波能利用型圆筒透空堤水动力特性实验研究

将波能装置与防波堤等海洋结构物相结合,将有助于提升其经济性,促进其应用。以一定间距平行排布多个圆筒振荡水柱装置（OWC）形成波能利用型圆筒透空堤,并基于二维波浪水槽物理模型实验对其水动力特性展开研究,重点关注筒间距、OWC吃水、波高对于波浪防护和波能转换的影响规律。结果表明：圆筒较为紧密排布时,高效波能转换的波频范围显著拓宽;较浅OWC吃水在获得近似波浪防护效果的同时波能转换性能更佳;波浪防护效果及波能转换性能受波高影响较小。波能利用型圆筒透空堤在实际应用时,应采用较小的筒间距和OWC吃水,以同时兼顾较好的波浪防护效果和波能转换性能。     

Performance of OWC wave energy converters: influence of turbine damping and tidal variability

The performance of oscillating water column (OWC) systems depends on a number of factors in a complex manner. The objective of this work is to analyse the influence of the wave conditions, the damping caused by the turbine and the tidal level on the efficiency of the conversion from wave to pneumatic energy that occurs in the OWC chamber. To achieve this, a comprehensive experimental campaign is carried out, involving in total 387 tests of a model OWC under varying wave conditions (both with regular and irregular waves), damping coefficients and tidal levels. It is found that the damping exerted by the turbine is the factor that most affects the chamber efficiency—even more than the wave conditions. It follows that a proper selection of the turbine is crucial not only to the performance of the turbine itself but also to that of the chamber, which reflects the importance of the turbine–chamber coupling in OWC systems. The next factor in order of importance is the wave period. Finally, we find that the influence of the tidal level, which is examined in this work for the first time, is significant under certain conditions. Copyright © 2014 John Wiley & Sons, Ltd.     

Large-scale experiments on the behaviour of a generalised Oscillating Water Column under random waves

This work investigates wave reflection and loading on a generalised Oscillating Water Column (OWC) wave energy converter by means of large scale (approximately 1:5–1:9) experiments in the Grosse Wellenkanal (GWK), in which variation of both still water depth and orifice (PTO) dimension are investigated under random waves. The model set-up, calibration methodology, reflection analyses and loadings acting on the OWC are reported. On the basis of wave reflection analysis, the optimum orifice is defined as that restriction which causes the smallest reflection coefficient and thus the greatest wave energy extraction. Pressures on the front wall, rear wall and chamber ceiling are measured. Maximum pressures on the vertical walls, and resulting integrated forces, are compared with available formulations for impulsive loading prediction, which showed significant underestimation for heaviest loading conditions.The present study demonstrates that a OWC structure can serve as a wave absorber for reducing wave reflection. Thus it can be integrated in vertical wall breakwaters, in place of other perforated low reflection alternatives. The possibility to convert air kinetic into electric energy, by means of a turbine, may give an additional benefit. Thus the installation of such kind of energy converters becomes interesting also in low energy seas.     

Oscillating-water-column wave energy converters and air turbines: A review

The ocean waves are an important renewable energy resource that, if extensively exploited, may contribute significantly to the electrical energy supply of countries with coasts facing the sea. A wide variety of technologies has been proposed, studied, and in some cases tested at full size in real ocean conditions. Oscillating-water-column (OWC) devices, of fixed structure or floating, are an important class of wave energy devices. A large part of wave energy converter prototypes deployed so far into the sea are of OWC type. In an OWC, there is a fixed or floating hollow structure, open to the sea below the water surface, that traps air above the inner free-surface. Wave action alternately compresses and decompresses the trapped air which is forced to flow through a turbine coupled to a generator. The paper presents a comprehensive review of OWC technologies and air turbines. This is followed by a survey of theoretical, numerical and experimental modelling techniques of OWC converters. Reactive phase control and phase control by latching are important issues that are addressed, together with turbine rotational speed control.     

A modified Wells turbine for wave energy conversion

The method of wave energy conversion utilises an oscillating water column (OWC). The OWC converts wave energy into low-pressure pneumatic energy in the form of bi-directional airflow. Wells turbine with its zero blade pitch setting has been used to convert this pneumatic power into uni-directional mechanical shaft power. Measurements in OWC based wave energy plants in India and Japan show that the airflow velocity is not equal in both directions. The velocity is more when the airflows out to the atmosphere (exhalation) than in the reverse direction. It may be advantageous to set the rotor blade pitch asymmetrically at a positive pitch so as to achieve a higher mean efficiency in a wave cycle. Towards this objective, performance characteristics of a turbine with different blade setting angles in steady flow were found by experimentation. Quasi-steady analysis was then used to predict the mean efficiency for a certain variation of air velocity with time. This variation with time was taken as pseudo-sinusoidal wherein the positive part of the cycle was taken as a half sine-wave whose amplitude is greater than that of the negative half sine-wave. Such a variation is representative of what happens in reality. For exhalation velocity amplitude to inhalation velocity ratios 0.8 and 0.6, a rotor blade setting angle of 2° was found to be optimum.     

