• Wind and Structures
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• v.10 no.5
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• pp.463-479
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• 2007

A series of wind tunnel sectional model dynamic tests of a twin-deck bridge were conducted at the CLP Power Wind/Wave Tunnel Facility (WWTF) of The Hong Kong University of Science and Technology (HKUST) to investigate the effects of gap-width on the self-excited vibrations and the dynamic and aerodynamic characteristics of the bridge. Five 2.9 m long models with different gap-widths were fabricated and suspended in the wind tunnel to simulate a two-degrees-of-freedom (2DOF) bridge dynamic system, free to vibrate in both vertical and torsional directions. The mass, vertical frequency, and the torsional-to-vertical frequency ratio of the 2DOF systems were fixed to emphasize the effects of gap-width. A free-vibration test methodology was employed and the Eigensystem Realization Algorithm (ERA) was utilized to extract the eight flutter derivatives and the modal parameters from the coupled free-decay responses. The results of the zero gap-width configuration were in reasonable agreement with the theoretical values for an ideal thin flat plate in smooth flow and the published results of models with similar cross-sections, thus validating the experimental and analytical techniques utilized in this study. The methodology was further verified by the comparison between the measured and predicted free-decay responses. A comparison of results for different gap-widths revealed that variations of the gap-width mainly affect the torsional damping property, and that the configurations with greater gap-widths show a higher torsional damping ratio and hence stronger aerodynamic stability of the bridge.

• Wind and Structures
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• v.30 no.2
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• pp.199-210
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• 2020

Building wind pressure coefficient transiting test is a new method to test the building wind pressure coefficient by using the wind generated by a moving vehicle, which is susceptible to natural wind and other factors. In this paper, the Commonwealth Advisory Aeronautical Research Council standard model with a scale ratio of 1:300 is used as the test object, and the wind pressure coefficient transiting test is repeated under different natural wind conditions to study the influence of natural wind. Natural wind is measured by an ultrasonic anemometer at a fixed location. All building wind pressure coefficient transiting tests meet the test conditions, and the vehicle's driving speed is 72 km/h. The mean wind pressure coefficient, the fluctuating wind pressure coefficient, and the correlation coefficient of wind pressure are used to describe the influence of natural wind on the building wind pressure coefficient transiting test qualitatively and quantitatively. Some rules, which can also help subsequent transiting tests, are also summarized.

• Wind and Structures
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• v.25 no.1
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• pp.39-61
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• 2017

Buffeting induced resonance (BIR) of hangers on long-suspension bridges is briefly reviewed, including mechanism and experimental verification. Taken the Xihoumen suspension bridge as a numerical example, sensitivities of the BIR of hangers to wind properties are investigated, including types of wind spectrum, turbulence intensity, and spacial coherence of wind fluctuations. Numerical simulations indicate that the BIR of hangers occur to both cases of different wind spectra, showing that it is insensitive to types of wind spectrum. On the other hand, it is found that the turbulence intensity affects buffeting of main cables almost in a linear manner, and so it does to the BIR of the hangers; however, the resonance factors, namely the ratio of the response of the hanger to that of the main cable, are little affected by the turbulence intensity. The spacial coherence of the wind fluctuations, although plays an important role on the buffeting responses of the main structure, has no substantial effects on the BIR of the hangers. Finally, replacement of steel strand with CFRP material has been verified as a very effective countermeasure against the BIR of hangers.

• Wind and Structures
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• v.27 no.6
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• pp.439-449
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• 2018

Wind loading of a tall building built amidst a group of buildings in urban environment is always greatly affected by shielding effects. Wind tunnel tests were carried out to assess the shielding provided by a row of low-rise or medium-rise buildings upstream a square-section tall building of height-to-breadth ratio 6. Mean and dynamic wind loads on the tall building were measured at different wind incidence angles and presented as interference factors (IFs). It is found that presence of a row of upstream buildings provides significant shielding to the tall building. At normal wind incidence, the mean along-wind loads and all components of fluctuating wind loads on the tall building are always reduced by shielding. Vortex shedding seems to still occur on the upper exposed part of the tall building but the vortex excitation levels are largely reduced. The degree of shielding is found to depend on a number of arrangement parameters of the row of upstream buildings. Empirical equations are proposed to quantify the shielding effect based on the wind tunnel data.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.63 no.7
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• pp.916-923
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• 2014

