scholarly journals Enhancement of a 3-DOF submerged wave energy device using bistability

2020 ◽  
Vol 3 (2) ◽  
pp. 73-82
Author(s):  
Benjamin Schubert ◽  
William S. P. Robertson ◽  
Benjamin S. Cazzolato
Keyword(s):  
Wave Energy ◽  
Degrees Of Freedom ◽  
Phase Relationship ◽  
Bistable System ◽  
Viscous Drag ◽  
Regular Waves ◽  
Point Absorber ◽  
Exciting Forces ◽  
Bistable Mechanism ◽  
The Impact

The dynamic response of a submerged CETO shaped quasi-point absorbing wave energy converter coupled to a bistable power take off is presented in this study. Whilst the impact of bistability has been shown in a limited number of situations to improve the amount of power generated, many models have been restricted to a single degree of freedom and often ignore drag effects. To overcome these model limitations, a submerged single tether point absorber with a bistable power take off was modelled using both 1 and 3 degrees of freedom. The device was subjected to regular waves and included a simple model of viscous drag. The bistable mechanism was provided by a magnetic dipole model quantified by a dimensionless parameter applicable to any bistable system. The performance of the device was is assessed by the theoretical power generated. Over each model, the previously observed benefit of bistability was not consistently obtained. Simulations of regular waves demonstrated an increase in generated power for suboptimal conditions for some frequencies, while a reduction in generated power was observed in optimal conditions. The performance increase showed strong correlation to the phase relationship between the motion and exciting forces as a result of bistability.

Experimental and numerical comparisons of self-reacting point absorber wave energy converters in regular waves

2015 ◽  
Vol 104 ◽  
pp. 370-386 ◽  
Author(s):  
Scott J. Beatty ◽  
Matthew Hall ◽  
Bradley J. Buckham ◽  
Peter Wild ◽  
Bryce Bocking
Keyword(s):  
Wave Energy ◽  
Regular Waves ◽  
Numerical Comparisons ◽  
Point Absorber ◽  
Wave Energy Converters ◽  
Energy Converters

Experimental Study on Model Predictive Control for a Point Absorber Type Wave Energy Converter With a Linear Generator

2018 ◽  
Author(s):  
Jun Umeda ◽  
Hiroki Goto ◽  
Toshifumi Fujiwara ◽  
Tomoki Taniguchi ◽  
Shunji Inoue
Keyword(s):  
Predictive Control ◽  
Wave Energy ◽  
Spectral Distribution ◽  
Time Horizon ◽  
Production Efficiency ◽  
Power Production ◽  
Irregular Waves ◽  
Regular Waves ◽  
Energy Converter ◽  
Point Absorber

This paper presents the experimental evaluation results of power production efficiency of model predictive control (MPC) on a wave energy converter (WEC) with a linear generator in regular and irregular waves. A bottom-fixed WEC of point absorber type was subjected to the WEC model in this paper. To compare the power production efficiency, the power production efficiency of the approximate complex-conjugate control with considering the copper loss (ACL) was also evaluated. In regular waves, the MPC performance was comparable to the ACL one in the power-production amount reasonably. In irregular waves which have narrow band spectral distribution, a same trend as the trend in regular waves was obtained. On the other hand, in irregular waves which have broadband spectral distribution, the MPC was more effective than the ACL. Moreover, Experiments in regular and irregular waves were carried out in the MPC under the constraint of the small heave displacement. The constraint of the displacement was approximately satisfied by the MPC. This is useful in practical operation. It is also investigated experimentally how time horizon affects the performance of the MPC. When the time horizon is short, the power production amount of the MPC increases.

