Monthly Archives: May 2013

Design of a horizontal axis tidal current turbine


Jai N. Goundar and M. Rafiuddin Ahmed – Applied Energy, November 2013

Abstract

Pacific Island Countries (PICs) have a huge renewable energy potential to meet their energy needs. Limited resources are available on land; however, large amount of ocean energy is available and can be exploited for power generation. PICs have more sea-area than land-area. Tidal current energy is very predictable and large amount of tidal current energy can be extracted using tidal current energy converters. A 10 m diameter, 3-bladed horizontal axis tidal current turbine (HATCT) is designed in this work. Hydrofoils were designed for different blade location; they are named as HF10XX. Continue reading

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CFD simulation of fixed and variable pitch vertical axis tidal turbine


Qihu Sheng, Syed Shah Khalid, Zhimin Xiong, Ghazala Sahib, and Liang Zhang – Journal of Marine Science and Application, June 2013

Abstract

In this paper, hydrodynamic analysis of vertical axis tidal turbine (both fixed pitch & variable pitch) is numerically analyzed. Two-dimensional numerical modeling & simulation of the unsteady flow through the blades of the turbine is performed using ANSYS CFX, hereafter CFX, which is based on a Reynolds-Averaged Navier-Stokes (RANS) model. A transient simulation is done for fixed pitch and variable pitch vertical axis tidal turbine using a Shear Stress Transport turbulence (SST) scheme. Main hydrodynamic parameters like torque T, combined moment C M , coefficients of performance C P and coefficient of torque C T , etc. are investigated. Continue reading

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Elisabetta Tedeschi, Jonas Sjolte, Marta Molinas, and Maider Santos – Energies, May 2013

Abstract

The future success of wave energy in the renewable energy mix depends on the technical advancements of the specific components and systems, on the grid access availability and, ultimately, on the economical profitability of the investment. Small and remote islands represent an ideal framework for wave energy exploitation, due both to resource availability and to the current high cost of electricity that mostly relies on diesel generation. Energy storage can be the enabling technology to match the intermittent power generation from waves to the energy needs of the local community. In this paper real data from La Palma, in the Canary Islands, are used as a basis for the considered test case. As a first step the study quantifies the expected power production from Wave Energy Converter (WEC) arrays, based on data from the Lifesaver point absorber developed by Fred Olsen. Then, a stochastic optimization approach is applied to evaluate the convenience of energy storage introduction for reducing the final cost of energy and to define the corresponding optimal rating of the storage devices.

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Finite depth effects on the wave energy resource and the energy captured by a point absorber


Adriana Monarcha Fernandes and Nuno Fonseca – Ocean Engineering, July 2013

Abstract

Most of the wave energy converters under development are planned for operation in shallow to intermediate water depths, typically 30 m to 70 m. However, the limited water depth reduces the wave energy resource as compared to offshore deep water. This paper presents an analysis of the water depth effects on the wave energy resource and on the energy absorbed by a floating device. The analysis is based on a procedure to modify the wave spectrum as the water depth reduces, namely the TMA method (Bouws et al., 1985. J. Geophys. Res. 90 (C1), 975–986). The method is based on the hypothesis that the similarity principle for the saturation range of shallow-water spectrum is not restricted to the equilibrium range, but is valid across the entire spectrum. A point absorber-type wave energy converter is modelled and the wave climatology of Figueira da Foz (Portugal) is used as a case study. Significant reduction has been identified for both the wave energy resource and wave energy converted as the water depth decreases. The presented methodology can be used for preliminary cost benefit analysis and decision making regarding the best water depth for installation of specific wave energy converters.

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Calculating weather windows: Application to transit, installation and the implications on deployment success


R.T. Walker, J. van Nieuwkoop-McCall, L. Johanning, and R.J. Parkinsonb – Ocean Engineering, May 2013

Abstract

In order to fully utilise test sites, marine energy device developers must be able to deploy, maintain and decommission their equipment in a timely and cost effective manner. In addition, the marine energy industry is moving towards array deployments and whilst these deployments present an excellent opportunity to maximise resource usage whilst minimising the associated costs, for example of deployment, it is essential that said deployment is performed in a cost effective manner. Critical to this is the knowledge of the metocean conditions at the site and the weather window availability, particularly when this is coupled with vessel availability and downtime costs.

In this paper a method is presented based on a Weibull model which uses cumulative distributions of the mean duration of persistence of exceedance. The method discussed has been applied in a case study for the South West of England using site specific environmental parameters and empirical expressions to calculate the accessible periods. The outcomes from the case study are applied to identify the accessible periods and the waiting time for marine operations, and a discussion is made regarding the installation of wave energy devices at the south west Wave Hub.

