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CONTENTS
Volume 19, Number 6, December 2014
 

Abstract
The effect of multiple roughness changes close to a building site was examined through three dimensional computational fluid dynamics (CFD) simulations conducted in a virtual boundary layer wind tunnel (V-BLWT). The results obtained were compared with existing wind speed models, namely ESDU-82026 and Wang and Stathopoulos (WS) model. The latter was verified by wind tunnel tests of sixty nine cases of multiple roughness patches, and also with a simplified 2D numerical model. This work extends that numerical study to three dimensions and also models roughness elements explicitly. The current numerical study shows better agreement with the WS model, that has shown better agreements with BLWT tests, than the ESDU model. This is in contrast to previous results of Wang and Stathopoulos, who concluded that CFD shows better agreement with the ESDU model. Many cases were simulated in a V-BLWT that has same dimensions as BLWT used in the original experiment and also in a reduced symmetrical version (S-BLWT) that takes advantage of regular arrangement of roughness blocks. The S-BLWT gives results almost identical to V-BLWT simulations, while achieving significant reduction on computational time and resources.

Key Words
computational fluid dynamics; virtual BLWT; inhomogeneous roughness; ESDU wind speed model; Wang and Stathopoulos wind speed model; explicit roughness modeling

Address
Daniel S. Abdi and Girma T. Bitsuamlak: Department of Civil and Environmental Engineering, University of Western Ontario, 1151 Richmond St, London, ON N6A 3K7, Canada

Abstract
Past high speed wind events have exposed the vulnerability of the roof systems of existing light-framed wood structures to uplift loading, contributing greatly to economic and human loss. This paper further investigates the behaviour of light-framed wood structures under the uplift loading of a realistic pressure distribution. A three-dimensional finite-element model is first developed to capture the behaviour of a recently completed full-scale experiment. After describing the components used to develop the numerical model, a comparison between the numerical prediction and experimental results in terms of the deflected shape at the roof-to-wall connections is presented to gain confidence in the numerical model. The model is then used to analyze the behaviour of the truss system under realistic and equivalent uniform pressure distributions and to perform an assessment of the use of the tributary area method to calculate the withdrawal force acting on the roof-to-wall connections.

Key Words
wood structures; structural behaviour; finite element; wind damage

Address
Ryan B Jacklin, Ashraf A. El Damattyand Ahmed A. Dessouki: Department of Civil and Environmental Engineering, The University of Western Ontario, London, Ontario Canada, N6A 5B9

Abstract
In this paper, a probability distribution which is consistent with the observed phenomenon at the roof corner and, also on other portions of the roof, of a low-rise building is proposed. The model is consistent with the choice of probability density function suggested by the statistical thermodynamics of open systems and turbulence modelling in fluid mechanics. After presenting the justification based on physical phenomenon and based on statistical arguments, the fit of alpha-stable distribution for prediction of extreme negative wind pressure coefficients is explored. The predictions are compared with those actually observed during wind tunnel experiments (using wind tunnel experimental data obtained from the aerodynamic database of Tokyo Polytechnic University), and those predicted by using Gumbel minimum and Hermite polynomial model. The predictions are also compared with those estimated using a recently proposed non-parametric model in regions where stability criterion (in skewness-kurtosis space) is satisfied. From the comparisons, it is noted that the proposed model can be used to estimate the extreme peak negative wind pressure coefficients. The model has an advantage that it is consistent with the physical processes proposed in the literature for explaining large fluctuations at the roof corners.

Key Words
peak wind pressure coefficients; low-rise buildings;alpha-stable distribution

Address
K. Balaji Rao, M.B. Anoop, P. Harikrishna, S. Selvi Rajan and Nagesh R. Iyer: CSIR-SERC, CSIR Campus, Taramani, Chennai 600 113, India

Abstract
The present paper discusses the characteristics of unsteady aerodynamic forces on long-span curved roofs. A forced vibration test is carried out in a wind tunnel to investigate the effects of wind speed, vibration amplitude, reduced frequency of vibration and rise/span ratio of the roof on the unsteady aerodynamic forces. Because the range of parameters tested in the wind tunnel experiment is limited, a CFD simulation is also made for evaluating the characteristics of unsteady aerodynamic forces on the vibrating roof over a wider range of parameters. Special attention is paid to the effect of reduced frequency of vibration. Based on the results of the wind tunnel experiment and CFD simulation, the influence of the unsteady aerodynamic forces on the dynamic response of a full-scale long-span curved roof is investigated on the basis of the spectral analysis.

Key Words
unsteady aerodynamic force; long-span curved roof; wind tunnel experiment; CFD simulation; dynamic response

Address
Wei Ding:School of Mechanics and Civil Engineering, China University of Mining and Technology, Xuzhou, China
Yasushi Uematsu: Department of Architectural and Building Science, Tohoku University, Sendai, Japan
Mana Nakamura: Nikken Steel and Sumitomo Metal Corporation, Tokyo, Japan
Satoshi Tanaka: Nikken Sekkei Ltd., Tokyo, Japan

Abstract
This study presents a comprehensive investigation of the aerostatic and buffeting response characteristics of a suspension bridge catwalk. The three-dimensional aerostatic response analysis was carried out taking into account the geometric nonlinearity and nonlinear dependence of wind loads on the angle of attack. The buffeting response analysis was performed in the time domain. The aerostatic and buffeting responses of the catwalk show strong coupling of vertical and lateral vibrations. The lateral displacement is the main component of the wind-induced static and buffeting response of the catwalk.

Key Words
catwalk; aerostatic response; buffeting response; suspension bridge

Address
Yongle Li, Dongxu Wang and Chupeng Wu: Department of Bridge Engineering, Southwest Jiaotong University, Chengdu, Sichuan 610031, P. R. China
Xinzhong Chen: Wind Science and Engineering Research Center, Department of Civil and Environmental Engineering,
Texas Tech University, Lubbock, Texas 79409-1023, USA


Abstract
The performance of the k-e and k-w two-equation turbulence models was investigated in computational simulations of the neutrally stratified atmospheric boundary layer developing above various terrain types. This was achieved by using a proposed methodology that mimics the experimental setup in the boundary layer wind tunnel and accounts for a decrease in turbulence parameters with height, as observed in the atmosphere. An important feature of this approach is pressure regulation along the computational domain that is additionally supported by the nearly constant turbulent kinetic energy to Reynolds shear stress ratio at all heights. In addition to the mean velocity and turbulent kinetic energy commonly simulated in previous relevant studies, this approach focuses on the appropriate prediction of Reynolds shear stress as well. The computational results agree very well with experimental results. In particular, the difference between the calculated and measured mean velocity, turbulent kinetic energy and Reynolds shear stress profiles is less than +-10% in most parts of the computational domain.

Key Words
neutrally stratified atmospheric boundary layer; atmospheric turbulence; computational modeling; steady Reynolds-Averaged-Navier-Stokes (RANS) equations; two-equation turbulence models; computational wind tunnel

Address
Franjo Juretić and Hrvoje Kozmar: Faculty of Mechanical Engineering and Naval Architecture, University of Zagreb,
Ivana Lučića 5, 10000 Zagreb, Croatia



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