1,721,004 research outputs found
A Non-linear elastodynamic model of a desmodromic valve train
No full textA lumped-parameter model of a motorbike engine's desmodromic valve train is developed for the simulation of the dynamic behaviour of such an uncommon train. The model takes into account several non-linear effects and is highly time-varying. The estimation of the model parameters is discussed and the effectiveness of the model is assessed by a comparison with experimental results. The model is employed to predict the magnitude of forces, impacts and bounces, and to detect unacceptable dynamic phenomena; thus, it may be used as a tool both in design optimization and diagnostics
Dynamic analysis of spur gear pairs: Steady-state response and stability of the SDOF model with time-varying meshing damping
No full textThe steady-state response and stability of the single degree of freedom (sdof) model of a pair of low contact ratio spur gears are studied. In the proposed model, a time-varying stiffness of the meshing tooth pairs and a viscous damping proportional to the meshing stiffness are considered. Gear errors of each meshing tooth pair are also included. A continuous closed-form solution was obtained for any rotational speed where there is no tooth separation. Transition curves separating stable and unstable regions are computed by Hill infinite determinant; different meshing stiffness are considered and the influence of both damping and contact ratios are investigated. One of the advantages of the technique used is the speed and accuracy of the computation of the responses and transition curves. Results obtained by the numerical simulation of the steady-state responses of two different pairs of spur gears are satisfactorily compared to experimental results. (C) 1997 Academic Press Limited
Bispectral analysis of the bilinear oscillator with application to the detection of fatigue cracks
No full textDamage detection by means of non-destructive testing plays an important role in ensuring the integrity of machine elements and structures. Vibration testing is an effective means of detecting crack development in structures. In this paper the effect of crack closure on the dynamic behaviour of cantilever beams is studied. Since the crack opens or closes depending on the direction of the vibration, the beam exhibits bilinear characteristics. The aim of the paper is to analyze the system response by using bispectral analysis which forms a subset of higher order statistical analysis. The study has been conducted both on simulated and experimental vibration signals. Firstly, a simplified model is employed to simulate the bilinear behaviour of a beam with a closing crack. The model is an oscillator with a bilinear restoring forcing function. The analysis of the forced vibrations of the model is performed by means of the harmonic balance method showing the occurrence of harmonics in the response spectrum which are strictly related to the bilinear nature of the model. Moreover, an experimental test carried out on a straight beam with a fatigue crack is presented. The beam is excited with white noise by means of a vibration shaker. The bispectral analysis performed both on the model and the actual structure shows high sensitivity to the non-linear behaviour of the system: that is to say, to the presence of the fatigue crack in the structure. In particular, the interactions between the frequency components contained in the signal response are analyzed. The results provide a possibility of using the bispectral analysis technique to detect damages in structures. © 1998 Academic Press
Use of higher order spectra in condition monitoring: Simulation and experiments
No full textIn (he field of machine condition monitoring one can observe that a link exists between machine vibrations and its health condition, that is. there is a change in the machine vibration signature when machine faults occur. Damages occurring in machine elements are often related to non-linear effects, which may lead to non-linearities in the machine vibration. This paper concerns the study of some systems by means of techniques based on Higher Order Spectra (HOS). These techniques are particularly useful in the situation where only a single measurement sensor is available. If a process is Gaussian then HOS provide no information that cannot be obtained from the second order statistics. On the contrary, HOS give information about a signal's non-Gaussianitv. Since a Gaussian input passing through a linear system leads to a Gaussian output, assuming the signal as an output of a system with a Gaussian input, then HOS make it possible to analyse the structure of the output signal and to provide information related to the non-linearity within the system. A simple model is presented with the aim of showing the effectiveness of the normalised version of poh spectra in detecting different kinds of system non-linearities. HOS are used to interpret the signal structure and the system's physical characteristics. Moreover, two experimental cases are presented. The HOS are applied to delect the presence of a fatigue crack in a straight beam and to analyse the vibration signal measured on a test bench for rolling element bearings Both third and fourth order spectra seem to provide a possibility of using HOS as a condition monitoring tool
Condition monitoring and diagnostics in automatic machines: Comparison of vibration analysis techniques
No full textThis paper assesses and compares the effectiveness and reliability of different vibration analysis techniques for fault detection and diagnostics in cam mechanisms used in high performance automatic packaging machines. Firstly, the results of the application of widely used techniques are given and their limitations are delineated. Secondly, the application of the wavelet transform is proposed, since the vibrations of this kind of machine are highly non-stationary. Finally, an inverse-filtering technique is used to recover the actual output link motion from the casing vibration, in order to enable condition monitoring and diagnostics to be carried out through the analysis of the mechanism motion. © 1997 Academic Press Limited
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