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CONTENTS
Volume 34, Number 5, May 2022
 


Abstract
Tornado-induced damages to high-rise buildings and low-rise buildings are quite different in nature. Tornado losses to high-rise buildings are generally associated with building envelope failures while tornado-induced damages to low-rise buildings are usually associated with structural or large component failures such as complete collapses, or roofs being torn off. While studies of tornado-induced structural damages tend to focus mainly on low-rise residential buildings, transmission towers, or nuclear power plants, the current rapid expansion of city centers and development of large-scale building complexes increases the risk of tornadoes impacting tall buildings. It is, therefore, important to determine how tornado-induced load affects tall buildings compared with those based on synoptic boundary layer winds. The present study applies an experimentally simulated tornado wind field to the Commonwealth Advisory Aeronautical Research Council (CAARC) building and estimates and compares its pressure coefficient effects against the Atmospheric Boundary Layer (ABL) flow field. Simulations are performed at the Wind Engineering, Energy and Environment (WindEEE) Dome which is capable of generating both ABL and tornadic winds. A model of the CAARC building at a scale of 1:200 for both ABL and tornado flows was built and equipped with pressure taps. Mean and peak surface pressures for TLV flow are reported and compared with the ABL induced wind for different time-averaging. By following a compatible definition of the pressure coefficients for TLV and ABL fields, the resulting TLV pressure field presents a similar trend to the ABL case. Also, the results show that, for the high-rise building model, the mean and 3-sec peak pressures are larger for the ABL case compared to the TLV case. These results provide a way forward for the code implementation of tornado-induced pressures on high-rise buildings.

Key Words
Atmospheric Boundary Layer (ABL); CAARC; high-rise building; pressure coefficient; Tornado-like Vortices (TLVs); WindEEE Dome

Address
Arash Ashrafi:WindEEE Research Institute, Western University, 2535 Advanced Ave., London, Ontario, Canada

Jubayer Chowdhury:1)WindEEE Research Institute, Western University, 2535 Advanced Ave., London, Ontario, Canada
2)CPP Wind Engineering Consultants, 7365 Greendale Road, Windsor, Colorado, USA

Horia Hangan:1)WindEEE Research Institute, Western University, 2535 Advanced Ave., London, Ontario, Canada
2)Faculty of Engineering and Applied Science, Ontario Tech University, Toronto, Canada


Abstract
Many factors should be considered by architects and designers for designing a tall building. Wind load is one of these important factors that govern the design of tall building structures and can become a serious challenge when buildings tend to be built very tall and slender. On the other hand, through the initial stages of a design process, choosing the design geometry greatly affects the wind-induced forces on a tall building. With this respect, geometric shapes with 3-fold rotational symmetry are one of the applied plan shapes in tall buildings. This study, therefore, aims to investigate the aerodynamic characteristics of 8 different geometrical shapes using Computational Fluid Dynamics (CFD) by measuring the drag and lift forces. A case study approach was conducted in which different building shape models have the same total gross area and the same height of 300 meters. The simulation was an incompressible transient flow that ran 1700 timesteps (85 seconds on the real-time scale). The results show a great difference between wind-induced force performance of buildings with different plan shapes. Generally, it is stated that the shapes with the same area, but with smaller perimeters, are better choices for reducing the drag force on buildings. Applying the lift force, the results show that the buildings with plan shapes that have rounded corners act better in crosswind flow while, those with sharp corners induce larger forces in the same direction. This study delivers more analytical understanding of building shapes and their behavior against the wind force through the parametric modelling.

Key Words
aerodynamic design; building geometry; CFD; tall building; triangular plan

Address
Hamidreza Rafizadeh:Faculty of Fine Arts, University of Tehran, Enghelab Square, 16 Azar St., Tehran, Iran

Matin Alaghmandan:Faculty of Architecture and Urbanism, Shahid Beheshti University, Daneshjoo Blvd, Velenjak St., Tehran, Iran

Saba Fattahi Tabasi:Faculty of Fine Arts, University of Tehran, Enghelab Square, 16 Azar St., Tehran, Iran

Saeed Banihashem:Faculty of Arts & Design, University of Canberra, 11 Kirinari St, Bruce ACT 2617, Australia

Abstract
To investigate the non-Gaussian properties of fluctuating wind pressures and the error margin of extreme wind loads on a long-span curved roof with matching and mismatching ratios of turbulence integral scales to depth (Lxu/D) a series of synchronized pressure tests on the rigid model of the complex curved roof were conducted. The regions of Gaussian distribution and non-Gaussian distribution were identified by two criteria, which were based on the cumulative probabilities of higher-order statistical moments (skewness and kurtosis coefficients, Sk and Ku) and spatial correlation of fluctuating wind pressures, respectively. Then the characteristics of fluctuating wind-loads in the non-Gaussian region were analyzed in detail in order to understand the effects of turbulence integral-scale. Results showed that the fluctuating pressures with obvious negative-skewness appear in the area near the leading edge, which is categorized as the non-Gaussian region by both two identification criteria. Comparing with those in the wind field with matching Lxu/D the range of non-Gaussian region almost unchanged with a smaller Lxu/D while the non-Gaussian features become more evident, leading to higher values of Sk, Ku and peak factor. On contrary, the values of fluctuating pressures become lower in the wind field with a smaller Lxu/D eventually resulting in underestimation of extreme wind loads. Hence, the matching relationship of turbulence integral scale to depth should be carefully considered as estimating the extreme wind loads of long-span roof by wind tunnel tests.

