Monthly Archives: November 2012

Hydrokinetic assessment of the Kvichak River near Igiugig, Alaska, using a two-dimensional hydrodynamic model


H. Toniolo – Energy and Power Engineering, 2012

Abstract

Two-dimensional hydrodynamic simulations were performed on a monthly basis along 2.5 km of the Kvichak River near Igiugig in southwest Alaska, USA, to estimate flow conditions and to assess the hydrokinetic potential of the river reach. Instantaneous power density function along the computational domain was calculated. Study results indicate that two areas may be suitable for deploying turbines. The best option is located near the town, where the channel is relatively straight. A second possible site is located near the end of the study reach (approximately 2.3 km, along the river, from Lake Illiamna). Monthly-averaged velocities along the thalweg ranged from 1.7 to 2.7 m/s; and from 1.1 to 2 m/s at the upstream and downstream sites, respectively. Similarly, averaged values for the instantaneous power density, reduced by an extraction coefficient, were approximately 1500 and 5500 W/m2 during April and September, respectively, at the upstream site, as well as 400 and 2500 W/m2 for the same months at the downstream site. It was found that a previous resource assessment, which considered cross-sectionally averaged velocities, substantially underestimated the available power density along the river reach. Finally, the importance of having adequate bathymetric data is demonstrated by comparing field measurements with model simulations.

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Fuzzy logic based reactive controller for heaving wave energy converters


M. Jama, A. Wahyudie, H. Noura, and A. Assi – 2012 International Conference on Renewable Energies for Developing Countries (REDEC) – November, 2012

Abstract

This paper presents a new control strategy based on fuzzy logic for maximizing the absorbed energy of heaving wave energy converters (WEC). The fuzzy logic controller is responsible of minimizing the discrepancy between the optimal reference buoy velocity and the actual buoy velocity, hence maximizing the captured power for irregular sea environment. The proposed controller performed well compared to a conventional fixed reactive control strategy.

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Protective, Modular Wave Power Generation System


J.M. Vvedensky and R.Y. Park – Technical Report submitted to DOE EERE Wind & Water Power Program, November, 2012

Abstract

The concept of small wave energy conversion modules that can be built into large, scalable arrays, in the same vein as solar panels, has been developed. This innovation lends itself to an organic business and development model, and enables the use of large-run manufacturing technology to reduce system costs. The first prototype module has been built to full-scale, and tested in a laboratory wave channel. The device has been shown to generate electricity and dissipate wave energy. Improvements need to be made to the electrical generator and a demonstration of an array of modules should be made in natural conditions.

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Influence of a velocity profile & support structure on tidal stream turbine performance


A. Mason-Jones, D.M O’Doherty, C.E. Morris, and T. O’Doherty – Renewable Energy, April, 2013

Abstract

With tidal turbine technology in its infancy prototype devices are likely to be positioned at locations where both the local marine environment and vessel navigation are favourable. However, as marine turbine technology develops toward economic viability there is a propensity for undesirable interactions with local shipping, higher turbulence levels and velocity shear through the water column to occur. The latter high shear could result from positioning the turbine lower in the water column, perhaps due to local shipping requirements. This paper helps to elucidate the performance of the tidal turbine and in particular the blade forces during rotation within a high shear velocity profile. A velocity profile from ADCP measurements was used as an inlet boundary for CFD analysis. The work shows that the presence of a suitably positioned stanchion downstream of the turbine will result in reduced performance characteristics over a complete rotation. However, the amplitude of the characteristics, in particular, the axial loading increases which would require careful design considerations.

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Seawave power farm design: A case study


V. Franzitta, A. Viola, and M. Trapanese – AASRI Procedia, 2012

Abstract

Current energy crisis and general concerns on environmental issues have triggered an ever increasing effort on harvesting renewable energies. Amongst renewable energy sources, sea wave energy is definitely the one that has been less utilised. This is probably caused by two reasons: i)the strong technical novelties that are required to extract thee energy that is contained in a highly and stochastically variable motion; ii)the difficulty of find a suitable electrical system able to convert the energy contained in the motion of the sea into electrical energy. In this paper we propose an approach to set up a general methodology toward the design of a sea wave farm. The first step is explained how to choose the conversion system, in the second step is discussed the connection scheme among the converters, in the third step is reported a case study of a whole sea wave farm.