Testing and control of a power take-off system for an oscillating-water-column wave energy converter

The paper concerns the development of the PTO (power take-off) control of an OWC (oscillating-water-column) spar-buoy wave energy converter. The OWC spar-buoy is an axisymmetric device consisting of a submerged vertical tail tube open at both ends, rigidly fixed to a floater that moves essentially in heave. The oscillating motion of the internal free surface relative to the floater-tube set, produced by the incident waves, makes the air flow through a novel self-rectifying air turbine: the biradial turbine. To reduce the losses of the PTO system at partial load, an electrical generator with a rated power twice the maximum expected average power conversion of the buoy was adopted. The control of the turbine-generator set under highly energetic sea-state conditions was experimentally investigated by means of tests performed in a PTO test rig. In the reported tests, the hydrodynamics of the OWC spar-buoy and the aerodynamics of the air turbine were numerically simulated in real-time and coupled with the experimental model of the turbine/electrical generator set in a hardware-in-the-loop configuration. The experimental results allowed the dynamic behaviour of the PTO to be characterized and provided validation of the proposed control algorithms that ensure operation within safe limits.     

Nonlinear 2D analysis of the efficiency of fixed Oscillating Water Column wave energy converters

This paper reports on the development of a two-dimensional, fully nonlinear Computational Fluid Dynamics (CFD) model to analyse the efficiency of fixed Oscillating Water Column (OWC) Wave Energy Conversion (WEC) devices with linear power take off systems. The model was validated against previous experimental, analytical and numerical results of others. In particular, the simulation results show excellent agreement with the analytical results obtained by Sarmento and Falcão [1] for linear waves in a 2D channel and with previous experiments by others on the interaction between nonlinear waves and a fixed barge. Results are presented for linear waves on the influence of the seaward wall draft and thickness of the OWC device on the resonant frequency and the capture efficiency of the OWC. The key outcome of the present work is that for fully nonlinear waves a substantial decrease in the hydrodynamic capture efficiency of the OWC device was observed with increasing wave height, which represents a significant departure from the linear wave case. The optimal pneumatic damping coefficient for the OWC was also found to be dependent on the wave height. By analysing the magnitude of the first and higher order components of the incident nonlinear waves and the response of the OWC it was found that the first order capture efficiency decreases with increasing wave height, which in turn implies that the OWC hydrodynamic system is fully nonlinear and that the behaviour of an OWC in a nonlinear wave train cannot be accurately represented by the superposition of the linear response to a number of component linear waves. These results have significant implications for the design and operation of practical OWC systems.     

A review on front end conversion in ocean wave energy converters

Harvesting the energy from ocean waves is one of the greatest attractions for energy engineers and scientists. Till date, plenty of methods have been adopted to harvest the energy from the ocean waves. However, due to technological and economical complexity, it is intricate to involve the majority of these energy harvesters in the real ocean environment. Effective utilization and sustainability of any wave energy harvester depend upon its adaptability in the irregular seasonal waves, situation capability in maximum energy extraction and finally fulfilling the economic barriers. In this paper, the front end energy conversions are reviewed in detail which is positioned in the first stage of the wave energy converter among other stages such as power take off (PTO) and electrical energy conversion. If the recent development of these front end energy conversion is well known then developing wave energy converter with economic and commercial viability is possible. The aim of this review is to provide information on front end energy conversion of a point absorber and emphasize the strategies and calamity to be considered in designing such kinds of devices to improve the energy harvesting competence. This will be useful to the engineers for speeding up the development of a matured point absorbing type wave energy converter.     

A time-domain numerical simulator for oscillating water column wave power plants

This paper presents a time-domain numerical simulator of oscillating water column (OWC) wave power plants. The whole problem (the simulation of the movements of the inner free surface due to the excitation of the outer sea-waves) is split into two subproblems: an outer one, dealing with the incident, diffracted and radiated waves, solved once for all, and an inner one, concerning the inner water volume behavior. The kernel of this simulator is a hybrid numerical method [Josset C, Clément AH, Duclos G. A hybrid method for time-domain simulation of oscillating water column wave power plants. Ocean Engineering, to appear.] which allows for the coupling of these two problems. After the validation of each part of this simulator, it was applied to the European wave energy power plant seated on Pico Island, Azores, first to estimate the annual performance of the plant, then to simulate different alternative configurations, in a way to improve the productivity.     