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Marine Current Energy Extraction Using Torsional Galloping Based Turbine


Mohammadmehdi Armandei and Antonio Carlos Fernandes – 2013 Offshore Technology Conference, May 2013

Abstract

One of the resources for alternative energy extraction in the area of offshore engineering is the marine current. Traditionally, the marine current energy is extracted through rotation based turbines. However, it became clear that to use of oscillation-based devices rather than the rotation-based ones has some advantages. Based on this idea, an innovative concept in energy extraction from the marine current is presented here. Continue reading

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Modelling and geometry optimisation of wave energy converters


Adi Kurniawan – NTNU, Doctoral Dissertation, April 2013

Abstract

The ultimate goal of wave energy undertaking is to find a solution that minimises the cost of delivered energy. Not only should a device maximise its energy absorption, but also the costs associated with absorbing and converting that energy into useful forms should be minimised. Towards realising this goal, this thesis contributes in three main areas, namely, numerical modelling, geometry optimisation, and geometry control.

The highlights of numerical modelling include the use of bond graph—a domain-independent, graphical representation of dynamical systems—in developing numerical models of wave energy converters (WECs), and the use of state-space models to represent the wave radiation terms. It is shown that bond graph is well-suited for modelling WECs, which involve interactions between multiple energy domains, and that state-space models of the wave radiation terms are efficient and sufficiently accurate for use in time-domain simulations of WECs. Both bond graph and state-space models are used in the modelling of a floating oscillating water column device, which, from the point of view of hydrodynamics, is a complex device involving various hydrodynamic radiation terms. Continue reading

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Permanent Magnet Linear Synchronous Generator for an Oscillating Hydrofoil in a Tidal Current Regime


S. Tarafdar, M. Abroshan, and M. Mirsalim – IACSIT International Journal of Engineering and Technology, April 2013

Abstract

This paper presents a novel method to extract energy from tidal currents by using a permanent magnet linear synchronous generator for an oscillating hydrofoil. In this work, an initial design of a linear generator is proposed for a biomimetically inspired oscillating hydrofoil system as a tidal energy generator. The device is designed to manipulate the flow stream and contained energy. It demonstrates a noticeable increase in efficiency when compared with data from existing industrial prototypes. Thus, a heightened theoretical coefficient of power and decreased cycle times are calculated for the device. The whole system is surveyed from the hydrofoil to the sample load. The main aim of the paper is to depict a new design in handling the hydrofoils in a tidal current regime.

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Sea level rise and tidal power plants in the Gulf of Maine


Holly E. Pelling and J.A. Mattias Green – Journal of Geophysical Research, May 2013

Abstract

The response of the Bay of Fundy and Gulf of Maine to large scale tidal power plants and future sea-level rise (SLR) is investigated using an established numerical tidal model. Free stream tidal turbines were simulated within the Bay of Fundy by implementing an additional bed friction term, Kt. The present day maximum tidal power output was determined to be 7.1 GW, and required Kt = 0.03. Extraction at this level would lead to large changes in the tidal amplitudes across the Gulf of Maine. With future SLR implemented the energy available for extraction increases with 0.5-1 GW per m SLR. SLR simulations without tidal power extraction revealed that the response of the semi-diurnal tides to SLR is highly dependent on how changes in sea-level are implemented in the model. When extensive flood defences are assumed at the present day coast line, the response to SLR is far larger than when land is allowed to (permanently) flood. For example, within the Bay of Fundy itself the M2 amplitude increases with nearly 0.12 m per m SLR without flooding, but it changes with only 0.03 m per m SLR with flooding. We suggest that this is due to the flooding of land cells changing the resonant properties of the basin.

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Hydrodynamic performance of a vertical-axis tidal-current turbine with different preset angles of attack


Guang Zhao, Ran-sheng Yang, Yan Liu, Peng-fei Zhao – Journal of Hydrodynamics, Ser. B, April 2013

Abstract

The instantaneous angle of attack on the blade has a significant effect on the hydrodynamic performance of a vertical-axis tidal-current turbine with straight blades. This paper investigates the influence of different preset angles of attack on the hydrodynamic performance of a three-bladed, vertical-axis, tidal-current turbine both experimentally and numerically. Experiments are carried out in a towing tank. This tested turbine’s solidity is 0.1146. The preset angles of attack on the blade are −3°, 0°, 3°, and 5°, in the experiments. Experimental results show that with the increase of the preset angle of attack from −3°, to 5°, the hydrodynamic performance of the turbine is improved significantly with the power coefficients being increased from 15.3% to 34.8%, respectively. Compared to the result of a 0° preset angle of attack, the performance of the turbine with positive preset angles of attack is experimentally demonstrated to be beneficial. This performance improvement is also shown by numerical simulations based on the Unsteady Reynolds Averaged Navier-Stokes (URANS) equations. In addition, the numerical results show that the optimal positive preset angle of attack is 7° for the turbine studied. The corresponding power coefficient is 38%. Beyond this optimal preset angle of attack, the hydrodynamic performance of the turbine decreases. Therefore, due to the dynamic stall phenomenon, an optimal preset angle of attack exists for any vertical-axis turbine. This value should be considered in the design of a vertical-axis tidal-current turbine.

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