scholarly journals Revisiting Theoretical Limits for One-Degree-of-Freedom Wave Energy Converters

2020 ◽  
pp. 1-11
Author(s):  
Nathan Tom
Keyword(s):  
Power Generation ◽  
Wave Energy ◽  
Degree Of Freedom ◽  
Upper And Lower Bounds ◽  
Complex Conjugate ◽  
Hydrodynamic Coefficients ◽  
Damping Coefficients ◽  
Wave Energy Converters ◽  
Heave Motion ◽  
Energy Converters

Abstract This work revisits the theoretical limits of one-degree-of-freedom wave energy converters (WECs). This paper considers the floating sphere used in the OES Task 10 WEC modeling and verification effort for analysis. Analytical equations are derived to determine bounds on displacement amplitude, time-averaged power (TAP), and power-take-off (PTO) force. A unique result found shows that the TAP absorbed by a WEC can be defined solely by the inertial properties and radiation hydrodynamic coefficients. In addition, a unique expression for the PTO force was derived that provides upper and lower bounds when resistive control is used to maximize power generation. For complex conjugate control, this same expression only provides a lower bound, as there is theoretically no upper bound. These bounds assist in comparing the performance of the floating sphere if it were to extract energy using surge or heave motion. The analysis shows because of differences in hydrodynamic coefficients for each oscillating mode, there are different frequency ranges that provide better power capture efficiency. The influence of a motion constraint on TAP while utilizing a nonideal power take-off is examined and found to reduce the losses associated with bidirectional energy flow. The expression to calculate TAP with a nonideal PTO is modified by the mechanical-to-electrical efficiency and the ratio of the PTO spring and damping coefficients. The PTO spring and damping coefficients were separated in the expression, allowing for limits to be set on the PTO coefficients to ensure net power generation.

Revisiting Theoretical Limits for One-Degree-of-Freedom Wave Energy Converters

2020 ◽  
Author(s):  
Nathan M. Tom
Keyword(s):  
Wave Energy ◽  
Wave Energy Converter ◽  
Degree Of Freedom ◽  
Upper And Lower Bounds ◽  
Complex Conjugate ◽  
Hydrodynamic Coefficients ◽  
Energy Converter ◽  
Damping Coefficients ◽  
Wave Energy Converters ◽  
Energy Converters

Abstract This work revisits the theoretical limits of one-degree-of-freedom wave energy converters. This paper considers the floating sphere used in the Ocean Energy Systems Task 10 Wave Energy Converter modeling and verification effort for analysis. Analytical equations are derived to determine bounds on the motion amplitude, time-averaged power, and power-take-off (PTO) force. A unique result was found that shows the time-averaged power absorbed by a wave energy converter can be defined solely by the inertial properties and radiation hydrodynamic coefficients. In addition, a unique expression for the PTO force amplitude was derived that has provided upper and lower bounds when resistive control is used to maximize power generation. For complex conjugate control, this same expression can only provide a lower bound, as there is theoretically no upper bound. These bounds are used to compare the performance of a floating sphere if it were to extract energy using surge or heave motion. The analysis shows that because of the differences in hydrodynamic coefficients of each oscillating mode, there will be different frequency ranges that provide better power capture efficiency. The influence of a motion constraint on power absorption while also utilizing a nonideal power take-off is examined and found to reduce the losses associated with bidirectional energy flow. The expression to calculate the time-averaged power with a nonideal PTO is modified by the mechanical-to-electrical efficiency and the ratio of the PTO spring and damping coefficients. The PTO spring and damping coefficients were separated in the expression, which allows for limits to be set on the possible values of PTO coefficients to ensure a net flow of power to the grid.

Active control for multi-degree-of-freedom wave energy converters with load limiting

2020 ◽  
Vol 159 ◽  
pp. 1177-1187 ◽  
Author(s):  
A.J. Hillis ◽  
C. Whitlam ◽  
A. Brask ◽  
J. Chapman ◽  
A.R. Plummer
Keyword(s):  
Active Control ◽  
Wave Energy ◽  
Degree Of Freedom ◽  
Wave Energy Converters ◽  
Energy Converters

A Hybrid Power Generation Platform Combining Floating Wind Turbine and Oscillating Water Column Wave Energy Converters

2019 ◽  
Author(s):  
Zheng Chen ◽  
Weijian Zeng ◽  
Ming Tan ◽  
Dahai Zhang ◽  
Yulin Si
Keyword(s):  
Power Generation ◽  
Wind Turbine ◽  
Water Column ◽  
Wave Energy ◽  
Wind Farms ◽  
Offshore Wind ◽  
Oscillating Water Column ◽  
Offshore Wind Farms ◽  
Wave Energy Converters ◽  
Energy Converters

Abstract Recent years have seen rapid development in offshore wind technology. Particularly, floating offshore wind turbines possess great potential in deep water coastal places around the world, though they are now still in the demonstration phase. At the same time, the unused wave energy is also abundant at the sites of offshore wind farms, especially those in deep sea regions. Collecting wave energy in offshore wind farms might benefit both total energy production and reduce maintenance cost. Therefore, integrating offshore wind turbine with wave energy conversion devices could be a good idea to achieve higher efficiency and lower cost. In this paper, we report a combined wind and wave energy power generation concept called WindOWC, which constits of a 5MW wind turbine and three oscillating-water-column (OWC) wave energy converters (WECs). The wind turbine is mounted on a semi-submersible floating platform, which is similar to OC4-semibsubmersible, and the OWCs are located in its three offset columns. In this design, the wind turbine and WECs share the same supporting platform and the power transmission system, thus is expected to reduce the cost of energy. Also, it is possible the OWCs may improve the platform dynamic performance by providing positive damping through controlling the air turbine rotational speed. In this work, we describe the geometry properties of the proposed WindOWC concept and conduct preliminary hydrodynamic analysis using potential flow theory. The ANSYS AQWA is used to obtain the system dynamic responses in frequency and time domain, respectively. The OWC dynamics and expected positive damping from them will be investigated in the future.

