Wave power absorption: Experiments in open sea and simulation

M. Eriksson, R. Waters, O.Svensson, J. Isberg, and M. Leijon- Journal of Applied Physics, 2007

Abstract

A full scale prototype of a wave power plant based on a direct drive linear generator driven by a point absorber has been installed at the west coast of Sweden. In this paper, experimentally collected data of energy absorption for different electrical loads are used to verify a model of the wave power plant including the interactions of wave, buoy, generator, and external load circuit. The wave-buoy interaction is modeled with linear potential wavetheory. The generator is modeled as a nonlinear mechanical damping function that is dependent on piston velocity and electric load. The results show good agreement between experiments and simulations. Potential wavetheory is well suited for the modeling of a point absorber in normal operation and for the design of future converters. Moreover, the simulations are fast, which opens up for simulations of wave farms.

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On validating numerical hydrodynamic models of complex tidal flow

Kester Gunn and Clym Stock-Williams – International Journal of Marine Energy, November 2013

Abstract

The construction of numerical hydrodynamic models is an important task for offshore renewable energy development, in particular for tidal current farms. An accurate understanding of the spatial variation in resource is necessary for optimally locating fixed measurement devices and turbines, as well as planning site operations.

This work presents a comprehensive methodology for the validation of numerical models in two and three dimensions. First, alternative methods practised in the literature for both time-domain and frequency-domain comparison are assessed and compared. Next, certain novel extended methods are presented for the validation of 3D data, which is not often attempted in the literature. In particular, the shear profiles encountered in real high-velocity sites do not often follow the traditional logarithmic laws, so a new parameterisation is presented and tested.

Finally, acoustic Doppler profiler (ADP) data are analysed and used in a case study validation exercise of a 3D hydrodynamic model of the Fall of Warness in the Orkney Islands, UK. Conclusions are drawn about the validity of the model, as well as the methodology applied.

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Mooring line fatigue damage evaluation for floating marine energy converters: Field measurements and prediction

Philipp R. Thies, Lars Johanning, Violette Harnois, Helen C.M. Smith, and David N. Parish – Renewable Energy, March 2014

Abstract

The vision of large-scale commercial arrays of floating marine energy converters (MECs) necessitates the robust, yet cost-effective engineering of devices. Given the continuous environmental loading, fatigue has been identified as one of the key engineering challenges. In particular the mooring system which warrants the station-keeping of such devices is subject to highly cyclic, non-linear load conditions, mainly induced by the incident waves.

The assessment of extreme wave analysis methods applied to potential marine energy sites using numerical model data

Atul Agarwal, Vengatesan Venugopal, and Gareth P. Harrison – Renewable and Sustainable Energy Reviews, November 2013

Abstract

The accurate estimation of extreme conditions, such as 100-yr return levels of significant wave height is an important aspect in the design of marine energy converters, offshore and coastal structures. This study investigates the different approaches for the estimation of extreme waves that have been applied in the past, and determines the 100-yr return levels using the high resolution ERA-Interim dataset produced by the European Centre for Medium-Range Weather Forecasts (ECMWF). It is demonstrated in the paper that fitting a Generalized Pareto Distribution to all exceedances over a high threshold is the most suitable approach. The estimates thus obtained are compared with previously computed estimates for buoys and offshore platforms. The effect of duration of data on the estimates is also investigated. Finally, a 100-yr return level map for the North Atlantic region is presented.

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Wave resource assessment along the Cornish coast (UK) from a 23-year hindcast dataset validated against buoy measurements

J.C.C. van Nieuwkoop, H.C.M. Smith, G.H. Smith, and L. Johanning – Renewable Energy, October, 2013

Abstract

Long-term knowledge of the wave climate of a potential wave energy site is essential for project planning and design, not only for an understanding of the resource variability, but also for the prediction of design wave conditions. The southwest region of the UK is at the forefront of the country’s wave energy development, with two operational test sites. However, no detailed long-term resource assessment has yet been performed. This paper presents a long-term wave hindcast for southwest England, performed using the numerical wave model SWAN, with a particular focus on two energy device test facilities: ‘Wave Hub’ on the energetic and exposed north Cornwall coast, and ‘FaB Test’ on the more sheltered south coast. A high-resolution wave model suite, aimed at establishing nearshore wave hindcasts, is described and evaluated. The suite is run for a 23-year period, starting in 1989 and continuing to 2011. The hindcast is compared with measurement data and the results are analysed for the two test sites. Special attention is given to the implications of present hindcast errors and how the hindcast errors can be minimized.

