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CONTENTS
Volume 23, Number 3, September 2016
 

Abstract
An adjustable, louver-type wind barrier was introduced in this study for improving the running safety and ride comfort of train on the bridge under the undesirable wind environment. The aerodynamic characteristics of both train and bridge due to this novel wind barrier was systematically investigated based on the wind tunnel tests. It is suggested that rotation angles of the adjustable blade of the louver-type wind barrier should be controlled within 90 to achieve an effective solution in terms of the overall aerodynamic performance of the train. Compared to the traditional grid-type wind barrier, the louver-type wind barrier generally presents better aerodynamic performance. Specifically, the larger decrease of the lift force and overturn moment of the train and the smaller increase of the drag force and torsional moment of the bridge resulting from the louver-type wind barrier were highlighted. Finally, the computational fluid dynamics (CFD) technique was applied to explore the underlying mechanism of aerodynamic control using the proposed wind barrier.

Key Words
louver-type wind barrier; aerodynamic coefficients; wind tunnel test; CFD

Address
Xuhui He, Kang Shi, Yunfeng Zou, Hanfeng Wang and Hongxi Qin: School of Civil Engineering, Central South University, Changsha, 410075, China;
National Engineering Laboratory for High Speed Railway Construction, Changsha, 410075, China
Teng Wu: Department of Civil, Structural and Environmental Engineering,University at Buffalo-The State Univ. of New York, Buffalo, NY 14260, USA



Abstract
Wind tunnel tests of a 1/2200-scale mountainous terrain model have been carried out to investigate local wind characteristics at a bridge location in southeast Tibet, China. Flows at five key locations on the bridge at deck level were measured for 26 directions. It was observed that wind characteristics (including mean wind velocity and overall turbulence intensity) vary significantly depending on the approaching wind direction and measurement position. The wind inclination angle measured in the study fluctuated between -18 and +16 and the ratio of mean wind velocity to reference wind velocity was small when the wind inclination angles were large, especially for positive wind inclination angles. The design standard wind speed and the minimum critical wind speed for flutter rely on the wind inclination angle and should be determined from the results of such tests. The variation of wind speed with wind inclination angles should be of the asymmetry step type. The turbulence characteristics of the wind were found to be similar to real atmospheric flows.

Key Words
mountainous terrain; approaching wind direction; wind inclination angle; turbulence characterization

Address
Lei Yan: Department of Bridge Engineering, Tongji University, 1239 Siping Road, Shanghai 200092, China;
State Key Laboratory of Disaster Reduction in Civil Engineering, Tongji University, 1239 Siping Road, Shanghai 200092, China;
Department of Mechanical Engineering, The University of Auckland, Private Bag 92019, Auckland 1142, New Zealand
Zhen S. Guo: Department of Bridge Engineering, Tongji University, 1239 Siping Road, Shanghai 200092, China;
Key Laboratory of Wind Resistance Technology of Bridges of Ministry of Transport, Tongji University, 1239 Siping Road, Shanghai 200092, China
Le D. Zhu: Department of Bridge Engineering, Tongji University, 1239 Siping Road, Shanghai 200092, China;
State Key Laboratory of Disaster Reduction in Civil Engineering, Tongji University, 1239 Siping Road, Shanghai 200092, China;
Key Laboratory of Wind Resistance Technology of Bridges of Ministry of Transport, Tongji University, 1239 Siping Road, Shanghai 200092, China
Richard G.J. Flay: Department of Mechanical Engineering, The University of Auckland, Private Bag 92019, Auckland 1142, New Zealand






Abstract
In recent years, the frequency and duration of supply interruption in electric power transmission system due to flashover increase yearly in China. Flashover is usually associated with inadequate electric clearance and often takes place in extreme weathers, such as downbursts, typhoons and hurricanes. The present study focuses on the wind-induced oscillation of conductor during the process when a downburst is passing by or across a specified transmission line. Based on a revised analytical model recently developed for stationary downburst, transient three-dimensional wind fields of moving downbursts are successfully simulated. In the simulations, the downbursts travel along various motion paths according to the certain initial locations and directions of motion assumed in advance. Then, an eight-span section, extracted from a practical 500 kV ultra-high-voltage transmission line, is chosen. After performing a non-linear transient analysis, the transient displacements of the conductors could be obtained. Also, an extensive study on suspension insulator strings\' rotation angles is conducted, and the electric clearances at different strings could be compared directly. The results show that both the variation trends of the transient responses and the corresponding peak values vary seriously with the motion paths of downburst. Accordingly, the location of the specified string, which is in the most disadvantageous situation along the studied line section, is picked out. And a representative motion path is concluded for reference in the calculation of each string

