1,720,962 research outputs found
Identification of linear mechanical systems by deconvolution techniques
No full textThis paper describes how the impulse response function of a linear and time invariant dynamic system can be computed numerically by deconvolution techniques, starting from its input and output time histories. The integral equation governing the problem is transformed into a severely ill-conditioned set of linear equations whose approximate solution is obtained through regularisation methods. A proposal, with the aim of taking into account the possible non-null initial conditions of the physical system, is suggested together with an algorithm that allows the definition of long impulse responses with limited computing effort. The implementation developed can deal with single input single output, single input multiple output and multiple input multiple output systems and has been tested both numerically and on two simple real structures. The advantages and disadvantages of these time domain techniques are discussed in comparison with the widely used frequency methods
A theoretical model of oscillations of paramagnetic or diamagnetic structures subject to passive magnetic elements
No full textA theoretical model and experimental validation of the oscillations of a para- or dia-magnetic beam subject to the effects of passive magnetic elements
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Dynamics of multi-span continuous straight bridges subject to multi-degrees of freedom moving vehicle excitation
Full text linkThe paper presents an analytical approach to the problem of vehicle–bridge dynamic interaction. Starting from early studies based on a simply supported beam interacting with a lumped mass moving at constant speed, in recent years researchers have improved the models of both the bridge and the vehicle. On this basis, the bridge is modelled here as a multi-span continuous isotropic plate; its response to external loads is defined by applying the mode superposition principle and takes into account both flexural and torsional mode shapes, the latter being usually neglected in the literature. The plate is considered proportionally damped and its modes are computed by means of the Rayleigh–Ritz method. The scheme adopted for the vehicle consists of a seven degrees-of-freedom system moving at constant speed over the isotropic rough bridge surface. The numerical investigation, based on these analytical models, refers to a three-span bridge and includes the importance of torsional mode shapes, of road surface irregularities and of vehicle speed
Natural frequencies and dampings identification using wavelet transform: application to real data
No full textThe wavelet transform is used as a time-frequency representation for system identification purposes. It is shown that wavelet analysis of the free response of a system allows the estimation of the natural frequencies and viscous damping ratios. The advantages of the wavelet transform in the analysis of the free decay of the system are underlined and a comparison with previous techniques is made. The accuracy of this method is confirmed by applying it to a numerical example and the acceleration responses from a real bridge under ambient excitations (the Queensborough Bridge in Vancouver, Canada). The results obtained agree with those previously obtained on the dynamic behaviour of the Queensborough Bridge
A comparison between the theoretical model and experimental outcomes of oscillations of para- or dia-magnetic structures subject to passive magnetic elements
No full textIdentification of the dynamic behavior of bridges under ambient excitation using wavelet transform
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