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CONTENTS
Volume 27, Number 2, August 2018
 

Abstract
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Key Words
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Address
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Abstract
At the University of Western Ontario (UWO), numerical tools represented in semi-closed form solution for the conductors and finite element modeling of the lattice tower were developed and utilized significantly to assess the behavior of transmission lines under downburst wind fields. Although these tools were validated against other finite element analyses, it is essential to validate the findings of those tools using experimental data. This paper reports the first aeroelastic test for a multi-span transmission line under simulated downburst. The test has been conducted at the three-dimensional wind testing facility, the WindEEE dome, located at the UWO. The experiment considers various downburst locations with respect to the transmission line system. Responses obtained from the experiment are analyzed in the current study to identify the critical downburst locations causing maximum internal forces in the structure (i.e., potential failure modes), which are compared with the failure modes obtained from the numerical tools. In addition, a quantitative comparison between the measured critical responses obtained from the experiment with critical responses obtained from the numerical tools is also conducted. The study shows a very good agreement between the critical configurations of the downburst obtained from the experiment compared to those predicted previously by different numerical studies. In addition, the structural responses obtained from the experiment and those obtained from the numerical tools are in a good agreement where a maximum difference of 16% is found for the mean responses and 25% for the peak responses.

Key Words
aero-elastic modeling; downburst; transmission line; cable; wind load; high- intensity wind; WindEEE

Address
Amal Elawady: Department of Civil and Environmental Engineering, Florida International University, Miami, United States
Haitham Aboshosha : Department of Civil Engineering, Ryerson University, Toronto, Ontario, Canada
Ashraf El Damatty: Department of Civil and Environmental Engineering, Western University, London, Ontario, Canada;
The Wind Engineering, Energy and Environment (WindEEE) Research Institute, Western University, London, Ontario, Canada;
Department of Structural Engineering, Faculty of Engineering, Cairo University, Egypt


Abstract
3D simulations based on an impinging jet were carried out to investigate the flow field of a steady downburst and its effects on a high-rise building by applying the SST k-w turbulence model. The vertical profile of radial wind speed obtained from the simulation was compared with experimental data and empirical models in order to validate the accuracy of the present numerical method. Then wind profiles and the influence of jet velocity and jet height were investigated. Focusing on a high-rise building, the flow structures around the building, pressure distributions on the building surfaces and aerodynamic forces were analyzed in order to enhance the understanding of wind load characteristics on a high-rise building immersed in a downburst.

Key Words
downburst; numerical study; impinging jet; high-rise building; flow structure; pressure distribution; aerodynamic force

Address
Guoqing Huang: School of Civil Engineering, Southwest Jiaotong University, Chengdu, Sichuan, 610031, China;
School of Civil Engineering, Chongqing University, Chongqing, 400044, China
Weizhan Liu and Qiang Zhou: School of Civil Engineering, Southwest Jiaotong University, Chengdu, Sichuan, 610031, China
Zhitao Yan:School of Civil Engineering, Chongqing University, Chongqing, 400044, China
Delong Zuo: Department of Civil, Environmental and Construction Engineering, Texas Tech University, Lubbock, TX 79409, USA


Abstract
Wall jet flow exists widely in engineering applications, including the simulation of thunderstorm downburst outflows, and has been investigated extensively by both experimental and numerical methods. Most previous studies focused on the scaling laws and self-similarity, while the effect of lip thickness and external stream height on mean velocity has not been examined in detail. The present work is a numerical study, using steady Reynolds-Averaged Navier Stokes (RANS) simulations at a Reynolds number of 3.5 X 104, of a turbulent plane wall jet with an external stream to investigate the influence of the wall jet domain on downstream development of the flow. The comparisons of flow characteristics simulated by the Reynolds stress turbulence model closure (Stress-omega, SWRSM) and experimental results indicate that this model may be considered reasonable for simulating the wall jet. The confined wall jet is further analyzed in a parametric study, with the results compared to the experimental data. The results indicate that the height and the width of the wind tunnel and the lip thickness of the jet nozzle have a great effect on the wall jet development. The top plate of the tunnel does not confine the development of the wall jet within 200b of the nozzle when the height of the tunnel is more than 40b (b is the height of jet nozzle). The features of the centerline flow in the mid plane of the 3D numerical model are close to those of the 2D simulated plane wall jet when the width of the tunnel is more than 20b.