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Patterns and cycles in the climate forecast system reanalysis wind and wave data


J.E. Stopa, K.F. Cheung, H.L. Tolman, A. Chawla – Ocean Modelling, November, 2012

Abstract

The Climate Forecast System Reanalysis and the corresponding WAVEWATCH III hindcast datasets allow climatic interpretation of winds as well as their impacts on waves. In this paper, we analyze the continuous 31 years of global wind and wave data in terms of climate patterns and cycles. Quarterly averages and percentile plots of the wind speed and wave height illustrate the seasonal pattern and distributions of extreme events, while the annual and inter-annual variability demonstrates the wind and wave climate. The data is correlated with published indices of known atmospheric cycles. The datasets show good correspondence with the Arctic Oscillation, Antarctic Oscillation, El Nino Southern Oscillation, and the Madden-Julian Oscillation in both the wind and wave fields. The results compare well with published climate studies on regional scales and provide important linkage to the global wave climate characteristics.

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Puget Sound tidal energy in-water testing and development project


C. Collar – US Department of Energy Final Technical Report, November, 2012

Abstract

Tidal energy represents potential for the generation of renewable, emission free, environmentally benign, and cost effective energy from tidal flows. A successful tidal energy demonstration project in Puget Sound, Washington may enable significant commercial development resulting in important benefits for the northwest region and the nation. This project promoted the United States Department of Energy’™s Wind and Hydropower Technologies Program’™s goals of advancing the commercial viability, cost-competitiveness, and market acceptance of marine hydrokinetic systems. The objective of the Puget Sound Tidal Energy Demonstration Project is to conduct in-water testing and evaluation of tidal energy technology as a first step toward potential construction of a commercial-scale tidal energy power plant. Continue reading

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Estimation of tidal power potential


R.A. Walters, M.R. Tarbotton, C.E. Hiles – Renewable Energy, March, 2013

Abstract

Several approaches can be used for estimating tidal power potential. From a theoretical point of view, others have shown that the problem can be reduced to a single or multiple boundary problem with simple geometry where each case has a well defined maximum power potential. From a practical point of view, the potential can be approximated from the ambient flow. Questions naturally arise whether the theoretical approach can be applied to a typical field-scale problem, and whether the practical approach has any validity. In order to provide more insight into these questions, form drag representing tidal turbines has been introduced into a numerical flow model. This is an unstructured grid model with an implicit treatment of wetting and drying that has been shown to be robust, accurate, and efficient for highly irregular coastal ocean environments and is well suited for this problem. The field site that has been examined is Minas Passage in the Bay of Fundy which provides an interesting practical perspective for this problem. In the end, only a fraction of the theoretical maximum power potential can be realized in practice because of physical constraints on the maximum form drag for tidal turbines.

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Modeling of the flow in a Darrieus water turbine: Wall grid refinement analysis and comparison with experiments


T. Maître, E. Amet, and C. Pellone – Renewable Energy, November, 2012

Abstract

This paper presents some aspects concerning the 2D RANS numerical modeling of a Darrieus cross flow marine turbine. Two main features of the modeling are studied. The first deals with the influence of the near wall grid density on the numerical results. Most of the available literature concerning the occurrence of stalling foils emphasizes the need for a fine grid mesh at wall fitting y+ around the unity or less at the first near wall cell center. Nevertheless, in the case of a Darrieus turbine, the influence of this parameter has not yet been studied precisely. In particular, the exact y+ specification is not known, and its influence either on the global turbine performance or on the local flow field, has not been outlined. The present work provides insight into the y+ influence in a 2D Darrieus turbine and deals with its maximum acceptable value. The second feature concerns the ability of a 2D modeling to represent, the actual 3D flow in the turbine. The power coefficients are compared to those obtained in the hydrodynamic LEGI tunnel on a small scale model. The experimental power coefficients are presented with their associated precision. The comparisons show a medium tip speed ratio range around the nominal point for which the instantaneous ratio of the experimental and numerical power coefficients is a constant significantly lower than 1 regardless of the azimuthal position of the blades. This constant ratio is thought to be representative of the tip and arm-blade junctions losses.

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Methodology for tidal turbine representation in ocean circulation model


T. Roc, D.C. Conley, and D. Greaves – Renewable Energy, March, 2013

Abstract

The present method proposes the use and adaptation of ocean circulation models as an assessment tool framework for tidal current turbine (TCT) array layout optimization. By adapting both momentum and turbulence transport equations of an existing model, the present TCT representation method is proposed to extend the actuator disc concept to 3-D large-scale ocean circulation models. Through the reproduction of experimental flume tests and grid dependency tests, this method has shown its numerical coherence as well as its ability to simulate accurately both momentum and turbulent turbine-induced perturbations in both near and far wakes in a relatively short period of computation time. Consequently the present TCT representation method is a very promising basis for the development of a TCT array layout optimization tool.

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