Numerical Simulation of Wake Effects in the Lee of a Farm of Wave Energy Converters

2009 ◽  
Author(s):  
Charlotte Beels ◽  
Peter Troch ◽  
Julien De Rouck ◽  
Tom Versluys ◽  
Griet De Backer
Keyword(s):  
Wave Energy ◽  
Equation Model ◽  
Staggered Grid ◽  
Water Volume ◽  
Wave Power ◽  
Power Absorption ◽  
Wave Energy Converters ◽  
Mild Slope Equation ◽  
Wake Effects ◽  
Energy Converters

The contribution of wave energy to the renewable energy supply is rising. To extract a considerable amount of wave power, Wave Energy Converters (WECs) are arranged in several rows or in a ‘farm’. WECs in a farm are interacting (e.g. The presence of other WECs influence the operational behaviour of a single WEC) and the overall power absorption is affected. In this paper wake effects in the lee of a single WEC and multiple WECs of the overtopping type, where the water volume of overtopped waves is first captured in a basin above mean sea level and then drains back to the sea through hydro turbines, are studied in a time-dependent mild-slope equation model. The wake behind a single WEC is investigated for uni- and multi-directional incident waves. The wake becomes wider for larger wave peak periods. An increasing directional spreading results in a faster wave regeneration and a shorter wake behind the WEC. The wake in the lee of multiple WECs is calculated for two different farm lay-outs, i.e. an aligned grid and a staggered grid, with varying lateral and longitudinal spacing. In general, the staggered grid results in the highest overall wave power absorption.

scholarly journals WAKE EFFECTS BEHIND A FARM OF WAVE ENERGY CONVERTERS FOR IRREGULAR LONG-CRESTED AND SHORT-CRESTED WAVES

2011 ◽  
Vol 1 (32) ◽  
pp. 53 ◽  
Author(s):  
Peter Troch ◽  
Charlotte Beels ◽  
Julien De Rouck ◽  
Griet De Backer
Keyword(s):  
Wave Energy ◽  
Equation Model ◽  
Staggered Grid ◽  
Water Volume ◽  
Wave Power ◽  
Power Absorption ◽  
Wave Energy Converters ◽  
Mild Slope Equation ◽  
Wake Effects ◽  
Energy Converters

The contribution of wave energy to the renewable energy supply is rising. To extract a considerable amount of wave power, Wave Energy Converters (WECs) are arranged in several rows or in a ’farm’. WECs in a farm are interacting (e.g. the presence of other WECs influence the operational behaviour of a single WEC) and the overall power absorption is affected. In this paper wake effects in the lee of a single WEC and multiple WECs of the overtopping type, where the water volume of overtopped waves is first captured in a basin above mean sea level and then drains back to the sea through hydro turbines, are studied using the time-dependent mild-slope equation model MILDwave. The wake behind a single WEC is investigated for long-crested and short-crested incident waves. The wake becomes wider for larger wave peak periods. An increasing directional spreading results in a faster wave regeneration and a shorter wake behind the WEC. The wake in the lee of multiple WECs is calculated for two different farm lay-outs, i.e. an aligned grid and a staggered grid, with varying lateral and longitudinal spacing. The wave power redistribution in and behind each farm lay-out is studied in detail using MILDwave. In general, the staggered grid results in the highest overall wave power absorption.

Introducing Wave Regeneration by Wind in a Mild-Slope Wave Propagation Model MILDwave to Investigate the Wake Effects in the Lee of a Farm of Wave Energy Converters

2011 ◽  
Author(s):  
Vasiliki Stratigaki ◽  
Peter Troch ◽  
Leen Baelus ◽  
Yannick Keppens
Keyword(s):  
Wave Propagation ◽  
Wave Energy ◽  
Propagation Model ◽  
Wave Power ◽  
Single Wave ◽  
Wave Energy Converters ◽  
Wake Effects ◽  
Wave Regeneration ◽  
Wave Propagation Model ◽  
Energy Converters

The increasing energy demand, the need to reduce greenhouse gas emissions and the shrinking reserves of fossil fuels have all enhanced the interest in sustainable and renewable energy sources, including wave energy. Many concepts for wave power conversion have been invented. In order to extract a considerable amount of wave power, single Wave Energy Converters (abbreviated as WECs) will have to be arranged in arrays or ‘farms’ using a particular geometrical layout, comprising large numbers of devices. As a result of the interaction between the WECs within a farm, the overall power absorption is affected. In general, the incident waves are partly reflected, transmitted and absorbed by a single WEC. Also, the wave height behind a large farm of WECs is reduced and this reduction may influence neighbouring farms, other users in the sea or even the coastline (wake effects of a WEC farm). The numerical wave propagation model MILDwave has been recently used to study wake effects and energy absorption of farms of WECs, though without taking into account wave regeneration by wind in the lee of the WEC-farm which can be significant in large distances downwave the WECs. In this paper, the implementation of wave growth due to wind in the hyperbolic mild-slope equations of the wave propagation model, MILDwave is described. Several formulations for the energy input from wind found in literature are considered and implemented. The performance of these formulations in MILDwave is investigated and validated. The modified model MILDwave is then applied for the investigation of the influence of the wind on the wakes in the lee of a farm of wave energy converters.