scholarly journals Extending Complex Conjugate Control to Nonlinear Wave Energy Converters

2020 ◽  
Vol 8 (2) ◽  
pp. 84
Author(s):  
David G. Wilson ◽  
Rush D. Robinett ◽  
Giorgio Bacelli ◽  
Ossama Abdelkhalik ◽  
Ryan G. Coe
Keyword(s):  
Energy Harvesting ◽  
Limit Cycle ◽  
Wave Energy ◽  
Limit Cycles ◽  
Reactive Power ◽  
Complex Conjugate ◽  
Linear Wave ◽  
Wave Energy Converters ◽  
Linear Limit ◽  
Energy Converters

This paper extends the concept of Complex Conjugate Control (CCC) of linear wave energy converters (WECs) to nonlinear WECs by designing optimal limit cycles with Hamiltonian Surface Shaping and Power Flow Control (HSSPFC). It will be shown that CCC for a regular wave is equivalent to a power factor of one in electrical power networks, equivalent to mechanical resonance in a mass-spring-damper (MSD) system, and equivalent to a linear limit cycle constrained to a Hamiltonian surface defined in HSSPFC. Specifically, the optimal linear limit cycle is defined as a second-order center in the phase plane projection of the constant energy orbit across the Hamiltonian surface. This concept of CCC described by a linear limit cycle constrained to a Hamiltonian surface will be extended to nonlinear limit cycles constrained to a Hamiltonian surface for maximum energy harvesting by the nonlinear WEC. The case studies presented confirm increased energy harvesting which utilizes nonlinear geometry realization for reactive power generation.

scholarly journals Electrical Power Generation from the Oceanic Wave for Sustainable Advancement in Renewable Energy Technologies

2020 ◽  
Vol 12 (6) ◽  
pp. 2178 ◽  
Author(s):  
Omar Farrok ◽  
Koushik Ahmed ◽  
Abdirazak Dahir Tahlil ◽  
Mohamud Mohamed Farah ◽  
Mahbubur Rahman Kiran ◽  
...  
Keyword(s):  
Power Generation ◽  
Renewable Energy ◽  
Electrical Power Generation ◽  
Wave Energy ◽  
Electrical Power ◽  
Extensive Literature ◽  
Energy Devices ◽  
Wave Energy Converters ◽  
Oceanic Wave ◽  
Energy Converters

Recently, electrical power generation from oceanic waves is becoming very popular, as it is prospective, predictable, and highly available compared to other conventional renewable energy resources. In this paper, various types of nearshore, onshore, and offshore wave energy devices, including their construction and working principle, are explained explicitly. They include point absorber, overtopping devices, oscillating water column, attenuators, oscillating wave surge converters, submerged pressure differential, rotating mass, and bulge wave converter devices. The encounters and obstacles of electrical power generation from the oceanic wave are discussed in detail. The electrical power generation methods of the generators involved in wave energy devices are depicted. In addition, the vital control technologies in wave energy converters and devices are described for different cases. At present, piezoelectric materials are also being implemented in the design of wave energy converters as they convert mechanical motion directly into electrical power. For this reason, various models of piezoelectric material-based wave energy devices are illustrated. The statistical reports and extensive literature survey presented in this review show that there is huge potential for oceanic wave energy. Therefore, it is a highly prospective branch of renewable energy, which would play a significant role in the near future.

Heave Motion Performance of Multiple Wave Energy Converters Arrayed in a Water Channel Resonator

2020 ◽  
Author(s):  
Jeongrok Kim ◽  
Il-Hyoung Cho
Keyword(s):  
Wave Energy ◽  
Water Channel ◽  
Standing Waves ◽  
Low Density ◽  
Energy Extraction ◽  
Multiple Wave ◽  
Wave Energy Converters ◽  
Internal Fluid ◽  
Heave Motion ◽  
Energy Converters

Abstract The performance of multiple wave energy converters (WECs) arranged in a Y-shaped water channel resonator (WCR) for amplifying the wave energy with low density was investigated. The WCR consists of a long channel and waveguide installed at the entrance. If the period of the incident wave coincides with the natural period of the fluid in the WCR, then resonance occurs, and the internal fluid is greatly amplified in the form of standing waves. The WECs were positioned at the anti-nodes of standing waves formed in the WCR to maximize energy extraction. We dealt with the heave motion, time-averaged power, and capture width ratio (CWR) of WECs, which are composed of a heaving cylinder and a linear generator. For this purpose, we used the boundary element method and WAMIT commercial code. In parallel, systematic model tests were conducted at the 2D wave tank in Jeju National University to validate the numerical solution. Both results were in good agreement. WECs with a short draft are efficient in energy extraction compared with WECs with a long draft. Numerical and experimental results reveal that the WECs arranged in a WCR have higher efficiency over a wide band of periods than a single WEC without a WCR. Therefore, the wave energy with low density can be amplified by the resonance of the internal fluid in the WCR.

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