Nombre total de résultats : 510
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Djamel BOUCHERMA (2017)
Thèse de doctorat

Dans ce travail, la résolution de l’équation d’état fractionnaire dmx(t)/dtm= Ax(t)+Be(t) , 0 < m< 1, représentant les systèmes linéaires fractionnaires d’ordre commensurable, pour tous les cas de figure des valeurs propres de la matrice d’état A et l’ordre de différentiation m a été proposé. Les expressions explicites des solutions homogènes et non homogènes de cette équation d’état fractionnaire ont été développées. Pour différentes valeurs propres de la matrice d’état A et l’ordre m, les solutions obtenues sont des combinaisons linéaires de fonctions fondamentales fractionnaires appropriées dont les transformées de Laplace sont des fonctions irrationnelles. Les approximations de ces fonctions irrationnelles par des fonctions rationnelles ont été obtenues pour que les solutions de l’équation d’état fractionnaire soient des combinaisons linéaires de fonctions exponentielles, cosinus, sinus, cosinus amorti et sinus amorti classiques. Des exemples illustratifs pour tous les cas de figure des valeurs propres de la matrice d’état A et l’ordre m ont été présentés et les résultats obtenus ont été très satisfaisants. Voir les détails

Mots clés : Décomposition modale

Vector Fourier transform analysis of stacked rectangular microstrip patches on isotropic and anisotropic substrates

Bouraiou, A. Amir, M. Fortaki, T. Bouttout, F. Khedrouche, D. Benghalia, A.  (2015)

Galerkin’s method in the vector Fourier transform domain is used for computing the resonant frequencies of two stacked rectangular patches embedded in a multilayered media containing isotropic and/or uniaxial anisotropic dielectrics. The proposed method for determining the dyadic Green’s functions of the stacked configuration leads to a new concise expression, allowing the computation of these dyadic easily by using simple matrix multiplications. Numerical results are presented for two stacked rectangular patches fabricated on a two-layered substrate. Numerical results are also obtained for another stacked configuration involving three patches and five layers. The set of TM modes of a rectangular cavity with magnetic side walls are used in the approximation of the currents on the patches. Through numerical convergence checks, it is found that for symmetrical patches, only one mode per patch suffices to obtain good convergence, while for unsymmetrical patches, additional basis functions should also be included in both the approximation of the current on the lower patch and the one on the upper patch. The validity of the solution is tested by comparing the computed results with the known experimental data. The numerical results indicate that the two constitutive resonators of the stacked structure, which determine the dual-frequency behavior of the antenna, depend on the relative sizes of the lengths of the patches. Also, the numerical results show that substrate dielectric anisotropy has a more pronounced effect on the lower resonance than on the upper resonance. With regard to the bandwidth, we show that in order to bring the stacked antenna the benefits of broad band, it is necessary that the antenna operates at its lower (upper) resonance when b2 > b1 (b2 < b1). Other results also indicate that the displacement of the upper patch along the resonant direction constitutes an efficient tool for widening the separation between the upper and lower resonances. Voir les détails

Mots clés : Stacked patches Unsymmetrical patches Dual-frequency operation Full-wave analysis

The solution of state space linear fractionalsystem of commensurate order withcomplex eigenvalues using regularexponential and trigonometric functions

Djamel Boucherm, Abdelfatah Charef, Hassene NEZZARI  (2017)

In a previous work, we have derived the generalsolution of the state space linear fractional system of commensurate order for real simple and multiple eigenvalues ofthe state space matrix. The obtained solutions of the homogeneous and non-homogeneous cases have been expressed as alinear combination of introduced fundamental functions. Inthis paper, the above work has been extended to solve thestate space linear fractional system of commensurate orderfor complex eigenvalues of the state space matrix. First, suitable fundamental functions corresponding to the differenttypes of complex eigenvalues of the state space matrix areintroduced. Then, the derived formulations of the resolutionapproach are presented for the homogeneous and the nonhomogeneous cases. The solutions are expressed in terms ofa linear combination of the proposed fundamental functionswhich are in the form of exponentials, sine, cosine, dampedsine and damped cosine functions depending on the commensurate fractional order. The results are validated by solving anillustrative example to demonstrate the effectiveness of theproposed analytical tool for the solution of the state spacelinear fractional system of commensurate order. Voir les détails

Mots clés : Complex eigenvalues · Fractional differential equation · Fundamental functions · Modal decomposition · Rational function · State space representation

Rational Function Approximationof a Fundamental Fractional OrderTransfer Function

Djamel Boucherm, Abdelfatah Charef, Hassene NEZZARI  (2017)

This paper introduces a rational function approximation of thefractional order transfer function ; for 0 to 0:5. Thisfractional order transfer function is one of the fundamental functions of thelinear fractional system of commensurate order corresponding to pure complexconjugate poles or eigenvalues, in sa. Hence, the proposed approximation willbe used in the solution of the linear fractional systems of commensurate order.Illustrative examples are given to show the exactitude and the efficiency of theapproximation method. Voir les détails