Laboratory experiment on using non-floating body to generate electrical energy from water waves

This paper describes an innovative method of using a non-buoyant body to harness ocean waves. All the point absorbers are buoyant in nature and move up due to buoyancy and come down because of gravity. The point absorbers are designed to move along the waves to make the device efficient. These devices face excessive stress during the rough weather on account of the extreme motion of waves and cause the total device failure. The present study shows that using a non-buoyant body for conventional point absorber principle is much efficient and safer than any other device proposed till today. A small scale wave energy converter with non-buoyant body was designed, fabricated and tested in small scale wave maker. An electrical generator was coupled with the device to generate electrical energy from harnessed waves. The generator was electrically loaded and the generated power was measured. It was found from the experiments that the proposed device showed a significant improvement in electricity generation and safety during extreme conditions. In addition to the electricity generation, the characteristics of the device were also studied by using various wave and device parameters.     

Numerical modelling in wave energy conversion systems

This paper deals with a numerical modelling devoted to predict the flow characteristics in the components of an oscillating water column (OWC) system used for the wave energy capture. In the present paper, the flow behaviour is modelled by using the FLUENT code. Two numerical flow models have been elaborated and tested independently in the geometries of an air chamber and a turbine, which is chosen of a radial impulse type. The flow is assumed to be three-dimensional (3D), viscous, turbulent and unsteady. The FLUENT code is used with a solver of the coupled conservation equations of mass, momentum and energy, with an implicit time scheme and with the adoption of the dynamic mesh and the sliding mesh techniques in areas of moving surfaces. Turbulence is modelled with the k–ε model. The obtained results indicate that the developed models are well suitable to analyse the air flows both in the air chamber and in the turbine. The performances associated with the energy transfer processes have been well predicted. For the turbine, the numerical results of pressure and torque were compared to the experimental ones. Good agreements between these results have been observed.     

Aerodynamic conversion of ocean power from wave to wire

The action of the ocean’s waves can be converted into a vertical motion by submerging an opening in the base of a chamber into the sea. The entrained water forces an oscillating airflow through the top of the chamber which vents to atmosphere via an air turbine. An electric generator completes the conversion chain. A design methodology that focuses on the aerodynamic stage which couples the oscillating water column (OWC) and the Wells air turbine will be presented. The turbine’s most influential design variables will be considered within the context of maximising the plant’s annual performance within the wave regime.     

Research priorities for assessing potential impacts of emerging marine renewable energy technologies: Insights from developments in Wales (UK)

The marine renewable energy industry is expanding globally in response to increased energy demands and the desire to curtail greenhouse gas emissions. Within the UK, Wales has the potential for the development of diverse marine renewable technologies, with a strong tidal range resource, areas of high tidal current energy, and a spatially limited wave energy resource. Targets have been set by the Welsh Government to increase the contribution of marine renewable energy to Wales' electricity generation, and the recent introduction of demonstration zones for tidal and wave energy aims to facilitate developers in device deployment. However, uncertainties remain about the potential impacts of devices, particularly for array scale deployments, planned at several sites, and for the extensive structures required to capture the tidal range resource. Here we review present knowledge of potential impacts, including physical, ecological and societal dimensions, and outline research priorities to provide a scientific basis on which to base decisions influencing the trajectory of Welsh marine renewable energy development.     

Experimental investigation in a Wells turbine under bi-directional flow

In this work an experimental study of flow through a Wells turbine with NACA0015 profiles submitted to an unsteady and bi-directional flow is presented.The experimental set-up of the Department of Mechanical, Chemical and Materials Engineering of the University of Cagliari (DIMCM), can simulate the real operation of a wave energy conversion device based on the principle of an oscillating water column (OWC) equipped with a Wells turbine. The set-up consists of a piston, controlled by a hydraulic system, that moves inside a cylindrical chamber open at the top where the Wells turbine is placed. The piston movement generates the airflow driving the turbine.Experimental investigations were carried out in proximity of the rotor blade using three-dimensional aerodynamic probes to perform a careful characterization of the flow field upstream and downstream of the turbine. The dynamic characteristic of the turbine in terms of dimensionless flow parameters was also determined. The real entity of the hysteresis phenomenon was highlighted for the phases of acceleration and deceleration of the unsteady flow through the turbine. Moreover, the existence of an appropriate correlation between the conventional dimensionless coefficients and a measurable and reliable physical variable was investigated.     