This paper proposes a low-cost switched-mode rectifier (SMR) for a small-scale wind turbine with a permanent magnet synchronous generator (PMSG) system. Also, a sensorless Fuzzy MPPT control is realized by the proposed system. In the PMSG system with the SMR, the synchronous impedance can be replaced as the input inductor of a boost converter. Moreover, the sensorless MPPT control using the Fuzzy technique is carried out by the duty-ratio regulation of the SMR. The relation between the generating power and the duty-ratio is ruled by the chain rule. The wind turbine model is implemented by the squirrel cage induction motor and generated the variable torque when the generator speed is varied. To verify the performance of the proposed system, simulation and experimental results are executed.

• 한국신재생에너지학회:학술대회논문집
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• 2007.06a
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• pp.362-365
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• 2007

In wind turbine blades, airfoils are required to have different spec when compared with airplane airfoil. Airfoils for wind turbine blade must have a high lift-to-drag ratio, moderate to high lift and especially low roughness sensitivity. Also an operation Re. No.s are lower than conventional airplane airfoils. At mid-span and inboard region, structural problems have to be considered. Especially, for stall regulated type, moderate stall behavior is essential part of design. For these reasons, airfoil design for HAWT blade is essential part of blade design. In this paper, root airfoil and tip airfoil are discussed. For a root region, 24% thickness airfoil is designed and for a top region, 12% thickness ratio is done. A inverse design method and panel method are used for rapid airfoil design. In this paper, a design method, features of airfoil shape and characteristics are discussed.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.4
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• pp.84-91
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• 2003

The paper presents a power control algorithm for a full pitch-controlled wind power system. The design of a pitch controller, in general, is performed by linearizing the torque in the vicinity of a operating point assuming the tip speed ratio is constant. For power control, however, the tip speed ratio is no longer a constant. In this study, a reference pitch model is derived in terms of a wind speed, angular velocity, and pitch angle. The reference pitch model is used to design a controller without linearizing the non-linear torque model of the blade. The validity of the algorithm is demonstrated with the results produced through sets of simulation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.1 s.232
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• pp.35-45
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• 2005

TR-E2 configuration designed by Bell Textron was tested in KARI 1-m wind tunnel. To explore aerodynamic characteristics for the given configuration, a $12\%$ scaled model was fabricated and tested. Wind tunnel test for TR-E2 had been performed by changing the incidence angles of wing and deflection angles of control surfaces. Test result showed that the lower wing incidence angle has more favorable lift to drag ratio compared with original design. Longitudinal and directional characteristics of TR-E2 were found to be stable for the pitch and yaw motions. However, the lateral stability of TR-E2 is not stable for certain control surface deflection.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.7
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• pp.1372-1377
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• 2011

This paper proposes the control method of MPPT(maximum power point tracking) for the wind energy generation system using the duty ratio control of boost type DC-DC converter. For a lower cost and a higher reliability, the wind and the generator velocity sensors are removed. MPPT control is implemented by changing the duty ratio of the boost converter. Chain rule is applied by using each function. The grid side inverter is controlled to regulate unity power factor. The proposed control method was analyzed mathematically and verified by the computer simulation using PSIM.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.28 no.5
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• pp.39-51
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• 2014

This paper deals with design of a direct-coupled, small-scaled permanent magnet generator (PMG) for wind power application. First, this paper determines rated power and speed of the PMG from measured characteristics of wind turbines. Second, we derive analytical solutions for the open-circuit field in order to determine optimum magnet thickness and pole pitch/arc ratio. Third, on the basis of open circuit field solutions, stator magnetic circuit including slot opening, teeth width and yoke thickness is designed. And then, a diameter of stator coil which agree with a required current density is calculated, and its turns are determined from the area of slot considering winding packing factor. Finally, finite element (FE) method is employed in analyzing the details of the designed PMG and, test results such as back-emf measurements are given to confirm the design.