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CONTENTS
Volume 30, Number 3, March 2020
 

Abstract
Net pressures on roofs and walls of buildings are dependent on the internal and external pressure fluctuations. The variation of internal and external pressures are influenced by the size and location of the openings. The correlation of external and internal pressure influences the net pressures acting on cladding on different parts of the roof and walls. The peak internal and peak external pressures do not occur simultaneously, therefore, a reduction can be applied to the peak internal and external pressures to obtain a peak net pressure for cladding design. A 1:200 scale wind tunnel model study was conducted to determine the correlations of external and internal pressures and effective reduction to net pressures (i.e., net pressure factors, 𝐹𝐶) for roof and wall cladding. The results show that external and internal pressures on the windward roof and wall edges are well correlated. The largest 𝐶𝑝̌,𝑛𝑒𝑡, highest correlation coefficient and the highest 𝐹𝐶 are obtained for different wind directions within 90

Key Words
external pressure; internal pressure; net pressure; correlation; combination factor; pressure factor; wind load; standard

Address
Geeth G. Bodhinayake, John D. Ginger, David J. Henderson: Department of Civil Engineering, James Cook University, James Cook Drive, Townsville, QLD 4811, Australia

Abstract
Downbursts are acknowledged for being a major loading hazard for horizontally-extending structures like transmission line systems. With these structures being inherently flexible, it is important to characterize the turbulence associated with the wind flow of downburst events being essential to quantify dynamic excitations on structures. Accordingly, the current study numerically characterizes the downburst wind field of open terrain simulated at the Wind Engineering, Energy and Environment (WindEEE) dome testing facility at The University of Western Ontario in Canada through a high-resolution large eddy simulation (LES). The study validates the numerical simulation considering both the mean and the turbulent components of the flow. It then provides a detailed visual description of the flow at WindEEE through the capabilities enabled by LES to identify the key factors affecting the flow. The study also presents the spatial distribution of turbulence intensities and length scales computed from the numerical model and compares them with previous values reported in the literature. The comparison shows the ability of the downburst simulated at WindEEE to reproduce turbulence characteristics similar to those reported from field measurements. The study also indicates that downburst turbulence is well-correlated circumferentially which imposes high correlated loads on horizontally-distributed structures such as transmission lines.

Key Words
downburst; WindEEE; Large Eddy Simulation (LES); turbulence; length scales; high intensity wind

Address
Ibrahim Ibrahim: 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
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



Abstract
Wind load and responses are the major factors which govern the design norms of tall buildings. Corner modification is one of the most commonly used minor shape modification measure which significantly reduces the wind load and responses. This study presents a comparison of wind load and pressure distribution on different corner modified (chamfered and rounded) Y plan shaped buildings. The numerical study is done by ANSYS CFX. Two turbulence models, k-epsilon and Shear Stress Transport (SST), are used in the simulation of the building and the data are compared with the previous experimental results in a similar flow condition. The variation of the flow patterns, distribution of pressure over the surfaces, force and moment coefficients are evaluated and the results are represented graphically to understand the extent of nonconformities due to corner modifications. Rounded corner shape is proving out to be more efficient in comparing to chamfered corner for wind load reduction. The maximum reduction in the maximum force and moment coefficient is about 21.1 % and 19.2 % for 50% rounded corner cut.

Key Words
computational fluid dynamics; corner modifications; force coefficient and moment coefficient

Address
Prasenjit Sanyal : Department of Civil Engineering, Meghnad Saha Institute of Technology, Kolkata-700150, India
Sujit Kumar Dalui: Department of Civil Engineering, Indian Institute of Engineering Science and Technology, Shibpur, Howrah-711103, India

Abstract
This paper deals with the design, wind tunnel testing, and performance analysis of small wind turbines targeting low-power applications. Three different small-size blade designs in terms of size, shape, and twisting angle are considered and tested. We conduct wind tunnel tests while measuring the angular speed of the rotating blades, the generated voltage, and the current under varying resistive loading and air flow conditions. An electromechanical model is also used to predict the measured voltage and power and verify their consistency and repeatability. The measurements are found in qualitative agreement with those reported in previously-published experimental works. We present a novel methodology to estimate the mechanical torque applied to the wind turbine without the deployment of a torque measuring device. This method can be used to determine the power coefficient at a given air speed, which constitutes an important performance indicator of wind turbines. The wind tunnel tests revealed the capability of the developed wind turbines to deliver more than 1225 mW when subject to an air flow with a speed of 7 m/s. The power coefficient is found ranging between 26% and 32%. This demonstrates the aerodynamic capability of the designed blades to extract power from the wind.

