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CONTENTS
Volume 31, Number 3, September 2020
 

Abstract
A method to reduce the wind pressure at the leading edge of a noise barrier was investigated by gradually lowering the height of a member added to the end of the noise barrier. The shape of the lowered height of the added member was defined by its length and slope, and the optimal variable was determined in wind tunnel testing via the boundary-layer wind profile. The goal of the optimal shape was to reduce the wind pressure at the leading edge of the noise barrier to the level suggested in the Eurocode and to maintain the base-bending moment of the added member at the same level as the noise-barrier section. Using parametric wind tunnel investigation, an added member with a slope of 1:2 that protruded 1.2 times the height of the noise barrier was proposed. This added member is expected to simplify, or at least minimize, the types of column members required to equidistantly support both added members and noise barriers, which should thereby improve the safety and construction convenience of noise-barrier structures.

Key Words
pressure; reduction; noise barrier; wind; free-standing wall

Address
Seong-Wook Han:1Department of Infrastructure Safety Research, Korea Institute of Civil Engineering and Building Technology,283 Goyangdae-ro, Ilsanseo-gu, Goyang-si, Gyeonggi-do 10223, Republic of Korea
Ho-Kyung Kim:2Department of Civil and Environmental Engineering, Seoul National University,1 Gwanak-ro, Gwanak-gu, Seoul 08826, Republic of Korea
Jun-Yong Park :Department of Urban Infrastructure, Seoul Institute of Technology,37 Maebongsan-ro, Mapo-gu, Seoul 03909, Republic of Korea
Sang Sup Ahn:Structure Research Division, Korea Expressway Corporation Research Institute,24 Dongbusunhwan-daero 17-gil, Hwaseong-si, Gyeonggi-do 18489, Republic of Korea

Abstract
Knowledge on the design value of extreme wind pressure coefficients (EWPC) of a specific zone of buildings is essential for the wind-resistant capacity of claddings. This paper presents a method to estimate the representative EWPC introducing the multivariate extreme value model. The spatial correlations of the extreme wind pressures at different locations can be consider through the multivariate extreme value. The moving average method is also adopted in this method, so that the measured point pressure can be converted to wind pressure of an area. The proposed method is applied to wind tunnel test results of a large flat roof building. Comparison with existing methods shows that it can give a good estimation for all target zones with different sizes.

Key Words
large zone; claddings; extreme wind pressure coefficient; multivariate extreme value theory; wind tunnel test

Address
Qingshan Yang:School of Civil Engineering, Chongqing University, 400044, Chongqing, P.R. China/ Beijing

Abstract
Aiming at the wind-resistant design of a sea-crossing arch bridge, the static aerodynamic coefficients of its girder (composed of stretches ofπ-shaped cross-section and box cross-section) were studied by using computational fluid dynamics (CFD) numerical simulation and wind tunnel test. Based on the comparison between numerical simulation, wind tunnel test and specification recommendation, a combined calculation method for the horizontal force coefficient of intermediate and small span bridges is proposed. The results show that the two-dimensional CFD numerical simulations of the individual cross sections are sufficient to meet the accuracy requirements of engineering practice.

Key Words
static aerodynamic force coefficients; numerical simulation; girder; wind tunnel test; arch bridge

Address
Institute of Bridge Engineering, Zhejiang University of Technology,288 Liuhe Road Hangzhou 310023, China

Abstract
Based on translation models, both Gaussian and non-Gaussian wind fields are generated using spectral representation method for investigating the influence of non-Gaussian characteristics and directivity effect of wind load on fatigue damage of wind turbine. Using the blade aerodynamic model and multi-body dynamics, dynamic responses are calculated. Using linear damage accumulation theory and linear crack propagation theory, crack initiation life and crack propagation life are discussed with consideration of the joint probability density distribution of the wind direction and mean wind speed in detail. The result shows that non-Gaussian characteristics of wind load have less influence on fatigue life of wind turbine in the area with smaller annual mean wind speeds. Whereas, the influence becomes significant with the increase of the annual mean wind speed. When the annual mean wind speeds are 7 m/s and 9 m/s at hub height of 90 m, the crack initiation lives under softening non-Gaussian wind decrease by 10% compared with Gaussian wind fields or at higher hub height. The study indicates that the consideration of the influence of softening non-Gaussian characteristics of wind inflows can significantly decrease the fatigue life, and, if neglected, it can result in non-conservative fatigue life estimates for the areas with higher annual mean wind speeds.

Key Words
non-Gaussian wind; wind field simulation; translation model; direction wind; wind-induced fatigue

Address
Ying Zhu:Railway Engineering Research Institute, China Academy of Railway Sciences Corporation Limited, Beijing 100081, China/ State Key Laboratory for Track Technology of High-speed Railway, Beijing 100081, China
Miao Shuang:State Nuclear Electric Power Planning Design & Research Institute Corporation Limited, Beijing 100095, China

Abstract
In the present work, the main features of primary vortices and the vorticity concentrations downstream of vortex bursting in crossflow plane of a delta wing with a sweep angle of A=700° were investigated under the variation of the sideslip angles, Β. For the pre-review of flow structures, dye visualization was conducted. In connection with a qualitative observation, a quantitative flow analysis was performed by employing Particle Image Velocimetry (PIV). The sideslip angles, Β were varied with four different angles, such as 0°, 4°, 12°, and 20° while angles of attack, a were altered between 25° and 35°. This study mainly focused on the instantaneous flow features sequentially located at different crossflow planes such as x/C=0.6, 0.8 and 1.0. As a summary, time-averaged and instantaneous non-uniformity of turbulent flow structures are altered considerably resulting in non-homogeneous delta wing surface loading as a function of the sideslip angle. The vortex bursting location on the windward side of the delta wing advances towards the leading-edge point of the delta wing. The trajectory of the primary vortex on the leeward side slides towards sideways along the span of the delta wing. Besides, the uniformity of the lift coefficient, CL over the delta wing plane was severely affected due to unbalanced distribution of buffet loading over the same plane caused by the variation of the sideslip angle, Β. Consequently, dissimilarities of the leading-edge vortices result in deterioration of the mean value of the lift coefficient, CL.

