The dynamic response of a continuous plate for different surface states

Several dynamic effects can be generated and simply observed by the passage of an external mobile exciter forces with different speeds on the surface of an orthotropic continuous plate. In the present paper one illustrates the dynamic behaviour of a thin, orthotropic, multi-span plate, subjected to the passage of moving exciters. In this model, the roughness of the surface of the plate is considered as the contact surface between mobile exciter and the plate. The modal and Newmark integration methods are used in order to solve the coupled plate–exciter equations of motion. One presents especially results which show clearly the influence of the surface states on the dynamic behaviour of the plate and also the generated interaction forces due to the surface roughness. In this paper one presents also the influence of the mobile exciter speeds on the plate dynamic response

Identification de l'évolution de l'usure d'un outil de tournage basée sur l'analyse des efforts de coupe et des vibrations

L’influence de l’usure des outils coupants sur la qualité de l’état de surface demeure un problème principal dans un procédé d'usinage. La surveillance des processus d'usinage joue alors un rôle très important pour éviter l'apparition de certains phénomènes non désirés, tels que l'usure excessive et la rupture de l'outil. Dans ce travail, nous proposons une méthode de surveillance basée conjointement sur l'analyse temporelle et l'analyse fréquentielle des signaux mesurés en tournage pour identifier l’usure de l’outil. Les objectifs principaux de ce travail sont de montrer, d’une part, la sensibilité d'indicateurs scalaires à la variation de l'usure et d’autre part de déterminer plusieurs indicateurs de l’usure à l’image des fréquences caractéristiques, du niveau vibratoire et des changements brusques qui permettent de déceler l’endommagement de l’outil de coupe. Cette dernière étude fréquentielle est basée sur une analyse multirésolution en ondelettes. Les résultats obtenus et présentés dans cet article, montrent l'efficacité de ces approches en tournage.Mots-clés : Usure d’outil- Effort de coupe - Signatures vibratoires - Indicateurs scalaires - Analyse fréquentielle- Analyse multirésolution en ondelettes

PRÉVISION DU RAYONNEMENT ACOUSTIQUE DE CYLINDRES FINIS EN PRÉSENCE D'ÉCOULEMENT UNIFORME ET DE SOURCES INTERNES PAR UNE MÉTHODE INTÉGRO-MODALE

An analytical study of radiation from finite cylindrical shell with infinite rigid extensions is presented. The shell is immersed in an infinite surrounding fluid at rest and contains flowing fluid. The shell is excited either by an harmonic driving force or by internal acoustic sources. The method of resolution consists in expanding the shell wall displacements in series of the simply supported shell eigen modes

Analyse de l'impact des paramètres de coupe et des vibrations sur la rugosité des pièces usinées en tournage à partir de la méthode de régression linéaire multiple

La rugosité des surfaces des pièces usinées par tournage joue un très grand rôle sur la qualité du produit fini. Notre étude consiste à développer un modèle basé sur des expériences pour la prédiction de la rugosité. Beaucoup de paramètres influent sur la rugosité d'une façon directe ou indirecte, à savoir les paramètres du régime de coupe tels que l'avance par tour, la vitesse de rotation, la profondeur de passe et les efforts de coupe générés aux contacts outil-pièce, sans oublier les vibrations de l'outil dues aux phénomènes de coupe. Pour mettre en évidence l'influence de tous ces paramètres, des expériences sont réalisées selon un plan factoriel. La détermination du modèle est obtenue par la technique de régression linéaire multiple, sa validation est confirmée par la comparaison de la rugosité obtenue par le modèle et la rugosité mesurée. L'application de cette technique statistique pour la prédiction de la rugosité montre sa fiabilité car l'erreur entre la valeur expérimentale et la valeur calculée par le modèle est négligeable

Dynamic amplification of a multi-span orthotropic bridge deck under vehicular movement

The response of a multi-span, continuous orthotropic bridge deck during truck loading is investigated to better understand the dynamic interaction between moving vehicles and highway bridge decks. The present study is based on a recently published, semi-analytical approach for free vibration in which the modal superposition method incorporates intermodal coupling. Herein, the bridge deck is modeled as a jointless, multi-span, orthotropic plate, and the vehicle is modeled as a dynamic, multi-body system. The road surface roughness randomness is modeled as a normal, stationary, random process described by its Power Spectral Density (PSD). The coupled equations of the motion vehicle/bridge deck are solved by Newmark’s method. An iterative process in each time step is performed to find the equilibrium between the bridge deck and vehicle tires using an uncoupled algorithm previously developed by other authors. Two numerical application examples are presented: an isotropic and an orthotropic, three-span bridge deck both crossed by an AASHTO-based vehicle model. In example one, the intermodal coupling affects the dynamic deflection of bridge deck but only slightly. Example two demonstrates that the loading mode and the vehicle speed have a significant influence on the Dynamic Amplification Factor. However, the most important parameter to affect the dynamic vehicle/bridge deck interaction force is the road’s surface roughness, as has been shown for other bridge types under various load conditions

Sound source localization by an inverse method using the measured dynamic response of a cylinder

International audienceThis work presents an experimental study to localize an acoustic source inside a cylindrical shell which is applied without contact with the structure. Since this source cannot be detected by direct measurements, the proposed method is based on the measurement of the velocity at some discrete points on the external surface of the shell by a Scanning Laser Vibrometer. The displacements integrated from the measured velocities will be injected into the equation of motion using finite difference schemes. First, some numerical simulations will be presented starting from exact data and then with uncertainties to simulate measurements. Before the regularization process was applied, the distributions resulting from measured velocities cannot be able to locate the acoustic source whenever the measurement uncertainties are present. In this case, a regularization technique based on the filtering of the wavenumber domain which is infected by the noise is applied. The regularization criterion has been applied to the distributions as results of measurements and there the localization of the acoustic source is clearly improved

Application of the Wavelet Multi-resolution Analysis and Hilbert transform for the prediction of gear tooth defects

In machine defect detection, namely those of gears, the major problem is isolating the defect signature from the measured signal, especially where there is significant background noise or multiple machine components. This article presents a method of gear defect detection based on the combination of Wavelet Multi-resolution Analysis and the Hilbert transform. The pairing of these techniques allows simultaneous filtering and denoising, along with the possibility of detecting transitory phenomena, as well as a demodulation. This paper presents a numerical simulation of the requisite mathematical model followed by its experimental application of acceleration signals measured on defective gears on a laboratory test rig. Signals were collected under various gear operating conditions, including defect size, rotational speed, and frequency bandwidth. The proposed method compares favourably to commonly used analysis tools, with the advantage of enabling defect frequency isolation, thereby allowing detection of even small or combined defects.Deposited by bulk importTS 11.02.1