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Depth variation of energy transport in fluid gravity waves
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
2010 (English)In: Journal of Renewable and Sustainable Energy, ISSN 1941-7012, Vol. 2, no 2, 023104- p.Article in journal (Refereed) Published
Abstract [en]

We calculate the distribution of energy flux as a function of the distance below the surface for propagating polychromatic gravity fluid surface waves. Linear theory has been used to derive closed-form expressions for the energy flux as a function of depth. In this context we discuss the power distribution for real ocean waves measured off the west coast of Sweden and compare this to the energy flux distribution for waves with Pierson-Moskowitz and Bretschneider spectral distributions. This is done in order to get an improved understanding of how to improve the power absorption in wave energy converters, and this is also discussed in this paper.

Place, publisher, year, edition, pages
2010. Vol. 2, no 2, 023104- p.
Keyword [en]
gravity waves, hydroelectric power, ocean waves, surface waves (fluid)
National Category
Engineering and Technology
URN: urn:nbn:se:uu:diva-140346DOI: 10.1063/1.3424711ISI: 000287922200005OAI: oai:DiVA.org:uu-140346DiVA: diva2:383456

11431539 energy flux distribution polychromatic gravity fluid surface waves energy transport linear theory closed-form expressions power distribution ocean waves Sweden Pierson-Moskowitz distribution Bretschneider spectral distributions power absorption wave energy converters

Available from: 2011-01-05 Created: 2011-01-05 Last updated: 2016-04-18Bibliographically approved
In thesis
1. Hydrodynamic Modelling for a Point Absorbing Wave Energy Converter
Open this publication in new window or tab >>Hydrodynamic Modelling for a Point Absorbing Wave Energy Converter
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Surface gravity waves in the world’s oceans contain a renewable source of free power on the order of terawatts that has to this date not been commercially utilized. The division of Electricity at Uppsala University is developing a technology to harvest this energy. The technology is a point absorber type wave energy converter based on a direct-driven linear generator placed on the sea bed connected via a line to a buoy on the surface.

The work in this thesis is focused mainly on the energy transport of ocean waves and on increasing the transfer of energy from the waves to the generator and load. Potential linear wave theory is used to describe the ocean waves and to derive the hydrodynamic forces that are exerted on the buoy. Expressions for the energy transport in polychromatic waves travelling over waters of finite depth are derived and extracted from measured time series of wave elevation collected at the Lysekil test site. The results are compared to existing solutions that uses the simpler deep water approximation. A Two-Body system wave energy converter model tuned to resonance in Swedish west coast sea states is developed based on the Lysekil project concept. The first indicative results are derived by using a linear resistive load. The concept is further extended by a coupled hydrodynamic and electromagnetic model with two more realistic non-linear load conditions.

Results show that the use of the deep water approximation gives a too low energy transport in the time averaged as well as in the total instantaneous energy transport. Around the resonance frequency, a Two-Body System gives a power capture ratio of up to 80 percent. For more energetic sea states the power capture ratio decreases rapidly, indicating a smoother power output. The currents in the generator when using the Two-Body system is shown to be more evenly distributed compared to the conventional system, indicating a better utilization of the electrical equipment. Although the resonant nature of the system makes it sensitive to the shape of the wave spectrum, results indicate a threefold increase in annual power production compared to the conventional system.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2011. 91 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 878
Ocean wave energy, Point absorber, Wave energy converter, Wave energy transport, Polychromatic wave, Linear generator, Resonance, Finite depth, Modelling
National Category
Electrical Engineering, Electronic Engineering, Information Engineering Marine Engineering Oceanography, Hydrology, Water Resources
Research subject
Engineering Science with specialization in Electronics
urn:nbn:se:uu:diva-160319 (URN)978-91-554-8214-5 (ISBN)
Public defence
2011-12-09, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Available from: 2011-11-17 Created: 2011-10-21 Last updated: 2011-11-23Bibliographically approved

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Isberg, JanEngström, JensLeijon, Mats
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