Impact of technical power take-off constraints on the power extraction of unidirectional and bidirectional point absorbers

2015 ◽  
Vol 34 (6) ◽  
pp. 1796-1806
Author(s):  
Alessandro Bozzetto ◽  
Ole Christian Spro ◽  
Elisabetta Tedeschi
Keyword(s):  
Wave Energy ◽  
Control Strategy ◽  
Energy Production ◽  
Power Performance ◽  
Content Type ◽  
Practical Applications ◽  
Power Extraction ◽  
Point Absorber ◽  
Point Absorbers ◽  
The Impact

Purpose – The purpose of this paper is to quantify the impact of the constraints of the power take-off system (PTO) on the power extraction of a point absorber wave energy converter (WEC). Such constraints include power, torque and maximum stroke limitations. Two different concepts, unidirectional and bidirectional point absorbers, are analysed, which both are relevant for practical applications in the wave energy industry. Design/methodology/approach – The two different cases of unidirectional and bidirectional point absorbers are analysed and directly compared. Moreover, a simplified control strategy is considered for the point absorber, which is based on a constant torque reference. The WEC performance is first evaluated in selected sea states and then the analysis is extended to assess the impact of the different solutions on the expected yearly wave energy production of the point absorber, when deployed at a specific location. The European Marine Energy Center (EMEC) is selected as the target site for the analysis. Findings – The analysis was performed in selected sea states and then it was extended to all the sea conditions occurring at the EMEC test site. The comparison between unidirectional and bidirectional operated devices suggested a clear superiority of the latter, ensuring similar power extraction at the expense of a halved required torque by the PTO. Moreover, a selective control strategy was implemented, and the results showed an increase in yearly energy production for the bidirectional device. Research limitations/implications – The study proved the importance of including the actual PTO constraints in the preliminary power assessment in order to avoid unrealistic overestimation of the expected power performance. Originality/value – The paper quantifies the power performance obtained with the application of such control strategy considering both unidirectional and bidirectional point absorbers. This analysis and comparison is extremely relevant since both unidirectional and bidirectional devices are reaching the market.

scholarly journals CFD Simulations of Floating Point Absorber Wave Energy Converter Arrays Subjected to Regular Waves

Energies ◽  
2018 ◽  
Vol 11 (3) ◽  
pp. 641 ◽  
Author(s):  
Brecht Devolder ◽  
Vasiliki Stratigaki ◽  
Peter Troch ◽  
Pieter Rauwoens
Keyword(s):  
Wave Energy ◽  
Wave Energy Converter ◽  
Floating Point ◽  
Regular Waves ◽  
Energy Converter ◽  
Cfd Simulations ◽  
Point Absorber

A point absorber wave energy converter with nonlinear hardening spring power-take-off systems in regular waves

2020 ◽  
Vol 234 (4) ◽  
pp. 820-829
Author(s):  
Zhongqiang Zheng ◽  
Zhipeng Yao ◽  
Zongyu Chang ◽  
Tao Yao ◽  
Bo Liu
Keyword(s):  
Nonlinear Wave ◽  
Conversion Efficiency ◽  
Wave Energy ◽  
Wave Energy Converter ◽  
Linear Wave ◽  
Regular Waves ◽  
Energy Converter ◽  
Point Absorber ◽  
Frequency State ◽  
Nonlinear Hardening

Point absorber wave energy converter is one of the most effective wave energy harness devices. Most of the wave energy converters generate energy by oscillating the floating body. Usually, the power-take-off system is simplified as a linear spring and a linear damper. However, the narrow frequency bandwidth around a particular resonant frequency is not suitable for real vibrations applications. Thus, a nonlinear hardening spring and a linear damper are applied in the power-take-off system. The bandwidth of hardening mechanism is discussed. The dynamic model of wave energy converter is built in regular waves with time domain method. The results show that the nonlinear wave energy converter has higher conversion efficiency than the linear wave energy converter more than the natural frequency state. The conversion efficiency of the nonlinear wave energy converter in the low frequency state is closed to the linear converter. The amplitude of the incident wave, the damping of the nonlinear wave energy converter and the nonlinear parameter [Formula: see text] affect the energy capture performance of the wave energy converter.