Numerical Modeling and Evaluation of Wave Energy Converters

2009 ◽  
Author(s):  
Heather Peng ◽  
Wei Qiu ◽  
Don Spencer
Keyword(s):  
Numerical Modeling ◽  
Frequency Domain ◽  
Wave Energy ◽  
Energy Production ◽  
Wave Power ◽  
Power Absorption ◽  
Wave Energy Converters ◽  
Numerical Studies ◽  
The Waves ◽  
Energy Converters

Wave energy converters use the motion of floating or submerged bodies to extract energy from the waves. Power absorption can be simulated using a simple linear damper with a resistance to motion which is proportional to velocity. Because of the interaction between energy production and motion, there will be an optimum rate of energy production for each wave frequency. Too much damping or too little damping can cause little energy produced. The wave absorption range also depends on the tuned frequency. In this paper, the maximum rates of energy absorption for submerged and floating wave energy converters are evaluated by employing the panel-free method for the motions of the converters in the frequency domain. A general expression for the wave power absorption is described. Numerical studies show that the optimal energy efficiencies of wave energy converters can be well predicted by employing the panel-free method for motion computations.

scholarly journals Hardware-in-the-Loop Validation of Model Predictive Control of a Discrete Fluid Power Power Take-Off System for Wave Energy Converters

Energies ◽  
2019 ◽  
Vol 12 (19) ◽  
pp. 3668
Author(s):  
Anders H. Hansen ◽  
Magnus F. Asmussen ◽  
Michael M. Bech
Keyword(s):  
Model Predictive Control ◽  
Predictive Control ◽  
Wave Energy ◽  
Fluid Power ◽  
Wave Power ◽  
Reactive Control ◽  
Power Extraction ◽  
Wave Energy Converters ◽  
Extraction Algorithm ◽  
Energy Converters

Model predictive control based wave power extraction algorithms have been developed and found promising for wave energy converters. Although mostly proven by simulation studies, model predictive control based algorithms have shown to outperform classical wave power extraction algorithms such as linear damping and reactive control. Prediction models and objective functions have, however, often been simplified a lot by for example, excluding power take-off system losses. Furthermore, discrete fluid power forces systems has never been validated experimentally in published research. In this paper a model predictive control based wave power extraction algorithm is designed for a discrete fluid power power take-off system. The loss models included in the objective function are based on physical models of the losses associated with discrete force shifts and throttling. The developed wave power extraction algorithm directly includes the quantized force output and the losses models of the discrete fluid power system. The experimental validation of the wave power extraction algorithm developed in the paper shown an increase of 14.6% in yearly harvested energy when compared to a reactive control algorithm.

Performance assessments of the fully submerged sphere and cylinder point absorber wave energy converters

2019 ◽  
Vol 33 (13) ◽  
pp. 1950168 ◽  
Author(s):  
Qianlong Xu ◽  
Ye Li ◽  
Yingkai Xia ◽  
Weixing Chen ◽  
Feng Gao
Keyword(s):  
Wave Height ◽  
Wave Energy ◽  
Interaction Analysis ◽  
Wave Power ◽  
Viscous Damping ◽  
Power Performance ◽  
Point Absorber ◽  
Wave Energy Converters ◽  
Submerged Sphere ◽  
Energy Converters

Fully submerged sphere and cylinder point absorber (PA), wave energy converters (WECs) are analyzed numerically based on linearized potential flow theory. A boundary element method (BEM) (a radiation–diffraction panel program for wave-body interactions) is used for the basic wave-structure interaction analysis. In the present numerical model, the viscous damping is modeled by an equivalent linearized damping which extracts the same amount of wave energy over one cycle as the conventional quadratic damping term. The wave power capture width in each case is predicted. Comparisons are also made between the sphere and cylinder PAs which have identical geometrical scales and submerged depths. The results show that: (i) viscous damping has a greater influence on wave power performance of the cylinder PA than that of the sphere PA; (ii) the increasing wave height reduces wave power performance of PAs; (iii) the cylinder PA has a better wave power performance compared to the sphere PA in larger wave height scenarios, which indicates that fully submerged cylinder PA is a preferable prototype of WEC.

