Current Issue : April - June Volume : 2017 Issue Number : 2 Articles : 6 Articles
Wind power is one of the important renewable energy sources. Currently, many\nresearches are focusing on improving the aerodynamic performance of wind turbine blades\nthrough simulations and wind tunnel testing. In the present study, the aerodynamic\nperformance of the perforated Eqwin blade (shell type blade) is investigated by using\nnumerical simulation. Three types of slots namely circular, horizontal rectangular and vertical\nrectangular were evaluated. It was found that the optimum angle of attack for a perforated shell\ntype blade was 12�º with maximum Cl/Cd value of 6.420. In general, for all the perforated blade\ncases, Cl/Cd tended to decrease as the slot size increased except for the circular slot with 5 mm\ndiameter. This was due to the disturbance of the airflow in lower side region which passed\nthrough the bigger slot size. Among the modified slots; the circular slot with diameter of 5 mm\nwould be the best slot configuration that can be considered for blade fabrication. The Cl/Cd\nobtained was 6.46 which is about 5% more than the value of the reference blade. Moreover, the\nintroduced slot would also reduce the overall weight of the blade by 1.3%....
This paper proposes a five-degree-of-freedom (5-DOF) hybrid magnetic bearing (HMB)\nfor direct-drive wind turbines, which can realize suspension in the 4-DOF radial and 1-DOF axial\ndirections. Only two sets of radial control windings are employed in the proposed HMB because only\none set of radial control windings can achieve the 2-DOF suspension in the radial direction. Unlike the\ntraditional active thrust magnetic bearings, this paper uses a cylindrical rotor core without a large\nthrust disc in the novel HMB. The numbers of the controller, power amplifier and system volume\ncan be reduced in the magnetic suspension system. This paper also presents the structure and basic\ncharacteristics of the proposed magnetic bearing. A precision equivalent magnetic circuit analysis of\nthe permanent magnet ring and control magnetic field is conducted in this study, in consideration of\nthe non-uniform distribution of magnetic density. Accordingly, the mathematical models, including\nthe suspension force expression, are derived based on the accurate equivalent magnetic circuit.\nThe basic principle of the structure parameter design is presented, based on the given key parameters.\nThe accuracy of the analytical method is further validated by 3D finite element analysis....
Numerical and experimental study to evaluate aerodynamic characteristics in supersonic\now over a double wedge airfoil is carried out using Fluent software and a supersonic\nwind tunnel, respectively. The Schlieren visualization method was also used\nto develop the experimental step of this study. The supersonic wind tunnel reached a\nproximately a Mach number of 1.8. The result got showed oblique shock waves visualization\non double-wedge airfoil and the numerical simulation, the flow behavior as\nfunction of Mach number, pressure, temperature and density in the flow field on the\ncomputational model. The simulation allowed to observe the shock wave and the\nexpansion fan in the leading and tailing edge of double-wedge airfoil. From the numerical\nand experimental comparison, an agreement at the shock wave angle and\nMach number was observed, with a difference about 1.17% from the experimental\nresults...
The energy absorption of the wave energy converters (WEC) characterized by a limited\nstroke length ââ?¬â?like the point absorbers developed at Uppsala Universityââ?¬â?depends on the sea level\nvariation at the deployment site. In coastal areas characterized by high tidal ranges, the daily energy\nproduction of the generators is not optimal. The study presented in this paper quantifies the effects\nof the changing sea level at theWave Hub test site, located at the south-west coast of England. This\narea is strongly affected by tides: the tidal height calculated as the difference between the Mean High\nWater Spring and the Mean LowWater Spring in 2014 was about 6.6 m. The results are obtained from\na hydro-mechanic model that analyzes the behaviour of the point absorber at the Wave Hub, taking\ninto account the sea state occurrence scatter diagram and the tidal time series at the site. It turns\nout that the impact of the tide decreases the energy absorption by 53%. For this reason, the need\nfor a tidal compensation system to be included in the design of the WEC becomes compelling. The\neconomic advantages are evaluated for different scenarios: the economic analysis proposed within\nthe paper allows an educated guess to be made on the profits. The alternative of extending the stroke\nlength of the WEC is investigated, and the gain in energy absorption is estimated....
The maximum power point tracking problem of variable-speed wind turbine systems is studied in this paper. The wind conversion\nsystems contain both mechanical part and electromagnetic part, which means the systems have time scale property. The wind\nturbine systems are modeled using singular perturbation methodology. A linear parameter varying (LPV) model is developed to\napproximate the nonlinear singularly perturbed model. Then stability and robust properties of the open-loop linear singularly\nperturbed system are analyzed using linear matrix inequalities (LMIs). An algorithm of designing a stabilizing state-feedback\ncontroller is proposed which can guarantee the robust property of the closed-loop system. Two numerical examples are provided\nto demonstrate the effectiveness of the control scheme proposed....
Recently, there is a growing interest in seismic qualification of ridges, buildings and\nmechanical equipment worldwide due to increase of accidents caused by earthquake.\nSevere earthquake can bring serious problems in the wind turbines and eventually\nlead to an interruption to their electric power supply. To overcome and prevent these\nundesirable problems, structural design optimization of a small vertical axis wind\nturbine has performed, in this study, for seismic qualification and lightweight by using\na Genetic Algorithm (GA) subject to some design constraints such as the maximum\nstress limit, maximum deformation limit, and seismic acceleration gain limit.\nAlso, the structural design optimizations were conducted for the four different initial\ndesign variable sets to confirm robustness of the optimization algorithm used. As a\nresult, all the optimization results for the 4 different initial designs showed good\nagreement with each other properly. Thus the structural design optimization of a\nsmall vertical-axis wind turbine could be successfully accomplished....
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