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Measurements of Relative Displacement and Tilting of a Piston Rod Transmission in a Submerged Linear Wave Energy Converter Operating with End Stop Impact
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)In: Journal of Offshore Mechanics and Arctic Engineering-Transactions of The Asme, ISSN 0892-7219, E-ISSN 1528-896XArticle in journal (Other academic) Submitted
Abstract [en]

A type of piston rod mechanical-lead through transmission has been designed and implemented inside the two first wave energy converter (WEC) prototypes at the Lysekil wave energy research site on the Swedish west cost. The transmission constitutes a direct drive which transfers the mechanical force, absorbed from the waves by a heaving surface-floating buoy, through an encapsulation and into a permanent magnet linear generator bolted to a foundation on the seabed, while sealing off the corrosive seawater. A set-up of 7 laser triangulation sensors have been installed in the second wave energy converter prototype to measure the relative displacement of the piston rod and seal housing in the mechanical lead-through in-situ. This paper presents measurements from full scale operation in two different sea states with end stop impact. Since wear is a successive process stretched out over time measurements have been performed for both sea states with 2.5 month separation. The experimental set-up and sensors are described. Equations for calculating tilt angles and azimuth angles for the piston rod are presented. Results from structure mechanical FEM simulations performed on the wave energy converter structure at end stop impact is also presented. The laser sensor measurements of the relative sideway displacements are correlated with measurements of the translator position and piston rod stroke length performed with a draw wire sensor. A force transducer is used for measuring the force in the buoy line to better understand the variations in motion due to changes in the buoy line axial force. Tilt angles and azimuth angles are presented for a wave period in each measurement period. The results are discussed and conclusions drawn with specific emphasis on the effects of the end stop impacts and wear on the funnel. The successive wear in the buoy line guiding system results in a 6 fold increase in relative tilt angle of the piston rod over a period of 2.5 months. A corresponding increase in motion is also seen for the seal housing, but to a lesser extent, indicating wear on the dynamic sealing system housed inside. The measurements of the relative displacement of the piston rod and seal housing are intended for further research.

Keyword [en]
wave energy converter, linear generator, direct drive, submerged transmission, piston rod, laser triangulation sensor, draw-wire sensor, force transducer, FEM simulation, relative displacement measurement, end stop impact
National Category
Energy Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
URN: urn:nbn:se:uu:diva-179735OAI: oai:DiVA.org:uu-179735DiVA: diva2:545957
Projects
The Lysekil Wave Power Project
Available from: 2012-08-21 Created: 2012-08-21 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Submerged Transmission in Wave Energy Converters: Full Scale In-Situ Experimental Measurements
Open this publication in new window or tab >>Submerged Transmission in Wave Energy Converters: Full Scale In-Situ Experimental Measurements
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Different wave power technologies are in development around the world in different stages of prototype testing. So far only a few devices have been deployed offshore at full scale for extended periods of time. Little data is published about how these different devices perform.

This thesis presents results from experiments with the full-scale offshore wave energy converters at the Lysekil research site on the Swedish west coast. The theories, experiments, measurements, performance evaluations and developments of the submerged transmission in the direct driven permanent magnet linear generator are in focus. The reciprocating submerged transmission fulfills the purpose of transmitting the absorbed mechanical wave energy through the capsule wall into the generator, while preventing the seawater from entering the capsule and reducing the life time of the converter.

A measuring system with seven laser triangulation sensors has been developed to measure small relative displacements between piston rod and seal housing in the submerged transmission with excellent accuracy for the purpose of evaluating both functional behavior and successive wear in-situ. A method for calculating relative tilt angles, azimuth angles, differential tilt angles, and successive wear in the submerged transmission has been developed. Additional sensors systems have been installed in the converter enabling correlation and a thorough investigation into the operating conditions of the transmission and the converter. The thesis presents unique results from the measurements. A data acquisition system transmits the signals from the converter on the seabed to an onshore measuring station. Results are presented in time-, frequency- and the time-frequency domain.

The results have given important information for further development of the submerged transmission, which is important to the survivability of the system. The thesis describes the status of research, and is a step that may influence future designs of wave energy devices for reaching survivability and a cost-effective renewable energy system.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2012. 214 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 961
Keyword
Wave energy converter, direct drive, submerged transmission, piston rod, seal housing, sealing system, laser triangulation sensor, offshore measurements, relative displacement, vibrations, tilt angle, tilting, wear estimation.
National Category
Energy Systems Marine Engineering Ocean and River Engineering Energy Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-179740 (URN)978-91-554-8440-8 (ISBN)
Public defence
2012-09-14, Polhemssalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:00 (English)
Opponent
Supervisors
Projects
The Lysekil Wave Power Project
Note

Published is a preprint version of the full text and should be combined by the errata.

Available from: 2012-08-24 Created: 2012-08-21 Last updated: 2013-01-22Bibliographically approved

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Strömstedt, Erland

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