Key Words
wall jet; confined; computational fluid dynamics; numerical simulation; Reynolds stress models

Address
Zhitao Yan: School of Civil Engineering and Architecture, Chongqing University of Science & technology, Chongqing 401331, China;
School of Civil Engineering, Chongqing University, Chongqing, China, 400045
Yongli Zhong: School of Civil Engineering, Chongqing University, Chongqing, China, 400045
Xu Chen: School of Civil Engineering, Southwest Jiaotong University, Chengdu 610031, China
Rory P. McIntyre and Eric Savory: Department of Mechanical and Materials Engineering, the University of Western Ontario, London, Canada, N6A 5B9


Abstract
Experiments were conducted in a large-scale Ward-type tornado simulator to study tornado-like vortices. Both flow velocities and the pressures at the surface beneath the vortices were measured. An interpretation of these measurements enabled an assessment of the mean flow field as well as the mean and fluctuating characteristics of the surface pressure deficit, which is a manifestation of the flow fluctuation aloft. An emphasis was placed on the effect of the aspect ratio of the tornado simulator on the characteristics of the simulated flow and the corresponding surface pressure deficit, especially the evolution of these characteristics due to the transition of the flow from a single-celled vortex to a two-celled vortex with increasing swirl ratio.

Key Words
tornado-like vortex; surface pressure deficit; aspect ratio; swirl ratio

Address
Zhuo Tang: National Wind Institute, Texas Tech University, Lubbock, TX 79409, USA
Delong Zuo: National Wind Institute, Texas Tech University, Lubbock, TX 79409, USA;
Department of Civil, Environmental and Construction Engineering, Texas Tech University, Lubbock, TX 79409, USA
Darryl James: Department of Mechanical Engineering, Texas Tech University, Lubbock, TX 79409, USA
Yuzuru Eguchi and Yasuo Hattori: Fluid Dynamics Sector, Civil Engineering Research Laboratory, Central Research Institute of Electric Power Industry,
Abiko 1646, Abiko-shi, Chiba-ken, 270-1194 Japan



Abstract
The effects of steep and shallow hills on a stationary tornado-like vortex with a swirl ratio of 0.4 are simulated and quantified as Fractional Speed Up Ratios (FSUR) at three different locations of the vortex with respect to the crests of the hills. Steady state Reynolds Averaged Naiver Stokes (RANS) equations closed using Reynolds Stress Turbulence model are used to simulate stationary tornadoes. The tornado wind field obtained from the numerical simulations is first validated with previous experimental and numerical studies by comparing radial and tangential velocities, and ground static pressure. A modified fractional speed-up ratio (FSUR) evaluation technique, appropriate to the complexity of the tornadic flow, is then developed. The effects of the hill on the radial, tangential and vertical flow components are assessed. It is observed that the effect of the hill on the radial and vertical component of the flow is more pronounced, compared to the tangential component. Besides, the presence of the hill is also seen to relocate the center of tornadic flow. New FSUR values are produced for shallow and steep hills.

Key Words
tornado; topography; speed-up; Fractional Speed Up Ratio (FSUR); numerical simulation

Address
Zoheb Nasir and Girma T. Bitsuamlak: Civil and Environmental Engineering/WindEEE Institute, Western University (formerly The University of Western Ontario),
1151 Richmond St, London, Canada


Abstract
Heavy damages to properties with attendant losses were frequently caused by tornadoes in recent years. This natural hazard is one of the most destructive wind events that must be fully studied and well understood in order to keep the safety of structures and infrastructure facilities. On June 23, 2016, a severe tornado, which is an Enhanced Fujita (EF) 4 storm, occurred in the rim of a coastal city named as Yancheng in China. Numerous low-rise buildings as well as facilities (e.g., transmission towers) were destroyed or damaged. In this paper, damages to structures and infrastructure facilities by the severe tornado are reviewed. The collapses of residential buildings, industrial structures and other infrastructure facilities are described. With an overview of the damages, various possible mechanisms of the collapse are then discussed and utilized to reveal the initiation of the damage to various facilities. It is hoped that this paper can provide a concise but comprehensive reference for the researchers and engineers to help understand the tornado effects on structures and expose the vulnerabilities that need to be improved in current wind-resistant design practices.

Key Words
tornado; damage; residential buildings; industrial structure; infrastructure facility; mechanism

Address
Tianyou Tao, Hao Wang, Chengyuan Yao, Zhongqin Zou and Zidong Xu: Key Laboratory of Concrete and Prestressed Concrete Structures of Ministry of Education,
Southeast University, Nanjing 211189, China



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