Lotfi Hammami

Characterization of Modal Damping of Sandwich Plates

The homogenization of the energy functional of a sandwich plate, its minimization and its discretization by finite element methods and modeling the viscoelastic core behavior by an hysteretic structural damping lead to the homogenized dynamic equation of a sandwich plate. The vibratory analysis permits the determination of the elastic eigenmodes and the characterization of the modal damping which will serve to the establishment of dynamical responses if we used the modal dynamic recombination method. The numerical results obtained show that the eigenmodes are not orthogonal to the damping matrix but are only weakly coupled. Besides, the modal damping matrix coefficients vary according to the ratio of the core thickness and the total thickness of sandwich plate and follow a second-order polynomial function of this ratio.

Simulation of Viscothermal Losses on the Acoustic Behaviour of a Thin Fluid Layer Enclosed Between Two Oscillating Plates

This article deals with a theoretical investigation for the analysis of a double-plate system enclosing a viscothermal fluid cavity. Dynamic equations of the coupled system are established in appropriate dimensionless form including the effects of viscosity and thermal conductivity of the fluid. The pressure wave equation is derived in in-plane form. This equation is solved analytically in the case of oscillating plate motions in order to determine the acoustic pressure in the cavity. Numerical results are presented for the case of two modal shapes. They show the importance of the viscothermal effects in the case of thin fluid layers.

Modal approach for dynamical analysis of sandwich plates

The dynamic equation of a sandwich plate is presented under the hypothesis of linear longitudinal displacement fields in each layer and an hysteretic structural damping of the viscoelastic core. A modal approach is adopted to investigate sandwich plate dynamical behaviour. First, the elastic eigenmodes are used in the characterisation of the modal damping. Then, the dynamical analysis is established using the modal dynamic recombination method and the result of modal damping characterisation. The numerical results obtained show that the eigenmodes are not orthogonal with respect to the damping matrix but are only weakly coupled. Besides, the modal damping matrix coefficients vary according to the ratio of the core thickness to the total thickness of the sandwich plate following a second order polynomial function. The modal approach with hysteretic modal damping characterisation is proposed in establishing dynamical responses. The results show that dynamical responses due to the use of a hysteretic diagonal modal damping matrix are in good agreement with those obtained when a full modal damping matrix is considered.

Angular Misalignment Effect on the Dynamic Behavior of Bearings

Dysfunction of rotating machines is often caused by shaft misalignment. This defect generates some important loads and vibrations, and can lead to a premature failure of a bearing, shaft or coupling. The objective of this study is to survey angular misalignment. The first part deals with the development of a theoretical model describing the phenomenon. This allows the vibration response as well as the reaction in the bearings to be analysed. The second part uses the finite element method to study the dynamic behavior of the bearings. The two methods showed a good concordance in results and enable the characterization of the angular misalignment.

On the use of the plane wave based method for vibro‐acoustic problems

Purpose – The purpose of this paper is to present the extension of plane wave based method.Design/methodology/approach – The mixed functional are discretized using enriched finite elements. The fluid is discretized by enriched acoustic element, the structure by enriched structural finite element and the interface fluid‐structure by fluid‐structure interaction element.Findings – Results obtained show the potentialities of the proposed method to solve a much larger class of wave problems in mid‐ and high‐frequency ranges.Originality/value – The plane wave based method has previously been applied successfully to finite element and boundary element models for the Helmholtz equation and elastodynamic problems. This paper describes the extension of this method to the vibro‐acoustic problem.