The identification of the motion of a rigid body by means of linear accelerometers is a problem already investigated by many researchers, but still debated. The optimisation of the number and placement of accelerometers is also another important aspect of the problem. In this study, an experimental procedure is proposed and applied to identify the rigid-body vibratory motion of the steering wheel of a sporting car, by means of six linear accelerometers. Some numerical simulations for investigating possible errors are also presented.

Francesca Di Puccio

Paola Forte

Identification of the 3D Vibratory Motion of a Rigid Body by Accelerometer Measurements

Vehicle noise and vibration levels are basic parameters in passenger comfort. Both static and dynamic stiffness of sheet metal parts is commonly increased by means of stiffening ribs. Vibrations are also reduced by adding a layer of damping material on the floor, the roof, the firewall and other parts of the vehicle. In common practice the panels to be treated are ribbed according to criteria based on the designer&#x2019;s experience, rather than on well defined design procedures and are uniformly covered by a layer of damping material. However, these are not efficient design solutions, especially with regard to the effectiveness of vibration reduction and to weight containment. In this paper a novel approach to achieve an optimal distribution of stiffening ribs and damping material will be presented. The proposed method is based on a Genetic Algorithm (G.A.) procedure which takes into account both the vibroacoustic performance and the weight and cost reduction. A simple case study will be illustrated to demonstrate the capabilities of the developed procedure.

M. Carfagni

P. Citti

L. Governi

M. Pierini

Vibroacoustic Optimization of Stiffening Ribs and Damping Material Distribution on Sheet Metal Parts

An approach for the use of the Weighted Least Squares method for time domain modal parameter identification is introduced. The approach enables standard identification methods to be employed in the usual manner, except that sections of the time records with high signal-noise ratios are given a greater emphasis in the identification process. It is shown how it is possible to apply the method to a wide range of applications, including the analysis of impulse response, input-output and time varying data. A number of different weighting schemes are explored, based upon exponential weighting and the envelope of the measured data. A series of simulated tests demonstrate how the performance of conventional time domain algorithms can be improved significantly with little extra computational effort though the use of a Weighted Least Squares scheme.

Jonathan E. Cooper

On the Use of Weighted Least Squares for Time Domain Modal Parameter Identification

The identification of a nonlinear system is performed using experimental data and two different techniques, i.e. a method based on the Wavelet transform and the Restoring Force Surface method. Both techniques exploit the system free response and result in the estimation of linear and nonlinear physical parameters.

V. Lenaerts

G. Kerschen

J.-C. Golinval

M. Ruzzene

E. Giorcelli

Validation of Two Nonlinear System Identification Techniques Using an Experimental Testbed

A critical analysis of the available methods for the assessment of structural concrete bridges through the observation of their dynamic response is carried out. A mathematical model for the evaluation of the natural frequencies shift due to bridge damage is applied to the case of an existing reinforced concrete bridge. The numerical results, along with the general structure of the mathematical problem, allow discussing some limitation and drawbacks of the dynamic methods. Namely the need for a reference set of the bridges dynamic properties before the onset of damage and the effect of the ambient temperature variation may lead, in many cases, to unreliable estimates of the structural condition of the investigated bridges.

M. Breccolotti

G. Franceschini

A.L. Materazzi

Sensitivity of Dynamic Methods for Damage Detection in Structural Concrete Bridges

This paper deals with the effects of generalized damping distributions on vibrating linear systems. The attention is focused on continuous linear systems with distributed and possibly non-proportional viscous damping, which are studied in terms of modal analysis, defining and discussing the orthogonality properties of their eigenfunctions.Exact expressions of the frequency response functions obtained by direct integration of the equations of motion are compared with the analogous formulas based on the superposition of modes. In addition, approximate expressions of the frequency response functions of both continuous and discrete (finite element models) systems in terms of their undamped eigenfunctions/eigenvectors are also considered and discussed.The presented methods are explained, compared and validated by means of numerical examples on a clamped-free Euler-Bernoulli beam.