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Evaluation of Various Technologies for Wave Energy Conversion in the Portuguese Nearshore

D. Silva, E. Rusu and C.G. Soares – Energies, March, 2013

Abstract

The objective of the present work is to perform an evaluation of the performance provided by various technologies for wave energy conversion in the Portuguese continental coastal environment. The wave climate in the target area is first analyzed using the results from three years of simulations with a wave prediction system based on numerical models. Based on the above data, diagrams for the bivariate distributions of the sea states occurrences, defined by the significant wave height and the energy period, are designed for both winters and whole years. On this basis, the output of five different technologies for the conversion of wave energy is assessed in some relevant locations from the Portuguese nearshore. According to the results obtained, the Portuguese continental coastal environment appears to be appropriate for the wave energy extraction. At the same time, the present work shows that the output of the wave energy conversion devices does not depend only on the average wave energy but is also dependent on the distribution of the wave energy among the sea states of different periods. For this reason, a good agreement between the characteristics of the power matrices of the wave energy converters operating in a certain place and the diagrams for the bivariate distributions of the sea states occurrences corresponding to the considered location represents a key issue in selecting the most appropriate technology for wave energy conversion.

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Displacement response to axial cycling of piles driven in sand

S.P. Rimoy, R.J. Jardine, J.R. Standing – Proceedings of the ICE – Geotechnical Engineering, March, 2013

Abstract

A review of the load applied to multi-pile offshore wind turbine foundations is presented, from which the need to consider the response to axial cyclic loading is emphasised. The paucity of available data on field tests on driven piles in sand is noted. A comprehensive data set of multiple axial cyclic and static tests conducted on seven industrial-scale steel pipe-piles at a marine sand site in Dunkerque, France, is re-examined in this paper. The effects of cycling on axial capacity are interpreted by reference to stable, metastable or unstable zones defined in a normalised cyclic stability interaction diagram. A detailed analysis is made of the load–displacement and stiffness response associated with each mode of cycling. It is shown that in all cases the piles’ cyclic stiffnesses show only minor changes until cyclic failure is approached. The patterns of permanent cyclic strain accumulation are sensitive to the applied mean and cyclic loading levels. Whereas displacements accumulate rapidly over just a few cycles in the unstable zone, extended cycling in the stable zone leads to minimal accumulated displacements and constant transient cyclic displacements.

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Evaluation of tidal stream resource in a potential array area via direct measurements

I. Fairley, P. Evans, C. Wooldridge, M. Willis, and I. Masters – Renewable Energy, September, 2013

Abstract

ADCP transects have used to characterise tidal stream resources in the Ramsey Sound area of Pembrokeshire, UK. Previous resource assessments have previously suggested that this area is one of the most promising for tidal stream deployments in the UK and this contribution confirms the commercial viability of the area. In this study three channels were considered: Ramsey Sound itself and two channels to the west formed by small offshore islands. Current velocities were used to compute the tidal energy flux through the channels. Maximum instantaneous peak flux through the three channels ranges from 180 MW to 70 MW. Flux cross-sections are presented and the impact of meso-scale bathymetric features on flux and on the cross-transect variation of maximum flux over the tidal cycle is described and discussed. Theoretical values of extractable power potential are calculated and range between 7.2 MW and 21.8 MW. These values are approximately ¼ of the average flux through the measured cross-section. One channel is identified as being preferable for the first stage of array deployments given greatest homogeneity of flux through the channel cross-section and it having the highest power potential.

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