Liste des documents
Simulation of the variation in temperaturein a material without and with default
In this article our principal study is the simulation ofthe variation in temperature in a solid material in absence and inpresence the default, in particular a fracture on the level of surfaceof material, and to see how the default influences on heat transferin a solid. The simulation is made by FLUENT software whichpermits us to solve the energy equation by finite volumes method. Voir les détails
Mots clés : heat transfer; simulation; material; default
IDENTIFICATION RÉCURSIVE DES SYSTÈMES À DÉRIVÉE FRACTIONNAIRE
Une méthode d’identification récursive d’une classe de systèmes d’ordre fractionnaire est présentée dans cet article. Il s’agit d’une extension de la méthode d’identification paramétrique des moindres carrés linéaires récursifs aux ordres fractionnaires. Le modèle considéré est de type ARX généralisé dont les ordres de dérivation sont distribués dans un intervalle réel fixé. La matrice de régression est composée de l’ensemble des dérivées fractionnaire de l’équation différentielle généralisée à un instant donné. Une simulation numérique a montré clairement la qualité de l’identification en utilisant cette approche. Voir les détails
Mots clés : Identification récursive, systèmes d’ordre fractionnaire, dérivée d’ordre fractionnaire.
ADJUSTABLE FRACTIONAL ORDER DIFFERENTIATOR
This paper deals with the design of digital adjustable fractional order differentiator approximation of the fractional order differentiator sm, for 0 < m < 1, in a given frequency band of interest. First, closed form digital infinite impulse response (IIR) adjustable fractional order differentiator is obtained based on an analog adjustable fractional order differentiator. Then, closed form digital finite impulse response (FIR) adjustable fractional order differentiator is derived from the digital IIR one. In both cases, the digital differentiator can be implemented by the digital Farrow structure. Finally, a numerical example is presented to illustrate the efficiency and the effectiveness of the proposed design method. Voir les détails
Mots clés : Fractional order differentiator, Digital IIR filters, Digital RIF filters, Farrow structure
Etude du soudage TIG de l’alliage d’aluminium 2024-T3
Les programmes récents de conception d'aéronefs sont caractérisés, sur le plan des matériaux, par l'introduction d'alliages soudables, qui semblent promis à un bel avenir. En se substituant à la technique traditionnelle d'assemblage par rivetage, le soudage ouvre la voie à un gain de masse, mais aussi à des réductions de coût en production, comme en maintenance, essentiellement grâce à une amélioration de la résistance à la corrosion et à la fatigue. Le savoir-faire, l’expérimentation et la compréhension technologique des différents paramètres du procédé de soudage à l’arc TIG (Tungsten Inert Gas) appliqué à l’alliage d’aluminium 2024 à l’état T3 (mise en solution, écrouissage et maturation) ne peuvent que nous aider à définir la démarche la plus juste ou efficace d’une modélisation nécessaire pour la prise en compte, dès la conception, du comportement de l’assemblage. Le travail présenté porte sur la définition d’un domaine opératoire de soudabilité de l’alliage étudié, d’une épaisseur de 2mm, et les conséquences métallurgique et mécanique de cet assemblage sur les propriétés du matériau. Concernant l’aspect opératoire, un programme d’essais, couplé à des mesures du champ thermique par thermographie infrarouge, nous a permis de comprendre l’influence des différents paramètres intervenant lors de l’opération de soudage (tension, intensité, vitesse de soudage, protection gazeuse, métal d’apport). D’un point de vue caractérisation, l’observation classique en microscopies optique et électronique couplée à la diffraction d’électrons rétrodiffusés (EBSD) nous a permis d’accéder à des informations sur la microstructure de la zone d’assemblage, nous permettant une meilleure compréhension du comportement mécanique du joint de soudure, caractérisé par des essais de microdureté et de traction. Voir les détails
Mots clés : soudage TIG, alliage 2024, microstructure, propriétés mécaniques
Wavelet Transform And Envelope Detection For Gear Fault Diagnosis .A Comparative Study
On-line vibration monitoring of Rotary Machinesis is a fundamental axis of development and industrial research. Itspurpose is to provide knowledge about the working condition ofmachines at each moment without stopping the production line.This method allows avoiding the production losses related tobreakdowns and reducing overall maintenance costs.Bearing fault diagnosis is important in vibration monitoringof any rotating machine. Early fault detection in machineries cansave millions of dollars in emergency maintenance cost.This paper presents the comparison results of Fault diagnosisTechniques of gear fault using two methods: Envelope Detection(ED) and Wavelet Transform (WT) using Morlet Wavelet thecomparative study is applied to real vibratory signals. Voir les détails
Mots clés : Vibration analysis, Fault Diagnosis, Wavelet Transform (WT), Envelope Detection (ED)
Performance evaluation of photovoltaic arrays subject to a Line-Ground fault
In this work, the effect of Line-to-Ground fault on the performance of photovoltaic (PV) arrays is analyzed. Due to the nature of their outdoor operation, PV arrays are subject to extreme weather conditions that affect their normal operation. The exposure of cables and junction boxes to such environmental conditions leads to different types of connection faults. Given that the frame of the PV panel is metallic, a short-circuit between the Line (positive charged wire) and the ground may occur frequently. A particle swarm optimization (PSO) based maximum power point tracking (MPPT) algorithm is then used to improve the efficiency of PV arrays. Simulation results show the large power loss caused by such type of fault and the effectiveness of the proposed approach in increasing the system's efficiency. Voir les détails
