| 1. |
- Castellucci, Valeria
(författare)
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Sea Level Compensation System for Wave Energy Converters
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The wave energy converter developed at Uppsala University consists of a linear generator at the seabed driven by the motion of a buoy on the water surface. The energy absorbed by the generator is negatively affected by variations of the mean sea level caused by tides, changes in barometric pressure, strong winds, and storm surges.The work presented in this doctoral thesis aims to investigate the losses in energy absorption for the present generation wave energy converter due to the effect of sea level variations, mainly caused by tides. This goal is achieved through the modeling of the interaction between the waves and the point absorber. An estimation of the economic cost that these losses imply is also made. Moreover, solutions on how to reduce the negative effect of sea level variations are discussed. To this end, two compensation systems which adjust the length of the connection line between the floater and the generator are designed, and the first prototype is built and tested near the Lysekil research site.The theoretical study assesses the energy loss at about 400 coastal points all over the world and for one generator design. The results highlight critical locations where the need for a compensation system appears compelling. The same hydro-mechanic model is applied to a specific site, the Wave Hub on the west coast of Cornwall, United Kingdom, where the energy loss is calculated to be about 53 %. The experimental work led to the construction of a buoy equipped with a screw jack together with its control, measurement and communication systems. The prototype, suitable for sea level variations of small range, is tested and its performance evaluated. A second prototype, suitable for high range variations, is also designed and is currently under construction.One main conclusion is that including the compensation systems in the design of the wave energy converter will increase the competitiveness of the technology from an economic point of view by decreasing its cost per kWh. The need for a cost-effective wave energy converter with increased survivability emphasizes the importance of the presented research and its future development.
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| 2. |
- Ekergård, Boel
(författare)
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Full Scale Applications of Permanent Magnet Electromagnetic Energy Converters : From Nd2Fe14B to Ferrite
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents research regarding a full scale linear ferrite permanent magnet generator, installed in a wave energy conversion system. The ferrite based magnetic circuit, supplementing the previous utilized Nd2Fe14B-magnet design, is designed with an electromagnetic numerical simulation tool, where the model is derived from Maxwell’s equations. The full scale design is, known to the author, the first developed linear ferrite based machine. The material change in the magnetic circuit required different mechanical solutions of the generator. The fundamental, primary theory and reasoning behind the new mechanical design is here presented, where sustainability, economy and production have been in focus and affected the final design. Two versions of the generator have been assembled and deployed at the projects experimental site on the Swedish west coast, and three more are under construction, planned to be installed during the autumn of 2013. Further, the thesis presents an electric conversion circuit based on the electric resonance phenomena. Full scale experimental results present a successfully achieved electric resonance between the linear wave energy generator and external circuit.Finally, research regarding a two pole permanent magnet motor for an electrical vehicle is presented. Detailed analytical and numerical calculations are utilized to investigate the losses in the machine over a wide frequency interval. The results indicate the possibility of an increased efficiency of electrical motors in electrical vehicle system and argue for elimination of the gearbox. The system total efficiency and mechanical stability can thereby be increased. The work concerning the wave energy converter is a part of a larger project, the Lysekil Wave Power Project, developed by a research group at Uppsala University, whereas the work concerning the electric motor so far has been carried out as an individual project. However, a future goal is to integrate the research on the electric motor for electric vehicles with ongoing research regarding a flywheel based electric driveline for an All Electric Propulsion System.
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| 3. |
- Wendt, Fabian, et al.
(författare)
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Ocean energy systemswave energy modelling task: Modelling, verification and validation ofwave energy converters
- 2019
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Ingår i: Journal of Marine Science and Engineering. - : MDPI AG. - 2077-1312. ; 7:11
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Tidskriftsartikel (refereegranskat)abstract
- The International Energy Agency Technology Collaboration Programme for Ocean Energy Systems (OES) initiated the OES Wave Energy Conversion Modelling Task, which focused on the verification and validation of numerical models for simulating wave energy converters (WECs). The long-term goal is to assess the accuracy of and establish confidence in the use of numerical models used in design as well as power performance assessment of WECs. To establish this confidence, the authors used different existing computational modelling tools to simulate given tasks to identify uncertainties related to simulation methodologies: (i) linear potential flow methods; (ii) weakly nonlinear Froude-Krylov methods; and (iii) fully nonlinear methods (fully nonlinear potential flow and Navier-Stokes models). This article summarizes the code-to-code task and code-to-experiment task that have been performed so far in this project, with a focus on investigating the impact of different levels of nonlinearities in the numerical models. Two different WECs were studied and simulated. The first was a heaving semi-submerged sphere, where free-decay tests and both regular and irregular wave cases were investigated in a code-to-code comparison. The second case was a heaving float corresponding to a physical model tested in a wave tank. We considered radiation, diffraction, and regular wave cases and compared quantities, such as the WEC motion, power output and hydrodynamic loading.
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