Monthly Archives: November 2013

Tidal turbine array optimisation using the adjoint approach


S.W. Funke, P.E. Farrell, and M.D. Piggott – Renewable Energy, March 2014

Abstract

Oceanic tides have the potential to yield a vast amount of renewable energy. Tidal stream generators are one of the key technologies for extracting and harnessing this potential. In order to extract an economically useful amount of power, hundreds of tidal turbines must typically be deployed in an array. This naturally leads to the question of how these turbines should be configured to extract the maximum possible power: the positioning and the individual tuning of the turbines could significantly influence the extracted power, and hence is of major economic interest. However, manual optimisation is difficult due to legal site constraints, nonlinear interactions of the turbine wakes, and the cubic dependence of the power on the flow speed. Continue reading

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Estimate of the tidal stream power resource of the Pentland Firth


Scott Draper, Thomas A.A. Adcock, Alistair G.L. Borthwick, and Guy T. Houlsby – Renewable Energy, March 2014

Abstract

The Pentland Firth is arguably the best-known candidate site for tidal stream power extraction worldwide. In this paper we estimate the maximum power that can be extracted by placing tidal stream power devices across the Pentland Firth and/or the individual sub-channels formed by the islands of Swona, Stroma and the Pentland Skerries. Using a depth-averaged numerical model, for the entire Firth we find that approximately 4.2 GW of power may be extracted, and this agrees reasonably well with predictions from an existing theoretical model. In contrast, for the sub-channels there is no single value to describe the power potential, but rather a range of power estimates because the extracted power from one sub-channel depends on the operation (or otherwise) of tidal devices placed in parallel sub-channels, or in series along the Firth. Continue reading

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Simulations of a vertical axis turbine in a channel


Anders Goude and Olov Ågren – Renewable Energy, March 2014

Abstract

The power coefficient of a turbine increases according to the predictions from streamtube theory for sites with a confined fluid flow. Here, a vertical axis turbine (optimized for free flow) has been simulated by a two-dimensional vortex method, both in a channel and in free flow. The first part of the study concerns the numerical parameters of channel simulations. It is found that for free flow and wide channels, a large number of revolutions is required for convergence (around 100 at the optimal tip speed ratio and increasing with higher tip speed ratio), while for smaller channels, the required number of revolutions decreases. Continue reading

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Wave-power absorption from a finite array of oscillating wave surge converters


E. Renzi, A. Abdolali, G. Bellotti, and F. Dias – Renewable Energy, March 2014

Abstract

Semi-analytical and fully numerical modelling is developed in the framework of the inviscid potential flow theory to investigate the dynamics of a wave farm made by flap-type wave energy converters in the nearshore. The hydrodynamic parameters and the efficiency of the system in typical layouts are calculated with both models. Good agreement is shown between the two approaches. Parametric analysis undertaken with the semi-analytical model allows to identify a near-resonant phenomenon which is responsible for increasing the absorbed power by the single elements of the array. Such result could be used as a preliminary design criterion. The numerical model is then applied to analyse a configuration of practical engineering interest, i.e. an array of two staggered converters. The dynamics arising in this more complex system is explained, showing that non-symmetric layouts can be less effective.

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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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Wave-structure interaction of offshore wave energy converters


William Finnegan – Doctoral Dissertation, National University of Ireland, Galway – November 2013

Abstract

With the continuing rise in oil prices and greater concern for the damage to the atmosphere, the world is continually looking for a cleaner and more sustainable form of energy. Ocean wave energy as a renewable source of energy, which as of yet is relatively unexploited, offers a possible solution to this energy crisis. The concept of harnessing ocean wave energy is by no means a new idea. However, the topic only gained international interest in the 1970s with the publication of Stephen Salter’s ground-breaking paper on his Wave Energy Duck. The current research study aims to aid the exploitation of this resource by developing robust and reliable analytical and numerical models. Continue reading

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Guidance on the use of synthetic fibre ropes for marine energy devices Deliverable 3.5.2 from the MERiFIC Project


Sam Weller, Peter Davies, Lars Johanning, and Stephen Banfield – MERiFIC Work Package 3, October 2013

Abstract

This report is a deliverable of MERiFIC Work Package 3: ‘Dynamic Behaviour of Marine Energy Devices’ involving the collaboration of IFREMER (Institut français de recherche pour l’exploitation de la mer) in France and the University of Exeter in the United Kingdom. Although synthetic ropes have been used for the station-keeping of offshore structures for the past two decades predominantly by the oil, gas and shipping industries, there is considerable interest in their utilisation for the station-keeping of marine renewable energy (MRE) devices. Continue reading

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A suitable metocean hindcast database for the design of Marine energy converters


Edwige Boudière, Christophe Maisondieu, Fabrice Ardhuin, Mickaël Accensi, Lucia Pineau-Guillou, and Jérémy Lepesqueur – International Journal of Marine Energy, November 2013

Abstract

Resource assessment as well as characterisation of site climatologies for the design of Marine Energy Converters requires data bases allowing an accurate description of the environmental forcing, especially waves and sea-states, on a high resolution grid. As a support to its research activities related to the development of marine renewable energies, Ifremer is building a specific hindcast data set for the assessment of sea-states climatologies. The main features of this database, built running an up-to-date configuration of the WaveWatch III® wave model on an unstructured grid extending from the South of the North Sea to the Bay of Biscay are presented here. Attention is given to the parameterization and forcing as well as the specific output data sets and validation processes.

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Wave prediction and its implementation on control systems of Wave Energy Converters


Peter Kracht, Boris Fischer, Sebastian Perez-Becker, and Jean-Baptiste Richard – MARINET Technical Report, 2013

Abstract

Many advanced control schemes have been proposed for wave energy converters (WEC), which offer the chance of significantly increasing the energy yield. Assessing the available literature so far most of these control schemes have only been investigated by simulations. These simulations are often based on assumptions such as that linear wave theory is applicable, that perfect models for the WEC/PTOs etc. are available or that an ideal prediction of the wave excitation force some distance in the future is available. Continue reading

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Power extraction from tidal channels – Multiple tidal constituents, compound tides and overtides


Thomas A.A. Adcock and Scott Draper – Renewable Energy, March 2014

Abstract

Many candidate sites for tidal stream power extraction are tidal channels, and the power that can be generated from these sites will be directly related to the amplitude and phase of the principal tidal constituents driving flow through the channel. This paper investigates this interaction between energy extraction and tidal constituents, and also the effect that power extraction may have on harmonics of the principal constituents (i.e. compound tides and overtides). Continue reading

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