1,721,113 research outputs found
A Methodology for the Study of Coupled Aeroelastic Phenomena
No full textA global model is identified inclusive of any whatsoever aeroelastic phenomenon, the linearization of which allows study of incipient aerodynamic instability through a solution methodology falling within the domain of the poles. With the variation of the mean stream velocity, study is made of the system's critical points and the form of the incipient instability represented by the same. Two structural examples are provided of the application of the methodology outlined
Gli effetti delle raffiche del vento sulle strutture snelle verticali
No full textGli studi originali sul fattore di raffica, sulla risposta massima e sulle forze statiche equivalenti riguardano le vibrazioni delle strutture nella direzione del vento. Le ricerche condotte nell’ultimo decennio in questo settore seguono due linee distinte: la prima è rivolta alla determinazione dei massimi effetti causati dalle vibrazioni nella direzione del vento; la seconda estende i metodi originali alle vibrazioni trasversali e torsionali. Gli autori hanno recentemente sviluppato un programma di ricerca finalizzato a riunire questi filoni derivando gli effetti massimi associati alla risposta 3-D delle strutture snelle verticali e mostrando che un’opportuna definizione di un coefficiente di raffica 3-D dell’effetto fornisce, attraverso una sola espressione analitica, qualunque effetto strutturale a qualsivoglia livello. In questo contesto è stata anche proposta una nuova definizione delle forze statiche equivalenti. Questa memoria fornisce un quadro generale e un giudizio critico dell’intera materia
A loading model for the interpretation of lateral vibrations of flexible footbridges
No full textThe excessive lateral sway motion caused by crowds walking across footbridges has attracted great public attention in
the past few years. Different possible mechanisms responsible for such lateral vibrations have been investigated in the
literature, assuming that synchronization between structural motion and pedestrians occurs. Based on a new forcing
model whose amplitude is a function of deck oscillations, a parametric excitation mechanism has been analysed by the
authors of the present paper, that can give rise to strong lateral vibrations of flexible footbridges. The proposed forcing
model is here validated through recent experimental results. Furthermore, it is applied for the analysis of pedestrianinduced
vibrations of a real footbridge when no evidence of synchronization between pedestrians and the footbridge
appears
Oscillazioni forzate di un cavo sospeso immerso in vento turbolento
No full textThe nonlinear random oscillations of a cable induced by a turbulent wind are investigated proponing a two degree-of-freedom model, with quadratic-cubic nonlinearities and parametric excitation terms arising from geometric and aerodynamic effects. The solution is developed in the frequency domain through the Volterra series expansion technique. The power spectral density function and the probability density function of the cable response are determined. The comparison with Monte Carlo numerical results points out an excellent convergence of the proposed procedure
Non-linear galloping of iced suspended cables with two-to-one internal resonance
No full textThe response of a perfectly flexible elastic suspended cable driven by mean wind speed, blowing perpendicularly to the cables’ plane is investigated using a two degree-of-freedom model. The modes are coupled through quadratic and cubic terms arising from geometric and aerodynamic effects. The associated linear frequencies are assumed to be in an almost 2:1 ratio so that internal resonance conditions occur. Steady-state amplitude solutions are determined as a function of the mean wind speed and their stability analyzed. The relevant importance of both kind of non-linearities is discussed
On the influence of the torsional stiffness on non-linear galloping of suspended cables
No full textA simplified three-dimensional non-linear discrete model of an iced suspended cable, excited by uniform wind velocity, is developed in quasi-static regime. It includes the whole non-linear effect of torsion, both on the mechanics and on the aerodynamics. By considering single cables for which torsional frequency is much higher than flexural ones, a quasi-static condensation is performed to obtain a model with only two translational degrees of freedom. The influence of torsional stiffness on critical wind speed is analysed, both in near-to-resonance and far-from-resonance conditions between in-plane and out-of-plane oscillations. A preliminary numerical analysis of the post-critical behaviour is performed
A nonlinear discrete model for wind-excited suspended cables
No full textIn the present paper the nonlinear discrete model of a cable driven by a turbulent wind is proposed in order
to take into account an arbitrary number of structural modes and of wind modes, obtaining a system of firstorder
ordinary differential equations driven by a vector of independent random processes. Nonlinearities
and parametric-excitation terms deriving from fluid-structure interaction are fully included. The
convergence of the modal expansions is preliminarily discussed through a realistic wind-excited cable. The
first examples highlights as higher modes can slightly modify the power spectral density function and the
probabilistic density function of the response, especially as regards in-plane motion, but they do not
introduce any qualitative difference
3-D gust effect factor for slender vertical structures
No full textOriginal studies on gust factor buffeting dealt with the alongwind displacement of structures. Research on this topic carried out since the nineties followed two distinct lines: the first determines the maximum effects due to the alongwind response; the second extends the original method from the alongwind response to crosswind and torsional responses. This paper represents the junction point of these research lines with reference to cantilever slender vertical structures. It derives the most relevant effects associated with the three-dimensional (3-D) wind-excited response of this structural type and shows that a suitable definition of one non-dimensional quantity, referred to as the 3-D gust effect factor, provides such effects at any level through a wide set of experimental, numerical and analytical procedures. A new definition of a 3-D equivalent static force consistent with this method is also introduced and critically compared with previous analogous statements
Condizioni critiche di stabilità per galloping flessionale accoppiato
No full textA coupled, linearized, flexural two degree-of-freedom model, describing a flexible structure subject to galloping, is analyzed. The results obtained through a perturbative technique show that the proposed method furnishes the classical solution of one degree-of-freedom model when a sufficient modal detuning exists, while various situations can occur near the perfect tuning
Generalized equivalent spectrum technique
No full textWind forces on structures are usually schematized by the sum of their mean static part and a nil mean fluctuation generally treated as a stationary process randomly varying in space and time. The multi-variate and multi-dimensional nature of such a process requires a considerable quantity of numerical procedures to carry out the dynamic analysis of the structural response. With the aim of drastically reducing the above computational burden, this paper introduces a method by means of which the external fluctuating wind forces on slender structures and structural elements are schematized by an equivalent process identically coherent in space. This process is identified by a power spectral density function, called the Generalized Equivalent Spectrum, whose expression is given in closed form
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