Mots clés : Fractional power zero  Linear fractional system  Irrational transfer function  Rational transfer function

Eccentricity Fault Diagnosis based on Wavelet Transform and Neuro-Fuzzy Inference System in Doubly-fed Induction Generator

Hichem MERABET, Tahar Bahi, Khouloud BEDOUD, Djalel DRICI  (2017)
Article de conférence

he development of wind turbine system is becoming very influential, in conditions of power qualityand very interesting for ecological protection. However, their potential is considerable in the world, thewind energy sources have drawn more and more attention all over the world recent years to improve theserious environment problems and deal with the shortage of fossil fuels in recent years [1]. The doubly-fedinduction generator (DFIG) is one of essential part of wind turbine system and has dominated in the field ofelectromechanical energy conversion system because of robustness and low cost [2]. So, for a substantialprofit, the diagnosis should be properly developed to ensure a production system more make safe.Production systems must be provided with reliable protection systems as any failure can lead to inevitabledamage [3].The occurrence of different faults can be completely in damage this machine type and inevitably cause theprocess to stop, resulting in loss of production consequently [4]. Therefore, it is necessary to develop amodel machine allow to detect the presence of the faults.Wind turbine is prone many failures and because of their size and localization, it is very costly to repair oremplace their component. In generally, mechanical faults are the most encountered in wind turbinessystems at the gearbox. These faults can occur at the level of ball, inner and outer race bearings, andflanges of the machine shaft. In scientific research tasks shows that rotor faults are more frequentbreakdowns, [5, 6]. In this paper we are interested to study the rotor eccentricity faults types [7].The DFIG in this type of faults can be subjected to counteract between the center of rotation of the shaftand the center of the rotor resulting the oscillations in the electromagnetic torque, uneven distribution of thecurrents in the rotor and the unbalance of stator current. This phenomenon is called static or dynamiceccentricity, and both at the same time creates the fault mixed eccentricity, whose origin may be related toincorrect positioning of the bearings during assembly or bearing failure [8, 9].Eccentricity Fault Diagnosis based on WaveletTransform and Neuro-Fuzzy Inference System inDoubly-fed Induction GeneratorMerabet. HichemResearch Center in Industrial Technologies (CRTI) P.O.Box 64, Cheraga, Algeria.h.merabet@csc.dzBahi. TaharElectrical Department, University of Annaba, Algeriatbahi@hotmail.comBedoud. khouloudResearch Center in Industrial Technologies (CRTI) P.O.Box 64, Cheraga, Algeria.k.bedoud@csc.dzDrici. DjalelResearch Center in Industrial Technologies (CRTI)P.O. Box 64, Cheraga, Algeria.d.drissi@csc.dzTSeveral methods of diagnosis are based on spectral analysis of the electromagnetic quantities, using themagnetic flux, stator current and the neutral voltage vibration signal analysis and especially the statorcurrent which requires only a current sensor [10, 11]. Therefore most of the recent research has bennedirected towards non-invasive techniques such as stator current and vibration signal analysis, motorsignature analysis with wavelet transform, courant envelope, Artificial Intelligence such as NeuralNetwork, Fuzzy Logic and Fuzzy Neural Network. The analysis of the stator currents in the waveletdomain remains the most commonly used because the spectrum results contains a source of information onthe majority of electrical and/or mechanical faults and magnetic properties can appear in the machine [12,13].The artificial intelligences based on fuzzy logic system inference, artificial neural network (ANN) orcombined structure techniques of artificial neural fuzzy interference system (ANFIS) are widely used in thenew monitoring[14, 15].Therefore, in order to increase the efficiency and the reliability of the monitoring in the field of the(DFIG) supervision, the proposed technique is based on wavelet transform and Neuro-Fuzzy inferencesystem (ANFIS).In this paper, the investment interest in wind turbine conversion system based on DFIG is presented.Then, we focus on the study of their designs and the development of a global model for doubly-fedgenerator in case of rotor eccentricity faults.Finally, in order to validate the considered method, the proposed model has been simulated and validatedby numerical simulations using MATLAB/Simulink. Voir les détails

Mots clés : eccentricity, fault, diagnosis, wavelet, ANFIS, DFIG

Characterization of Structural Noise Patterns and Echo Separation in the Time-Frequency Plane for Austenitic Stainless Steels.

M. Khelil, J-H Thomas, L. Simon, R. El Guerjouma, M. Boudraa  (2017)

The aim of this study is to characterize the structural noise for a better flaw detection in heterogeneous materials (steels, weld, composites...) using ultrasonic waves. For this purpose, the continuous wavelet transform is applied to ultrasonic A-scan signals acquired using an ultrasonic non destructive testing (NDT) device. The time-scale representation provided, which highlights the temporal evolution of the spectral content of the A-scan signals, is relevant but can lead to misinterpretation. The problem is to identify if each pattern from the wavelet representation is due to the structural noise or the flaw. To solve this problem, a detection technique based on statistical significance testing in the time-scale plane is used. Information about the structural noise signals is injected into the decision process using an autoregressive model, which seems relevant according to the spectral content of the signal. The approach is tested on experimental signals, obtained by ultrasonic NDT of metallic materials (austenitic stainless steel) then on a weld in this steel and indeed enables to distinguish the components of the signal as flaw echoes, which differ from the structural noise. Voir les détails

Mots clés : Austenitic stainless steels, Structural noise, Flaw detection, Wavelet transform, Autoregressive model, Significance testing

Elaboration des Couches Minces du ZnO Déposé par la Méthode Spray Pyrolysis à partir de Trois Sources : Application Capteur de Température.

