Wave Energy

A linearized model for estimating the performance of submerged resonant wave energy converters

by Sergio Camporeale

co-authored with P.G.F. Filianoti
publieshed in: Renewable Energy, Volume 33, Issue 4, April 2008, Pages 631–641

A realistic performance analysis of oscillating water column wave energy converters (WECs) addresses to a set of... more A realistic performance analysis of oscillating water column wave energy converters (WECs) addresses to a set of non-linear differential equations that need to be integrated in time, by using a stochastic approach, under the hypothesis of random wind-generated sea waves, for all the sea states which characterize the location of the system. Non-linearities of the differential equations have several origins:
• minor and major losses of the unsteady flow of water and air;
• compressibility of air and heat exchange with the walls of the air chamber;
• non-linear characteristics of the turbine.
Under the hypothesis of random sea waves with Gaussian distribution, the authors propose an original methodology for linearizing the differential equations that describe the flow motion inside a wholly submerged WEC. Under such hypothesis, the linearized model can be used for predicting the power output by means of the calculations in the frequency domain and for control design. The developed methodology has been applied to the estimation of the performance of the new “resonant sea wave energy converters”, called REWEC, patented by Boccotti in 1998, and consisting of several caissons, characterized by a structure similar to the caissons of the traditional breakwaters and placed on the seabed, close one to each other, to form a submerged breakwater. Each caisson is connected to a vertical duct wholly beneath the sea level, where a hydraulic Wells turbine is placed.

The matching between turbine and resonance characteristic of the system is carefully analysed in order to maximize the energy conversion efficiency.

Some results, given for a small installation in the Mediterranean sea, confirm that the REWEC system is able to absorb a large share of the incident wave energy due to a very simple regulation system which permits the tuning on sea states with different significant heights.

Quantifying the Global Wave Power Resource

by Clym Stock-Williams

Published in Journal of Renewable Energy, 2012

Justifying continued development and large-scale deployment of Wave Energy Converters (WECs) requires quantification... more Justifying continued development and large-scale deployment of Wave Energy Converters (WECs) requires quantification of the potential resource. Currently, estimates are available for individual countries or, at low accuracy, for global resource. Additionally, existing estimates do not provide insight into potential future markets, i.e. the location of the resource.

Here, NOAA WaveWatch III data are analysed for a 6-year period to calculate wave energy potential. The global market is then quantified by calculating the energy flux across a line 30 nautical miles offshore. Results are presented by country, continent, hemisphere and for the globe.

Confidence values are also presented in the form of 95% confidence intervals. These limits provide insight into the uncertainty associated with the length of dataset used and the variability of the resource. This enables direct comparison with other resource assessment studies, whether using numerical model or measured data. An extensive survey of previous global and regional resource estimates is also conducted, in order to compare both results and methods.

Supplementing this, extractable resource is estimated by considering the deployment of an illustrative WEC (Pelamis P2). The global wave power resource is 2.11 ± 0.05 TW, of which 4.6% is extractable with the chosen WEC configuration.

Detailed CFD analysis of the steady flow in a Wells turbine under incipient and deep stall conditions

by Sergio Camporeale

co-authored with M. Torresi and G. Pascazio, published in ASME Transactions, Journal of Fluids Engineering, vol. 131,issue 7, ISSN: 0098-2202

This paper presents the results of the numerical simulations carried out to evaluate the performance of a high... more This paper presents the results of the numerical simulations carried out to evaluate the performance of a high solidity Wells turbine designed for an oscillating water column wave energy conversion device. The Wells turbine has several favourable features (e.g., simplicity, high rotational speed) but is characterised by a relatively narrow operating range with high effciency. The aim of this work is to investigate the flow field through the turbine blades in order to offer a descrip-
tion of the complex flow mechanism that originates separation and, consequently, low effciency at high flow-rates. Simulations have been performed by solving the Reynolds-averaged Navier–Stokes equations together with three turbulence models, namely, the Spalart–Allmaras,k-ω, and Reynolds stress models. The capability of the three models to provide an accurate prediction of the complex flow through the Wells turbine has been assessed in two ways: the comparison of the computed results with the available experimental data and the analysis of the flow by means of the anisotropy
invariant maps. Then, a detailed description of the flow at different flow-rates is provided, focusing on the interaction of the tip leakage flow with the main stream and enlightening its role on the turbine performance.

