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CONTENTS
Volume 13, Number 4, July 2010
 

Abstract
CFD techniques try to find their way in the bridge engineering realm nowadays. However, there are certain fields where they offer superior performance such as conceptual bridge design and bidding design. The CFD studies carried out for the conceptual design of a 425 m length cable-stayed bridge are presented. A CFD commercial package has been employed to obtain for a set of cross-sections the aerodynamic coefficients considering 2D steady state. Additionally, for those cross-sections which showed adequate force coefficients, unsteady 2D simulations were carried out to detect the risk of vortex shedding. Based upon these computations the effect on the aerodynamic behavior of the deck cross-section caused by a number of modifications has been evaluated. As a consequence, a new more feasible cross-section design has been proposed. Nevertheless, if the design process proceeds to a more detailed step a comprehensive set of studies, comprising extensive wind tunnel tests, are required to better find out the aerodynamic bridge behavior.

Key Words
CFD; RANS; conceptual structural design; cable-stayed bridges.

Address
F. Nieto, S. Hernandez, J.A. Jurado and A. Baldomir: School of Civil Engineering, Universidad de A Coruna, Campus de Elvina s/n. 15071 A Coruna, Spain

Abstract
During the past decade, many electrical transmission tower structures have failed during downburst events. This study is a part of a research program aimed to understand the behaviour of transmission lines under such localized wind events. The present study focuses on the assessment of the dynamic behaviour of the line conductors under downburst loading. A non-linear numerical model, accounting for large deformations and the effect of pretension loading, is developed and used to predict the natural frequencies and mode shapes of conductors at various loading stages. A turbulence signal is extracted from a set of full-scale data. It is added to the mean component of the downburst wind field previously evaluated from a CFD analysis. Dynamic analysis is performed using various downburst configurations. The study reveals that the response is affected by the background component, while the resonant component turns to be negligible due large aerodynamic damping of the conductors.

Key Words
dynamic analysis; free vibration; downburst; turbulence; finite element; transmission line conductors.

Address
Mohamed M. Darwish and Ashraf A. El Damatty: Department of Civil and Environmental Engineering, The University of Western Ontario London, Ontario, Canada, N6A 5B9
Horia Hangan: Boundary Layer Wind Tunnel, The University of Western Ontario London, Ontario, Canada, N6A 5B9

Abstract
Researches on the Reynolds number effect on bridge decks have made slow progress due to the complicated nature of the subject. Heretofore, few studies on this topic have been made. In this paper, aerostatic coefficients, Strouhal number (St), pressure distribution and Reynolds number (Re) of Great Belt East Bridge and Sutong Bridge were investigated based on deterministic vortex method (DVM). In this method, Particle Strength Exchange (PSE) was chosen to implement the simulation of the flow around bluff body and to analyze the micro-mechanism of the aerostatic loading and Reynolds number effect. Compared with the results obtained from wind tunnel tests, reliability of numerical simulation can be proved. Numerical results also showed that the Reynolds number effect on aerostatic coefficients and Strouhal number of the two bridges can not be neglected. In the range of the Reynolds number from 105 to 106, it has great effect on the Strouhal number of Sutong Bridge, while the St is difficult to obtain from wind tunnel tests in this range.

Key Words
bridge sections, Reynolds number effect, particle strength exchange method, aerostatic coefficients, Strouhal number.

Address
Zhiyong Zhou: State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University, Shanghai, 200092, China
Rujin Ma: Department of Bridge Engineering, Tongji University, Shanghai, 200092, China

Abstract
Appropriate scaling methods for wind tunnel modelling of building internal pressures induced through a dominant opening were investigated. In particular, model cavity volume distortion and geometric scaling of the opening details were studied. It was found that while model volume distortion may be used to scale down buildings for wind tunnel studies on internal pressure, the implementation of the added volume must be done with care so as not to create two cavity resonance systems. Incorrect scaling of opening details was also found to generate incorrect internal pressure characteristics. Furthermore, the effective air slug or jet was found to be longer when the opening was near a floor or sidewall as evidenced by somewhat lower Helmholtz frequencies. It is also shown that tangential flow excitation of Helmholtz resonance for off-centre openings in normal flow is also possible.

Key Words
scaling; volume distortion; internal pressure; Helmholtz resonance.

Address
Rajnish N Sharma, Simon Mason and Philip Driver: Department of Mechanical Engineering, The University of Auckland, Private Bag 92019, Auckland 1142, New Zealand

Abstract
A three-dimensional flow simulation was performed to investigate the wind flow around wind-power generation facilities on mountainous area of complex terrain. A digital map of eastern mountainous area of Korea including a wind farm was used to model actual complex terrain. Rotating wind turbines in the wind farm were also modeled in the computational domain with detailed geometry of blade by using the frozen rotor method. Wind direction and speed to be used as a boundary condition were taken from local meteorological reports. The numerical results showed not only details of flow distribution in the wind farm but also the variation in the performance of the wind turbines due to the installed location of the turbines on complex terrain. The wake effect of the upstream turbine on the performance of the downstream one was also examined. The methodology presented in this study may be used in selecting future wind farm site and wind turbine locations in the selected site for possible maximum power generation.

Key Words
wind engineering; wind farm; wind turbine; complex terrain; CFD (computational fluid dynamics); frozen rotor method.

Address
Myungsung Lee, Seung Ho Lee and Nahmkeon Hur: Department of Mechanical Engineering, Sogang University, Sinsoo 1, Mapo, Seoul 121-742, Korea
Chang-Koon Choi: Department of Civil and Environmental Engineering, KAIST, Daejeon 305-701, Korea


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