Category Archives: Component Development

Shape design and numerical analysis on a 1 MW tidal current turbine for the south-western coast of Korea


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Patrick Mark Singh and Young-Do Choi, Renewable Energy – August 2014

Abstract

The study concentrates on the shape design and numerical analysis of a 1 MW horizontal axis tidal current turbine (HATCT), which can be applied near the southwest regions of Korea. On the basis of actual tidal current conditions of south-western region of Korea, configuration design of 1 MW class turbine rotor blade is carried out by blade element momentum theory (BEMT). The hydrodynamic performance including the lift and drag forces, is conducted with the variation of the angle of attack using an open source code of X-Foil. The optimized blade geometry is used for Computational Fluid Dynamics (CFD) analysis with hexahedral numerical grids. This study focuses on developing a new hydrofoil and designing a blade with relatively shorter chord length in contrast to a typical TCT blade. Therefore, after a thorough study of two common hydrofoils, (S814 and DU-91-W2-250, which show good performance for rough conditions), a new hydrofoil, MNU26, is developed. The new hydrofoil has a 26% thickness that can be applied throughout the blade length, giving good structural strength. Power coefficient, pressure and velocity distributions are investigated according to Tip Speed Ratio by CFD analysis. As cavitation analysis is also an important part of the study, it is investigated for all the three hydrofoils. Due to the shorter chord length of the new turbine blade in contrast to a typical TCT blade design, a Fluid Structure Interaction (FSI) analysis is also done. Concrete conclusions have been made after comparing the three hydrofoils, considering their performance, efficiency, occurrence of cavitation and structural feasibility.

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In-tank tests of a dielectric elastomer generator for wave energy harvesting


R. Vertechy, M. Fontana, G. P. Rosati Papini, and D. Forehand – Proc. SPIE Electroactive Polymer Actuators and Devices (EAPAD), March 2014

Abstract

Wave energy harvesting is one of the most promising applications for Dielectric Elastomer Generators. A simple and interesting concept of a Wave Energy Converter based on Dielectric Elastomers is the Polymeric Oscillating Water Column (Poly-OWC). In this paper, preliminary experimental results on the assessment of a small-scale Poly-OWC prototype are presented. The scale of the considered prototype is 1:50. Tests are conducted in a wave-flume by considering sea state conditions with different wave amplitudes and frequencies. The obtained experimental results confirm the viability of the Poly-OWC device.

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Experimental Study of Darrieus-Savonius Water Turbine with Deflector: Effect of Deflector on the Performance


Kaprawi Sahim, Kadafi Ihtisan, Dyos Santoso, and Riman Sipahutar – International Journal of Rotating Machinery, February 2014

Abstract

The reverse force on the returning blade of a water turbine can be reduced by setting a deflector on the returning blade side of a rotor. The deflector configuration can also concentrate the flow which passes through the rotor so that the torque and the power of turbine can be considerably increased. The placing of Savonius in Darrieus rotor is carried out by setting the Savonius bucket in Darrieus rotor at the same axis. The combination of these rotors is also called a Darrieus-Savonius turbine. This rotor can improve torque of turbine. Experiments are conducted in an irrigation canal to find the performance characteristics of presence of deflector and Savonius rotor in Darrieus-Savonius turbine. Results conclude that the single deflector plate placed on returning blade side increases the torque and power coefficient. The presence of Savonius rotor increases the torque at a lower speed, but the power coefficient decreases. The torque and power coefficient characteristics depend on the aspect ratio of Savonius rotor.

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Comparison and Sensitivity Investigations of a CALM and SALM Type Mooring System for Wave Energy Converters


Arthur Pecher, Aligi Foglia, and Jens Peter Kofoed – Journal of Marine Science and Engineering, February 2014

Abstract

A quasi-static analysis and sensitivity investigation of two different mooring configurations—a single anchor leg mooring (SALM) and a three-legged catenary anchor leg system (CALM)—is presented. The analysis aims to indicate what can be expected in terms of requirements for the mooring system size and stiffness. The two mooring systems were designed for the same reference load case, corresponding to a horizontal design load at the wave energy converter (WEC) of 2000 kN and a water depth of 30 m. This reference scenario seems to be representative for large WECs operating in intermediate water depths, such as Weptos, Wave Dragon and many others, including reasonable design safety factors. Around this reference scenario, the main influential parameters were modified in order to investigate their impact on the specifications of the mooring system, e.g. the water depth, the horizontal design load, and a mooring design parameter.

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Analytical and experimental evaluation of energy storage using work of buoyancy force


Abdul Hai Alami – Journal of Renewable and Sustainable Energy, 2014

Abstract

This paper presents theoretical formulation of, and experiments on a method of energy storage using the work of buoyancy force. The experiments proved that the energy storage using buoyancy force is an effective approach, as the experimental efficiency was found to exceed the theoretical estimation due to material properties of the buoys. The storage of mechanical energy without subsequent conversion into electrical energy has many advantages, including more compact storage setups, higher energy density retrieval, and higher efficiencies. For the current system, the efficiency of energy storage exceeds 37%. This value corresponds to earlier work by the author conducted for a single buoy, extending the prospects and applications of this approach to a better position in non-conventional energy storage applications.

