Numerical Analysis and Parameter Optimization of a Portable Two-Body Attenuator Wave Energy Converter

2021 ◽  
Author(s):  
Joseph Capper ◽  
Jia Mi ◽  
Qiaofeng Li ◽  
Lei Zuo
Keyword(s):  
Drag Coefficient ◽  
Wave Energy ◽  
Degree Of Freedom ◽  
Wave Energy Converters ◽  
Ocean Wave Energy ◽  
Significant Difference ◽  
Power Maximization ◽  
Study Power ◽  
Body Cross Section ◽  
Three Degree Of Freedom

Abstract Easily portable, small-sized ocean wave energy converters (WECs) may be used in many situations where large-sized WEC devices are not necessary or practical. Power maximization for small-sized WECs amplifies challenges that are not as difficult with large-sized devices, especially tuning the device’s natural frequency to match the wave frequency and achieve resonance. In this study, power maximization is performed for a small-sized, two-body attenuator WEC with a footprint constraint of about 1m. A thin, submerged tuning plate is added to each body to increase added mass without significantly increasing hydrostatic stiffness in order to reach resonance. Three different body cross-section geometries are analyzed. Device power absorption is determined through time domain simulations using WEC-Sim with a simplified two-degree-of-freedom (2DOF) model and a more realistic three-degree-of-freedom (3DOF) model. Different drag coefficients are used for each geometry to explore the effect of drag. A mooring stiffness study is performed with the 3DOF model to investigate the mooring impact. Based on the 2DOF and 3DOF power results, there is not a significant difference in power between the shapes if the same drag coefficient is used, but the elliptical shape has the highest power after assigning a different approximate drag coefficient to each shape. The mooring stiffness study shows that mooring stiffness can be increased in order to increase relative motion between the two bodies and consequently increase the power.

On the Control of Three-Degree-of-Freedom Wave Energy Converters

2017 ◽  
Author(s):  
Shangyan Zou ◽  
Ossama Abdelkhalik
Keyword(s):  
Wave Energy ◽  
Degree Of Freedom ◽  
Linear Quadratic ◽  
Linear Quadratic Optimal Control ◽  
Wave Energy Converters ◽  
Control Comparison ◽  
Quadratic Optimal Control ◽  
Pseudo Spectral Method ◽  
Three Degree Of Freedom ◽  
Pseudo Spectral

The control of a three-degree-of-freedom (3-DOF) wave energy converter (WEC) is considered in this paper. Recently, several methods have been developed in the literature for this problem. This paper is a comparison between three methods: the non-linear model predictive control, the pseudo-spectral method, and the time-variant linear quadratic optimal control. Comparison between the three methods is presented in terms of the harvested energy.

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

Ocean Wave Energy Converters - A Perspective

2012 ◽  
Vol 36 (5) ◽  
pp. 707-715 ◽  
Author(s):  
Nanjundan Parthasarathy ◽  
Kui Ming Li ◽  
Yoon-Hwan Choi ◽  
Yeon-Won Lee
Keyword(s):  
Wave Energy ◽  
Ocean Wave ◽  
Wave Energy Converters ◽  
Ocean Wave Energy ◽  
Energy Converters

A review on front end conversion in ocean wave energy converters

2015 ◽  
Vol 9 (3) ◽  
pp. 297-310 ◽  
Author(s):  
Nagulan Santhosh ◽  
Venkatesan Baskaran ◽  
Arunachalam Amarkarthik
Keyword(s):  
Wave Energy ◽  
Ocean Wave ◽  
Wave Energy Converters ◽  
Ocean Wave Energy ◽  
Front End ◽  
Energy Converters

Computational Modeling of Rolling Wave-Energy Converters in a Viscous Fluid1

2015 ◽  
Vol 137 (6) ◽  
Author(s):  
Yichen Jiang ◽  
Ronald W. Yeung
Keyword(s):  
Wave Energy ◽  
Performance Metrics ◽  
Vortex Method ◽  
Inviscid Fluid ◽  
Mathematical Form ◽  
Wave Energy Converters ◽  
Ocean Wave Energy ◽  
Real Fluid ◽  
Fluid Theory ◽  
Energy Absorbing

The performance of an asymmetrical rolling cam as an ocean-wave energy extractor was studied experimentally and theoretically in the 70s. Previous inviscid-fluid theory indicated that energy-absorbing efficiency could approach 100% in the absence of real-fluid effects. The way viscosity alters the performance is examined in this paper for two distinctive rolling-cam shapes: a smooth “Eyeball Cam (EC)” with a simple mathematical form and a “Keeled Cam (KC)” with a single sharp-edged keel. Frequency-domain solutions in an inviscid fluid were first sought for as baseline performance metrics. As expected, without viscosity, both shapes, despite their differences, perform exceedingly well in terms of extraction efficiency. The hydrodynamic properties of the two shapes were then examined in a real fluid, using the solution methodology called the free-surface random-vortex method (FSRVM). The added inertia and radiation damping were changed, especially for the KC. With the power-take-off (PTO) damping present, nonlinear time-domain solutions were developed to predict the rolling motion, the effects of PTO damping, and the effects of the cam shapes. For the EC, the coupled motion of sway, heave and roll in waves was investigated to understand how energy extraction was affected.

scholarly journals A Survey of Power Take-off Systems of Ocean Wave Energy Converters

2019 ◽  
Author(s):  
Zhenwei Liu ◽  
Ran Zhang ◽  
Han Xiao ◽  
Xu Wang
Keyword(s):  
Energy Conversion ◽  
Wave Energy ◽  
Clean Energy ◽  
Ocean Wave ◽  
Direct Drive ◽  
Wave Energy Conversion ◽  
Drive Power ◽  
Wave Energy Converters ◽  
Ocean Wave Energy ◽  
Energy Converters

Ocean wave energy conversion as one of the renewable clean energy sources is attracting the research interests of many people. This review introduces different types of power take-off technology of wave energy converters. The main focus is the linear direct drive power take-off devices as they have the advantages for ocean wave energy conversion. The designs and optimizations of power take-off systems of ocean wave energy converters have been studied from reviewing the recently published literature. Also, the simple hydrodynamics of wave energy converters have been reviewed for design optimization of the wave energy converters at specific wave sites. The novel mechanical designs of the power take-off systems have been compared and investigated in order to increase the energy harvesting efficiency.

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