Liste des documents
Experimental investigation of notch effect and ply number on mechanicalbehavior of interply hybrid laminates (glass/carbon/epoxy)
The great advantages of hybrid composite materials reside in the synergistic effect of their constituent materialsand that make them very attractive for advanced applications. Nevertheless, the interactive effect of the intrinsicproperties of each element further complicates understanding of their behavior. In this study, an experimentalanalysis of the mechanical behavior of interply hybrid laminates (glass/carbon/epoxy) and the estimation of thehybridization effect with respect to mono-reinforced laminates were carried out. It has been found that theincorporation of 25% carbon fibers in the glass/epoxy laminates contributes significantly to improving theirtensile mechanical properties but they degrade as the number of glass plies increase. In addition, investigationswere carried out on the sensitivity of these materials to geometric imperfections. To this end, the influence of acircular notch has been highlighted. From the results obtained, it was found that the greatest loss of properties isrecorded for the hybrid materials; however, they remain the most resistant. Voir les détails
Mots clés : Hybrid composite materials, laminates, notch, mechanical properties
Rolling Bearing Fault Diagnosis Based on an Improved Denoising Method Using the Complete Ensemble Empirical Mode Decomposition and the Optimized Thresholding Operation
Vibration signals are widely used in monitoring and diagnosing of rolling bearing faults. These signals are usually noisy and masked by other sources, which may therefore result in loss of information about the faults. This paper proposes an improved denoising method in order to enhance the sensitivity of kurtosis and the envelope spectrum for early detection of rolling bearing faults. The proposed method is based on a complete ensemble empirical mode decomposition with an adaptive noise (CEEMDAN) associated with an optimized thresholding operation. First, the CEEMDAN is applied to the vibration signals to obtain a series of functions called the intrinsic mode functions (IMFs). Second, an approach based on the energy content of each mode and the white noise characteristic is proposed to determine the trip point in order to select the relevant modes. By comparing the average energy of all the unselected IMFs with the energy of each selected IMFs, the singular IMFs are selected. Third, an optimized thresholding operation is applied to the singular IMFs. Finally, the kurtosis and the envelope spectrum are used to test the effectiveness of the proposed method. Different experimental data of the Case Western Reserve University Bearing Data Center are used to validate the effectiveness of the proposed method. The obtained experimental results illustrate well the merits of the proposed method for the diagnosis and detection of rolling bearing faults compared to those of the conventional method. Voir les détails
Mots clés : Vibration analysis, bearing Fault diagnosis, CEEMDAN, Denoising, thresholding operation, envelope, Kurtosis
Enhancement of rolling bearing fault diagnosis based on improvement of empirical mode decomposition denoising method
Signal processing is a widely used tool in the field of monitoring and diagnosis of rolling bearing faults. The vibration signals of rolling bearing contain important information which can be used for early detection and diagnosis of faults. These signals are usually noisy and masked by other sources and therefore the information about the fault can be lost. In this work, we propose an enhancement of rolling bearing fault diagnosis based on the improvement of empirical mode decomposition (EMD) denoising method. This method is made to extract the useful fault signal in order to use the detection indicators such as the kurtosis and the envelope spectrum. Firstly, EMD is applied to the vibration signals to obtain a series of functions called the intrinsic mode functions (IMFs). Secondly, we present an approach based on the energy content of each mode to determine the trip point which allows selecting the relevant modes. The singular selected IMFs are determined by comparing the average energy of all the unselected IMFs with the energy of each selected IMFs; then, an optimized thresholding operation is performed to denoise these IMFs. Finally, the kurtosis and spectral envelope analysis were investigated for early detection and localization of the fault position. Different experimental data are used to validate the effectiveness of the proposed method. The obtained results showed that the proposed method is more efficient and more sensitive to the early detection and diagnosis of rolling bearing faults than the conventional denoising method. Voir les détails
