Monthly Archives: October 2013

Wake studies of a 1/30th scale horizontal axis marine current turbine


Luke Myers and A.S. Bahaj – Ocean Engineering, April 2007

Abstract

A 0.4 m diameter (1:30th scale) horizontal axis marine current turbine (MCT) was tested in a circulating water channel. The turbine performance and wake characteristics were determined over a range of flow speeds and rotor thrust coefficients. Measurements of the water surface elevation profiles indicated increasing variation and surface turbulence with increasing flow speeds. Blockage-type effects (where the measured point velocity was greater than the inflow velocity) occurred around the sides of the rotor for all flow speeds. Although the effects were exaggerated at model scale, it is expected that reasonable variations in water level and flow velocity could also occur over a full scale MCT array.

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A new method for failure modes and effects analysis and its application in a hydrokinetic turbine system


Liang Xie – Missouri University of Science and Technology, Masters Thesis, 2013

Abstract

The traditional failure modes and effects analysis (FMEA) is a conceptual design methodology for dealing with potential failures. FMEA uses the risk priority number (RPN), which is the product of three ranked factors to prioritize risks of different failure modes. The three factors are occurrence, severity, and detection. However, the RPN may not be able to provide consistent evaluation of risks for the following reasons: the RPN has a high degree of subjectivity, it is difficult to compare different RPNs, and possible failures may be overlooked in the traditional FMEA method. Continue reading

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Filed under Economics, Operation and Maintenance

An ocean kinetic energy converter for low-power applications using piezoelectric disk elements


C. Viñolo, D. Toma, A. Mànuel, and J. del Rio – The European Physical Journal Special Topics, September 2013

Abstract

The main problem facing long-term electronic system deployments in the sea, is to find a feasible way to supply them with the power they require. Harvesting mechanical energy from the ocean wave oscillations and converting it into electrical energy, provides an alternative method for creating self-contained power sources. However, the very low and varying frequency of ocean waves, which generally varies from 0.1 Hz to 2 Hz, presents a hurdle which has to be overcome if this mechanical energy is to be harvested. In this paper, a new sea wave kinetic energy converter is described using low-cost disk piezoelectric elements, which has no dependence on their excitement frequency, to feed low-consumption maritime-deployed electronic devices. The operating principles of the piezoelectric device technique are presented, including analytical formulations describing the transfer of energy. Finally, a prototypical design, which generates electrical energy from the motion of a buoy, is introduced. The paper concludes with the the behavior study of the piezoelectric prototype device as a power generator.

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New approaches in harnessing wave energy: With special attention to small islands


M. Fadaeenejad, R. Shamsipour, S.D. Rokni, and C. Gomes – Renewable and Sustainable Energy Reviews, January 2014

Abstract

The application of renewable energies has increased rapidly in the previous decade to solve some problems such as growing energy demand and environmental issues. Wave power as a high potential renewable energy, is more predictable compared to other renewable sources. Although there are many research works about wave energy, however a few of them considered a suitable wave energy converter (WEC) as a power system for remote islands. Wave energy potential for remote islands is discussed in this review by regarding environmental impacts, various types of wave energy converters and applied wave power projects for various islands. The results show that wave energy plays a key role for sustainable development of offshore islands by considering the traditional looks and environmental protection.

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Assessment of the impacts of tidal stream energy through high-resolution numerical modeling


V. Ramos, R. Carballo, M. Álvarez, M. Sánchez, and G. Iglesias – Energy, November 2013

Abstract

When planning the installation of a tidal farm, the disturbances on the marine environment associated with its operation must be studied in detail. The objectives of this paper are to assess the impacts on the hydrodynamics (water level and flow velocity) and to determine how these impacts can alter the tidal resource. For this purpose, a high-resolution model of Ria de Ribadeo (NW Spain) is used to describe the potential effects resulting from the operation of two prospective tidal farms. Two different scenarios of extracted power from the flow (high and low) are analyzed. Overall, it is found that the impact on the water level is negligible, but that on the flow velocity is significant. The velocity is reduced upstream and downstream the farm, and increased beside it. These effects are enhanced in the scenario with the higher power extraction. Finally, these modifications in the flow pattern alter the available energy density at the tidal turbine, with a reduction of 21% and 12% for the high and low levels of power extraction, respectively.