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An Adaptive Nonlinear MPPT Controller for Stand Alone Marine Current Energy Conversion Systems


Khan, N.; Rabbi, S.F. ; Hinchey, M.J. ; Rahman, M.A. – 39th Annual Conference of the IEEE Industrial Electronics Society, IECON 2013, November 2013

Abstract

This paper presents an online estimation based adaptive nonlinear maximum power point tracking (MPPT) controller for a stand-alone permanent magnet synchronous generator (PMSG) based marine current energy conversion system. The proposed control strategy requires no flow sensor and also does not need the parameters of a PMSG. A nonlinear control algorithm for the load side converter to extract maximum power has been proposed to adequately deal with the inherent nonlinearities in the energy conversion system. A Lyapunov based online estimation approach is used to continually estimate the time varying input voltage and the output load resistance of the converter. Detailed simulation results of the proposed nonlinear controller namely adaptive backstepping are presented and fully analyzed. Simulation results demonstrate that the proposed nonlinear controller can incessantly extract maximum power from the ocean current at various flow speeds.

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Preliminary Design of Axial Flux Permanent Magnet Machine for Marine Current Turbine


Ju Hyung Kim and B. Sarlioglu – 39th Annual Conference of the IEEE Industrial Electronics Society, IECON 2013, November 2013

Abstract

This paper presents an analytical analysis and application of axial flux permanent magnet machine design to marine current turbine. Marine current is a prominent renewable energy source because of its predictable current profile. Rim-driven, direct-drive type is favorable for the marine current turbine application in terms of maintenance and reliability. The axial flux permanent magnet machine is a candidate machine type that not only reduces machine manufacturing costs, but also achieves high performance. The general sizing equation technique is implemented to produce the machine size. The magnetic flux relationship among air gap, stator yoke, rotor yoke, and permanent magnet is taken into account to calculate core material size of the machine. FEA simulation results are compared with analytical calculations. The proposed machine and the reference machine design results are briefly compared. Moreover, machine cost is estimated based on the volume of the proposed machine.

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Experimental study of abrasion characteristics for critical sliding components for use in hydrokinetic devices


A. Bromaghin, M. Ali, T. Ravens, T. Petersen, and J. Hoffman – Renewable Energy, June 2014

Abstract

Hydrokinetic devices have lately reemerged as a promising solution for harnessing energy from renewable sources such as rivers, tidal currents, or artificial channels. This paper describes a customized test flume that is capable of conducting tribological related experiments on sliding components (bearing, shaft, and generator seals) commonly used in hydrokinetic devices. Often while deployed, wear on bearing, shaft, and seal assemblies introduces undesirable clearances between contacting surfaces, which potentially can affect the performance of hydrokinetic devices. Continue reading

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Numerical Study of Flow around Diffusers with Different Geometry using CFD Applied to Hydrokinetic Turbines Design


Léo Daiki Shinomiya, Déborah Aline Tavares Dias do Rio Vaz, Amanda Maria Bizzinotto Ferreira, Taygoara Felamingo de Oliveira, José Gustavo Coelho, André Luiz Amarante Mesquita, and Jerson Rogério Pinheiro Vaz – 22nd International Congress of Mechanical Engineering, November 2013

Abstract

The use of diffuser on the hydrokinetic turbines improves its efficiency, exceeding the Betz limit (59.26%). The diffusers are technologies which has the function of causing an effect of increase in flow velocity that arrives on the turbine blades. This effect is caused by acceleration of the fluid particles due to the pressure drop downstream of the diffuser. In this paper, one describes a numerical study of the flow around three different geometries diffusers applied to the horizontal axis hydrokinetic turbine design. We evaluate the behavior of the diffuser velocity speed-up ratio in order of ranking the efficiencies of three different geometries. The numerical study is performed using computational fluid dynamic (CFD). The numerical model is validated using experimental data available in the literature. The results are applied to the case of a hydrokinetic turbine and the horizontal axis shows were satisfactory.

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Design and Experimental Analysis of AC Linear Generator with Halbach PM Arrays for Direct-Drive Wave Energy Conversion


Zhang, J; Yu, H.; Chen, Q.; Hu, M.; Huang, L.; and Liu, Q. – IEEE Transactions on Applied Superconductivity, November 2013

Abstract

To convert wave energy into more suitable forms efficiently, a single-phase permanent magnet (PM) AC linear generator directly coupled to wave energy conversion is presented in this paper. Magnetic field performance of Halbach PM arrays is compared with that of radially magnetized (R-magnetized) structure. Then, the change of parameters in the geometry of slot and Halbach PM arrays’ effect on the electromagnetic properties of the generator are investigated, and the optimization design guides are established for key design parameters. Finally, the simulation results are compared with test results of the prototype in wave energy conversion experimental system. Due to test and theory analysis results of prototype concordant with the Finite element analysis results, the proposed model and analysis method are correct and meet the requirements of direct-drive wave energy conversion system.

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