Measurements of Relative Displacement and Tilting of a Piston Rod Transmission in a Submerged Linear Wave Energy Converter Operating with End Stop Impact
(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
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.
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
Research subject Engineering Science with specialization in Science of Electricity
IdentifiersURN: urn:nbn:se:uu:diva-179735OAI: oai:DiVA.org:uu-179735DiVA: diva2:545957
ProjectsThe Lysekil Wave Power Project