Mnaouar Chouchane

Internal combustion engine valve clearance fault classification using multivariate analysis of variance and discriminant analysis

This paper investigates the classification of a valve clearance fault in an internal combustion diesel engine using vibration time domain features extracted from signal segments measured at several points on the engine bloc. Signals containing a large number of engine cycles are used to obtain a number of observations of each feature. The set of features is thus considered a set of variables. A stepwise variable selection algorithm based on univariate and multivariate analysis of variance is then used to sort the variables according to their diagnostic ability. The algorithm is also used to construct sets of variables of increasing size used to improve fault classification. Four commonly used supervised classifiers are trained and then tested, giving roughly the same percentage of correct classification. The tested classifiers confirmed that the use of more variables selected by the stepwise variable selection algorithm increases the percentage of correct classification.

Nonlinear stability analysis of a flexible rotor-bearing system by numerical continuation

A rotor supported by hydrodynamic bearings may undergo unstable motion and may exhibit several nonlinear phenomena in the vicinity of the critical stability speed. This paper presents a stability analysis of a flexible rotor supported by journal bearings using a nonlinear dynamic model and a short bearing approximation. Numerical continuation is applied to determine the boundaries of stability and the bifurcations of the limit cycles. Nonlinear phenomena such as jumping motion and bi-stability domain are predicted. An extended stability chart has also been determined including the domains of stable oscillatory motion. The investigation also includes the effect of rotor flexibility and bearing characteristics on the stability boundaries and on the safe operating speed range. For a selected range of bearing parameters, two Hopf bifurcation regions are found for high rotor stiffness, three regions for low stiffness and four bifurcation regions in transition between high and low stiffness. It has also been found that the stable operating speed range decreases with rotor flexibility and bearing parameter.

Feature Extraction Using S-Transform and 2DNMF for Diesel Engine Faults Classification

This paper investigates the supervised classification of a distribution fault of an internal combustion Diesel engine using vibration measurement. For 3 inlet valve clearance values, the standard S-transform is used to produce a time-frequency representations of the vibration signals. The large size of time frequency images is then reduced to a set of lower sizes using two-dimensional non-negative matrix factorization . A multilayers perceptron neural network is then trained and applied to classify the test data. The optimal size of feature set is computed, for the best classification and the lowest elapsed CPU time at the training and testing classification phases. It has been found that the performance of the multilayers perceptron neural network classifier is, generally, enhanced and the CPU time is minimized for a reduced feature set size.

Prediction of the nonlinear hysteresis loop for fluid-film bearings by numerical continuation

A nonlinear dynamic model of a short journal bearing is used to predict the steady-state motion of the journal and its successive bifurcations in the neighbourhood of the stability critical speed. Numerical continuation is applied to determine the branch of equilibrium point and its bifurcation into stable or unstable limit cycles. It has been found that the unstable limit cycles undergo a single limit point bifurcation whereas the stable limit cycles undergo two successive limit point bifurcations. Thus, the bi-stability domain, the potential jumping from small to large motion and the hysteresis loop motion are predicted.

Injection Fault Detection of a Diesel Engine by Vibration Analysis

In this paper, the potential of vibration analysis for early detection of fuel injection faults in an internal combustion diesel engine, having six cylinders in line, has been investigated. The main sources of vibration of a diesel engine, as well as the mechanism of propagation of these sources to the engine structure have been presented. Using the tarring screw of the injector, the injection pressure in one of the cylinders has been gradually reduced from its nominal value, respectively, by 10 and 50%. Two signals are acquired using an analog-to-digital dynamic acquisition card. The first is the TDC signal in cylinder 1 measured using an inductive sensor. The second is the vibration signal which has been measured, on the cylinder head of the engine using a piezoelectric accelerometer. The vibration signal has been analyzed in the crank-angle domain, the frequency domain using the Fast Fourier Transformation, and in the angle-frequency domain using the Short Fourier Transform. The analysis of the injection fault signals in the three domains showed that in the crank-angle domain, a visual analysis gives limited information; in the frequency domain, the identification of the cylinder with the faulty injector is not possible; and in the angle-frequency domain, the detection of the injection fault and the identification of the faulty cylinder are possible and not complicated.

