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Modelling a point absorbing wave energy converter by the equivalent electric circuit theory: A feasibility study
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. (Wave Energy)
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. Univ Southampton, Energy & Climate Change Div, Fac Engn & Environm, Southampton, Hants, England.
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.

Place, publisher, year, edition, pages
2015. Vol. 117, 164901
Keyword [en]
wave energy
National Category
Ocean and River Engineering
Identifiers
URN: urn:nbn:se:uu:diva-252486DOI: 10.1063/1.4918903ISI: 000353831100058OAI: oai:DiVA.org:uu-252486DiVA: diva2:810573
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
In thesis
1. Hydrodynamic Modelling of Wave Power using Electrical Equivalent Circuit Theory
Open this publication in new window or tab >>Hydrodynamic Modelling of Wave Power using Electrical Equivalent Circuit Theory
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
wave energy, hydrodynamic modelling, electric circuit, force and power analysis
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-238264 (URN)
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
2. Modelling Wave Power by Equivalent Circuit Theory
Open this publication in new window or tab >>Modelling Wave Power by Equivalent Circuit Theory
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The motion of ocean waves can be captured and converted into usable electricity. This indicates that wave power has the potential to supply electricity to grids like wind or solar power. A point absorbing wave energy converter (WEC) system has been developed for power production at Uppsala University. This system contains a semi-submerged buoy on the water surface driving a linear synchronous generator placed on the seabed. The concept is to connect many small units together, to form a wave farm for large-scale electricity generation.

A lot of effort has gone into researching how to enhance the power absorption from each WEC unit. These improvements are normally done separately for the buoy, the generator or the electrical system, due to the fact that modelling the dynamic behavior of the entire WEC system is complicated and time consuming. Therefore, a quick, yet simple, assessment tool is needed. 

This thesis focuses on studying the use of the equivalent circuit as a WEC system modelling tool. Based on the force analysis, the physical elements in an actual WEC system can be converted into electrical components. The interactions between the regular waves, the buoy, and the Power Take-off mechanism can be simulated together in one circuit network. WEC performance indicators like the velocity, the force, and the power can be simulated directly from the circuit model. Furthermore, the annual absorbed electric energy can be estimated if the wave data statistics are known.

The linear and non-linear equivalent circuit models developed in this thesis have been validated with full scale offshore experimental results. Comparisons indicate that the simplest linear circuit can predict the absorbed power reasonably well, while it is not so accurate in estimating the peak force in the connection line. The non-linear circuit model generates better estimations in both cases. To encourage researchers from different backgrounds to adapt and apply the circuit model, an instruction on how to establish a non-linear equivalent circuit model is supplied, as well as on how to apply the model to accelerate the decision making process when planning a WEC system.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2015. 75 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1309
Keyword
Wave energy, hydrodynamics, electric circuit, electrical analogy, energy absorption, force, system modelling, Simulink, engineering science, renewable energy
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-265270 (URN)978-91-554-9390-5 (ISBN)
Public defence
2015-12-11, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Funder
Swedish Energy AgencyStandUpSwedish Research Council, KOF11 2011-6312Swedish Research Council, 621-2009-3417
Available from: 2015-11-19 Created: 2015-10-26 Last updated: 2016-01-13

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