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Physical and Mathematical Modeling of a Wave Energy Converter Equipped with a Negative Spring Mechanism for Phase Control

1
Department of Civil Engineering, Aalborg University, DK-9220 Aalborg, Denmark
2
Department of Marine Technology, Norwegian University of Science and Technology (NTNTU), NO-7491 Trondheim, Norway
3
CorPower Ocean AB, 114 28 Stockholm, Sweden
*
Author to whom correspondence should be addressed.
Energies 2018, 11(9), 2362; https://doi.org/10.3390/en11092362
Received: 11 July 2018 / Revised: 24 August 2018 / Accepted: 4 September 2018 / Published: 7 September 2018
A wave-energy converter has been studied through the combination of laboratory experiments and numerical simulations. The converter model is a semi-submerged axi-symmetric buoy with a circular cross section with a diameter of 26 cm at the water plane. The buoy is pitching about a fixed external axis oriented such that the buoy works primarily in heave. The laboratory model is equipped with a spring mechanism referred to as WaveSpring, which works to shift the resonance period and increase the response bandwidth of the system. A controlled electric actuator was connected and programmed to provide a velocity-proportional force for power extraction. The buoy mass was varied at two levels and the experimental setup was exposed to a selection of regular and irregular waves. The power take-off (PTO) damping was set as a function of sea state. A mathematical model for global motion response was developed based on linear hydrodynamic theory and rigid-body dynamics. Comparison of laboratory measurements and numerical simulation results shows that the dominant physical effects have been well captured by the mathematical model. Overall, the study gives an experimental verification that a negative spring mechanism mounted in parallel with the power take-off machinery of a wave energy converter may be used to increase the average converted power. View Full-Text
Keywords: point absorber; negative spring; renewable ocean energy; power take-off; hydrostatic stiffness; phase control point absorber; negative spring; renewable ocean energy; power take-off; hydrostatic stiffness; phase control
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Têtu, A.; Ferri, F.; Kramer, M.B.; Todalshaug, J.H. Physical and Mathematical Modeling of a Wave Energy Converter Equipped with a Negative Spring Mechanism for Phase Control. Energies 2018, 11, 2362.

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