Liste des documents
PSO Optimization with Autoregressive Modeling and Support Vector Machines for Bearing Fault Diagnosis
As an effective tool in pattern recognition and machine learning, support vector machine (SVM) has been adopted abroad. In developing a successful SVM classifier, extracting feature is very important. This paper proposes the application of Autoregressive Modeling to SVM for feature extraction. To improve the classification accuracy for bearing fault prediction, particle swarm optimization (PSO) is employed to simultaneously optimize the SVM kernel function parameter and the penalty parameter. The results have shown feasibility and effectiveness of the proposed approach Voir les détails
Mots clés : machine learning, Support vector machine, SVM, Autoregressive Modeling, feature extraction
La Méthode Descente De Gradient Pour La ReconstructionTomographique Des Images 2D A Rayon-X
Cet article concerne la reconstruction tomographique 2D d’images à rayon-x. Le problème dereconstruction tomographique est un problème inverse c.-à-d. Estimer l’objet à partir de ses projections. Dans cetravail, nous avons établi une étude détaillée sur la méthode de descente de gradient, qui s’inscrit dans le cadredes méthodes itératives de reconstruction tomographique. Ces méthodes consistent à exprimer le problèmedirectement sous une forme discrète. Grâce aux résultats de simulation, nous avons montré que l’algorithme degradient offre une bonne qualité de reconstruction en termes des critères d’évaluation en plus la qualité visuelledes images reconstruites. Voir les détails
Mots clés : Reconstruction Tomographique, problème inverse, projections, Descente de Gradient
Robustness of Radon transform to white additive noise: General case study
A detailed study is presented on the robustness of the Radon transform to additive white noise for the general case of a rectangular grey-level image. Voir les détails
Mots clés : radon transform, white additive noise
NONDESTRUCTIVE EVALUATION OF THE CARBON CONTENT IN STEEL
The aim of this work is to propose an experimental method to evaluate the steel carbon content by ultrasound. The sample is immersed in a water tank in order to analyze it under various incidences of sound waves. Longitudinal wave velocities are measured by immersion by using a 5-MHz frequency probe. Transverse wave velocities are measured in a contact mode by using a 4-MHz transverse wave transducer. The attenuation coefficients of ultrasonic longitudinal and transverse waves are deduced from three successive basic echoes through the sample. The effects of some heat treatments on ultrasonic parameters are also studied. The measurement of ultrasonic parameters in steel offers an interesting possibility of tracing the carbon content and, at the same time, provides information on the steel structure and its elasticity Voir les détails
Mots clés : carbon content, steel, ultrasonic waves.
CHARACTERIZATION OF THE CRITICALLY REFRACTED LONGITUDINAL (LCR) WAVES AND THEIR USE IN DEFECT DETECTION
The critically refracted longitudinal (LCR) waves are used in various domains of nondestructive evaluation, especially for residual stress measurements. However, few works have characterized the associated ultrasonic beam. In this article, the characterization of the LCR ultrasonic beam, both numerically and experimentally, is first clarified in order to provide some answers to questions that arise about its behavior in elastic solids. The aim of the second part of this work is to investigate the use of the LCR waves for the detection of surface defects of different sizes in aluminum. For that, the effect of defects at fixed depth (5 mm) with various diameters (2, 4, 6, and 8 mm) and fixed diameter (8 mm) with various depths (5, 7, and 10 mm) in an aluminum sample have been investigated at frequencies around 1 MHz. It has been experimentally found that the amplitude of the (LCR) wave decreases and its frequency spectrum changes with a given defect. The rate of the decrease of the amplitude and the change in the spectrum is related to the increase of the defect depth. The study shows that the effect on the propagating of the LCR waves is larger as the defect depth increases.The critically refracted longitudinal (LCR) waves are used in various domains of nondestructive evaluation, especially for residual stress measurements. However, few works have characterized the associated ultrasonic beam. In this article, the characterization of the LCR ultrasonic beam, both numerically and experimentally, is first clarified in order to provide some answers to questions that arise about its behavior in elastic solids. The aim of the second part of this work is to investigate the use of the LCR waves for the detection of surface defects of different sizes in aluminum. For that, the effect of defects at fixed depth (5 mm) with various diameters (2, 4, 6, and 8 mm) and fixed diameter (8 mm) with various depths (5, 7, and 10 mm) in an aluminum sample have been investigated at frequencies around 1 MHz. It has been experimentally found that the amplitude of the (LCR) wave decreases and its frequency spectrum changes with a given defect. The rate of the decrease of the amplitude and the change in the spectrum is related to the increase of the defect depth. The study shows that the effect on the propagating of the LCR waves is larger as the defect depth increases. Voir les détails
Mots clés : critical angle, critically refracted longitudinal (LCR) wave, main lobe, NDE, NDT, surface defect
Champ thermique sous l'effet de la réaction chimique d'une réforme de la pile à combustible à oxyde solide SOFC DIR-interne direct
Les effets directs de reformage interne dans une pile à combustible à oxyde solide (SOFC) sur les champs thermiques sont étudiés par modélisation mathématique. Cette étude présente les champs thermiques d'une pile à combustible standard (Ni-YSZ / YSZ / LSM) anode en charge. Cette étude est également faite dans le plan perpendiculaire à l'écoulement des gaz. La pile à combustible est alimenté par de l'air et de carburant, CH4, H2, CO2, CO et H2O où la naissance du phénomène de la réforme (DIR-SOFC) interne direct. Il est basé sur la réforme de réactions chimiques, de la vapeur et de réaction de reformage réaction du gaz à l'eau. Le but principal de ce travail est la visualisation des champs de température sous l'influence des réactions chimiques mondiales et la confirmation du comportement thermique de cette réaction chimique. Les champs thermiques sont obtenus par un programme informatique (Fortran). Voir les détails
Mots clés : SOFC, Direct internal reforming, Global chemical reactions, Thermal fields
Dynamic Response of a Stand Alone DC Side Wind Energy Conversion System with Battery Energy Storage to a Wind Gust.