On the park effect in arrays of oscillating wave energy converters

This paper aims to provide guidelines for designing the layout of arrays of oscillating Wave Energy Converters (WECs) based on a review of the literature of wave interactions and park effect in WEC arrays that has been published over the past 30 years.First, the fundamentals of wave energy absorption by oscillating bodies are summarised, and the principal differences between the park effect in arrays of wave energy converters and wind turbines are highlighted. Then, the numerical approaches commonly used to deal with WEC arrays are outlined briefly and their limitations are discussed. It is argued that, at present, only Boundary Element Methods (BEM) are capable of the appropriate analysis. Finally, previous work on wave interactions and park effect in WEC arrays is reviewed. Similar trends are found in these studies, which allow conclusions to be drawn regarding the significance of the park effect as a function of the number of WECs in the array and their spacing. Based on these conclusions, the following tentative guidelines are proposed:For small arrays of conventional devices (fewer than 10 devices of typical dimension 10–20 m) with usual layouts (regular or shifted grids with separating distance of order 100–200 m), the park effect appears to be negligible. For larger arrays (more than 10 devices), a negative park effect seems to be increasingly important with increasing number of rows (the lines of WECs perpendicular to the incident wave direction). Therefore, the number of rows should remain as small as possible, with a separating distance as large as possible. For arrays of non-conventional WECs (WECs of typical dimensions much larger than 10–20 m), no information has been found. However, trends similar to the previous cases could be expected, provided that aspect ratios are maintained.     

不等截面串联双管浮体模型波浪能量转换特性研究

提出一种具有后弯管和直通管2种工作模式的新型振荡水柱装置,并通过水槽实验来探讨做功方式、波周期、波高及质量等因素对该装置从波浪能到气动能量转换的影响。水槽实验表明,当模型工作在后弯管模式下,气室中气流双向做功时,规则波中的俘获宽度比（CWR）最高可达138.6%,随机波中的CWR最高可达94%;气流单向做功时,规则波中CWR最高可达113.7%,随机波中CWR最高可达81.9%。当模型工作在直通管模式下,气流双向做功时,规则波中CWR最高可达81.1%,随机波中CWR最高可达66.2%;气流单向做功时,规则波中CWR最高可达53.9%,随机波中CWR最高可达42.1%。模型在随机波实验中后弯管、直通管工作模式的CWR峰值分别能达到“巨鲸号”的3倍、2倍,显然模型的后弯管工作模式具有更高的能量转换特性。     

Performance estimation of bi-directional turbines in wave energy plants

Oscillating water column(OWC)based wave energy plants have been designed with several types of bidirec-tional turbines for converting pneumatic power to shaft power.Impulse turbines with linked guide vanes andfixed guide vanes have been tested at the Indian Wave Energy plant.This was after initial experimentation withWell's turbines.In contrast to the Well's turbine which has a linear damping characteristic,impulse turbines havenon-linear damping.This has an important effect in the overall energy conversion from wave to wire.Optimizingthe wave energy plant requires a turbine with linear damping and good efficiency over a broad range of flow co-efficient.This work describes how such a design can be made using fixed guide vane impulse turbines.The In-dian Wave Energy plant is used as a case study.     

基于遗传算法的二自由度波浪能装置阵列优化

针对浮子式波浪能装置阵列发电效率提升问题,采用遗传算法对一种二自由度浮子式波浪能发电装置阵列进行优化排布。首先介绍二自由度波浪能发电装置及其阵列数学模型;然后开展二自由度装置阵列优化模型的构建及其遗传算法求解研究;接着对100 m×100 m海域范围内分别开展2、3、5个装置阵列的排布优化计算,并对2个装置阵列的优化结果进行验证,分析波浪能装置阵列影响因子q增大的机理;计算结果表明遗传算法能有效优化二自由度装置阵列排布,增强阵列中各装置之间的相互作用,提升波浪能装置阵列发电效率。     

A novel radial self-rectifying air turbine for use in wave energy converters

The flow through the air turbine of an oscillating water column (OWC) wave energy converter is reciprocating and is random and highly variable. It is not surprising that the time-averaged efficiency of the air turbine is substantially lower than that of a conventional turbine working in nearly steady conditions. A new type of radial-flow self-rectifying turbine (named here biradial turbine) is described in the paper. The two inlet/outlet openings of the rotor are axially offset from each other and face radially the surrounding space. The turbine is symmetrical with respect to a plane perpendicular to its axis of rotation. The rotor blades are surrounded by a pair of radial-flow guide-vane rows. Each guide vane row is connected to the rotor by an axisymmetric duct whose walls are flat discs. A two-dimensional flow method is used first as a preliminary design tool for the turbine geometry. More detailed numerical results are then obtained with the aid of a commercial three-dimensional real-fluid CFD code, which allows a more refined geometry optimization to be carried out, and yields results for flow details through the turbine and for the turbine overall performance under several operating conditions.     

中心管底部形状对浮标波能转换性能影响的实验研究

为改善中心管振荡水柱式波力发电浮标的能量转换性能,对中心管底部设计了四4种模型并在造波水槽中进行实验研究。试验结果表明,直管型中心管俘获宽度比最小,实验测得最高为4.12%,底部有一定锥度的模型会提高俘获宽度比,目前实验最高为19.25%,并出现较高的双峰值,提高了通频带,峰值周期也随锥度的不同出现了移动。试验得到的较佳模型需要进一步优化和实验,为设计适应不同海况的发电浮标提供基础数据。