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Numerical Modelling and Mechanical Studies on a Point Absorber Type Wave Energy Converter
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.ORCID iD: 0000-0003-1022-0480
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Oceans cover two thirds of the Earth’s surface and the energy potential of ocean waves as a renewable energy source is huge. It would therefore be a tremendous achievement if the vast mechanical energy in waves was converted into a form of energy that could be used successfully by society. For years, scientists and engineers have endeavored to exploit this renewable energy by inventing various generators designed to transform wave energy into electrical energy. Generally, this sort of generator is called a Wave Energy Converter (WEC).

In this thesis, the research is based on the WEC developed in the Lysekil Project. The Lysekil Project is led by a research group at Uppsala University and has a test site located on the west coast of Sweden. The project started in 2002. So far, more than ten prototypes of the WEC have been deployed and relevant experiments have been carried out at the test site. The WEC developed at Uppsala University can be categorized as a point absorber. It consists of a direct-drive linear generator connected to a floating buoy. The linear generator is deployed on the seabed and driven by a floating buoy to extract wave energy. The absorbed energy is converted to electricity and transmitted to a measuring station on land.

The work presented in this thesis focuses on building a linear generator model which is able to predict the performance of the Lysekil WEC. Studies are also carried out on the damping behavior of the WEC under the impact of different sea climates. The purpose is to optimize the energy absorption with a specific optimal damping coefficient. The obtained results indicate an optimal damping for the Lysekil WEC which can be used for optimizing the damping control.

Additionally, the impact two central engineering design features (the translator weight and the stroke length) are investigated. The aim is to find a reasonable structural design for the generator which balances the cost and the energy production.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. , 76 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1443
Keyword [en]
linear generator, point absorber, numerical modelling, power production, optimal damping
National Category
Engineering and Technology
Research subject
Engineering Science
Identifiers
URN: urn:nbn:se:uu:diva-305650ISBN: 978-91-554-9731-6OAI: oai:DiVA.org:uu-305650DiVA: diva2:1038812
Public defence
2016-12-07, 80101, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:00 (English)
Opponent
Supervisors
Available from: 2016-11-14 Created: 2016-10-20 Last updated: 2016-11-16
List of papers
1. Review on electrical control strategies for wave energy converting systems
Open this publication in new window or tab >>Review on electrical control strategies for wave energy converting systems
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2014 (English)In: Renewable & sustainable energy reviews, ISSN 1364-0321, Vol. 31, 329-342 p.Article, review/survey (Refereed) Published
Abstract [en]

Renewable energy techniques are now gaining more and more attention as the years pass by, not only because of the threat of climate change but also, e.g. due to serious pollution problems in some countries and because the renewable energy technologies have matured and can be depended upon an increasing degree. The energy from ocean waves bares tremendous potential as a source of renewable energy, and the related technologies have continually been improved during the last decades. In this paper, different types of wave energy converters are classified by their mechanical structure and how they absorb energy from ocean waves. The paper presents a review of strategies for electrical control of wave energy converters as well as energy storage techniques. Strategies of electrical control are used to achieve a higher energy absorption, and they are also of interest because of the large variety among different strategies. Furthermore, the control strategies strongly affect the complexity of both the mechanical and the electrical system, thus not only impacting energy absorption but also robustness, survivability, maintenance requirements and thus in the end the cost of electricity from ocean waves.

Keyword
Wave energy converter, Electrical control, Wave power, Energy storage
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-223773 (URN)10.1016/j.rser.2013.11.053 (DOI)000332591700027 ()
Available from: 2014-04-25 Created: 2014-04-24 Last updated: 2016-10-27Bibliographically approved
2. Status Update of the Wave Energy Research at Uppsala University
Open this publication in new window or tab >>Status Update of the Wave Energy Research at Uppsala University
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2013 (English)Conference paper (Refereed)
Place, publisher, year, edition, pages
Aalborg, Denmark: , 2013
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-212701 (URN)
Conference
10th European Wave and Tidal Conference (EWTEC)
Available from: 2013-12-13 Created: 2013-12-13 Last updated: 2016-11-24
3. Wave Energy Research at Uppsala University and The Lysekil Research Site, Sweden: A Status Update
Open this publication in new window or tab >>Wave Energy Research at Uppsala University and The Lysekil Research Site, Sweden: A Status Update
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2015 (English)Conference paper (Refereed)
Abstract [en]

This paper provides a summarized status update ofthe Lysekil wave power project. The Lysekil project is coordinatedby the Div. of Electricity, Uppsala University since 2002, with theobjective to develop full-scale wave power converters (WEC). Theconcept is based on a linear synchronous generator (anchored tothe seabed) driven by a heaving point absorber. This WEC has nogearbox or other mechanical or hydraulic conversion systems,resulting in a simpler and robust power plant. Since 2006, 12 suchWECs have been build and tested at the research site located atthe west coast of Sweden. The last update includes a new andextended project permit, deployment of a new marine substation,tests of several concepts of heaving buoys, grid connection,improved measuring station, improved modelling of wave powerfarms, implementation of remote operated vehicles forunderwater cable connection, and comprehensive environmentalmonitoring studies.

