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CONTENTS
Volume 35, Number 4, October 2022
 


Abstract
Wind tunnel test is often adopted to assess the site-specific wind characteristics for the design of bridges as suggested by current design standards. To investigate the wind characteristics of flat and mountainous terrain, two topographic models are tested in a boundary layer wind tunnel. The wind characteristics, including the vertical and horizontal mean wind speed distributions, the turbulence intensity, and the wind power spectra, are presented. They are investigated intensively in present study with the discussions on the effect of wind direction and the effect of topography. It is indicated that for flat terrain, the wind direction has negligible effect on the wind characteristics, however, the assumption of a homogenous wind field for the mountainous terrain is not applicable. Further, the non-homogeneous wind field can be defined based on a proposed approach if the wind tunnel test or on-site measurement is performed. The calculated turbulence intensities and wind power spectra by using the measured wind speeds are also given. It is shown that for the mountainous terrain, engineers should take into account the variability of the wind characteristics for design considerations.

Key Words
flat terrain; mountainous terrain; nonhomogeneous wind field; turbulence intensity; wind power spectra; wind tunnel test

Address
Jiawu Li, Jun Wang, Feng Wang and Guohui Zhao:1) School of Highway, Chang'an University, Xi'an 710064, Shannxi, China
2)Key Laboratory for Bridge and Tunnel of Shannxi Province, Chang' an University, Xi'an, China

Shucheng Yang:1) School of Highway, Chang'an University, Xi'an 710064, Shannxi, China
2)Key Laboratory for Bridge and Tunnel of Shannxi Province, Chang' an University, Xi'an, China
3)Civil and Environmental Department, Western University, London, Ontario, Canada

Abstract
The conformal mapping method (CMM) has been broadly exploited in the study of fluid flows over airfoils and other research areas, yet it's hard to find relevant research in bridge engineering. This paper explores the feasibility of CMM in streamlined box girder bridges. Firstly, the mapping function transforming a unit circle to the streamlined box girder was solved by CMM. Subsequently, the potential flow solution of aerostatic pressure on the streamlined box girder was obtained and was compared with numerical simulation results. Finally, the aerostatic pressure attained by CMM was utilized to estimate the aerostatic coefficient and flutter performance of the streamlined box girder. The results indicate that the solution of the aerostatic pressure by CMM on the windward side is satisfactory within a small angle of attack. Considering the windward aerostatic pressure and coefficient of correction, CMM can be employed to estimate the rate of change of the lift and moment coefficients with angle of attack and the influence of the geometric shape of the streamlined box girder on flutter performance.

Key Words
aerostatic coefficients; aerostatic pressure; conformal mapping method; flutter; streamlined box girder

Address
Lianhuo Wu, Mingjin Zhang and Yongle Li:Department of Bridge Engineering, Southwest Jiaotong University, Chengdu, 610031, China

J. Woody Ju and Jingxi Qi:Department of Civil and Environmental Engineering, University of California, Los Angeles, Los Angeles, CA 90095, USA

Abstract
Light-weight or low-damped structures may encounter the unsteady galloping instability that occurs at low reduced wind speeds, where the classical quasi-steady assumption is invalid. Although this unsteady phenomenon has been widely studied for rectangular cross sections with one side perpendicular to the incidence flow, the effect of the mean wind angle of attack has not been paid enough attention yet. With four sectional models of different side ratios and geometric shapes, the presented research focuses on the effect of the wind angle of attack on unsteady galloping instability. In static tests, comparatively strong vortex shedding force was noticed in the middle of the range of flow incidence where the lift coefficient shows a negative slope. In aeroelastic tests with a low Scruton number, the typical unsteady galloping, which is due to an interaction with vortex-induced vibration and results in unrestricted oscillation initiating at the Karman vortex resonance wind speed, was observed for the wind angles of attack that characterize relatively strong vortex shedding force. In contrast, for the wind angles of attack with relatively weak shedding force, an "atypical" unsteady galloping was found to occur at a reduced wind speed clearly higher than the Kármán-vortex resonance one. These observations are valid for all four wind tunnel models. One of the wind tunnel models (with a bridge deck cross section) was also tested in a turbulent flow with an intensity about 9%, showing only the atypical unsteady galloping. However, the wind angle of attack with the comparatively strong vortex shedding force remains the most unfavorable one with respect to the instability threshold in low Scruton number conditions.

