Oscillating Water Column based wave energy plants convert wave energy into low pressure pnuematic power in the form of bi-directional air flows. Air turbines which are capable of rotating uni-directionally in bi-directional air flow, otherwise also known as self-rectifying turbines, are used to extract mechanical shaft power which is further converted into electrical power by a generator. This paper reviews the state of the art in self-rectifying impulse air turbines. New results on optimum parameters for the fixed-guide-vane impulse turbine are also presented. Starting characteristics and conversion efficiencies of two types of impulse turbines are compared with the well known Wells turbine. © 2001 Elsevier Science Ltd. All rights reserved.

Sundarm Moses Santhakumar

Flow of fluids

Hydraulic turbines

Oscillations

BI-DIRECTIONAL AIR FLOWS

IMPULSE TURBINES

WAVE ENERGY CONVERSION

ENERGY CONVERTER

turbine

wave

Wave energy

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IIT Madras

A review of impulse turbines for wave energy conversion

Renewable Energy

The oscillating water column, which has a pneumatic section, can convert wave energy to air pressure, and thus, it rotates the turbine. The system has an inherent weakness of having low efficiency. Typically, the small Wells or axial turbines without any modifications have an efficiency of less than 40% under good sea wave condition which is a drawback and considered as less efficient to extract energy from the oceans. In this paper, the performance of the turbine is studied and analyzed by a computational fluid dynamics technique. ANSYS commercial code is used to discretize the mass, momentum, energy equations, and the turbine efficiency was evaluated. Different guide vane angles and turbine diameters were considered for the simulations. The modified turbines are simulated to operate in various rotational speeds which are similar to an actual working of oscillating water column. This helps to find a suitable operational range for the proposed turbine for energy extraction. It was found that the bigger turbines are expected to produce relatively higher efficiencies at lower speeds and lower pressures. © 2018, The Institution of Engineers (India).

Journal of The Institution of Engineers (India): Series C

Performance Analysis of an Air Turbine for Ocean Energy Extraction Using CFD Technique

This paper deals with the efficiency maximization of a wave energy converter (WEC). The WEC is an oscillating water column (OWC) device and drives a permanent magnet synchronous generator (PMSG) through a bidirectional flow impulse-turbine. The converter faces challenges such as large peak-to-average power ratio, low overall efficiency, and inefficient energy absorption for regular and irregular sea states. In this context, a higher order sliding mode controller (HOSMC) was proposed, and its gains were optimized to control through the best efficiency point tracking (BEPT) of the turbine. The flow through the turbine-passage was simulated by the computational fluid dynamics (CFD) technique, and the BEPT characteristics were obtained. An adaptive inertia-weight particle-swarm algorithm and a grouped grey-wolf algorithm were used for optimization. The Optimized HOSMC reduced chattering, minimized the reaching time and improved the mean efficiency by about 67% compared to the uncontrolled cases. In addition, the relative improvement of the mean efficiency was at least 4.8% compared to conventional controllers. The controller reduced the peak-to-average power ratio of at least 35.6% relative to the uncontrolled case of the turbine under different sea states. © 2019 Elsevier Ltd

Energy

Optimization based higher order sliding mode controller for efficiency improvement of a wave energy converter

The interest in wave energy converters (WECs) is increasing, the study of grid connection of WEC along with the control system has become inevitable. WEC such as an oscillating water column (OWC) device involves conversions in various physical domains, thus a model describing the conversions at each stage and coupling between them should be accurate yet simple enough to reduce the computation time involved. The already existing models do not include all the components of wave to wire conversion. This paper presents a wave to wire model for control system studies. The model reduction technique is used to create a dynamically equivalent model for any large systems have more interconnecting stages. The dynamics involved in conversion stages are hydrodynamic and aerodynamic coupling at the capture chamber, aerodynamic and thermodynamic coupling inside the capture chamber, aerodynamic and rotor dynamic coupling in air turbine; and rotor dynamics and generator dynamics in the turbine generator coupling. Thus, a wave to wire model is represented to capture all the dynamics involved. It is observed that the model retains its fundamental physics, improves the computation time and reduces the number of unknowns to describe the state-space of OWC system. The accuracy and efficiency of the model is investigated through various static and dynamic analyses and found acceptable for OWC-WEC control system studies. © Springer Nature Singapore Pte Ltd. 2019.

Lecture Notes in Civil Engineering

Control-oriented wave to wire model of oscillating water column

Wave energy converters (WECs) face difficulties such as low operating range, low power output and, fluctuating power. A seamless synchronization among WEC components is required to get a better performance. For control system studies, the model should capture all the necessary dynamics involved in each conversion stages, however the interlinked complexity in each subsystem increases the computation time. This article presents a reduced order wave-to-wire (WTW) model of an oscillating water column (OWC) based WEC. The approach involves modeling of hydrodynamic and aerodynamic coupling of the capture chamber, aerodynamic and thermodynamic coupling inside the capture chamber, aerodynamic and rotor dynamic coupling in air turbine; and rotor dynamics and generator dynamics in the turbine generator coupling. The result shows that the model retains its fundamental dynamics and reduces the number of unknowns to describe the state space. The model indicates the correlation of each variable represented in the state space. The model predicted power output for different sea state. It also shows that the accuracy and the efficiency of the model are acceptable for OWC-WEC control system studies. The present model can be used as a time domain tool to design an effective control system for OWC device for different sea states, and the overall device performance can be improved significantly. © 2018 Elsevier Ltd

Ocean Engineering

Development of a reduced order wave to wire model of an OWC wave energy converter for control system analysis

The extraction of wave energy through self-rectifying air turbine is one of the emerging technologies for oscillating water column (OWC) based wave energy devices. In the present effort, a bi-directional impulse (BDI) turbine is designed and the performance parameters were found numerically and compared with an existing unidirectional impulse (UDI) turbine. A brief analytical formulation through similarity laws, to find a dynamically similar BDI turbine using pressure drop vs flow characteristics, gives the approximate diameter range equivalent to the reference UDI turbine. The results are used to reduce the range of diameters and it is found that the characteristics are matching with the reference UDI turbine. The maximum and minimum diameters among the selected range are considered for detailed computational fluid dynamics (CFD) analysis. These two BDI turbines are modeled and meshed in ICEM CFD 14.5. The commercial CFD code CFX 14.5 is used for the numerical simulations. The Reynolds-averaged Navier-Stokes (RANS) equations with the standard k-? scalable wall function model are solved to obtain the performance parameters. A detailed flow physics of the BDI turbines has also been included. Copyright © 2017 ASME.

ASME 2017 Gas Turbine India Conference, GTINDIA 2017

Evaluation of impulse turbines for a wave energy converter

Transactions of the Japan Society of Mechanical Engineers Series B

Effect of Guide Vanes on the Performance of a Wells Turbine.

Impulse Turbine with Self-Pitch-Controlled Guide Vanes for Wave Power Generator. Control of Guide Vanes Connected by Link Motion.

Journal of the Visualization Society of Japan

Impulse Turbine with Self-Pitch-Controlled Tandem Guide Vanes for Wave Energy Conversion

Impulse Turbine with Self-Pitch-Controlled Guide Vanes for Wave Power Generator. Improvement of Performance by the Use of Tandem Guide Vanes.

JSME international journal. Ser. 2, Fluids engineering, heat transfer, power, combustion, thermophysical properties

Studies on the Wells Turbine for Wave Power Generator (Turbine Characteristics and Design Parameter for Irregular Wave)

Journal	Renewable Energy
ISSN	09601481
Open Access	No