Mots clés : Vibration analysis, bearing Fault diagnosis, EMD, threshold Denoising, energy, Relevant mode selection, envelope, Kurtosis
Rolling bearing fault diagnosis based on improved complete ensemble empirical mode of decomposition with adaptive noise combined with minimum entropy-deconvolution
The vibration signals provide useful information about the state of rolling bearing and the diagnosis of the faults requires an accurate analysis of these signals. Several methods have been developed for diagnosing rolling bearing faults by vibration signal analysis. In this paper, we present an improvement of the technique Complete Ensemble Empirical Mode Decomposition with Adaptive Noise (CEEMDAN), this technique is combined with the Minimum Entropy Deconvolution (MED) and the correlation coefficient to diagnose defects. First, the vibration signal was decomposed by the improved CEEMDAN decomposition into several oscillatory modes called Intrinsic Mode Function (IMF). After calculation of the correlation coefficients between the original signal and their IMFs, the modes with higher coefficients are selected as the relevant modes. Secondly, the MED technique is applied to the selected modes in order to improve the sensitivity of the scalar and frequency indicators of faults detection. Finally, kurtosis and envelope analysis are used to detect and locate the defect position. The simulation is carried out using the Case Western University data base and the results obtained show that the proposed method provides very good results for the early detection and diagnosis of defects and can efficiently extract the defective characteristics of the rolling bearing. Voir les détails
Mots clés : vibration signal, rolling bearing fault, complementary ensemble empirical mode decomposition, coefficient correlation, minimum entropy deconvolution, Kurtosis, Envelope analysis
Aeroelastic analysis of the air foil bearings in steady state
In recent decades, turbomachinery has known a special development with the aim of lightening rotating components of machinery and preserving the environment all for improving operating performances. The key elements in the turbomachinery are the air foil bearings that support rotors rotating at high speeds. In this paper, we are interested in the aero-elastic study of air foil bearing in stationary régime. The deformable structure contains a corrugated foils (bumps) fixed on a top-foil rigid which forms with rotor and air an elasto-aerodynamic contact. Numerical modeling was developed based on the Reynolds equation and an elastic deformation model of the bump depending on aerodynamic pressure, bump geometry and its mechanical proprieties. This problem non-linear is resolved using finite difference discretization and Newton-Raphson method. Finally, the calculations show the pressure distribution and field of film thickness as well as other fluid-structure interaction characteristics due to the functional conditions. Voir les détails
Mots clés : air bearing, aero-elastic, foil structure, film thickness, charge capacity
Robust Fuzzy On–Off Synthesis Controller for Maximum Power Point Tracking of Wind Energy Conversion
Due to the major discrepancy between the exigent demands regarding the electrical energy quality and the irregular nature of the wind, which is characterized by random and instantaneous speed variations, it is vital to determine the optimal operating point that maximizes the efficiency of the obtained electrical energy in the grid from wing generators. The present paper addressed the above-mentioned problem by introducing a fuzzy logic control system in the standard on–off control strategy. The purpose is to maximize the power point tracking of wind energy and to reduce the mechanical loads in which variable wind speed is considered. This idea has the ability to drive the conversion system to its optimal operating point, thereby solving the switching component problem (also referred to as the chattering problem) of the standard on–off control strategy. To examine the validity of the proposed idea, the obtained results are compared with those given by the standard on–off control strategy wherein our method can ensure a better dynamic behavior of the wind energy conversion system. Voir les détails
Mots clés : Wind Energy Conversion System (WECS), Maximum Power Point Tracking (MPPT), Standard and fuzzy on–off controller, Induction generator (IG)
Improved Sliding Mode Controller for Maximum Power Point Tracking of WECS.