scholarly journals Performance of an Array of Oblate Spheroidal Heaving Wave Energy Converters in Front of a Wall

Water ◽  
2020 ◽  
Vol 12 (1) ◽  
pp. 188 ◽  
Author(s):  
Eva Loukogeorgaki ◽  
Ifigeneia Boufidi ◽  
Ioannis K. Chatjigeorgiou
Keyword(s):  
Wave Energy ◽  
Vertical Wall ◽  
Integral Equation Method ◽  
Boundary Integral ◽  
Power Absorption ◽  
Enhanced Absorption ◽  
Wave Energy Converters ◽  
Oblate Spheroidal ◽  
Specific Frequency ◽  
Energy Converters

In this paper, we investigate the performance of a linear array of five semi-immersed, oblate spheroidal heaving Wave Energy Converters (WECs) in front of a bottom-mounted, finite-length, vertical wall under perpendicular to the wall regular waves. The diffraction and radiation problems are solved in the frequency domain by utilizing the conventional boundary integral equation method. Initially, to demonstrate the enhanced absorption ability of this array, we compare results with the ones corresponding to arrays of cylindrical and hemisphere-shaped WECs. Next, we investigate the effect of the array’s distance from the wall and of the length of the wall on the physical quantities describing the array’s performance. The results illustrate that the array’s placement at successively larger distances from the wall, up to three times the WECs’ radius, induces hydrodynamic interactions that improve the array’s hydrodynamic behavior, and thus its power absorption ability. An increase in the length of the wall does not lead to any significant power absorption improvement. Compared to the isolated array, the presence of the wall affects positively the array’s power absorption ability at specific frequency ranges, depending mainly on the array’s distance from the wall. Finally, characteristic diffracted wave field patterns are presented to interpret physically the occurrence of the local minima of the heave exciting forces.

scholarly journals Wave Power Absorption by Arrays of Wave Energy Converters in Front of a Vertical Breakwater: A Theoretical Study

Energies ◽  
2020 ◽  
Vol 13 (8) ◽  
pp. 1985 ◽  
Author(s):  
Dimitrios N. Konispoliatis ◽  
Spyridon A. Mavrakos
Keyword(s):  
Wave Energy ◽  
Cylindrical Wave ◽  
Hydrodynamic Characteristics ◽  
Linear Potential ◽  
Theoretical Evaluation ◽  
Power Absorption ◽  
Array Configuration ◽  
Wave Energy Converters ◽  
Vertical Breakwater ◽  
Energy Converters

The present paper deals with the theoretical evaluation of the efficiency of an array of cylindrical Wave Energy Converters (WECs) having a vertical symmetry axis and placed in front of a reflecting vertical breakwater. Linear potential theory is assumed, and the associated diffraction and motion radiation problems are solved in the frequency domain. Axisymmetric eigenfunction expansions of the velocity potential are introduced into properly defined ring-shaped fluid regions surrounding each body of the array. The potential solutions are matched at the boundaries of adjacent fluid regions by enforcing continuity of the hydrodynamic pressures and redial velocities. A theoretical model for the evaluation of the WECs’ performance is developed. The model properly accounts for the effect of the breakwater on each body’s hydrodynamic characteristics and the coupling between the bodies’ motions and the power take-off mechanism. Numerical results are presented and discussed in terms of the expected power absorption. The results show how the efficiency of the array is affected by (a) the distance between the devices and the wall, (b) the shape of the WEC array configuration, as well as (c) the angle of the incoming incident wave.

scholarly journals Grid Connection of Wave Power Farm Using an N-Level Cascaded H-Bridge Multilevel Inverter

2013 ◽  
Vol 2013 ◽  
pp. 1-9 ◽  
Author(s):  
Rickard Ekström ◽  
Mats Leijon
Keyword(s):  
Wave Energy ◽  
Power Sharing ◽  
Multilevel Inverter ◽  
Wave Power ◽  
Good Correspondence ◽  
Large Wave ◽  
N Level ◽  
Wave Energy Converters ◽  
Grid Connection ◽  
Energy Converters

An N-level cascaded H-bridge multilevel inverter is proposed for grid connection of large wave power farms. The point-absorber wave energy converters are individually rectified and used as isolated DC-sources. The variable power characteristics of the wave energy converters are discussed, and a method of mitigating this issue is demonstrated. The complete power control system is given in detail and has been experimentally verified for a single-phase setup of the 9-level inverter. Theoretical expressions of the power sharing between multilevel cells are derived and show good correspondence with the experimental results.

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