Maximizing the Efficiency of Wave-Energy Plant Using Complex-Conjugate Control

1992 ◽  
Vol 206 (4) ◽  
pp. 225-236 ◽  
Author(s):  
P Nebel
Keyword(s):  
Wave Energy ◽  
Complex Conjugate ◽  
Hydrodynamic Coefficients ◽  
Energy Absorber ◽  
Energy Plant ◽  
Practical Engineering ◽  
Engineering Constraints ◽  
Monochromatic Waves

A method of determining the hydrodynamic coefficients of a floating wave-energy absorber is outlined, and the coefficients of a Salter's duck are measured experimentally. A complex-conjugate synthesizer, derived from these coefficients, is used both theoretically and experimentally to predict and to measure the efficiency of a duck in unidirectional monochromatic waves. The synthesis produces a higher efficiency over a greater bandwidth than has been achieved before. The reason for the improvement in efficiency is explained, and conclusions are drawn about the implications of complex-conjugate control for predicting practical engineering constraints on the design of a full-sized wave-energy absorber.

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.

Dynamic Analysis and Configuration Design of a Two-Component Wave-Energy Absorber

2012 ◽  
Author(s):  
Christophe Cochet ◽  
Ronald W. Yeung
Keyword(s):  
Wave Energy ◽  
Degrees Of Freedom ◽  
Outer Cylinder ◽  
Rigid Body Dynamics ◽  
Contact Forces ◽  
Energy Extraction ◽  
Energy Absorber ◽  
Compound Cylinder ◽  
Motion Study ◽  
Heave Motion

The wave-energy absorber being developed at UC Berkeley is modeled as a moored compound cylinder, with an outer cylinder sliding along a tension-tethered inner cylinder. With rigid-body dynamics, it is first shown that the surge and pitch degrees of freedom are decoupled from the heave motion. The heaving motion of the outer cylinder is analyzed and its geometric proportions (radii and drafts ratios) are optimized for wave-energy extraction. Earlier works of Yeung [1] and Chau and Yeung [2,3] are used in the present heave-motion study. The coupled surge-pitch motion can be solved and can provide the contact forces between the cylinders. The concept of capture width is used to characterize the energy extraction: its maximization leads to optimal energy extraction. The methodology presented provides the optimal geometry in terms of non-dimensional proportions of the device. It is found that a smaller radius and deeper draft for the outer cylinder will lead to a larger capture width and larger resulting motion.

A Point Set Analysis Method for Hull Blocks Based on CPD and Engineering Constraints

2020 ◽  
Vol 36 (02) ◽  
pp. 105-114
Author(s):  
Guan Guan ◽  
Hongling Liao
Keyword(s):  
Data Analysis ◽  
Multiobjective Optimization ◽  
Error Distribution ◽  
Analysis Method ◽  
Practical Engineering ◽  
Coherent Point Drift ◽  
Point Set ◽  
Optimal Data Analysis ◽  
Important Basis ◽  
Engineering Constraints

A point set analysis method considering the practical engineering constraints has been proposed in this article. First, the coherent point drift method was used to obtain the initial values of data analysis. Second, the error distribution in different directions was expressed by weight vectors. Last, the multiobjective optimization model was built and the engineering constrains were introduced into the multioptimization objective function to achieve the optimal data analysis results. The experimental results proved that the method could obtain the reasonable data analysis results, which met the engineering constraints. It provides the important basis for the subsequent assembly.