Experimental methods for Power Take-off (PTO) simulation of a Wave Energy Converter

by Nuno Ferreira

Discussion of megaclast transport and erosion of rocky shorelines

by Jasper Knight

Knight, J. 2011. Discussion of megaclast transport and erosion of rocky shorelines: a comment on Williams (2010). Irish Journal of Earth Sciences, 29, 23-24.

A recent paper by Williams (2010) described examples of very large boulders (termed megaclasts) found around the... more A recent paper by Williams (2010) described examples of very large boulders (termed megaclasts) found around the western coast of the Aran Islands, Galway Bay, that had been moved landward across high-elevation cliff platforms and organised into ridges far from the cliff edge. Williams argued that wave overtopping of high cliffs caused clast detachment, and subsequent landward bores were sufficiently powerful to transport and emplace the megaclasts. Here I highlight some important limitations of Williams’ arguments, and show that clast detachment and transport involves more complex processes and conditions that are not considered in his paper. This limits the extent to which Williams’ paper can explain the presence of megaclasts in the Aran Islands.

SuperGen research helps to answer long standing problem of shoreline 'exposure' - Poster

by Robert Beharie

1st Prize Winner of the SuperGen Assembly 2011 Poster Competition.

A relevant quantitative measurement of shoreline wave action, required to determine shoreline ecological impacts from... more A relevant quantitative measurement of shoreline wave action, required to determine shoreline ecological impacts from localised wave energy reduction by WEC arrays, has been the main aim of this research.

Current qualitative methods for estimating shoreline wave action are been based upon wave propagation models and ecological surveys that have been found to be inadequate. Many commentators have expressed doubts that it would ever be possible to make progress in this field…

Power Absorption Measures and Comparisons of Selected Wave Energy Converters

by Adi Kurniawan

Modelling and Simulation of a Floating Oscillating Water Column

by Adi Kurniawan

Bond graph modelling of a wave energy conversion system with hydraulic power take-off

by Adi Kurniawan

Grid Integration of Wave and Tidal Energy

by Anne Blavette

Proceedings of the 30th International Conference on Ocean, Offshore and Artic Engineering, OMAE2011 (2011)

Dynamic Characteristics of Wave and Tidal Energy Converters & a Recommended Structure for Development of a Generic Model for Grid Connection

by Anne Blavette

report of the International Energy Agency - Ocean Energy Systems

Integrating Wave and Tidal Current Power: Case Studies Through Modelling and Simulation

by Anne Blavette

report of the International Energy Agency - Ocean Energy Systems

Grid Integration of Wave Energy in Ireland: A Case Study

by Anne Blavette

Proceedings of the International Conference on Ocean Energy, Bilbao, Spain (2010)

Control systems for Wraspa

by Keith Gunura

"Exploring Links Between Wave Regime Changes and Biotic Assemblages." SuperGen Marine Assembly 2009 - Poster

by Robert Beharie

Understanding the ecological effects from the anthropogenic reduction of wave energy impacting upon the coastline has... more Understanding the ecological effects from the anthropogenic reduction of wave energy impacting upon the coastline has become increasingly important due to environmental protection legislation. Developers are now required by governments to provide an environmental impact assessment (EIA) prior to any installations, yet consultants producing EIA’s face the problem of having no prior data from the installation of large scale wave energy converter (WEC) arrays. They also have no quantitative method of determining to what extent the shoreline ecology could be affected through any changes to the wave energy regime.