Analytical Modeling and Analysis of a Bimorph Piezoelectric Energy Harvester

Energy harvesting from piezoelectric devices is a promising technology which is used to convert ambient energy extracted from the environment into electrical energy in the aim of supplying power for small electronic devices. Unimorph and bimorph cantilever beams have been used as basic piezoelectric energy harvesters. In this paper, a bimorph piezoelectric cantilever beam under base excitation is considered. An analytical model based on the Euler–Bernoulli beam assumption has been used to estimate the generated power. Series and parallel connections of the two piezoelectric layers are considered. To make an objective comparison of the generated power by several harvesters, the first natural frequency of the beam has been fixed by increasing simultaneously the beam thickness and the tip mass. The calculated frequency responses associated to the bimorph cantilever beam without tip mass have been validated based on the previous publications. It has been found that an increase of the tip mass and the beam thickness leads to a higher power generation. More power is produced in the case of a series connection.

Active Vibration Control of a Rotor Bearing System Using Piezoelectric Patch Actuators and an LQR Controller

Active vibration control (AVC) is used to overcome the limits of passive control. This chapter presents a design of an active vibration controller for a rotor bearing system using active piezoelectric patch actuators bonded on the surface of the rotor shaft. These devices are used to compensate the unbalance forces by applying control moments. The finite element method is used to construct a discrete rotor bearing system model. The design uses proximity probes to measure lateral vibration of the rotor bearing system. A Linear quadratic regulator (LQR) controller based on a full state feedback is designed to provide the adequate activation power to the piezoelectric patches. Rotordynamic analysis is carried out to obtain the Campbell diagram, the natural frequencies, and the critical speeds of the rotor bearing system. The designed active vibration controller reduced significantly rotor lateral vibration at constant rotating speed. A higher reduction rate has been obtained at the first critical speed.

Stability Analysis of an Unbalanced Journal Bearing with Nonlinear Hydrodynamic Forces

The research reported in this paper is based on a nonlinear two degree of freedom model of an unbalanced rigid rotor bearing system. The nonlinearity is introduced into the model through closed form expressions of the short bearing hydrodynamic forces. The model in its nondimensional form depends on three nondimensional parameters: the bearing modulus, the rotor rotating speed and unbalance. For the balanced system, numerical continuation is applied to predict the branch of equilibrium positions of the journal and its bifurcation into stable or unstable limit cycles at the linear stability threshold speed. For the unbalanced system, however, numerical integration is used to find the bifurcation diagrams using the rotor speed as a bifurcation parameter. Poincare sections are used to characterize the journal motion. The investigation is carried out for three bearing parameters covering a large domain of rotor bearing conditions. The effect of unbalance on the journal motion is investigated in each case. Compared to the balanced system, it has been found that unbalance may introduce, at different speed ranges, periodic oscillations at multiple periods of rotation, quasi-periodic oscillations and chaotic motion. The effect of unbalance on journal motion is highlighted and closely related to the bifurcation diagram of the balanced rotor.

Application of the Numerical Continuation Method in the Prediction of Nonlinear Behavior of Journal Bearings

Numerical continuation as a tool for analyzing nonlinear differential equations has proven to be very useful especially for the interactive numerical investigation. This paper examines the nonlinear behavior of a rigid rotor symmetrically supported by two identical short journal bearings. Within this contribution, bifurcation analyses and nonlinear phenomena of this rotor bearing system are investigated using MATCONT which is a numerical continuation package for the study of dynamical systems and their bifurcations.

Numerical Continuation of Equilibrium Point and Limit Cycles of a Rigid Rotor Supported by Floating Ring Bearings

Today, floating ring bearings are commonly used in rotors of high-speed turbochargers because of their low cost and their vibration suppressing capability. Nevertheless, and similar to conventional hydrodynamic bearings, floating ring bearings may exhibit self-excited vibrations and become unstable above the instability threshold speed. In this paper, a nonlinear dynamic model of a perfectly balanced rigid rotor supported by two identical floating ring bearings is used to determine the rotor vibration behavior. The hydrodynamic forces are modeled by applying the short bearing theory and the half Sommerfeld conditions for both fluid films. Numerical continuation is applied to determine stable or unstable limit cycles bifurcating from the equilibrium point at the Hopf bifurcation. This paper shows that the stable limit cycles undergo a single limit point bifurcation however no bifurcation is predicted for the unstable limit cycles.