A Twin Unidirectional Impulse Turbine With Fluidic Diode for Wave Energy Conversion

2015 ◽  
Author(s):  
Hideki Sato ◽  
Manabu Takao ◽  
Shinya Okuhura ◽  
Miah Md. Ahsraful Alam ◽  
Toshiaki Setoguchi
Keyword(s):  
Wave Energy ◽  
Air Flow ◽  
Wind Tunnel Test ◽  
Past Study ◽  
Impulse Turbine ◽  
Energy Plant ◽  
Fluidic Diode ◽  
Major Fault ◽  
Unsteady Flow Condition ◽  
Low Efficiency

As an air turbine equipped with oscillating water column (OWC) based wave energy plant, a rectification-valve system has been invented to date. However, this turbine system has problems with the durability of the valves and the complex mechanism. Moreover, it has a major fault in that the valves must be large for high output. Therefore, a twin unidirectional impulse turbine topology has been suggested in previous studies in order to use conventional unidirectional turbines without valves [1, 2]. The topology is composed of two unidirectional impulse turbines. However, the past study indicated that the mean efficiency of the topology was shown to be low, when the performance prediction of the topology in oscillating airflow was carried out by means of quasi-steady analysis [2]. Further, the cause of the low efficiency is because part of the air flow gets through the unidirectional impulse turbine in the direction of low efficiency [2]. In this study, a fluidic diode [3, 4] is adopted in order to suppress the air flow rate into the inefficient turbine in a twin unidirectional impulse turbine topology for wave energy plant, and the effect of the fluidic diodes on the performance of twin unidirectional impulse turbine topology is investigated by a wind tunnel test and computational fluid dynamics (CFD). Further, its usefulness is discussed from a view point of the turbine mean efficiency under unsteady flow condition.

Response of the Mega-Float Equipped With Novel Wave Energy Absorber

2003 ◽  
Author(s):  
Sotaro Masanobu ◽  
Shunji Kato ◽  
Katsuya Maeda ◽  
Yasuhiro Namba
Keyword(s):  
Wave Energy ◽  
Structural Design ◽  
Estimation Method ◽  
The Novel ◽  
Additional Structure ◽  
Energy Absorber ◽  
General Wave ◽  
Wave Drift ◽  
Drift Force ◽  
Hydroelastic Response

The hydroelastic response is significant from the viewpoint of the structural design of a Mega-Float. Equipping a Mega-Float with some additional structures, such as vertical plates, is one of the ways to reduce the hydroelastic response easily. However, in general, wave drift force acting on the Mega-Float may be increased, when the Mega-Float is equipped with the additional structures to reduce the response. In the present study, we developed a novel additional structure that was effective in the reduction of both hydroelastic response and wave drift force. Furthermore, we estimated the response of Mega-Float equipped with the additional structures, and compared the result with the value measured in at-sea experiments. As a result, we confirmed both the effectiveness of the novel additional structure and the validity of the estimation method.

Numerical Simulation and Optimization of a Wave Energy Converter for the Izu Islands Sea in Japan

2014 ◽  
Author(s):  
Takeshi Kamio ◽  
Makoto Iida ◽  
Chuichi Arakawa
Keyword(s):  
Numerical Simulation ◽  
Wave Energy ◽  
Power Output ◽  
Test Site ◽  
Wave Energy Converter ◽  
Complex Conjugate ◽  
Maximum Output ◽  
Energy Converter ◽  
Simulation And Optimization ◽  
Izu Islands

The purpose of this study is the numerical simulation and control optimization of a wave energy converter to estimate the power at a test site in the Izu Islands. In Japan, ocean energy is once again being seriously considered; however, since there are many inherent problems due to severe conditions such as the strong swells and large waves, estimations are important when designing such devices. The numerical simulation method in this study combines the wave interaction analysis software WAMIT and an in-house time-domain simulation code using the Newmark-β method, and introduces approximate complex-conjugate control into the code. The optimized parameters were assessed for a regular sine wave and an irregular wave with a typical wave spectrum. With the optimized parameters, average and maximum output power were estimated for the observed wave data at the test site. The results show a more than 100 kW average power output and a several times larger maximum power output.

scholarly journals Research on the System Simulation for a Fixed O. W. C. Type Wave Energy Absorber

1984 ◽  
Vol 1984 (156) ◽  
pp. 255-263 ◽  
Author(s):  
Takeshi Kinoshita ◽  
Koichi Masuda ◽  
Shogo Miyajima ◽  
Wataru Kato
Keyword(s):  
Wave Energy ◽  
System Simulation ◽  
Energy Absorber ◽  
Type Wave
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