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CONTENTS
Volume 7, Number 2, March 2004
 

Abstract
In this paper the capacity of Covariance Proper Transformation (CPT) analyses to provide information about the wind loading mechanisms of bluff bodies is investigated through the application to square cylinders. CPT is applied to the fluctuating pressure distributions on a single cylinder, as well as on a pair of cylinders in the tandem and side by side arrangements, with different separations. Both smooth and turbulent flow conditions are considered. First, through the analysis of the contributions of each CPT mode to the total fluctuating aerodynamic forces, a correspondence between modes and aerodynamic components is sought, which is then verified through examination of the mode shapes. When a correspondence between modes and aerodynamic components is found, an attempt is made to separate the different frequency contributions to the aerodynamic forces, provided by each mode. From the analyses it emerges that (a) in most cases each mode is associated to one single force component, that (b) retaining a limited number of modes allows reproducing the aerodynamic forces with a rather good accuracy, and that (c) each mode is mainly associated with one frequency of excitation.

Key Words
wind loading; pressure fluctuations; Covariance Proper Transformation; wind tunnel testing; square cylinders.

Address
Enrico T. de Grenet; Department of Civil Engineering, University of Florence, Via S. Marta, 3 50139, Florence, ItalyrnFrancesco Ricciardelli; Department of Mechanics and Materials, University of Reggio Calabria, Via Graziella, Feo di Vito 89060, Reggio Calabria, Italy

Abstract
The response of tall buildings to gust buffeting is usually evaluated assuming that the structural damping is of a viscous nature. In addition, when dampers are incorporated in the design to mitigate the response, their effect is allowed for increasing the building modal damping ratios by a quantity corresponding to the additional energy dissipation arising from the presence of the devices. Even though straightforward, this procedure has some degree of inaccuracy due to the existence of a memory effect, associated with the damping mechanism, which is neglected by a viscous model. In this paper a more realistic viscoelastic model is used to evaluate the response to gust buffeting of tall buildings provided with energy dissipation devices. Both cases of viscous and hysteretic inherent damping are considered, while for the dampers a generic viscoelastic behaviour is assumed. The Laguerre Polynomial Approximation is used to write the equations of motion and find the frequency response functions. The procedure is applied to a 25-story building to quantify the memory effects, and the inaccuracy arising when the latter is neglected.

Key Words
gust buffeting; alongwind response; viscoelastic damping; viscoelastic memory; Laguerre Polynomial Approximation.

Address
A. Palmeri; Dipartimento di Costruzioni e Tecnologie Avanzate, University of Messina, Salita Sperone 31, 98166, Messina, ItalyrnF. Ricciardelli; Dipartimento di Meccanica e dei Materiali, University of Reggio Calabria, Via Graziella, Feo di Vito, 89060, Reggio Calabria, ItalyrnG. Muscolino; Dipartimento di Costruzioni e Tecnologie Avanzate, University of Messina, Salita Sperone 31, 98166, Messina, ItalyrnA. De Luca; Dipartimento di Analisi e Progettazione Strutturale, University of Naples

Abstract
This paper presents a time-domain approach for analyzing nonlinear random vibrations of long-span suspended cables under transversal wind. A consistent continuous model of the cable, fully accounting for geometrical nonlinearities inherent in cable behavior, is adopted. The effects of spatial correlation are properly included by modeling wind velocity fluctuation as a random function of time andrnof a single spatial variable ranging over cable span, namely as a one-variate bi-dimensional (1V-2D) random field. Within the context of a Galerkin

Key Words
suspended cable; wind velocity; random field; digital simulation; Proper Orthogonal Decomposition; nonlinear vibrations.

Address
M. Di Paola; Dipartimento di Ingegneria Strutturale e Geotecnica, Universit? di Palermo, Viale delle Scienze, 90128, Palermo, ItalyrnG. Muscolino and A. Sofi; Dipartimento di Costruzioni e Tecnologie Avanzate, Universit? di Messina, Salita Sperone 31, 98166, S.Agata-Messina, Italy

Abstract
A technique for the simulation of atmospheric boundary layers in wind tunnels is developed and tested experimentally. The device consists of a grid made of seven horizontal and vertical evenly distributed bars in which air injection holes are drilled in order to influence the flow in the wind tunnel. The air flow in each bar can be controlled independently. Firstly, the device is used together with a rough carpet, which covers the test section floor, in order to simulate the boundary-layer characteristics over an open rural area. Hot-wire measurements, performed at different positions in the test-section, show the capability of the grid in generating the required boundary layer. An acceptable agreement with statistical values of mean velocity and turbulence profiles has been achieved, together with a good span-wise homogeneity. The results are also compared with those of a passive simulation technique based on the use of spires.

Key Words
wind tunnel tests; atmospheric boundary layers simulation; active grid; turbulence profiles; hot-wire measurements.

Address
A. Talamelli; DIEM, Dipartimento di Meccanica e Aeronautica, Universit? di Bologna, ItalyrnL. Riparbelli; Dipartimento di Ingegneria Aerospaziale, Universit? di Pisa, ItalyrnJ. Westin; KTH Mechanics, Stockholm, Sweden


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