Tahar Fakhfakh

Acoustic analysis of hydrodynamic and elasto-hydrodynamic oil lubricated journal bearings

The purpose of the present paper is to investigate the effect of elastic deformation of bearing liner on the acoustic behavior of oil lubricated journal bearings. Analysis is performed for hydrodynamic(HD) and elasto-hydrodynamic (EHD) lubrications. Dynamic behavior and acoustical properties are investigated through an analysis of pressure fluctuation calculated from the Reynolds equation governing the flow in the clearance space of the journal bearing. This is solved numerically using the finite difference method with the successive over relaxation technique. In elasto-hydrodynamic lubrication, the finite element method with in iteration scheme is adopted to solve both Reynolds equation and the three-dimensional elasticity equation representing the displacement field in the bearing shell. The results show that the sound pressure level of the bearing is markedly influenced by the flexibility of the bearing liner, the viscosity of lubricant and the load applied to journal. HD analysis shows that the journal centre’s orbit, from a disturbed position, converges to the static equilibrium position faster than EHD lubrication. The results of the present paper could aid in the design of low-noise rotor-bearing systems supported by oil lubricated journal bearings.

Experimental investigation of damage detection in plate-like structure using combined energetic approaches

In this paper, an experimental investigation of damage detection in plate-like structure using energetics approaches is presented. Two energetics approaches are developed to localize the damage in structure at low-, medium-, and high-frequency range. The first one is the inverse simplified energy method, which is used for the identification of the excitation source and the detection of damage in medium and high frequencies. The second one is the curvature method, which is used for the damage detection in the low and medium frequencies. The main novelty of this paper is to combine these energetics approaches in order to localize the damage in all frequency bands. Experimental examples with different characteristics of plate were performed for the validation purpose. Results show that the presented methods can detect precisely the defects location in plate-like structures.

Parametric Study on the Efficiency of an Inverse Energetic Approach to Identify the Boundary Acoustic Sources

This paper presents a parametric study of the microphones distribution effect in the identification of the boundary acoustic sources acting in the acoustic cavities through the knowledge of the acoustic energy densities measurement. An energetic approach, also called the simplified energy method (MES) was developed to predict the energy densities distribution for the acoustic applications. MES can also be applied to structures to determine energy densities. This energy method can solve inverse problems in order to localize and quantify the structural and the acoustic boundary sources at medium and high frequency ranges, thanks the inverse formulation of this energetic approach (IMES). The main novelty of this paper is to study the performances of this inverse energetic approach in the quantification and localization of the boundary acoustic sources acting in the acoustic cavities. Numerical investigation concerning 3D acoustic cavity was performed to test the validity of the presented technique using different number of acoustic sources and distance between the microphones repartition and the cavity walls. The numerical results show that the inverse simplified energy method (IMES) has an excellent performance in identifying and detecting the boundary acoustic sources at medium and high frequency ranges from the knowledge of the acoustic energy densities measurement.