The study concerns particularly the DC side of the wind system, the continuity of the AC one being already studied in. Then,this work elaborates an analysis of the DC components, particularly the system conversion and storage of the wind system conversion. Indeed, the battery is a storage buffer essential in our case for isolated network. We emphasize its importance by evaluating its various features. The AC study concerned the analysis and simulation of a low speed Permanent Magnet Synchronous Generator (PMSG) driven by a vertical wind turbine through a Pulse-Width Modulation (PWM) voltage inverter. Renewable resources are in constant fluctuation. Therefore, in order to maximize the efficiency of the renewable energy system it is necessary to track the maximum power point of the input source. In this system, the maximizing is assured while considering the optimal power curve as load characteristic, with the knowledge of the turbine characteristic Cp (λ). The study was accomplished on MATLAB/Simulink and Script platforms. Voir les détails
Mots clés : Permanent Magnet Synchronous generator, mdel, DC side, Storage, Small Wind Turbine
PV Cell Temperature/ PV Power Output Relationships Homer Methodology Calculation
Because of the intermittent solar irradiation whichhighly influences the resulting energy production, the majoraspects in the design of PV power generation systems are thereliable power supply of the consumer under varyingatmospheric conditions and the corresponding total system cost.Thus it is necessary to select the number of PV modules andbatteries, and their installation details such as the power will beuninterruptedly supplied to the electrical load, andsimultaneously the minimum system cost would be achieved.But it’s especially so judicious to take into account the wholesystem parameters such as cell temperature, a task ensured byseveral software tools as Homer from the NREL Laboratory.As known, meteorological parameters especially the arraytemperature, do not remain constant the whole day long, butchange considerably. Then, it is worth investigating the influenceof the daily average temperature variation on the predictedperformances of the optimized system.It’s so important to seize how such software proceeds to get around any result calculation and a possible problem at the same time.So, the goal achieved through this study is to investigate theinfluence of the cell temperature and head changing effects onthe system performances. So an approach by a mathematical formalism is then indispensable. Voir les détails
Mots clés : solar layer, PV cell temperature, PV power output, mathematical formulation, calculation, Homer.
MPPT Control of a Small PV Generation System under Diverse Weather Conditions
The power induced in the photovoltaic modules is influenced by the intensity of solar cell irradiation, temperature of solar cells and moreover by the load. Therefore, to maximize the efficiency of the renewable energy system, it is necessary to track the maximum power point of the input source. In this work, we tie to present the constituent of a weak power PV chain dedicated to the storage on battery. The battery bank is connected to the DC network via a DC/DC boost converter, called the storage converter, used for controlling the network.Indeed, the battery is only imperative buffer storage in this case. The PV units are connected to the DC network via its own DC/DC converter, called PV converter, to ensure the required power flow. The purpose of the proposed model is the simulation of the complete system behavior from the electric and energy point of view. A maximum power point tracker (MPPT) scheme is applied through the boost converter to improve the energy conversion efficiency. Fuzzy algorithm based on linguistic rules describing the operator’s control strategy is applied to control the step-up converter for MPPT. On the other hand, Fuzzy logic control based on coarse and fine mode is incorporated in order to reduce not only the time required to track the maximum power point but also power fluctuation. A confrontation with a P and O method performed. Another fuzzy battery-charge controller is also applied. Simulation results show that the proposed fuzzy controller exhibits a better performance than the controller based upon the P and O method. Voir les détails
Mots clés : Photovoltaic, simulation, MPPT; DC-DC converter, Fuzzy controller
AC Corrosion Induced by High Voltage Power Line on Cathodically Protected Pipeline
The implications of the influence of alternating currents on buried pipelines are of great concern to all pipeline owners in world. The relevance of the interference is always increasing for operational personnel and for the protection of buried metallic structures from corrosion. The paper studies the electromagnetic interference problem between an existing high voltage power line and a newly designed underground pipeline cathodically protected. Induced voltages and currents are evaluated for steady state operating conditions of the power line. It is found that on pipelines suffering from A.C. interference traditional pipe-to-soil potential measurements do not guarantee efficient cathodic protection against corrosion. A specific approach to assess the effectiveness of cathodic protection should be adopted. Voir les détails
Mots clés : Induced Voltages, Electric Power Transmission Lines, pipeline, AC Corrosion, cathodic protection, soil resistivity, AC interference