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CONTENTS
Volume 35, Number 5, November 2022
 


Abstract
Over the past few decades, the use of wind tunnels has been increasing as a result of the rapid growth of cities and the urge to build taller and non-typical structures. While the accuracy of a wind tunnel study on a tall building requires several aspects, the precise extraction of wind pressure plays a significant role in a successful pressure test. In this research study, a lowcost expandable synchronous multi-pressure sensing system (SMPSS) was developed and validated at Ryerson University's wind tunnel (RU-WT) using electronically scanning pressure sensors for wind tunnel tests. The pressure system consists of an expandable 128 pressure sensors connected to a compact data acquisition and a host workstation. The developed system was examined and validated to be used for tall buildings by comparing mean, root mean square (RMS), and power spectral density (PSD) for the base moments coefficients with the available data from the literature. In addition, the system was examined for evaluating the mean and RMS pressure distribution on a standard low-rise building and were found to be in good agreement with the validation data.

Key Words
aerodynamics; pressure system; synchronous multi-pressure sensing system; wind engineering; wind load; wind tunnel

Address
Moustafa Aboutabikh and Haitham Aboshosha:Department of Civil Engineering, Ryerson University, 350 Victoria, St. M5B 2K3, Toronto, Canada

Ahmed Elshaer:1)Department of Civil Engineering, Ryerson University, 350 Victoria, St. M5B 2K3, Toronto, Canada
2)Department of Civil Engineering, Lakehead University, 955 Oliver Rd., P7B 5E1, Thunder Bay, ON, Canada

Abstract
Due to the complex terrain around high-speed railways, the windbreaks were established along different landforms, resulting in irregular windbreak transition regions between different subgrade infrastructures (flat ground, cutting, embankment, etc). In this paper, the effect of a windbreak transition on the wind flow around railways subjected to crosswinds was studied. Wind tunnel testing was conducted to study the wind speed change around a windbreak transition on flat ground with a uniform wind speed inflow, and the collected data were used to validate a numerical simulation based on a detached eddy simulation method. The validated numerical method was then used to investigate the effect of the windbreak transition from the flat ground to cutting (the "cutting" is a railway subgrade type formed by digging down from the original ground) for three different wind incidence angles of 90°, 75°, and 105°. The deterioration mechanism of the flow fields and the reasons behind the occurrence of the peak wind velocities were explained in detail. The results showed that for the windbreak transition on flat ground, the impact was small. For the transition from the flat ground to the cutting, the influence was relatively large. The significant increase in the wind speeds was due to the right-angle structure of the windbreak transition, which resulted in sudden changes of the wind velocity as well as the direction. In addition, the height mismatch in the transition region worsened the protective effect of a typical windbreak.

Key Words
computational fluid dynamics (CFD); crosswinds; flow structures; railway; windbreak transition; wind tunnel test

Address
Zheng-Wei Chen:Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, PR China

Syeda Anam Hashmi and Hassan Hemida: Birmingham Centre for Railway Research and Education, School of Civil Engineering, University of Birmingham B15 2TT, UK

Tang-Hong Liu, Wen-Hui Li, Dong-Run Liu and Hong-Kang Li: Key Laboratory of Traffic Safety on Track of Ministry of Education, School of Traffic & Transportation Engineering,
Central South University, Changsha 410075, PR China

Zhuang Sun:Chengdu Fluid Dynamics Innovation Center, Chengdu 610072, PR China


Abstract
This study investigates the applicability of the direct identification of flutter derivatives in the time domain using Rational Function Approximation (RFA), where the extraction procedure requires either a combination of at least two wind speeds or one wind speed. In the frequency domain, flutter derivatives are identified at every wind speed. The ease of identifying flutter derivatives in the time domain creates a paradox because flutter derivative patterns sometimes change in higher-order polynomials. The first step involves a numerical study of RFA extractions for different deck shapes from existing bridges to verify the accurate wind speed combination for the extraction. The second step involves validating numerical simulation results through a wind tunnel experiment using the forced vibration method in one degree of freedom. The findings of the RFA extraction are compared to those obtained using the analytical solution. The numerical study and the wind tunnel experiment results are in good agreement. The results show that the evolution pattern of flutter derivatives determines the accuracy of the direct identification of RFA.

Key Words
flutter derivatives; rational function approximation; time domain extraction

Address
Herry Irpanni, Hiroshi Katsuchi and Hitoshi Yamada:Department of Civil Engineering, Yokohama National University, 79-8, Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan


Abstract
As central-slotted box decks usually have excellent flutter performance, studies on this type of deck mostly focus on the vortex-induced vibration (VIV) control. Yet with the increasing span lengths, cable-supported bridges may have critical wind speeds of wind-induced static instability lower than that of the flutter. This is especially likely for bridges with a central-slotted box deck. As a result, the overall aerodynamic performance of such a bridge will depend on its wind-induced static stability. Taking a 1400 m-main-span cable-stayed bridge as an example, this study investigates the influence of a series of deck shape parameters on both static and flutter instabilities. Some crucial shape parameters, like the height ratio of wind fairing and the angle of the inner-lower web, show opposite influences on the two kinds of instabilities. The aerodynamic shape optimization conducted for both static and flutter instabilities on the deck based on parameter-sensitivity studies raises the static critical wind speed by about 10%, and the overall critical wind speed by about 8%. Effective VIV countermeasures for this type of bridge deck have also been proposed.

Key Words
aerodynamic shape optimization; central-slotted box deck; flutter; super-long-span cable-stayed bridge; vortexinduced vibration; wind-induced static stabi

Address
Ledong Zhu,Cheng Qian and Qing Zhu:1)State Key Laboratory of Disaster Reduction in Civil Engineering, Tongji University, Shanghai 200092, China
2)epartment of Bridge Engineering, Tongji University, Shanghai 200092, China
3)Key Laboratory of Transport Industry of Bridge Wind Resistance Technology, Tongji University, Shanghai 200092, China

Yikai Shen:Shanghai Research Institute of Building Sciences, Shanghai 200092, China

Abstract
Wind turbine blades are adjusted in real-time according to the wind conditions and blade deformations to improve power generation efficiency. It is necessary to predict and reduce the aeroelastic deformations of wind turbine blades. In this paper, the equivalent model of the blade is established by the finite element method (FEM), and the aerodynamic load of the blade is evaluated based on the blade element momentum (BEM) theory. The aeroelastic coupling model is established, in which the bending-torsion coupling effect of the blade is taken into account. The steady and dynamic aeroelastic deformations are calculated. The influences of the blade section's shear centre position and the blade's sweepback design on the deformations are analyzed. The novel approaches of reducing the twist angle of the blade by changing the shear centre position and sweepback of the blade are presented and proven to be feasible.

Key Words
aeroelastic deformation; blade element momentum theory; finite element method; load reduction; wind turbine blade

Address
Shaojun Du and Fengming Li:College of Aerospace and Civil Engineering, Harbin Engineering University, Harbin 150001, China

Jingwei Zhou:Xinjiang Goldwind Science & Technology Co., Ltd., Urumqi 830000, China


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