S. Sorrentino

A. Fasana

S. Marchesiello

Frequency Domain Analysis of Continuous Systems with Viscous Generalized Damping

Certain results are presented in this paper on damped vibration of a laminated cantilever beam with a single closing delamination. In order to investigate this task the finite element method has been applied in the current study. For modelling the beam higher order shear deformation beam finite elements have been used. The vibration of the beam is investigated in the time domain using a dynamic contact algorithm developed by the authors. The algorithm is based on the Newmark method and also incorporates a Newton-Raphson based procedure for resolving the equation of motion. The time series obtained from solving the equation of motion have been subsequently analysed in the frequency domain by using FFT (Fast Fourier Transform). The vibration responses of the beam due to various harmonic and impulse excitations, at different delamination locations, and for different delamination lengths, as well as changes in the dissipation of damping energy due to the delamination, have all been considered in the paper.

W. Ostachowicz

A. &#x17b;ak

Vibration of a Laminated Beam with a Delamination Including Contact Effects

A double-ended cantilever beam as a distributed parameter dynamic vibration absorber has been applied to a single-degree-of-freedom system subjected to harmonic forces.In this investigation, the beam has been analyzed under the well known model of Timoshenko and the computation of best parameters is based on the Chebyshev&#x2019;s optimality criterion.This is somewhat novel in the field since:
 <list><list-item>The design of cantilever beams as dynamic vibration absorbers is usually made under the hypotheses of the Euler-Bernoulli theory;</list-item><list-item>It is the first time that the Chebyshev&#x2019;s criterion is applied to the design of a double-ended cantilever beam used as a dynamic vibration absorber.</list-item></list>For a ready use of the results herein presented, design charts allow a quick choice of optimal parameters such as tuning ratio and mass ratio.

M. Cavacece

L. Vita

Optimal Cantilever Dynamic Vibration Absorbers by Timoshenko Beam Theory

Trains current collection for traction motors is obtained by means of a sliding contact between the overhead line (OHL) and the collector strips mounted on the pantograph head. The normal force by which the collector presses against the contact wire ensures the contact pressure for the electrical contact. As the train speed increases, the variation of contact force between pantograph and catenary increases, and the pantograph-OHL dynamic interaction becomes greater. This condition causes excessive mechanical wear and contact wire uplift (for high values of contact forces), and leads to high percentage of contact loss, arcing and electrically related wear.The topic of actively controlled pantograph is gaining more interest as a tool to increase the performance of the current collection at high speed. In the last few years, it appears possible to transfer the knowledge based on numerical experiments, to the real operating condition. An important step in this direction is the set up of a laboratory hardware in the loop test-rig in which the control strategies and the actuation can be tested, before tests performing in real life conditions, in order to demonstrate their actual feasibility. The present paper describes an hardware in the loop (HIL) test-rig developed by the authors, which allows to reproduce the dynamical interaction between overhead lines and pantograph in high speed railways. Using the described laboratory set-up, experimental investigation on the problems related with pantograph-OHL interaction can be performed, very similarly to the real life operating conditions, with the advantage of varying test parameters and conditions easily.

A. Collina

A. Facchinetti

F. Fossati

F. Resta

Hardware in the Loop Test-Rig for Identification and Control Application on High Speed Pantographs

The fact that a complex-damped model may represent the dynamic behaviour of elasto-mechanical systems when acted upon by a magnetic field was brought to the attention of the structural dynamics community very recently by Professor Bruno A. D. Piombo and his colleagues at the Politecnico di Torino. In this paper a thorough analysis of the single degree-of-freedom complex-damped mass-spring system is presented. The analysis includes the root locus, the (non-causal) impulse response, the frequency response and the transmissibility. Regions of different behaviour in the frequency response and transmissibility are described in detail. The stiffening behaviour observed in Prof. Piombo's experiments and known as the &#x22;phantom effect&#x22; is demonstrated by the complex-damped model.

Elvio Bonisoli

John E. Mottershead

Complex-Damped Dynamic Systems in the Time and Frequency Domains

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Shock and Vibration publishes papers on all aspects of shock and vibration, especially in relation to civil, mechanical and aerospace engineering applications, as well as transport, materials and geoscience.&nbsp;

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Chief Editor&nbsp;Dr Tai Thai&nbsp;is based at the University of Melbourne and his current research focuses on high strength materials for sustainable construction of buildings, bridges and other infrastructure.

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Shock and Vibration

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