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Tracking a Wave Power Buoy Using a Network Camera: System Analysis and First Results
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.
2009 (English)In: Volume 4: Ocean Engineering; Ocean Renewable Energy; Ocean Space Utilization, Parts A and B, Honolulu, Hawaii, 2009, 799-807 p.Conference paper, Published paper (Refereed)
Abstract [en]

Anobservation system has been set up on a small isleton the Swedish west coast. The purpose of the systemis to monitor the wave buoys in The Lysekil Project.The project is an attempt to harvest wave energy usinglinear generators and point absorbing buoys. The observation system isself-sufficient and uses a network camera to follow the buoymotions. The first results from the camera, which has beenoperating since July 2008, have been analyzed to examine themotion tracking capabilities of the system. The motion tracking wouldwork as a complement to the other measurements that arebeing done on the buoy. The method for extracting motiondata from the two-dimensional pictures is presented. The results aregraphs of translative buoy motion in two dimensions, and rotationalmotion about two different axes. The vertical buoy motion forthe studied sequence is in the range of ±0.5 m.

Place, publisher, year, edition, pages
Honolulu, Hawaii, 2009. 799-807 p.
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:uu:diva-113302DOI: 10.1115/OMAE2009-79121OAI: oai:DiVA.org:uu-113302DiVA: diva2:290361
Conference
ASME 2009 28th International Conference on Ocean, Offshore and Arctic Engineering (OMAE2009) May 31–June 5, 2009 , Honolulu, Hawaii, USA
Available from: 2010-01-26 Created: 2010-01-26 Last updated: 2014-04-29Bibliographically approved
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
2. Buoy Geometry, Size and Hydrodynamics for Power Take Off Device for Point Absorber Linear Wave Energy Converter
Open this publication in new window or tab >>Buoy Geometry, Size and Hydrodynamics for Power Take Off Device for Point Absorber Linear Wave Energy Converter
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Wave energy converters of point absorber type have been developed and constructed. Full scale experiments have been carried out at sea and electricity has been successfully delivered. Linear permanent magnet generators together with a subsea substation and buoys of various geometric shapes have been investigated theoretically and experimentally. The design has in large extent an electronic approach, keeping the mechanical part of it as simple as possible, due to the long life span and reliability of electric components.

Because of the nature of a linear generator, the internal translator with permanent magnets has a limited stroke length which will be reached when the buoy is exposed to large wave heights. Internal springs at the top and bottom of the generator prevent the translator from hitting the generator hull. Inertial forces due to the mass and velocity of the translator and the buoy and its heave added mass compresses the spring. The added mass is a rather large part of the total moving mass. Simulations of a converter with a vertical cylindrical buoy and with a toroidal buoy were conducted, as well as real sea experiments with converters with cylindrical buoys of two different sizes and a toroidal buoy. The overloads are likely to affect the design and service life of the generator, the buoy and the wire which interconnects them.

Buoy shapes with as much excitation force as possible and as little heave added mass as possible were sought. A toroidal buoy caused less overloads on the generator at sea states with short wave periods and relatively large wave height, but for sea states with very long wave periods or extremely high waves, the magnitude of the overloads was mainly determined by the maximum displacement of the buoy.

Snap loads on the interconnecting wire, as the slack wire tensed up after a very deep wave trough, were found to be greater but of the same order of magnitude as forces during the rest of the wave cycle.

During a 4 day period at various wave conditions, two converters with cylindrical buoys proved efficiency between 11.1 % and 24.4 %. The larger buoy had 78 % larger water plane area than the other buoy which resulted in 11 % more power production. Short wave period was beneficial for the power production.

Infinite frequency heave added mass was measured for a cylindrical buoy at real sea and found to be greater than the linearly calculated theoretical added mass.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2014. 71 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1130
Keyword
point absorber, wave, energy, converter, ocean, wec, toroidal, buoy, torus, cylindrical, cylinder, experiment, full scale, trial, sea, energy, renewable
National Category
Energy Engineering Fluid Mechanics and Acoustics
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-220344 (URN)978-91-554-8902-1 (ISBN)
Public defence
2014-04-28, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2014-04-04 Created: 2014-03-13 Last updated: 2014-09-18Bibliographically approved

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Tyrberg, SimonGravråkmo, HalvarLeijon, Mats

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