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Hydrodynamic Modelling of Wave Power using Electrical Equivalent Circuit Theory
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. (Wave Energy)
2014 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Ocean wave energy can be harnessed and converted into electric energy nowadays. This provides a possibility for populations that live on islands or along coastlines to utilize the renewable and safe power produced by ocean waves. Point absorbing wave energy converter (WEC) is one example of such devices for electrical power production from ocean waves. It is composed of a floating buoy on the water surface, and a linear generator that sits on seabed and is connected with the buoy via a line. Electricity is generated when the buoy moves up and down in the waves.

The geometry and dimensions of the floating buoy have dominant influences on the energy absorption. This thesis introduces an equivalent electric circuit for modelling the  hydrodynamic interaction between the wave and a cylindrical buoy. The model allows a rapid assessment of the velocity, force in the connection line and output power, by which the system design and optimization can be performed faster and easier.

The electric circuit model is based on the WEC's dynamic force analysis, and the electric components' parameters are determined from analytical approximations of the hydrodynamic coefficients. The simulation results of the equivalent circuit for one typical wave climate in Lysekil has been presented, and the results indicate a good fitting with former experimental results.

The thesis also includes a hydrodynamic study for a torus shaped buoy, which aims at  applying a theoretical background for a force measurement experiment. A comparison has been conducted between the torus buoy and two similar cylindrical buoys. Preliminary WAMIT simulation results demonstrate that the force in the connection line will be 5% bigger by using the torus buoy. It is also found that the torus buoy is advantageous for its larger excitation force and smaller added mass. A brief introduction of the 500kN force measurement system and the communication test have been introduced as well.

Place, publisher, year, edition, pages
Uppsala universitet, 2014. , 50 p.
Series
UURIE / Uppsala University, Department of Engineering Sciences, ISSN 0349-8352
Keyword [en]
wave energy, hydrodynamic modelling, electric circuit, force and power analysis
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:uu:diva-238264OAI: oai:DiVA.org:uu-238264DiVA: diva2:770681
Presentation
2014-04-16, Å4001, 14:15 (English)
Opponent
Supervisors
Funder
Swedish Research CouncilSwedish Energy Agency
Available from: 2014-12-15 Created: 2014-12-11 Last updated: 2015-10-26Bibliographically approved
List of papers
1. Modelling a point absorbing wave energy converter by the equivalent electric circuit theory: A feasibility study
Open this publication in new window or tab >>Modelling a point absorbing wave energy converter by the equivalent electric circuit theory: A feasibility study
2015 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 117, 164901Article in journal (Refereed) Published
Abstract [en]

There is a need to have a reliable tool to quickly assess wave energy converters (WECs). This paper explores whether it is possible to apply the equivalent electric circuit theory as an evaluation tool for point absorbing WEC system modelling. The circuits were developed starting from the force analysis, in which the hydrodynamic, mechanical, and electrical parameters were expressed by electrical components. A methodology on how to determine the parameters for electrical components has been explained. It is found that by using a multimeter, forces in the connection line and the absorbed electric power can be simulated and read directly from the electric circuit model. Finally, the circuit model has been validated against the full scale offshore experiment. The results indicated that the captured power could be predicted rather accurately and the line force could be estimated accurately near the designed working condition of the WEC.

Keyword
wave energy
National Category
Ocean and River Engineering
Identifiers
urn:nbn:se:uu:diva-252486 (URN)10.1063/1.4918903 (DOI)000353831100058 ()
Funder
Swedish Research Council, KOF11 2011-6312Swedish Energy AgencySwedish Research Council, 6212009-3417
Note

Manuscript title: An equivalent circuit for hydrodynamic modelling in wave power system

Corrections in Journal of Applied Physics Vol 118, Issue 8, article number 189903. DOI: 10.1063/1.4935617

Available from: 2015-05-07 Created: 2015-05-07 Last updated: 2017-12-04Bibliographically approved
2. Force in the connection line for a wave energy converter: simulation and experimental setup
Open this publication in new window or tab >>Force in the connection line for a wave energy converter: simulation and experimental setup
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2014 (English)In: 33Rd International Conference On Ocean, Offshore And Arctic Engineering, 2014, Vol 9A: Ocean Renewable Energy, San Francisco, USA, 2014Conference paper, Published paper (Refereed)
Abstract [en]

In order to capture ocean wave energy and transform it into electric energy, Uppsala University has developed a point absorber wave energy converter (AVEC) for electricity production. For a better understanding of a torus shaped buoy's performance, this paper conducts a force analysis under linear conditions, to investigate the hydrodynamic characteristic and line force differences between the torus buoy that is going to be deployed, and two similar cylindrical buoys. The result reveals the line force fromthis torus buoy is roughly 5% larger than from cylindrical buoys for the most energy dense wave climate in Lysekil test site, and negative added mass phenomena won't have a significant impact for the line force. To measure the line force, a force measurement system has been designed. A detailed description is given on the design of the 500 kN force measurement system, and the major differences compared with former force measurement systems. Onshore test result has also been presented. With the force measurement experiment, hydrodynamic analysis for torus buoy can be validated when the system performs linearly, and extreme force for storm weather can be monitored to provide information for future WEC structure's mechanical design.

Place, publisher, year, edition, pages
San Francisco, USA: , 2014
National Category
Ocean and River Engineering Energy Systems
Identifiers
urn:nbn:se:uu:diva-237543 (URN)000363499000007 ()978-0-7918-4553-0 (ISBN)
Conference
33rd International Conference on Ocean, Offshore and Arctic Engineering
Available from: 2014-12-03 Created: 2014-12-03 Last updated: 2016-01-12Bibliographically approved
3. Experimental results on power absorption from a wave energy converter at the Lysekil wave energy research site
Open this publication in new window or tab >>Experimental results on power absorption from a wave energy converter at the Lysekil wave energy research site
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2015 (English)In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 77, 9-14 p.Article in journal (Refereed) Published
Abstract [en]

Power generation from wave power has a large potential to contribute to our electric energy production, and today, many wave power projects are close to be commercialized. However, one key issue to solve for many projects is to decrease the cost per installed kW. One way to do this is to investigate which parameters that have a significant impact on the wave energy converters (WEC) performance. In this paper, experimental results on power absorption from a directly driven point absorbing WEC are presented. The experiments have been carried out at the Lysekil research site in Sweden. To investigate the performance of the WEC, the absorbed power and the speed of the translator are compared. The result confirms that the buoy size and the translator weight have a large impact on the power absorption from the generator. By optimizing the buoy size and translator weight, the WEC is believed to produce power more evenly over the upward and downward cycle. Moreover, to predict the maximum power limit during normal operation, a simulation model has been derived. The results correlates well with experimental data during normal operation. 

National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-238267 (URN)10.1016/j.renene.2014.11.050 (DOI)000349504800002 ()
Available from: 2014-12-11 Created: 2014-12-11 Last updated: 2017-12-05Bibliographically approved
4. Lysekil Research Site, Sweden: A status update
Open this publication in new window or tab >>Lysekil Research Site, Sweden: A status update
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2011 (English)In: 9th European Wave and Tidal Energy Conference, Southampton, UK, 2011, 2011Conference paper, Published paper (Refereed)
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-160039 (URN)
Conference
9th European Wave and Tidal Energy Conference, Southampton, UK, 5-9 September 2011
Available from: 2011-10-13 Created: 2011-10-13 Last updated: 2017-01-25

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