Keyword
Wave energy, point absorber, experiments, arrays, generators, ROVs
National Category
Electrical Engineering, Electronic Engineering, Information Engineering Ocean and River Engineering
Identifiers
urn:nbn:se:uu:diva-265218 (URN)
Conference
Proceedings of the 11th European Wave and Tidal Energy Conference. Nantes, France, September 2015
Available from: 2015-10-26 Created: 2015-10-26 Last updated: 2016-11-24Bibliographically approved
4. Linear generator-based wave energy converter model with experimental verification and three loading strategies
Open this publication in new window or tab >>Linear generator-based wave energy converter model with experimental verification and three loading strategies
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2016 (English)In: IET Renewable Power Generation, ISSN 1752-1416, E-ISSN 1752-1424, Vol. 10, no 3, 349-359 p.Article in journal (Refereed) Published
Abstract [en]

Within the Lysekil wave energy research project at the Swedish west coast, more than ten Wave Energy Converters (WECs) prototypes have been developed and installed in an ocean based test site. Since 2006 various experiments have been conducted and the generated electricity was delivered to shore at a nearby island. While experiments are essential for the development of wave energy converters, theoretical studies and simulations are an important complement – not only in the search for advanced designs with higher efficiency, but also for improving the economic viability of the studied concepts. In this paper a WEC model is presented. The model consists of three subsystems: i) the hydrodynamic source, ii) the linear generator model, and iii) the electrical conversion system. After the validation with the experimental results at the research site, the generator model is connected to three passive load strategies – linear resistive load, passive rectification and resonance circuit. The paper focuses on analysing the operation of the model coupled with three load cases. The results prove that the WEC model correctly simulates the linear generator developed in the Lysekil Project. Moreover, the comparison among different load cases is made and discussed. The results gives an indication of the efficiency of energy production as well as the force ripples and resulting mechanical loads on the wave energy converters.

Keyword
linear machines; electric generators; wave power generation; ocean waves; power convertors; power grids; power generation economics; hydrodynamics; rectifying circuits; circuit resonance; load (electric); power generation planning; linear generator-based wave energy converter model; experimental verification; loading strategy; ocean-based test site; grid connection; WEC model; economic viability; hydrodynamic source; electrical conversion system; passive load strategy; linear resistive load; passive rectification; resonance circuit; Lysekil Project; energy production efficiency; force ripples; mechanical load
National Category
Energy Systems Ocean and River Engineering
Identifiers
urn:nbn:se:uu:diva-283546 (URN)10.1049/iet-rpg.2015.0117 (DOI)000371789100008 ()
Funder
SweGRIDS - Swedish Centre for Smart Grids and Energy StorageSwedish Research CouncilSwedish Energy AgencyVINNOVAGöran Gustafsson Foundation for promotion of scientific research at Uppala University and Royal Institute of TechnologySwedish Research Council, 621-2009-3417
Available from: 2016-04-13 Created: 2016-04-13 Last updated: 2016-10-27Bibliographically approved
5. A study on the damping coefficient of a direct-drive type wave energy converter
Open this publication in new window or tab >>A study on the damping coefficient of a direct-drive type wave energy converter
(English)Manuscript (preprint) (Other academic)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-303828 (URN)
Available from: 2016-09-24 Created: 2016-09-24 Last updated: 2016-10-27
6. Impact of Generator Stroke Length on Energy Production for a Direct Drive Wave Energy Converter
Open this publication in new window or tab >>Impact of Generator Stroke Length on Energy Production for a Direct Drive Wave Energy Converter
2016 (English)In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 9, no 9, 730Article in journal (Refereed) Published
Abstract [en]

The Lysekil wave energy converter (WEC), developed by the wave energy research group of Uppsala University, has evolved through a variety of mechanical designs since the first prototype was installed in 2006. The hundreds of engineering decisions made throughout the design processes have been based on a combination of theory, know-how from previous experiments, and educated guesses. One key parameter in the design of the WECs linear generator is the stroke length. A long stroke requires a taller WEC with associated economical and mechanical challenges, but a short stroke limits the power production. The 2-m stroke of the current WECs has been an educated guess for the Swedish wave climate, though the consequences of this choice on energy absorption have not been studied. When the WEC technology is considered for international waters, with larger waves and challenges of energy absorption and survivability, the subject of stroke length becomes even more relevant. This paper studies the impact of generator stroke length on energy absorption for three sites off the coasts of Sweden, Chile and Scotland. 2-m, 4-m, and unlimited stroke are considered. Power matrices for the studied WEC prototype are presented for each of the studied stroke lengths. Presented results quantify the losses incurred by a limited stroke. The results indicate that a 2-m stroke length is likely to be a good choice for Sweden, but 4-m is likely to be necessary in more energetic international waters.

Keyword
wave energy converter (WEC); electrical control; damping force; wave energy
National Category
Environmental Engineering
Identifiers
urn:nbn:se:uu:diva-303356 (URN)10.3390/en9090730 (DOI)000383547900067 ()
Funder
SweGRIDS - Swedish Centre for Smart Grids and Energy StorageSwedish Research Council, 621-2009-3417Swedish Energy AgencyVINNOVAGöran Gustafsson Foundation for promotion of scientific research at Uppala University and Royal Institute of Technology
Available from: 2016-09-17 Created: 2016-09-17 Last updated: 2016-10-27Bibliographically approved

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