Mots clés : Photovoltaic (PV) arrays, Line-Ground fault, Particle Swarm Optimization (PSO), Maximum Power Point Tracking (MPPT)
Détection et Classification de Defaults dans les Machines Tournantes par l’Analyse en Composante Principale Multi-Echelle
L’analyse en composantes principales à multi-échelles (MSPCA) et le classificateur Neuro logique floue sont considérés parmi les méthodes modernes, et qui est utilisée dans nombreux applications de classifications. D’entre eux une nouvelle application dans les machines tournantes, le diagnostic des defaults est proposé. Le modèle ACP à multi-échelle est construit par la variance des cinq niveaux de décomposition en ondelette. Comme un vecteur de caractéristiques, ces caractéristiques sont entrainées par le classificateur neuro flou pour diagnostiquer le défaut. La performance de la méthode sera discutée, et les résultants montrent l’efficacité de l’approche proposée. Voir les détails
Mots clés : ACP multi échelle, Classifieur Neuro flou, diagnostique de défaut
Surface degradation of HDPE-100 pipe: Effects of some aggressive environments (solvents)
In this study, external and internal surfaces of a high density polyethylene (HDPE-100) pipe are characterized in terms of roughness and hardness in order to understand surface variances in the as-received material and to appreciate surface quality for electrofusion welding or resistance to given aggressive environments. The effects resulting from the action of 3 environmental stress cracking agents that might be in contact with pipe surfaces are studied separately following a specific protocol. In the initial state (as-received pipe), it was found that the outer surface is rougher and harder than the inner surface. In contact with distilled water, the external surface roughness increased slightly by 6% while hardness decreased by 14% although the roughness of the internal face of the tube revealed a small decrease (<5%). The effect of hydrochloric acid was examined with varying concentrations and it was observed that roughness augmented with concentration while hardness remained relatively constant after a major drop by 40% and 32% for outer and inner surfaces respectively. Finally, in the cases of oxidizing agents, dichloromethane (CH2Cl2) and (50:50) mixture of toluene and methanol, a significant disturbance of surface quality is observed and led to a hardness decrease of both outer and inner surfaces of by 20% and 16% respectively. The mechanical properties are also affected as revealed in literature studies. Crystallinitymeasurements confirm the gap between outer (51.55%) and inner (61.31%) surfacesindicating that degradation has taken place at the structural level when HDPE wasin contact with those aggressive agents. After exposure to these environments, results indicate that crystallinity fell approximately one third compared to as-received material, therefore reducing resistance to fracture and pipe lifetime. Voir les détails
Mots clés : polyethylene pipe, surface roughness, hardness, degradation, aggressive environments, crystallinity
Mechanical Properties Study of HDPE Wall Pipes Exposed to Sulfuric Acid and Toluene-Methanol Mixture: Comparison Between Filament and Standard Specimens
In this paper, results of two experimental studies are presented and compared. They concern the evolution of mechanical properties through the wall of a HDPE pipe used to transport natural gas. In the first study, specimens filaments (ISO 3341) machined in the form of continuous and uniform chips are used, while the second considers standard shapes according to ISO 527. Both approaches have shown that there is a significant variation in the mechanical properties through the tube wall from the outer side towards the inner side. The filament method is quicker and easier in preparation compared to the second method which comprises complicated machining operations. Immersion in aggressive environments such as sulfuric acid and toluene-methanol showed degradation of major properties. The mechanical properties obtained with the filaments are generally greater (between 6% and 14% higher), but in the case of H2SO4, the difference can reach up to 32% in comparison with control samples. The linear relationship between E and σy is preserved in those oxidative environments indicating the usefulness of HDPE filaments testing Voir les détails
Mots clés : polyethylene, Pipe, mechanical properties, pipe wall, aggressive environment, degradation
Combination between STFT and DWT for Fault Detection and Diagnosis in Rotating Machinery by Vibration Monitoring
Signal analysis with fixed time-frequency resolution, such as the Short-Time Fourier Transform(STFT), is a common tool for many industrial applications in rotating machinery condition monitoring allowing effective implementation via the Fast Fourier Transform (FFT).However, the fixed time-frequency resolution of the STFT can lead to the undesirable smearing of events in both timeand frequency. In this paper, we propose a combination between STFT and DWT for the faults detection and diagnosis in a rotating machine. An implementation procedure for the fault detection and diagnosis in rotating machinery at real-time has been presented out in this paper. The experimental results confirm that this procedure serves as a good tool to fault detection and diagnosis in rotating machinery. Voir les détails
Mots clés : I. Atoui, R. Boulkroune, A. Grid, and R. Saidi