Ali Akrout

VIBRATORY BEHAVIOR OF A DOUBLE PANEL SYSTEM BY THE OPERATIONAL MODAL ANALYSIS

The present study tackles the vibratory behavior of a double panel system by operational modal analysis (OMA) using one of the major techniques of blind source separation (BSS), which is the independent component analysis (ICA). For this purpose, the OMA method and the ICA concept are presented and exploited in order to identify the eigenmodes of a double panel system. Then, results obtained by the OMA technique are presented and compared with those achieved by the modal recombination method. Since a good argument is observed, this approach can be used in conjunction with experimental works.

One stage spur gear transmission crankcase diagnosis using the independent components method

The preventive diagnosis of mechanical systems presents a promising tool for increasing the production because it allows the industry to save time and money. In fact, the conventional diagnosis process is based on the FRF method which can be used to determine the inside defects frequencies of the system. Hence, this paper presents a new and a useful idea based on the blind source separation (BSS) which allow determining the wave form and the excitation frequency of internal defects present in a given mechanism by using only the structural vibratory response of the system. Numerical example of a one stage spur gear transmission crankcase including a spur gear pairs, shafts, rolling element bearings and a casing composed by three rigid plates and one flexible plate is presented and analysed in this paper. The separation results show a good agreement between original and estimated sources. This demonstrates the usefulness of the proposed method in the diagnosis process.

ESTIMATION OF DYNAMIC SYSTEM'S EXCITATION FORCES BY THE INDEPENDENT COMPONENT ANALYSIS

This paper deals with a numerical investigation for the estimation of dynamic systems excitation sources using the independent component analysis (ICA). In fact, the ICA concept is an important technique of the blind source separation (BSS) method. In this case, only the dynamic responses of a given mechanical system are supposed to be known. Thus, the main difficulty of such problem resides in the existence of any information about the excitation forces. For this purpose, the ICA concept, which consists on optimizing a fourth-order statistical criterion, can be highlighted. Hence, a numerical procedure based on the signal sources independency in the ICA concept is developed. In this work, the analytical or the finite element (FE) dynamic responses are calculated and exploited in order to identify the excitation forces applied on discrete (mass-spring) and continuous (beam) systems. Then, estimated results obtained by the ICA concept are presented and compared to those achieved analytically or by the FE and the modal recombination methods. Since a good agreement is obtained, this approach can be used when the vibratory responses of a dynamic system are obtained through sensors measurements.

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.