0000000000283202
AUTHOR
Ali El Hafidi
Vibration reduction on city buses: Determination of optimal position of engine mounts
International audience; This study is composed of three essential parts. The first part describes an indirect semi-experimental method which is used to reconstruct the excitation force of an operating diesel engine from the acceleration data measured at the mounting points. These internal forces can not be directly measured with force sensors; they have to be derived from the dynamic deformation of the engine support, so a theoretical analysis is carried out to derive the equations for the force re-construction.The second part deals with prevention of low frequency vibration of the powertrain from spreading to the rest of the vehicle. Three uncoupling techniques are used to minimize these v…
Étude Du Comportement Thermomécanique De Structures Recouvertes De Patchs Visco-Contraints
International audience; La thermographie infrarouge est une méthode qui permet d'obtenir la carte de luminance de la scène thermique observée, de la convertir en température apparente et d'afficher ou d'enregistrer le résultat sous la forme d'une image de la distribution de la température. Nous l'utilisons ici, pour la détection à distance, des sources d'énergie dans des structures formées de poutres recouvertes de patchs viscoélastiques.
Numerical vibroacoustic analysis of plates with constrained-layer damping patches
International audience; A numerical vibroacoustic model that can manage multilayered plates locally covered with damping patches is presented. All the layers can have an on-axis orthotropic viscoelastic behavior. Continuity of displacements and transverse shear stresses at each interface is enforced, which permits to write the entire displacement field in function of the displacements of the-common-first layer, leading to a two-dimensional plate model. The problem is then discretized by Rayleigh-Ritz's method using a trigonometric basis that includes both sine and cosine functions in order to treat various boundary conditions. The excitation can be of mechanical kind (concentrated or distri…
Vibroacoustic Simulation of Heterogeneous Multilayer Composite Plates Involving Low Young's Modulus Viscoelastic Material
The vibroacoustic behavior of composite multilayered plates involving high Young’s modulus ratios between adjacent layers, like sandwich panels and passive constrained layer damped plates, is studied. As classical plate models give poor results with such structures, a specific model has been used. It is an equivalent single layer model, with a five unknown displacement field which takes into account a variation of transverse shear strains into the thickness. A classical sandwich structure is simulated, its natural frequencies are compared to those given by other models and a 3D finite element simulation which is taken as reference. A second study concerns a composite plate with a damping pa…
Prediction of Dissipative Properties of Flax Fibers Reinforced Laminates by Vibration Analysis
This study proposes an experimental-numeric method to identify the viscoelastic properties of flax fibres reinforced composite laminate (flax/epoxide). The used method consists in identifying the evolutions of both loss factor and stiffness when vibrational frequency changes. In this way, several free-free symmetrically guided beams are excited on a dynamic range of 10 to 4000 Hz with sweep sine excitation focused around the 4-first’s modes. Fractional derivative Zener model is used to identify the on-axis ply complex moduli and describe the laminate dissipative linear behavior with the classical laminate theory. Results obtained on a quasi-isotropic laminate show that this model adequately…
A study of noise transmission through cylindrical shell using modal truncation approach
International audience; The study of the vibroacoustic behaviour of cylindrical structure like aircraft fuselage requires the establishment of very large models, and the numerical results which can be obtained are often difficult to interpret. On the other hand, the study of simple structures such as cylindrical shells is useful to validate the criteria and tools that can be used to simplify the models of complex structures. The presented study concerns the sound transmission through a cylindrical shell coupled to a cavity and subjected to an incident acoustic wave. Noise reduction is obtained and validated by a numerical method which uses structural and acoustical modes. A criterion for se…