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CONTENTS
Volume 9, Number 6, November 2006
 

Abstract
This article synthesizes the literature on the meteorology, experimental simulation, and wind engineering ramifications of intense downburst outflows. A novel design of a large-scale test facility and experimental evidence of its validity are presented. A two-dimensional slot jet is used to simulate only the outflow region of a downburst. Profiles of mean velocity and turbulence quantities are acquired using hot-wire anemometry. Comparison with the literature provides empirical evidence that supports the current approach. A geometric analysis considers the validity of applying a two-dimensional approximation for downburst wind loading of structures. This analysis is applicable to power transmission lines in particular. The slot jet concept can be implemented in a large boundary layer wind tunnel to enable large-scale laboratory experiments of thunderstorm wind loads on structures.

Key Words
downburst outflow; microburst outflow; localized intense wind; thunderstorm wind load; large-scale wind tunnel; two-dimensional wall jet; slot jet; frontal curvature.

Address
Department of Mechanical & Materials Engineering,rnThe University of Western Ontario, London, Ont., Canada, N6A 5B9

Abstract
A more applicable optimization model for extracting flutter derivatives of bridge decks is presented, which is suitable for time-varying weights for fitting errors and different lengths of vertical bending and torsional free vibration data. A stochastic search technique for searching the optimal solution of optimization problem is developed, which is more convenient in understanding and programming than the alternate iteration technique, and testified to be a valid and efficient method using two numerical examples. On the basis of the section model test of Sutong Bridge deck, the flutter derivatives are extracted by the stochastic search technique, and compared with the identification results using the modified least-square method. The Empirical Mode Decomposition method is employed to eliminate noise, trends and zero excursion of the collected free vibration data of vertical bending and torsional motion, by which the identification precision of flutter derivatives is improved.

Key Words
flutter derivatives extraction; parameter identification; empirical mode decomposition; stochastic search technique; section model.

Address
Department of Bridge Engineering, State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University, Shanghai 200092, China

Abstract
This paper is devoted to the non linear quasi-steady aerodynamic loading. A linear approximation is often used to compute the response of structures to buffeting forces. Some researchers have however shown that it is possible to account for the non linearity of this loading. This non linearity can come (i) from the squared velocity or (ii) from the shape of the aerodynamic coefficients (as functions of the wind angle of attack). In this paper, it is shown that this second origin can have significant implications on the design of the structure, particularly when the non linearity of the aerodynamic coefficient is important or when the transverse turbulence is important.

Key Words
non linear wind loading; non Gaussian; stochastic; aerodynamic coefficient.

Address
Department of Material Mechanics and Structures, University of Lieg, Belgium

Abstract
This paper presents numerical results of pedestrian-level wind environment around the base of a row of tall buildings by CFD. Four configurations of building arrangement are computed including a single square tall building. Computed results of pedestrian-level wind flow patterns and wind speeds are compared to previous wind tunnel measurement data to enable an assessment of CFD predictions. The CFD model uses the finite-volume method with RNG k-e model for turbulence closure. It is found that the numerical results can reproduce key features of pedestrian-level wind environment such as corner streams around corners of upwind building, sheltered zones behind buildings and channeled high-speed flow through a building gap. However, there are some differences between CFD results and wind tunnel data in the wind speed distribution and locations of highest wind speeds inside the corner streams. In locations of high ground-level wind speeds, CFD values match wind tunnel data within ?0%.

Key Words
CFD; pedestrian-level winds; wind environment; building interaction.

Address
K. M. Lam; Department of Civil Engineering, University of Hong Kong, Pokfulam Road, Hong KongrnA. P. To; Ove Arup & Partners Hong Kong Limited, 5/F, Festival Walk, Tat Chee Avenue, Kowloon Tong, Hong Kong

Abstract
The demand for energy in the world increases everyday. Blade energy which is wind turbine is a significant resource which must be appreciated in this field. Especially, in places where wind potential is high, the usage of wind energy is a beneficial factor for every country

Key Words
wind turbine; mathematical modelling; rotor blade.

Address
Ali Vardar; Uludag University, Faculty of Agriculture, Department of Agricultural Machinery, 16059 Bursa, TurkeyrnBulent Eker; Trakya University, Faculty of Agriculture, Department of Agricultural Machinery, 59030 Tekirdag, Turkey


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