Some Extensions of the Classical Approach to Strip Theory of Ship Motions, Including the Calculation of Mean Added Forces and Moments

1978 ◽  
Vol 22 (01) ◽  
pp. 1-19 ◽  
Author(s):  
Theodore A. Loukakis ◽  
Paul D. Scfavounos
Keyword(s):  
Degrees Of Freedom ◽  
Equations Of Motion ◽  
Dynamical Theory ◽  
Forced Oscillations ◽  
Ship Motions ◽  
Regular Waves ◽  
Strip Theory ◽  
Calm Water ◽  
Exciting Forces ◽  
New Formulation

The application of the dynamical theory to the problem of a ship moving with constant forward speed on a free surface has been extended to include the exciting forces in oblique regular waves. As a result, it has become possible to derive a new formulation for the equations of motion, for a ship moving with five degrees of freedom. The application of the same theory has yielded formulas for the calculation of the mean added resistance and drift force in oblique regular waves and the calculation of all mean forces and moments for the forced oscillations of a ship in calm water.

scholarly journals On Power-Absorption Degrees of Freedom for Point Absorber Wave Energy Converters

2020 ◽  
Vol 8 (9) ◽  
pp. 711
Author(s):  
Jinming Wu
Keyword(s):  
Wave Energy ◽  
Degrees Of Freedom ◽  
Center Of Mass ◽  
Width Ratio ◽  
Rotational Inertia ◽  
Wave Power ◽  
Cylindrical Shape ◽  
Internal Mass ◽  
Power Absorption ◽  
Point Absorber

Point absorbers are extensively employed in wave energy conversion. In this work, we studied the point absorber with the buoy of a vertical cylindrical shape. Wave power absorption is obtained through the relative motion between the buoy and an internal mass. Three power-absorption degrees of freedom are investigated, i.e., surge, heave, and pitch, together with the influence of wave compliance of the buoy. Results show that, to absorb more power, the internal mass should be as large as possible for power absorption in translational degrees of freedom, i.e., surge and heave. The total rotational inertia should be as large as possible and the center of mass should be as low as possible for power absorption in pitch. Wave compliance of the buoy slightly enhances the power absorption in surge, but significantly weakens the power absorption in pitch. Surge is the best degree of freedom for power absorption owing to the highest efficiency, indicated by the largest capture width ratio. The simple resistive control is found to be adequate for wave power absorption of the self-reacting point absorber.

scholarly journals Real-Time Nonlinear Model Predictive Controller for Multiple Degrees of Freedom Wave Energy Converters with Non-Ideal Power Take-Off

2021 ◽  
Vol 9 (8) ◽  
pp. 890
Author(s):  
Ali S. Haider ◽  
Ted K. A. Brekken ◽  
Alan McCall
Keyword(s):  
Real Time ◽  
Nonlinear Model ◽  
Wave Energy ◽  
Degrees Of Freedom ◽  
Nonlinear Effects ◽  
Integrated Treatment ◽  
Viscous Drag ◽  
Model Predictive Controller ◽  
Highly Nonlinear ◽  
Predictive Controller

An increase in wave energy converter (WEC) efficiency requires not only consideration of the nonlinear effects in the WEC dynamics and the power take-off (PTO) mechanisms, but also more integrated treatment of the whole system, i.e., the buoy dynamics, the PTO system, and the control strategy. It results in an optimization formulation that has a nonquadratic and nonstandard cost functional. This article presents the application of real-time nonlinear model predictive controller (NMPC) to two degrees of freedom point absorber type WEC with highly nonlinear PTO characteristics. The nonlinear effects, such as the fluid viscous drag, are also included in the plant dynamics. The controller is implemented on a real-time target machine, and the WEC device is emulated in real-time using the WECSIM toolbox. The results for the successful performance of the design are presented for irregular waves under linear and nonlinear hydrodynamic conditions.

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