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research-article

Experimental and numerical studies of dynamic behaviours of a hydraulic power take-off cylinder using spectral representation method

[+] Author and Article Information
Moisés Brito

CERIS, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa, Portugal
moises.brito@tecnico.ulisboa.pt

Luis Teixeira

Instituto de Mecánica de los Fluidos e Ingeniería Ambiental (IMFIA), Facultad de Ingeniería, Universidad de la República, Montevideo, Uruguay
luistei@fing.edu.uy

Ricardo B. Canelas

CERIS, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa, Portugal
ricardo.canelas@tecnico.ulisboa.pt

Rui Miguel Lage Ferreira

CERIS, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa, Portugal
ruimferreira@tecnico.ulisboa.pt

Maria Graça Neves

Harbours and Maritime Structures Division, Hydraulics and Environment Department, Laboratório Nacional de Engenharia Civil (LNEC), Av. do Brasil 101, 1700-066 Lisboa, Portugal
gneves@lnec.pt

1Corresponding author.

ASME doi:10.1115/1.4037464 History: Received March 06, 2017; Revised July 18, 2017

Abstract

Hydraulic cylinders are generally used as power take-off (PTO) mechanisms in wave energy converters (WECs). The dynamic behaviour of its PTO force, which integrates friction and pressure forces, is a difficult constraint to include in an analytical or in a numerical model. In this paper, the PTO force characteristics of a hydraulic cylinder are experimentally and numerically investigated under different magnitudes of controlled excitation force. In order to characterize the dynamic behaviours of PTO force the displacement, acceleration and pressure in the cylinder chamber for given excitation forces are measured. The pressure force is calculated using the measured value of the pressure, and the friction force is calculated based on the equation of motion using measured values of the pressure, excitation force and acceleration of the piston. Experimental results show clearly a strong nonlinear force-velocity characteristics, including stochastic and hysteretic behaviours. To model the hysteretic behaviour the modified LuGre model is used for the friction force and a new approach is proposed for the pressure force. To model the stochastic behaviour of the friction and pressure forces the spectral representation method is used. The systematically comparison between measured and simulated results shows that the numerical model captures most of dynamic behaviours of PTO force.

Copyright (c) 2017 by ASME
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