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CONTENTS
Volume 2, Number 4, December 1999
 

Abstract
Turbulence effects on surface pressures of rectangular on two-dimensional rectangular cylinders. Particular attention is given to possible effects of turbulence integral scale on fluctuation and peak pressures. The mean, standard deviation, peak pressure coefficients, spectra and cross-correlation of fluctuating pressures were measured to investigate the nature of the separation and reattachment phenomenon in turbulent flows over a wide range of turbulence intensity and integral scale.

Key Words
bluff body aerodynamics; turbulence effects; surface pressures; wind tunnel testing.

Address
Department of Building and Construction, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong KongrnDepartment of Mechanical Engineering, Monash University, Clayton, VIC 3168, Australia

Abstract
Multiple tuned mass dampers are proposed to suppress the vertical and torsional buffeting and to increase the aerodynamic stability of long-span bridges. Each damper has vertical and torsional frequencies, which are tuned to the corresponding frequencies of the structural modes to suppress the resonant effects. These proposed dampers maintain the advantage of traditional multiple mass dampers, but have the added capability of simultaneously controlling vertical and torsional buffeting responses. The aerodynamic coupling is incorporated into the formulations, allowing this model to effectively increase the critical speed of a bridge for either single-degree-of-freedom flutter or coupled flutter. The reduction of dynamic response and the increase of the critical speed through the attachment of the proposed dampers to the bridge are also discussed. Through a parametric analysis, the characteristics of the multiple tuned mass dampers are studied and the design parameters - including mass, damping, frequency bandwidth, and total number of dampers - are proposed. The results indicate that the proposed dampers effectively suppress the vertical and the torsional buffeting and increase the structural stability. Moreover, these tuned mass dampers, designed within the recommended parameters, are not only more effective but also more robust than a single TMD against wind-induced vibration.

Key Words
multiple tuned mass dampers; buffeting; flutter; long-span bridge.

Address
Department of Civil Engineering, Tamkang University, Tamsui, Taiwan, 251, R.O.C.

Abstract
A discrete vortex method (DVM) has been developed at the Department of Aerospace Engineering, University of Glasgow, to predict unsteady, incompressible, separated flows around closed bodies. The basis of the method is the discretisation of the vorticity field, rather than the velocity field, into a series of vortex particles that are free to move in the flow. This paper gives a brief description of the method and presents the results of calculations on static and transversely oscilating square section cylinders. The results demonstrate that the method successfully predicts the character of the flow field at different angles of incidence for the static case. Vortex lock-in around the resonance point is successfully captured in the oscillatory cases. It is concluded that the vortex method results show good agreement, both qualitatively and quantitatively, with results from various experimental data.

Key Words
vortex method; bluff bodies; square cylinder; vortex-induced vibration.

Address
Department of Aerospace Engineering, University of Glasgow, G12 8QQ, U.K.

Abstract
Accurate turbulence modeling is an essential prerequisite for the use of Computational Fluid Dynamics( CFD) in Wind Engineering. At present the most popular turbulence model for general engineering flow problems is the k-e model. Models such as this are based on the isotropic eddy viscosity concept and have well documented shortcomings (Murakami et al. 1993) for flows encountered in Wind Engineering. This paper presents an objective assessment of several available alternative models. The CFD results for the flow around a full-scale (6m) three-dimensional surface mounted cube in an atmospheric boundary layer are compared with recently obtained data. Cube orientations normal and skewed at 45 degree to the incident wind have been analysed at Reynolds at Reynolds number of greater than 10x6 . In addition to turbulence modeling other aspects of the CFD procedure are analysed and their effects are discussed.

Key Words
turbulence model; wind engineering; anisotropy; full-scale; bluff body; computational fluid dynamics; buildings; k-e.

Address
School of Civil Engineering, The University of Nottingham, Nottingham, NG7 2RD, U.K.

Abstract
In recent years, rainscreen walls based on the pressure equalization principle are often used in building construction. To improve the understanding of the influence of several design parameters on the pressure equalization performance of such wall systems, a theoretical consideration of the problem may be more appropriate. On this basis, this paper presents two theoretical models, one based on mass balance and the other based on the Helmholtz resonator theory, for the prediction of cavity pressure in rigid rainscreen walls. New measures to assess the degree of pressure equalization of sufficiently accurate and efficient in predicting the cavity pressure variations. Further, the performance of the proposed model is evaluated utilizing the data obtained from full-scale tests and the results are discussed in detail.

Key Words
performance; prediction; pressure equalization; rainscreen walls.

Address
Faculty of Architecture, Building and Planning, FAGO, Technical University of Eindhoven, Postbus 613, 5600 MB Eindhoven, The Netherlands


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