Key Words
aerodynamic coefficients; angle of attack; dye visualization; particle image velocimetry; sideslip angle; slender delta wing; vortex bursting

Address
Mehmet O. TASCI, Besir SAHIN and Huseyin AKILLI:1Department of Mechanical Engineering, Çukurova University, Adana, Turkey
Ilyas KARASU:2Department of Aerospace Engineering, Adana Alparslan Türkeş Science and Technology University, Adana, Turkey

Abstract
The inerter-based vibration absorber (IVA) is an enhanced variation of Tuned Mass Damper (TMD). The parametric optimization of absorbers in the previous research mainly considered only two decision variables, namely frequency ratio and damping ratio, and aimed to minimize peak displacement and acceleration individually under the excitation of the across-wind load. This paper extends these efforts by minimizing two conflicting objectives simultaneously, i.e., the extreme displacement and acceleration at the top floor, under the constraint of the physical mass. Six decision variables are optimized by adopting a constrained multi-objective evolutionary algorithm (CMOEA), i.e., NSGA-II, under fluctuating across- and along-wind loads, respectively. After obtaining a set of optimal individuals, a decision-making approach is employed to select one solution which corresponds to a Tuned Mass Damper Inerter/Tuned Inerter Damper (TMDI/TID). The optimization procedure is applied to parametric optimization of TMDI/TID installed in a 340-meter-high building under wind loads. The case study indicates that the optimally-designed TID outperforms TMDI and TMD in terms of wind-induced vibration mitigation under different wind directions, and the better results are obtained by the CMOEA than those optimized by other formulae. The optimal TID is proven to be robust against variations in the mass and damping of the host structure, and mitigation effects on acceleration responses are observed to be better than displacement control under different wind directions.

Key Words
inerter-based vibration absorber; multi-objective evolutionary algorithm; decision-making approach; wind-induced vibration; high-rise buildings

Address
Qinhua Wang, Haoshuai Qiao,Nayandeep Tiwari:Department of Civil and Environmental Engineering, Shantou University, Shantou City, Guangdong Province, China
Wenji Li, Yugen You, Zhun Fan:Department of Electronic and Information Engineering, Shantou University, Shantou City, Guangdong Province, China

Abstract
A systematic set of low-speed wind tunnel experiments was performed at Re = 6.5x104 and 1.1x105 to study the mean wind loading experienced by surface-mounted finite-height square prisms for different aspect ratios, incidence angles, and boundary layer thicknesses. The aspect ratio of the prism was varied from AR = 1 to 11 in small increments and the incidence angle was changed from α= 0° to 45° in increments of 1°. Two different boundary layer thicknesses were used: a thin boundary layer with δ/D = 0.8 and a thick boundary layer with δ/D = 2.0–2.2. The mean drag and lift coefficients were strong functions of AR, α, and δ/D, while the Strouhal number was mostly influenced by α. The critical incidence angle, at which the prism experiences minimum drag, maximum lift, and highest vortex shedding frequency, increased with AR, converged to a value of αc = 18° ±2° once AR was sufficiently high, and was relatively insensitive to changes in δ/D. A local maximum value of mean drag coefficient was identified for higher-AR prisms at low α. The overall behaviour of the force coefficients and Strouhal number with AR suggests the possibility of three flow regimes.

Key Words
bluff body; surface-mounted finite-height square prism; wind loading; vortex shedding; drag coefficient; lift coefficient; critical incidence angle

Address
Department of Mechanical Engineering, University of Saskatchewan, 57 Campus Drive, Saskatoon, Saskatchewan, S7N 5A9, Canada

Abstract
The statistical characteristics of typhoon wind speed records tend to have a considerable time-varying trend; thus, the stationary wind model may not be appropriate to estimate the wind characteristics of typhoon events. Several nonstationary wind speed models have been proposed by pioneers to characterize wind characteristics more accurately, but comparative studies on the applicability of the different wind models are still lacking. In this study, three landfall typhoons, Ampil, Jongdari, and Rumbia, recorded by ultrasonic anemometers atop the Shanghai World Financial Center (SWFC), are used for the comparative analysis of stationary and nonstationary wind characteristics. The time-varying mean is extracted with the discrete wavelet transform (DWT) method, and the time-varying standard deviation is calculated by the autoregressive moving average generalized autoregressive conditional heteroscedasticity (ARMA-GARCH) model. After extracting the time-varying trend, the longitudinal wind characteristics, e.g., the probability distribution, power spectral density (PSD), turbulence integral scale, turbulence intensity, gust factor, and peak factor, are comparatively analyzed based on the stationary wind speed model, time-varying mean wind speed model and time-varying standard deviation wind speed model. The comparative analysis of the different wind models emphasizes the significance of the nonstationary considerations in typhoon events. The time-varying standard deviation model can better identify the similarities among the different typhoons and appropriately describe the nonstationary wind characteristics of the typhoons.

Key Words
Field measurement; Landfall typhoons; Nonstationary wind characteristics; Time-varying mean; Time-varying standard deviation

Address
State Key Laboratory of Disaster Reduction in Civil Engineering, Tongji University, Shanghai 200092, China


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