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Spectral Parameters and Wave Energy Converter Performance
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.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Wave energy converter performance is typically specified for given values of significant wave height Hm0 and energy period T-10, in a matrix. For such a representation to be valid, it must be assumed that two parameters determine the performance of the wave energy converter satisfactorily. However, studying performance data for the wave energy converter L1 at the Lysekil research site, it can be seen that for measurements with similar values of Hm0 and T-10, there are values of relative absorption that range from 5 % to 25 %. It therefore seems probable that the properties of the sea state that are not captured using Hm0 and T-10 have an effect on how a WEC performs. It has been proposed in the literature that the width of the wave spectrum is one such property. In this paper, six parameters that describe spectral width have been tested against performance data to look for correlations. In addition to this, the performance data was tested against peak period and standard deviation of peak frequency, as found through wavelet analysis. Out of the parameters tested, κ and ε1 displayed the strongest correlation with relative absorption. Even this correlation was not very strong however, and did only exhibit an r2-value of 0.39 in a linear fit for L1 connected to a 4.9 Ω load. It was also found that the lowest absorption values were connected to the lowest and highest values for peak period.

National Category
Energy Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
URN: urn:nbn:se:uu:diva-160084OAI: oai:DiVA.org:uu-160084DiVA: diva2:448201
Available from: 2011-10-14 Created: 2011-10-14 Last updated: 2012-01-04
In thesis
1. Buoy and Generator Interaction with Ocean Waves: Studies of a Wave Energy Conversion System
Open this publication in new window or tab >>Buoy and Generator Interaction with Ocean Waves: Studies of a Wave Energy Conversion System
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

On March 13th, 2006, the Division of Electricity at Uppsala University deployed its first wave energy converter, L1, in the ocean southwest of Lysekil. L1 consisted of a buoy at the surface, connected through a line to a linear generator on the seabed. Since the deployment, continuous investigations of how L1 works in the waves have been conducted, and several additional wave energy converters have been deployed.

This thesis is based on ten publications, which focus on different aspects of the interaction between wave, buoy, and generator. In order to evaluate different measurement systems, the motion of the buoy was measured optically and using accelerometers, and compared to measurements of the motion of the movable part of the generator - the translator. These measurements were found to correlate well. Simulations of buoy and translator motion were found to match the measured values.

The variation of performance of L1 with changing water levels, wave heights, and spectral shapes was also investigated. Performance is here defined as the ratio of absorbed power to incoming power. It was found that the performance decreases for large wave heights. This is in accordance with the theoretical predictions, since the area for which the stator and the translator overlap decreases for large translator motions. Shifting water levels were predicted to have the same effect, but this could not be seen as clearly.

The width of the wave energy spectrum has been proposed by some as a factor that also affects the performance of a wave energy converter, for a set wave height and period. Therefore the relation between performance and several different parameters for spectral width was investigated. It was found that some of the parameters were in fact correlated to performance, but that the correlation was not very strong.

As a background on ocean measurements in wave energy, a thorough literature review was conducted. It turns out that the Lysekil project is one of quite few projects that have published descriptions of on-site wave energy measurements.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2011. 52 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 872
Keyword
Wave power, Measurement systems, Marine technology, Energy conversion, Renewable energy, Energy absorption, Wave resource, Oceanic engineering, Linear generators, Point absorbers, Sea trials, Camera systems, Accelerometers, Offshore experiments
National Category
Energy Engineering Marine Engineering Energy Systems Ocean and River Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-160085 (URN)978-91-554-8192-6 (ISBN)
Public defence
2011-12-02, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2011-11-11 Created: 2011-10-14 Last updated: 2012-01-09Bibliographically approved

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Lindroth [formerly Tyrberg], Simon

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