Key Words
sharp-edged bluff body; unsteady galloping; vortex induced vibration; wind angle of attack; wind tunnel tests

Address
Cong Chen, Niccolo Wieczorek, Julian Unglaub and Klaus Thiele: Institute of Steel Structures, Technische Universität Braunschweig, Beethovenstr. 51, Brunswick, 38106, Lower Saxony, Germany

Bingyu Dai:Zhejiang Province Institute of Architectural Design and Research (ZIAD), Anji Road 18, Hangzhou, 310006, Zhejiang Province, China

Abstract
The pressure-mitigating effects of a high-speed train passing through a tunnel with a partially reduced cross-section are investigated via the numerical approach. A compressible, three-dimensional RNG k-Εturbulence model and a hybrid mesh strategy are adopted to reproduce that event, which is validated by the moving model test. Three step-like tunnel forms and two additional transitions at the tunnel junction are proposed and their aerodynamic performance is compared and scrutinized with a constant cross-sectional tunnel as the benchmark. The results show that the tunnel step is unrelated to the pressure mitigation effects since the case of a double-step tunnel has no advantage in comparison to a single-step tunnel, but the excavated volume is an essential matter. The pressure peaks are reduced at different levels along with the increase of the excavated earth volume and the peaks are either fitted with power or logarithmic function relationships. In addition, the Arc and Oblique-transitions have very limited gaps, and their pressure curves are identical to each other, whereas the Rec-transition leads to relatively lower pressure peaks in CP max, CP min, and ΔCP, with 5.2%, 4.0%, and 4.1% relieved compared with Oblique-transition. This study could provide guidance for the design of the novel railway tunnel.

Key Words
aerodynamic force; cross-section; high-speed train; railway tunnel; transient pressure

Address
Wenhui Li, Tanghong Liu, Xiaoshuai Huo, Zijian Guo and Yutao Xia:1)Key Laboratory of Traffic Safety on Track of Ministry of Education, School of Traffic & Transportation Engineering,
Central South University, Changsha 410075, PR China
2)Joint International Research Laboratory of Key Technology for Rail Traffic Safety, Changsha 410075, PR China
3)National & Local Joint Engineering Research Center of Safety Technology for Rail Vehicle, Changsha 410075, PR China

Abstract
Analyzing the typhoon wind hazards is crucial to determine the extreme wind load on engineering structures in the typhoon prone region. In essence, the typhoon hazard analysis is a high-dimensional problem with randomness arising from the typhoon genesis, environmental variables and the boundary layer wind field. This study suggests a dimension reduction approach by decoupling the original typhoon hazard analysis into two stages. At the first stage, the randomness of the typhoon genesis and environmental variables are propagated through the typhoon track model and intensity model into the randomness of the key typhoon parameters. At the second stage, the probability distribution information of the key typhoon parameters, combined with the randomness of the boundary layer wind field, could be used to estimate the extreme wind hazard. The Chinese southeast coastline is taken as an example to demonstrate the adequacy and efficiency of the suggested decoupling approach.

Key Words
decoupling approach; probability density evolution method; typhoon hazards; typhoon intensity; typhoon track

Address
Xu Hong:1)College of Civil Engineering, Hefei University of Technology, Tunxi Road 193, Anhui Province, 230009, China
2)Anhui Key Laboratory of Civil Engineering Structures and Materials, Tunxi Road 193, Anhui Province, 230009, China

Jie Li:1)College of Civil Engineering, Tongji University, 1239 Siping Road, Shanghai 200092, China
2)State Key Laboratory of Disaster Reduction in Civil Engineering, Tongji University, 1239 Siping Road, Shanghai 200092, China


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