Key Words
long-span roof; non-Gaussian features; peak factor; probability distribution; turbulence integral scale

Address
Xiongwei Yang:Research Centre for Wind Engineering, Southwest Jiaotong University,
No. 111, Section 1, North 2nd Ring Road, Chengdu, Sichuan, China, 610031

Qiang Zhou:1)Research Centre for Wind Engineering, Southwest Jiaotong University,
No. 111, Section 1, North 2nd Ring Road, Chengdu, Sichuan, China, 610031
2)Key Laboratory for Wind Engineering of Sichuan Province, Southwest Jiaotong University,
No. 111, Section 1, North 2nd Ring Road, Chengdu, Sichuan, China, 610031

Yongfu Lei:Research Centre for Wind Engineering, Southwest Jiaotong University,
No. 111, Section 1, North 2nd Ring Road, Chengdu, Sichuan, China, 610031

Yang Yang:Key Laboratory for Wind Engineering of Sichuan Province, Southwest Jiaotong University,
No. 111, Section 1, North 2nd Ring Road, Chengdu, Sichuan, China, 610031

Mingshui Li:Key Laboratory for Wind Engineering of Sichuan Province, Southwest Jiaotong University,
No. 111, Section 1, North 2nd Ring Road, Chengdu, Sichuan, China, 610031

Abstract
Vortex-induced vibration (VIV) is a significant concern when designing slender structures with square cross sections. VIV strongly depends on structural dynamics and flow states, which depend on the conditions of the approaching flow and shape of a structure. Therefore, the effects of the angle of attack on the coupling effects of VIV for a square cylinder are expected to be significant in practice. In this study, the aerodynamic forces for a fixed and elastically mounted square cylinder were measured using wind pressure tests. Aerodynamic forces on the stationary cylinder are firstly discussed by comparisons of variation of statistical aerodynamic force and wind pressure coefficient with wind angle of attack. The coupling effect between the aerodynamic forces and the motion of the oscillating square cylinder by VIV is subsequently investigated in detail at typical wind angels of attack with occurrence of three typical flow regimes, i.e., leading-edge separation, separation bubble (reattachment), and attached flow. The coupling effect are illustrated by discussing the onset of VIV, characteristics of aerodynamic forces during VIV, and interaction between motion and aerodynamic forces. The results demonstrate that flow states can be classified based on final separation points or the occurrence of reattachment. These states significantly influence coupling effects of the oscillating cylinder. Vibration enhances vortex shedding, which creates strong fluctuations in aerodynamic forces. However, differences in the lock-in range, aerodynamic force, and interaction process for angles of attack smaller and larger than the critical angle of attack revealed noteworthy characteristics in the VIV of a square cylinder.

Key Words
angle of attack; coupling effect; square cylinder; Vortex-Induced Vibration (VIV); wind tunnel test

Address
Deqian Zheng:School of Civil Engineering, Henan University of Technology, 100 Lianhua Road, Zhengzhou, Henan, China

Wenyong Ma:2)Innovation Center for Wind Engineering and Wind Energy Technology of Hebei Province, 17 Beierhuan Road, Shijiazhuang, Hebei, China
3)School of Civil Engineering, Shijiazhuang Tiedao University, 17 Beierhuan Road, Shijiazhuang, Hebei, China

Xiaobin Zhang:School of Civil Engineering, Shijiazhuang Tiedao University, 17 Beierhuan Road, Shijiazhuang, Hebei, China

Wei Chen:School of Mechanical Engineering, Shijiazhuang Tiedao University, 17 Beierhuan Road, Shijiazhuang, Hebei, China

Junhao Wu:School of Civil Engineering, Henan University of Technology, 100 Lianhua Road, Zhengzhou, Henan, China

Abstract
The flow around a high-speed train with three underbody structures in the bogie area is numerically investigated using the improved delayed detached eddy simulation method. The vortex structure, pressure distribution, flow field structure, and unsteady velocity of the wake are analyzed by vortex identification criteria Q, frequency spectral analysis, empirical mode decomposition (EMD), and Hilbert spectral analysis. The results show that the structures of the bogie and its installation cabin reduce the momentum of fluid near the tail car, thus it is easy to induce flow separation and make the fluid no longer adhere to the side surface of the train, then forming vortices. Under the action of the vortices on the side of the tail car, the wake vortices have a trend of spanwise motion. But the deflector structure can prevent the separation on the side of the tail car. Besides, the bogie fairings do not affect the formation process and mechanism of the wake vortices, but the fairings prevent the low-speed fluid in the bogie installation cabin from flowing to the side of the train and reduce the number of the vortices in the wake region.

Key Words
bogie; EMD; high-speed train; improved delayed detached eddy simulation; wak

Address
Dongwei Wang:School of Mechanical Engineering, Southwest Jiaotong University, Chengdu, 610031, China

Chunjun Che:1)School of Mechanical Engineering, Southwest Jiaotong University, Chengdu, 610031, China
2)Technology and Equipment of Rail Transit Operation and Maintenance Key Laboratory of Sichuan Province, Chengdu, 610031, China

Zhiying He:School of Mechanical Engineering, Southwest Jiaotong University, Chengdu, 610031, China



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