Due to the major discrepancy between the exigent demands regarding the electrical energy quality and the irregular characters of the wind, which is characterized by a random and instantaneous speed variation, it is suitable to determine the optimal operating point that maximizes as much as possible the efficiency of the obtained electrical energy in the grid. The present paper deals with the above-mentioned problem by introducing an additional low-frequency component in the standard sliding mode control strategy. The purpose is to maximize the power point tracking of wind energy and to reduce the mechanical loads where the variable wind speed is considered. This idea has the ability to drive the conversion system to the optimal operating point by which the switched component problem, commonly called also the chattering problem of the standard sliding mod control strategy that should be solved. To examine the validity of the proposed idea, the obtained results are compared with those given by the standard sliding mode control strategy wherein our method can ensure a better dynamic behavior of the wind energy conversion system. Voir les détails
Mots clés : Maximum Power Point Tracking MPTT, Standard and Improved Sliding mode controller, Induction Generator IG
Friction stir welding process improvement through coupling an optimizationprocedure and three-dimensional transient heat transfer numerical analysis
The present study deals with the improvement of the Friction Stir Welding process, through the prediction of theoptimal operating conditions, necessary for welding typical Aluminum-Lithium alloy material AA2195-T8. Anoptimization strategy coupled with 3D transient heat transfer computation were used to improve the FSWprocess parameters such as welding velocity, tool rotation velocity, tool diameter and applied force. The optimizationprocedure is based on three criteria: the control of the maximum temperature during FSW; the minimizationof the Heat Affected Zone (HAZ) length and finally the reduction of the total welding energy. Theobtained optimal parameters have given an ideal welding temperature in the workpiece, thereby ensuring goodwelding quality, gain in energy consumption and decrease both the welding time and the HAZ length. Voir les détails
Mots clés : Friction Stir Welding (FSW), Heat transfer, finite volume method, SQP algorithm optimization method
Particle Swarm Optimization Based Maximum Power Point Tracking Algorithm for Photovoltaic Energy Conversion System
In order to extract the maximum power from PV system, the maximum power point tracking (MPPT) method is one of the most popular and widely used and it has always been applied in photovoltaic energy conversion system. However, this method exhibits fluctuations among the maximum power point (MPP) due to the nature of unpredicted and changes of the environmental parameters. Therefore, it is significant to include an intelligent controller that can track the maximum peak regardless of parameters variations such as: irradiation and temperature. This paper describes the design and development of particle swarm optimization (PSO) based maximum power point tracking (MPPT) algorithm for photovoltaic energy conversion system. The proposed MPPT is simple, flexible, accurate and efficient in maximum photovoltaic power tracking. In this work, MATLAB/Simulink simulation package is used to simulate the performance of the proposed MPPT algorithm. The performance of the proposed PSO algorithm is evaluated by comparing it with the conventional P&O method in terms of tracking speed and accuracy. The simulation results demonstrate that the tracking capability of the PSO algorithm is more efficient, comparing to the traditional one, particularly under parameters variation conditions. Voir les détails
Mots clés : Photovoltaic systems, Maximum Power Point Tracking (MPPT), Particle Swarm Optimization (PSO), perturb and observe (P&O)
Experimental and numerical analysis of mode?I interlaminar fractureof composite pipes
A common industrial production process for composites is filament winding, widely used for the production of axially symmetriccomponents. In these composite components, delamination is a predominant failure mechanism. The current workfocuses on investigating experimentally the effect of the initial crack and fiber bridging length on the mode-I delaminationresistance curve (R-curve) behavior of various double cantilever beam (DCB) specimens. For this purpose, the magnitudesof initiation and propagation fracture toughness (GIC-init and GIC-prop) and the compliance C are calculated. DCB specimenswith a stacking sequence of [± 50]6 and various initial crack lengths of a0 = 33, 37, 59 and 70 mm are manufactured from areal composite pipe using filament winding process. In order to evaluate the critical energy release rate in mode-I, variousfracture tests are conducted on these specimens. The greatest bridging zone length dues to good penetration of two adjacentlayers of the delamination interface. Moreover, the results indicate that the fiber bridging length has a significant effect onthe GIC and the largest value of fiber bridging causes a large fracture toughness value. Finally, numerical simulations areperformed using finite element (FE) method and GIC-init measurements obtained experimentally are compared to the numericalfindings. The numerical displacements and GIC-init, calculated from the numerical displacements, are found to be in goodagreement compared to the experimental results. Voir les détails
Mots clés : Filament wound composite, Critical energy release rate, Propagation energy release rate, DCB specimen, Fiber bridging