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Research Papers: Applications

Experimental and Numerical Studies of Dynamic Behaviors 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,
Lisboa 1049-001, Portugal
e-mail: moises.brito@tecnico.ulisboa.pt

Luis Teixeira

Facultad de Ingeniería,
Instituto de Mecánica de los Fluidos
e Ingeniería Ambiental (IMFIA),
Universidad de la República,
Montevideo 11300, Uruguay
e-mail: luistei@fing.edu.uy

Ricardo B. Canelas

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

Rui M. L. Ferreira

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

Maria G. Neves

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

1Corresponding author.

Contributed by the Tribology Division of ASME for publication in the JOURNAL OF TRIBOLOGY. Manuscript received March 6, 2017; final manuscript received July 18, 2017; published online September 29, 2017. Assoc. Editor: Stephen Boedo.

J. Tribol 140(2), 021102 (Sep 29, 2017) (13 pages) Paper No: TRIB-17-1072; doi: 10.1115/1.4037464 History: Received March 06, 2017; Revised July 18, 2017

Hydraulic cylinders are generally used as power take-off (PTO) mechanisms in wave energy converters (WECs). The dynamic behavior 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 behaviors 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 behaviors. To model the hysteretic behavior, the modified LuGre model is used for the friction force and a new approach is proposed for the pressure force. To model the stochastic behavior 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 behaviors of PTO force.

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References

Figures

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Fig. 1

Schematic representation (not to scale) of the side view of hydraulic cylinder: (a) experimental setup, illustrating the position of the experimental apparatus and the geometry of the mechanical system and (b) cylinder details

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Fig. 2

Experimental setup used in the irregular motion applied to the OWSC: (a) schematic representation (not to scale) of the side view, illustrating the position of the experimental apparatus and (b) photograph

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Fig. 3

Time series measured for T = 5.1 and 7.0 s: (a) and (b) x(t), (c) and (d) x˙(t), (e) and (f) Fexc(t), and (g) and (h) Fp(t)

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Fig. 4

Dynamic behavior measured during regular x˙ variation for T = 5.1 and 7.0 s: (a) and (b) FPTO(x˙), (c) and (d) Ff(x˙), and (e) and (f) Fp(x˙)

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Fig. 5

Measured and fitting power spectrum density: (a) fluctuation signal of Ff and (b) fluctuation signal of Fp

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Fig. 6

Comparison between measured versus simulated scatter diagrams obtained with and without stochastic components for T = 5.1 and 7.0 s: (a) and (b) Ff and (c) and (d) Fp

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Fig. 7

Comparison between measured and simulated time series for T = 5.1 and 7.0 s: (a) and (b) FPTO(t), (c) and (d) Ff(t), and (e) and (f) Fp(t)

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Fig. 8

Comparison of measured and simulated results for T = 5.1 s: (a) FPTO(x˙), (b) FPTO(x), (c) Ff(x˙), (d) Ff(x), (e) Fp(x˙), and (f) Fp(x)

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Fig. 9

Comparison of measured and simulated results for T = 7.0 s: (a) FPTO(x˙), (b) FPTO(x), (c) Ff(x˙), (d) Ff(x), (e) Fp(x˙), and (f) Fp(x)

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Fig. 10

Comparison between measured and simulated time series: (a) θ(t), (b) θ˙(t), (c) Fp(t), and (d) FPTO(t)

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