K. Bedoud, R. Saidi, H. Nezzari  (2014)
Article de conférence

Aujourd’hui il existe une demande croissante sur des systèmes industriels plus sûrs et plus fiables qui sont essentiellement contrôlés par des capteurs de température, pour satisfaire cette demande, nous nous somme intéressés à la réalisation des capteurs à base de couches minces. A cet effet, nous avons choisi l’oxyde de zinc « ZnO » qui fait partie de la famille des semi-conducteurs et les oxydes conducteurs transparents « TCO ». Ce choix est justifié par le compromis entre les propriétés optiques et électriques d’oxyde de zinc, sa stabilité thermique et chimique très élevées, sa non toxicité ainsi que son abondance dans la nature et son coût bas. De plus, il présente un gap de 3,3 eV et une énergie de liaison excitonique de 60 meV. Dans ce travail, des couches minces de ZnO ont été déposées par la technique de spray pyrolyse, à partir de trois différentes sources « Chlorure de Zinc », « Acétate de Zinc » et « Nitrate de Zinc » avec une molarité de 0.1mol/l ou t = 5 min sur des substrats en verre chauffés à une température de 280°C.Notre travail porte sur l’étude de l’influence de la méthode de déposition ainsi que les sources utilisées sur les propriétés structurales, optiques et électriques de ces couches. Pour cela, nous avons utilisé la spectroscopie de transmission optique UV–Visible pour les caractérisations optiques, la technique de deux pointes pour les caractéristiques électriques et nous souhaitons faire la diffraction des rayons X pour les caractérisations structurales de nos couches. Voir les détails

Mots clés : couches minces, spray pyrolyse, propriétés optiques, semi-conducteur, ZnO.

Numerical Simulation of CdTe thin films solar cells using AMPS

Samah BOUDOUR, Moufdi HADJA, Idris BOUCHAMA, Sihem AZIEZ  (2016)
Article de conférence

The numerical modeling and simulation is much needed for the realization of thin films solar cells before that device is in fact produced. In this study we have simulated a theoretical configuration based on SnO2/CdS/CdTe/MoTe heterojunction solar cell under AM 1.5 illumination using the Analysis of Microelectronic and Photonic Structures (AMPS-1D) software tool in one dimension. The effect of physical properties variations is well thought-out on the evaluation of performance (VOC, JSC, FF and Efficiency) in CdTe thin films solar cells Voir les détails

Mots clés : AMPS, Numerical simulation, CdTe, Thin-films solar cells

Signal Quality Improvement Using a New TMSSE Algorithm:Application in Delamination Detection in Composite Materials

a.benammar, A.KECHIDA, R.Drai  (2017)

This paper introduces a novel method to improvethe quality of ultrasonic phased array signals for localizingwith accuracy delamination defects. The improvementis achieved by the introduction of a new threshold for theShannon energy. In first, we have applied the threshold modifiedS-transform algorithm (TMST) in the case of ultrasoundB-scan. Thereafter, we have adapted and applied the StransformShannon energy (SSE) algorithm in the field ofultrasonic testing. At last, we have proposed a novel algorithmbased on threshold modified S-transform and Shannonenergy (TMSSE) to increase the improvement of the ultrasoundB-scan. A simulation study has been carried outsimulating a composite material containing three defects indifferent positions in order to highlight the phenomenon ofdelamination. Experimental tests were performed on a sampleof carbon fiber reinforced polymer composite material(CFRP) with a delamination defect close to the front face.Both experimental and simulated results show that the proposedmethod can improve the quality of ultrasound B-scanwhich enhances the localization of delamination defects. Voir les détails

Mots clés : Ultrasonic signal

Segmentation of the Weld Radiographic Images by the Level Set Method using the Kernel Fuzzy C-Means Clustering.

N. Chetih, N. Ramou, Y. Boutiche, M. SAHNOUN  (2016)
Article de conférence

In this paper, we are interested to segment weld radiographic images using the level set method (LSM) based on kernel fuzzy c-means clustering (KFCM) in order to extract the region of interest (weld defects) and to improve the precision of segmentation. The proposed approach contains two successive necessary stages. The first one consists in the application of kernel fuzzy c-means algorithm to get a clustered image. The second stage is based on the using of the appropriate class of the clustered image as an initial contour of the level set method to extract the defects boundaries. The experimental results have shown that the proposed model can extract successfully the interest region from image and confirm its efficiency for welding defects segmentation. Voir les détails

Mots clés : Level set, kernel fuzzy c-means, weld defects, weld radiographic images, image segmentation