Parameterisation of Radiation Forces for Multiple Degree-of-Freedom Wave Energy Converters Using Moment-Matching

2020 ◽  
Vol 30 (4) ◽  
pp. 395-402
Author(s):  
Nicolás Faedo ◽  
Yerai Peña-Sanchez ◽  
John V Ringwood
Keyword(s):  
Wave Energy ◽  
Degree Of Freedom ◽  
Moment Matching ◽  
Wave Energy Converters ◽  
Radiation Forces ◽  
Energy Converters

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.

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

scholarly journals Moment-Matching-Based Identification of Wave Energy Converters: the ISWEC Device

2018 ◽  
Vol 51 (29) ◽  
pp. 189-194
Author(s):  
Nicolás Faedo ◽  
Yerai Peña-Sanchez ◽  
John V. Ringwood
Keyword(s):  
Wave Energy ◽  
Moment Matching ◽  
Wave Energy Converters ◽  
Energy Converters

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.

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