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Filed under Modeling, Resource Assessment

Planning tidal stream turbine array layouts using a coupled blade element momentum – computational fluid dynamics model


Rami Malki, Ian Masters, Alison J. Williams, and T. Nick Croft – Renewable Energy, March 2014

Abstract

A coupled blade element momentum – computational fluid dynamics (BEM–CFD) model is used to conduct simulations of groups of tidal stream turbines. Simulations of single, double and triple turbine arrangements are conducted first to evaluate the effects of turbine spacing and arrangement on flow dynamics and rotor performance. Wake recovery to free-stream conditions was independent of flow velocity. Trends identified include significant improvement of performance for the downstream rotor where longitudinal spacing between a longitudinally aligned pair is maximised, whereas maintaining a lateral spacing between two devices of two diameters or greater increases the potential of benefitting from flow acceleration between them. This could significantly improve the performance of a downstream device, particularly where the longitudinal spacing between the two rows is two diameters or less. Due to the computational efficiency of this modelling approach, particularly when compared to transient computational fluid dynamics simulations of rotating blades, the BEM–CFD model can simulate larger numbers of devices. An example of how an understanding of the hydrodynamics around devices is affected by rotor spacing can be used to optimise the performance of a 14 turbine array is presented. Compared to a regular staggered configuration, the total power output of the array was increased by over 10%.

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Integrating wave energy into the power grid: Simulation and forecasting


Gordon Reikard – Ocean Engineering, November 2013

Abstract

A major issue in integrating renewable energy into power grids is short-term forecasting. If some share of electric power is derived from renewable sources, gaps between demand and supply must be made up by other forms of generation. Because of the uniquely short-lived nature of electricity, utilities need to be able to forecast over horizons of a few hours. Up to now, studies of wave energy have relied primarily on the flux, due to the unavailability of data on power flows. This study analyzes the power output using simulations. Continue reading

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Filed under Grid, Modeling

Status of micro-hydrokinetic river technology in rural applications: A review of literature


Herman Jacobus Vermaak, Kanzumba Kusakana, and Sandile Philip Koko – Renewable and Sustainable Energy Reviews, January 2014

Abstract

Apparently, most hydrokinetic literatures mainly concentrate on large-scale technologies such as waves, tides and ocean current applications. This could be one of the reasons delaying the utilization of small-scale hydrokinetic river technology in rural areas. This paper therefore critically reviews the current status of micro-hydrokinetic river (MHR) technology for rural applications. Relevant research literatures based on developments, applications, design, operation as well as different MHR technologies involved in rural electrification projects have been reviewed. After conducting these reviews it has become clear that one of the key barriers hindering the employment of MHR technology in rural areas with access to flowing water is the lack of research demonstrating the technical, economic and environmental benefits of this technology compared to other rural electrification techniques. Studies that look towards the long-term perspective of techno-economic analysis inclusive of capital, maintenance and running costs computations need to be carried out promoting the interest in utilizing this technology. This paper will aid researchers to identify areas that need to improve as well as encourage public bodies to implement proper energy policies regarding the MHR technology usage in rural areas. It will also create awareness among site owners, investors, project developers and decision makers regarding the potential benefits of using this technology in rural areas especially in countries with little or no elevation.

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Filed under Economics, Sector Overview

Methods for predicting seabed scour around marine current turbine


Long Chen and Wei-Haur Lam – Renewable and Sustainable Energy Reviews, January 2014

Abstract

Marine energy sources are able to make significant contributions to future energy demands. Marine current has huge potential to supply renewable energy as compared to the other energy sources. Marine environment is harsh for the installation and operation of marine current turbine (MCT). Seabed scour around marine current turbine is induced when the flow suppression occurs at the seabed. Seabed scour is widely recognised as a difficult engineering problem which is likely to cause structural instability. The study found that the previous works mainly focus on the bridge piers, wind turbines and ship propeller jets induced scour. Little information to date was found to predict the MCT induced scour. The current paper proposes the potential equations to predict the MCT induced scour. The study also recommends the consideration of the rotor into the existing equations for future research.

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Synergy of multiple cylinders in flow induced motion for hydrokinetic energy harvesting


Eun Soo Kim – University of Michigan, Doctoral Dissertation, 2013

Abstract

Vortex Induced Vibrations for Aquatic Clean Energy (VIVACE) Converter is a converter of marine hydro-kinetic energy invented in the Marine Renewable Energy Lab (MRELab) and patented by the University of Michigan. It harnesses hydrokinetic energy from ocean/tidal/river currents. In its simplest form the VIVACE Converter is a single circular cylinder on springs with a power take-off system. Using passive turbulence control, VIVACE maximizes and utilizes flow induced motion in the form of vortex induced vibration or interference/proximity/wake/soft/hard galloping. MRELab has achieved back-to-back vortex induced vibration and galloping for a single cylinder with passive turbulence control thus more than doubling the range of synchronization of flow induced motion (FIM). Continue reading

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Filed under Experiments, System Development