters, these results can be used by researchers, engineers, ship owners to assess whether bow foil technology can improve a particular ship’s performance and reduce emissions
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