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CONTENTS
Volume 10, Number 2, March 2007
 

Abstract
Estimations of wind flow over terrain are often needed for applications such as pollutant dispersion, transport safety or wind farm location. Whilst field studies offer very detailed information regarding the wind potential over a small region, the cost of instrumenting a natural fetch alone is prohibitive. Wind tunnels offer one alternative although wind tunnel simulations can suffer from scale effects and high costs as well. Computational Fluid Dynamics (CFD) offers a second alternative which is increasingly seen as a viable one by wind engineers. There are two issues associated with CFD however, that of accuracy of the predictions and set-up and simulation times. This paper aims to address the two issues by demonstrating, by way of an investigation of wind potential for the Askervein Hill, that a good level of accuracy can be obtained with CFD (10% for the speed up ratio) and that it is possible to automate the simulations in order to compute a full wind rose efficiently. The paper shows how a combination of script and session files can be written to drive and automate CFD simulations based on commercial software. It proposes a general methodology for the automation of CFD applied to the computation of wind flow over a region of interest.

Key Words
CFD; automation; wind rose.

Address
Herve P. Morvan; School of Civil Engineering, the University of Nottingham, Nottingham, NG7 2RD, UK
Paul Stangroom; Prospect, 42 Friar Gate, Derby DE1 1DA, UK
Nigel G. Wright; School of Civil Engineering, the University of Nottingham, Nottingham, NG7 2RD, UK

Abstract
To gain understanding of the applicability of carbon fiber reinforced polymer (CFRP) cable in cable-supported bridges, based on the Runyang Bridge and Jinsha Bridge, a suspension bridge using CFRP cables and a cable-stayed bridge using CFRP stay cables are schemed, in which the cable\'s cross-sectional area is determined by the principle of equivalent axial stiffness. Numerical investigations on the dynamic behavior, aerostatic and aerodynamic stability of the two bridges are conducted by 3D nonlinear analysis, and the effect of different cable materials on the wind resistance is discussed. The results show that as CFRP cables are used in cable-supported bridges, (1) structural natural frequencies are all increased, and particularly great increase of the torsional frequency occurs for suspension bridges; (2) under the static wind action, structural deformation is increased, however its aerostatic stability is basically remained the same as that of the case with steel cables; (3) for suspension bridge, its aerodynamic stability is superior to that of the case with steel cables, but for cable-stayed bridge, it is basically the same as that of the case with steel stay cables. Therefore as far as the wind resistance is considered, the use of CFRP cables in cable-supported bridges is feasible, and the cable\'s cross-sectional area should be determined by the principle of equivalent axial stiffness.

Key Words
cable-supported bridges; carbon fiber reinforced polymer cable; dynamic behavior; aerostatic stability; aerodynamic stability.

Address
College of Civil Engineering and Architecture, Zhejiang University of Technology, Hangzhou 310032, P.R. China

Abstract
This paper examines the extreme gust profiles obtained by conditionally sampling full-scale velocity data obtained in the lower part of the atmospheric boundary layer. It is demonstrated that three different types of behaviour can be observed in the streamwise component of velocity. In all cases the corresponding vertical velocity component illustrates similar behaviour. An idealised horseshoe vortex model and a downburst model are investigated to examine if such structures can explain the behaviour observed. In addition, an empirical model is developed for an isolated gust corresponding to each of the three types of behaviour observed. It is possible that the division of the gust profile into three different types may lead to an improvement in the correlation of extreme gust events with respect to type.

Key Words
gust shapes; conditional sampling; ensemble averaging; downbursts; hairpin vortex structures.

Address
A. Scarabino; Departamento Aeronautica, Universidad Nacional de La Plata, Calle 116 e/ 47 y 48, 1900 La Plata, Argentina
M. Sterling; School of Engineering, The University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK
P. J. Richards; School of Engineering, University of Auckland, New Zealand
C. J. Baker and R. P. Hoxey; School of Engineering, The University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK

Abstract
The Proper Orthogonal Decomposition (POD) is a statistical method particularly suitable and versatile for dealing with many problems concerning wind engineering and several other scientific and humanist fields. POD represents a random process as a linear combination of deterministic functions, the POD modes, modulated by uncorrelated random coefficients, the principal components. It owes its popularity to the property that only few terms of the series are usually needed to capture the most energetic coherent structures of the process, and a link often exists between each dominant mode and the main mechanisms of the phenomenon. For this reason, POD modes are normally used to identify low-dimensional subspaces appropriate for the construction of reduced models. This paper provides a state-of-the-art and some prospects on POD, with special regard to its framework and applications in wind engineering. A wide bibliography is also reported.

Key Words
aerodynamics; aeroelasticity; digital simulation; fluid dynamics; meteorology; proper orthogonal decomposition; structural dynamics; turbulence; wind engineering.

Address
DISEG, Department of Structural and Geotechnical Engineering, University of Genoa, Via Montallegro, 1, 16145 Genoa, Italy

Abstract
Few mathematical methods attracted theoretical and applied researches, both in the scientific and humanist fields, as the Proper Orthogonal Decomposition (POD) made throughout the last century. However, most of these fields often developed POD in autonomous ways and with different names, discovering more and more times what other scholars already knew in different sectors. This situation originated a broad band of methods and applications, whose collation requires working out a comprehensive viewpoint on the representation problem for random quantities. Based on these premises, this paper provides and discusses the theoretical foundations of POD in a homogeneous framework, emphasising the link between its general position and formulation and its prevalent use in wind engineering. Referring to this framework, some applications recently developed at the University of Genoa are shown and revised. General remarks and some prospects are finally drawn.

Key Words
aerodynamics; digital simulation; proper orthogonal decomposition; random processes; turbulence; wind engineering.

Address
DISEG, Department of Structural and Geotechnical Engineering, University of Genoa, Via Montallegro, 1, 16145 Genoa, Italy

Abstract
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Key Words
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Address
Fujun Peng and Ming Gu; State Key Laboratory for Disaster Reduction in Civil Engineering,
Tongji University, Shanghai, 200092, P. R. China
Hans-Jurgen Niemann; Boundary Layer Wind Tunnel Laboratory, Ruhr-Universitat Bochum, D-44780 Bochum, Germany


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