Key Words
miniature wind turbine; wind tunnel testing; performance analysis; energy harvesting; electromechanical model

Address
Ehab Basta: Department of Mechanical Engineering, American University of Sharjah, Sharjah 26666, UAE
Mehdi Ghommem: Department of Mechanical Engineering, American University of Sharjah, Sharjah 26666, UAE
Lotfi Romdhane: Department of Mechanical Engineering, American University of Sharjah, Sharjah 26666, UAE
Abdessattar Abdelkefi: Department of Mechanical and Aerospace Engineering, New Mexico State University, Las Cruces, NM 88003, USA

Abstract
High-rise buildings are very slender and flexible. Their low stiffness values make them vulnerable to horizontal loads, such as those associated with wind or earthquakes. For high-rise buildings, the threat to serviceability caused by wind-induced vibration is an important problem. To estimate the serviceability under wind action, the response acceleration of a building at the roof height is used. The response acceleration is estimated by the same wind speed at all wind directions. In general, the effect of wind direction is not considered. Therefore, the response accelerations obtained are conservative. If buildings have typical plans and strong winds blow from relatively constant wind directions, it is necessary to account for the wind direction to estimate the response accelerations. This paper presents three methods of evaluating the response accelerations while considering the effects of wind direction. These three serviceability evaluation methods were estimated by combining the wind directional frequency data obtained from a weather station with the results of a response analysis using wind tunnel tests. Finally, the decrease in the efficiencies of the response acceleration for each serviceability evaluation method was investigated by comparing the response acceleration for the three methods accounting for wind direction with the response acceleration in which wind direction was not considered.

Key Words
serviceability evaluation method; Weibull parameter; wind directional frequency

Address
Hye-Jin Ryu:Department of Architectural Engineering, Kumoh National Institute of Technology, 61 Daehak-ro, Gumi-si, Gyeongsangbuk-do, Republic of Korea
Dong-Hyeon Shin:Department of Architectural Engineering, Kumoh National Institute of Technology, 61 Daehak-ro, Gumi-si, Gyeongsangbuk-do, Republic of Korea
Young-Cheol Ha:Department of Architectural Engineering, Kumoh National Institute of Technology, 61 Daehak-ro, Gumi-si, Gyeongsangbuk-do, Republic of Korea

Abstract
Gusts generated by downburst have caused a great variety of structural damages in many regions around the world. It is of great significance to accurately evaluate the downburst-induced wind load on high-rise building for the wind resistance design. The main objective of this paper is to propose a computational modeling approach which can satisfactorily predict the mean and fluctuating wind pressure coefficients induced by downburst on high-rise building surfaces. In this study, using an impinging jet to simulate downburst-like wind, and simultaneous pressure measurements are obtained on a high-rise building model at different radial locations. The model test data are used as the database for developing back propagation neural network (BPNN) models. Comparisons between the BPNN prediction results and those from impinging jet test demonstrate that the BPNN-based method can satisfactorily and efficiently predict the downburst-induced wind pressure coefficients on single and overall surfaces of high-rise building at various radial locations.

Key Words
downburst; pressure coefficient; high-rise building; impinging jet; BP neural network

Address
Zhiyuan Fang: School of Civil Engineering, Chongqing University, Chongqing 400045, China
Zhisong Wang: School of Civil Engineering, Chongqing University, Chongqing 400045, China
Zhengliang Li: School of Civil Engineering, Chongqing University, Chongqing 400045, China

Abstract
Based on wind tunnel tests, this paper investigates the aerodynamic behavior of a large span canopy roof with elliptical plan and hyperbolic paraboloid shape. The statistics of pressure coefficients and the peak factor distributions are calculated for the top and bottom faces of the roof, and the Gaussian or non-Gaussian characteristics of the pressure time-histories in different areas of the roof are discussed. The cross-correlation of pressures at different positions on the roof, and between the top and bottom faces is also investigated. Combination factors are also evaluated to take into account the extreme values of net loads, relevant to the structural design of canopies.

Key Words
wind-induced pressures; wind tunnel tests; hyperbolic paraboloid roofs; canopy roofs; pressure coefficients; pressure correlation.

Address
Fabio Rizzo: Department of Engineering and Geology, University

Abstract
A novel approach is presented to improve dynamic responses of a pedestrian bridge by utilizing decorative wind chimes. Through wind tunnel tests, it was verified that wind chimes can provide stabilization effects against flutter instability, especially at positive or negative wind angles of attack. At zero degrees of angle of attack, the wind chimes can change the flutter pattern from rapid divergence to gradual divergence. The decorative wind chimes can also provide damping effects to suppress the lateral sway motion of the bridge caused by pedestrian footfalls and wind forces. For this purpose, the swing frequency of the wind chimes should be about the same as the structural frequency, which can be achieved by adjusting the swing length of the wind chimes. The mass and the swing damping level are other two important and mutually interactive parameters in addition to the swing length. In general, 3% to 5% swing damping is necessary to achieve favorite results. In the study case, the equivalent damping level of the entire system can be increased from originally assumed 1% up to 5% by using optimized wind chimes.

Key Words
wind chimes; pedestrian bridge; aerodynamic stability; flutter; pedestrian-induced motion; wind tunnel tests; control of dynamic response

Address
Wei-ya Liu: OCT Group, Shenzhen 518053, China
Hai-jun Tang: OCT Group, Shenzhen 518053, China
Xiaoyue Yang : Zhejiang University, College of Civil Engineering and Architecture, Hangzhou 310058, China
Jiming Xie: Zhejiang University, College of Civil Engineering and Architecture, Hangzhou 310058, China



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