An oscillating wave energy converter with nonlinear snap-through Power-Take-Off systems in regular waves

Floating oscillating bodies constitute a large class of wave energy converters, especially for offshore deployment. Usually the Power-Take-Off (PTO) system is a directly linear electric generator or a hydraulic motor that drives an electric generator. The PTO system is simplified as a linear spring and a linear damper. However the conversion is less powerful with wave periods off resonance. Thus, a nonlinear snap-through mechanism with two symmetrically oblique springs and a linear damper is applied in the PTO system. The nonlinear snap-through mechanism is characteristics of negative stiffness and double-well potential. An important nonlinear parameter γ is defined as the ratio of half of the horizontal distance between the two springs to the original length of both springs. Time domain method is applied to the dynamics of wave energy converter in regular waves. And the state space model is used to replace the convolution terms in the time domain equation. The results show that the energy harvested by the nonlinear PTO system is larger than that by linear system for low frequency input. While the power captured by nonlinear converters is slightly smaller than that by linear converters for high frequency input. The wave amplitude, damping coefficient of PTO systems and the nonlinear parameter γ affect power capture performance of nonlinear converters. The oscillation of nonlinear wave energy converters may be local or periodically inter well for certain values of the incident wave frequency and the nonlinear parameter γ, which is different from linear converters characteristics of sinusoidal response in regular waves.

[1]  Yaowen Yang,et al.  Toward Broadband Vibration-based Energy Harvesting , 2010 .

[2]  Yang Liu,et al.  Research on energy conversion system of floating wave energy converter , 2014 .

[3]  Torgeir Moan,et al.  Hybrid frequency-time domain models for dynamic response analysis of marine structures , 2008 .

[4]  J. Falnes.  Ocean Waves and Oscillating Systems , 2002 .

[5]  B. Mann,et al.  Nonlinear dynamics for broadband energy harvesting: Investigation of a bistable piezoelectric inertial generator , 2010 .

[6]  Andrew Hulme,et al.  The wave forces acting on a floating hemisphere undergoing forced periodic oscillations , 1982, Journal of Fluid Mechanics.

[7]  W. Cummins.  THE IMPULSE RESPONSE FUNCTION AND SHIP MOTIONS , 2010 .

[8]  S.G. Burrow,et al.  A Resonant Generator with Non-Linear Compliance for Energy Harvesting in High Vibrational Environments , 2007, 2007 IEEE International Electric Machines & Drives Conference.

[9]  Dahai Zhang,et al.  Design of a hydraulic power take-off system for the wave energy device with an inverse pendulum , 2014 .

[10]  Neil D. Sims,et al.  Energy harvesting from the nonlinear oscillations of magnetic levitation , 2009 .

[11]  António F.O. Falcão,et al.  Wave energy utilization: A review of the technologies , 2010 .

[12]  Ryan L. Harne,et al.  A review of the recent research on vibration energy harvesting via bistable systems , 2013 .

[13]  António F.O. Falcão,et al.  Nonlinear dynamics of a tightly moored point-absorber wave energy converter , 2013 .

[14]  W. E. Cummins,et al.  The Impulse Response Function and Ship Motion , 1962 .

[15]  T. Ma,et al.  Opportunities for using non-linear oscillators to enhance energy harvesting from impulsively loaded structures , 2011 .

[16]  I. Kovacic,et al.  Potential benefits of a non-linear stiffness in an energy harvesting device , 2010 .

[17]  Odd M. Faltinsen,et al.  Sea loads on ships and offshore structures , 1990 .

[18]  Thor I. Fossen,et al.  Practical aspects of frequency-domain identification of dynamic models of marine structures from hydrodynamic data , 2011 .

[19]  R.P.F. Gomes,et al.  Hydrodynamic optimization of an axisymmetric floating oscillating water column for wave energy conversion , 2012 .

[20]  Johannes Falnes,et al.  Ocean Waves and Oscillating Systems: Gravity Waves on Water , 2002 .