Fakher Chaari

Condition Monitoring of Machinery in Non-Stationary Operations

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Analytical investigation on the effect of gear teeth faults on the dynamic response of a planetary gear set

Due to excessive service load, inappropriate operating conditions or simply end of life fatigue, damage can occur in gears. When a fault, either distributed or localised, is incurred by gears, the stiffness and consequently vibration characteristics of the damaged tooth will change. In this work an analytical formulation of the time varying geannesh stiffness was derived. Two local tooth faults are modelled: tooth pitting and crack. Their influence on the gearmesh stiffness is analysed. A planetary gear set is presented as a case study to implement the tooth fault modelling. The response shows amplitude modulation resulting in high activity of sidebands.

Advances in Condition Monitoring of Machinery in Non-stationary Operations

Part 1. Signal Processing -- Part 2. Data Mining -- Part 3. Condition Monitoring Techniques.

Influence of the non-linear Hertzian stiffness on the dynamics of a spur gear system under transient regime and tooth defects

The non-linear dynamic behaviour of a single stage spur gear reducer is investigated in transient regime. The gear pair excitation is the result of motor torque variation and the fluctuation of meshing stiffness. The non-linearity is induced by the Hertzian contact force between teeth. Tooth crack and breakage are also modelled. The equations of motion of the transmission are solved iteratively using implicit type numerical integration technique Newmark-β with Newton-Raphson method. The numerical simulation results are analysed in time and frequencies fields. These results confirm the influence of the Hertzian stiffness on the dynamic behaviour of the system especially in the transient regime. Tooth defects contribute to the aggravation of the vibration levels.

Application of the Operational Modal Analysis Using the Independent Component Analysis for a Quarter Car Vehicle Model

This paper investigates the dynamic behavior of a quarter car vehicle system using the Operational Modal Analysis (OMA) . This method is applied using one of the major techniques of the Blind Source Separation (BSS) which is the Independent Component Analysis (ICA) . Compared to the classical modal analysis, the Operational Modal Analysis presents the advantage that it is only based on the vibratory responses of the structure in order to identify its modal parameters. To validate this approach in the case of a quarter car vehicle model , the estimated results obtained by the OMA methods are presented and compared with those obtained by the modal recombination method.

Electrical Modeling for Faults Detection Based on Motor Current Signal Analysis and Angular Approach

Recently, Motor Current Signal Analysis (MCSA) appears as an effective tool for fault diagnosis in rotating machinery and proved to be sufficient for detecting localized mechanical faults in electromechanical systems operating in stationary conditions. In the case of non-stationary conditions, speed variations must be distinguished from angular velocity perturbation caused by the presence of a defect. In the framework of diagnosis of rotating machinery, angular approaches are well suited to make monitoring resistive to speed disturbances. This paper proposes a reformulation of the MCSA associated with angular approach in modeling multiphysic behavior. The resulting model described in this paper can be used to investigate of the influence of the Instantaneous Angular Speed (IAS) variations on the electrical responses of the whole rotating system.

ASYMPTOTIC NUMERICAL METHOD FOR THE DYNAMIC STUDY OF NONLINEAR VIBRATION ABSORBERS

Vibrations are usually undesired phenomena as they may cause discomfort, disturbance, damage, and sometimes destruction of machines and structures. It must be reduced or controlled or eliminated. One of the most common methods of vibration control is the use of the dynamic absorber. The paper is interested in the study of a nonlinear two degrees of freedom (DOF) model. To solve nonlinear equation of motion a high order implicit algorithm is proposed. It is based on the introduction of a homotopy, an implicit scheme of Newmark and the use of techniques of Asymptotic Numerical method (ANM). We propose also a regularization of the contact force to overcome the difficulty of the singularity in this model. A comparison will be presented between the results obtained by the proposed algorithm and those using the classical Newton–Raphson and Newmark time scheme.

Model Based Investigation on a Two Stages Gearbox Dynamics under Non-stationary Operations

Machinery in industry using gearboxes covers many applications. The efficiency of such transmission cannot be achieved without a special attention to their dynamic behavior. Meshing as internal excitation, variable loads as external excitation and the presence of errors are the main factors that affect the dynamic behavior. This paper will discuss through a model based approach the influence of all of the three factors with an application on a two stages spur gears transmission. The transmission is modeled with a time varying loading conditions, the corresponding evolution of meshing stiffness function is derived and a local damage is introduced. The dynamic response is simulated. The responses show correlation between amplitude/energy of signal and applied value of load. It means that traditional energy based diagnostic approach should be revised for non-stationary operations

Nonlinear modeling and simulation of spur gear with defected bearings

Purpose – The aim of this paper is to present a theoretical model to simulate the dynamic behavior of a spur gear, taking into account its ball bearings defects.Design/methodology/approach – The proposed model is based on the implicit Newmark‐β with Newton‐Raphson numerical integration technique in order to analyze the impact of the worn bearings on the non linear dynamic behavior of one stage spur gear transmission system.Findings – The dynamic behavior of spur gear is studied taking into account ball bearings defects thanks to the proposed model.Originality/value – A new numerical model is proposed to simulate the dynamic behavior of rotating spur gear system taking into account both waviness and backlash defects.

Effect of Load Shape in Cyclic Load Variation on Dynamic Behavior of Spur Gear System

Transmissions including spur gears are widely used in several industrial applications. They are characterized by high efficiency and capability to transmit high torques. A special attention should be made for transmissions running under varying loading conditions which have to be well monitored. The presence of this variability associated with defects that may occur in the transmission will complicate its condition monitoring. The first step to overcome this difficulty is to identify and characterize the dynamic response of the transmission in healthy conditions subjected to variable loading conditions. In this paper, a model based approach is presented in order investigate the influence of the loading shape on the vibration characteristics of the transmission. A dynamic model of a one stage spur gear transmission including a time varying loading conditions is developed. Two cases of loading conditions are considered. A parametric study is achieved and main conclusions are discussed.