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CONTENTS
Volume 12, Number 3, May 2009
 

Abstract
A physical and numerical steady flow impinging jet has been used to simulate the bulk characteristics of a downburst-like wind field. The influence of downdraft tilt and surface roughness on the ensuing wall jet flow has been investigated. It was found that a simulated downdraft impinging the surface at a non-normal angle has the potential for causing larger structural loads than the normal impingement case. It was also found that for the current impinging jet simulations, surface roughness played a minor role in determining the storm maximum wind structure, but this influence increased as the wall jet diverged. However, through comparison with previous research it was found that the influence of surface roughness is Reynolds number dependent and therefore may differ from that reported herein for full-scale downburst cases. Using the current experimental results an empirical model has been developed for laboratory-scale impinging jet velocity structure that includes the influence of both jet tilt and surface roughness.

Key Words
Downburst; microburst; impinging jet; tilted jet; surface roughness; empirical model

Address
M.S. Mason; School of Civil Engineering, University of Sydney, NSW, Australia
G.S. Wood; Cermak Peterka Petersen, St. Peters, NSW, Australia
D.F. Fletcher; School of Chemical and Biomolecular Engineering, University of Sydney, NSW, Australia

Abstract
Aerodynamic flutter control for long-span cable-supported bridges was investigated based on three basic girder sections, i.e. streamlined box girder section, box girder section with cantilevered slabs and two-isolated-girder section. Totally four kinds of aerodynamic flutter control measures (adding fairings, central-slotting, adding central stabilizers and adjusting the position of inspection rail) were included in this research. Their flutter control effects on different basic girder sections were evaluated by sectional model or aeroelastic model wind tunnel tests. It is found that all basic girder sections can get aerodynamically more stabled with appropriate aerodynamic flutter control measures, while the control effects are influenced by the details of control measures and girder section configurations. The control effects of the combinations of these four kinds of aerodynamic flutter control measures, such as central-slotting plus central-stabilizer, were also investigated through sectional model wind tunnel tests, summarized and compared to the flutter control effect of single measure respectively.

Key Words
Aerodynamic instability; flutter control; cable-supported bridge; fairing, central-slotting; central stabilizer

Address
Yongxin Yang and Yaojun Ge; State Key Lab for Disaster Reduction in Civil Engineering, Tongji University, Shanghai, China

Abstract
This study examines the accuracy of large-eddy simulation (LES) to simulate the flow around a large irregular sloping complex terrain. Typically, real built up environments are surrounded by complex terrain geometries with many features. The complex terrain surrounding The Hong Kong University of Science and Technology campus was modelled and the flow over an uphill slope was simulated. The simulated results, including mean velocity profiles and turbulence intensities, were compared with the flow characteristics measured in a wind tunnel model test. Given the size of the domain and the corresponding constraints on the resolution of the simulation, the mean velocity components within the boundary layer flow, especially in the stream-wise direction were found to be reasonably well replicated by the LES. The turbulence intensity values were found to differ from the wind tunnel results in the building recirculation zones, mostly due to the constraints placed on spatial and temporal resolutions. Based on the validated mean velocity profile results, the flow-structure interactions around these buildings and the surrounding terrain were examined.

Key Words
complex terrain; uphill slope; boundary layer; CFD; large eddy simulation

Address
C. F. Tsang; CLP Wind/Wave Tunnel Facility, The Hong Kong University of Science and Technology, Hong Kong SAR
Kenny C. S. Kwok; CLP Wind/Wave Tunnel Facility, The Hong Kong University of Science and Technology, Hong Kong SAR
, School of Engineering, University of Western Sydney, Australia
Peter A. Hitchcock; CLP Wind/Wave Tunnel Facility, The Hong Kong University of Science and Technology, Hong Kong SAR
Desmond K. K. Hui; Transport Department, Hong Kong SAR

Abstract
This paper develops and discusses a method by which it is possible to evaluate the Equivalent Static Force (ESF) of wind in the case of long-span bridges. Attention is focused on the alongwind direction. The study herein carried out deals with the classical problems of determining the maximum effects due to the alongwind action and the corresponding ESFs. The mean value of the maximum alongwind displacement of the deck is firstly obtained both by the spectral analysis and the Gust Response Factor (GRF) technique. Successively, in order to derive the other wind-induced effects acting on the deck, the Gust Effect Factor (GEF) technique is extended to long-span bridges. By adopting the GRF technique, it is possible to define the ESF that applied on the structure produces the maximum alongwind displacement. Nevertheless the application of the ESF so obtained does not furnish the correct maximum values of other wind-induced effects acting on the deck such as bending moments or shears. Based on this observation, a new technique is proposed which allows to define an ESF able to simultaneously reproduce the maximum alongwind effects of the bridge deck. The proposed technique is based on the GEF and the POD techniques and represents a valid instrument of research for the understanding of the wind excitation mechanism.

Key Words
Long-span bridge; alongwind effects; Proper Orthogonal Decomposition; Gust Effect Factor technique; Equivalent Static Force

Address
Alessandra Fiore and Pietro Monaco; Politecnico di Bari, Department of Civil and Environmental Engineering, Via Orabona 4, 70125 Bari, Italy

Abstract
The paper is concerned with the numerical study of the cross-wind response of the 295 m-tall six-flue industrial chimney, located in the power station of Belchatow, Poland. The response of the chimney due to turbulent wind flow is caused by the lateral turbulence component and vortex excitation with taking into account motion-induced wind forces. The cross-wind response has been estimated by means of the random vibration approach. Three power spectral density functions suggested by Kaimal, Tieleman and Solari for the evaluation of the lateral turbulence component response are taken into account. The vortex excitation response has been calculated by means of the Vickery and Basu

Key Words
numerical analysis; tall chimney; lateral and vortex shedding responses; motion-induced wind force

Address
Piotr G?rski; Opole University of Technology, ul. Katowicka 48, Opole, Poland

Abstract
Ning Zhang; School of Atmospheric Sciences, Nanjing University, Nanjing 210093, China, State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China Weimei Jiang; School of Atmospheric Sciences, Nanjing University, Nanjing 210093, China Zhiqiu Gao; State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China Fei Hu; State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China Zhen Peng; School of Atmospheric Sciences, Nanjing University, Nanjing 210093, China

Key Words


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