Key Words
multi-span conductor; flashover; moving downburst; motion path; wind-induced oscillation

Address
Wenjuan Lou, Jiawei Wang and Yong Chen: Institute of Structure Engineering, Zhejiang University, Hangzhou 310058, China
Zhongbin Lv and Ming Lu: Henan Electric Power Research Institute, Zhengzhou 450052, China

Abstract
This paper presents the experimental results of the wind tunnel tests for three symmetric, rectangular, tall building models on a typical open terrain considering the torsional motion-induced vibrations. The time histories of the wind pressure on these models under different reduced wind speeds and torsional amplitudes are obtained through the multiple point synchronous scanning pressure technique. Thereafter, the characteristics of both the Root Mean Square (RMS) coefficients and the spectra of the base shear/torque in the along-wind, across-wind, and torsional directions, respectively, are discussed. The results show that the RMS coefficients of the base shear/torque vary in the three directions with both the reduced wind speeds and the torsional vibration amplitudes. The variation of the RMS coefficients in the along-wind direction results mainly from the change of the aerodynamic forces, but sometimes from aeroelastic effects induced by torsional vibration. However, the variations of the RMS coefficients in the across-wind and torsional directions are caused by more equal weights of both the aerodynamic forces and the aeroelastic effects. As such, for the typical tall buildings, the modification of the aerodynamic forces in the along-wind, across-wind, and torsional directions, respectively, and the aeroelastic effects in the across-wind and torsional directions should be considered. It is identified that the torsional vibration amplitudes and the reduced wind speeds are two significant parameters for the aerodynamic forces on the structures in the three directions.

Key Words
tall buildings; wind tunnel test; torsional motion-induced vibration; wind loads; aeroelastic effects

Address
Lianghao Zou: School of civil engineering, Wuhan University, 299 bayi Road, Wuhan, 430072 China;
Department of Civil and Environmental Engineering, Louisiana State University, Baton Rouge,Louisiana 70803 USA
Guoji Xu, C.S. Cai: Department of Civil and Environmental Engineering, Louisiana State University, Baton Rouge,Louisiana 70803 USA
Shuguo Liang: School of civil engineering, Wuhan University, 299 bayi Road, Wuhan, 430072 China


Abstract
Ice accretions on stay cables may result in the instable vibration of galloping, which would affect the safety of cable-stayed bridges. A large number of studies have investigated the galloping vibrations of transmission lines. However, the obtained aerodynamics in transmission lines cannot be directly applied to the stay cables on cable-stayed bridges. In this study, linear and nonlinear single degree-of-freedom models were introduced to obtain the critical galloping wind velocity of iced stay cables where the aerodynamic lift and drag coefficients were identified in the wind tunnel tests. Specifically, six ice shapes were discussed using section models with geometric scale 1:1. The results presented obvious sudden decrease regions of the aerodynamic lift coefficient for all six test models. Numerical analyses of iced stay cables associated to a medium-span cable-stayed bridge were carried out to evaluate the potential galloping instability. The obtained nonlinear critical wind velocity for a 243-meter-long stay cable is much lower than the design wind velocity. The calculated linear critical wind velocity is even lower. In addition, numerical analyses demonstrated that increasing structural damping could effectively mitigate the galloping vibrations of iced stay cables.

Key Words
galloping vibrations; stay cables; ice accretions; aerodynamic force coefficients; critical wind velocity

Address
Shouying Li, Tao Huang and Zhengqing Chen: Key Laboratory for Wind and Bridge Engineering of Hunan Province, College of Civil Engineering,Hunan University, Changsha 410082, China
Teng Wu: Department of Civil, Structural and Environmental Engineering, University at Buffalo-The State Univ. of New York, Buffalo, NY 14260, USA



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