Liste des publications
Enhanced the modeling accuracy by the design of new photovoltaic models including the proposed nonlinear thermal resistors
This article proposes new photovoltaic (PV) models, with which the modeling accuracies are much improved, regardless of wide absolute temperature variations. The desired PV models are designed by an equivalent electrical circuit consisting of a single diode and two proposed nonlinear thermal resistors. The realization of such resistors is therefore the key contribution of this article since they significantly increase the degrees of freedom of similar circuits, including fixed resistors. As a result, the given modeling accuracies are clearly improved not only under standard test conditions but also in more severe climatic environments, characterized by high absolute temperatures. To achieve this goal, the parameters of the two proposed PV models were optimized using the gnetic algorithm, where a fitness function for each PV model is well minimized. Each fitness function was previously formulated from comparing actual output currents, prerecorded from the existing ISOFOTON I-50 PV panel, by predicted output currents, computed using the Lambert-W function. The given performances by the proposed PV models were compared with those provided by the standard PV ones where the given simulation results reveal the superiority of the proposed PV models under different weather conditions. Voir les détails
Mots clés : Genetic algorithm, Lambert-W function, Photovoltaic, Resistance-based metallic conductor, Resistance-based thermistance material, standard climatic condition
Robust adaptive sliding mode control strategy of uncertain nonlinear systems
This paper presents a robust adaptive sliding mode controller scheme as applied to a class of uncertain nonlinear systems with parametric uncertainties and external disturbances. First, a sliding mode control technique is designed. Then, the proposed robust adaptive control schemes are applied to estimate the parametric uncertainties and the upper bound value of the external disturbances by using adaptive laws, ensure robustness in presence of parametric uncertainties and external disturbances, and reduce chattering problem by introducing an hyperbolic tangent function. Lyapunov stability theory is used to analyze the stability of the closed-loop system. As an exemplar, the schemes have been applied to a quadrotor unmanned aerial vehicle (QUAV) model. Simulation results for the control of the QUAV model are provided to illustrate the performance of the proposed robust adaptive sliding mode control scheme and demonstrate that the proposed method has good tracking performance. The simulation results clearly prove the effectiveness of our approach. Voir les détails
Mots clés : adaptive control, Robust control, Sliding mode control, uncertain nonlinear systems, parametric uncertainties, external disturbances, adaptive laws, Lyapunov stability theory, quadrotor unmanned aerial vehicle
Microstructural Investigation and Oxidation Performance of Nickel‑Based Superalloys
An as-received IN738LC blade root material has been firstly characterized, in order to appreciate its structural, micro- structural and morphological properties. Different observations and analysis (OM, XRD, SEM/EDS, etc.) showed that our sample is mainly constituted of γ´ precipitates in a Ni-rich matrix (γ solution), a γ/γ´ eutectic and some carbides. After that, the oxidation behavior of IN738LC superalloy has been investigated to assess the oxidized formed layers. For this purpose, isothermal oxidation experiences have been carried out at 950 and 1150 °C for various times (24h, 48h and 72h). The differ- ent microstructures of oxides and substrate obtained after oxidation tests were observed and analyzed by scanning electron microscopy (SEM/EDS). The oxidation kinetics were monitored by samples weight change with time. Composition and phase evolutions, mean crystallite size and strain appeared in this superalloy, were determined by X-ray diffraction (XRD) patterns. Last, the adhesion of the growing oxides onto the substrate was evaluated by the scratch test. The main results of these investigations reveal that microstructure parameters strongly depend on temperature and durations of the process. Moreover, the oxidation kinetics of the alloys follows a parabolic rate law both at 950 °C and at 1150 °C. From XRD and EDS analysis, the major phases seen are Cr2O3, TiO2, Al2O3, NiO and NiCr2O4, which contribute to a better oxidation resistance. The oxide scales increase with time and temperature, they are compact, dense, distributed uniformly and adherent at 950°C/72h, while they are relatively larger and non-uniform at 1150 °C. On the other hand, the adhesion of the oxides at 1150°C is fairly weak, and oxidation products flake off quite easily, which indicated weakening of the protection. Voir les détails
Mots clés : Turbine blade, Inconel 738LC, Oxidation kinetics, microstructure, Strain, Adhesion
Structural, Magnetic, Dielectric and Piezoelectric Properties of Multiferroic PbTi1−xFexO3−δ Ceramics
PbTi1−xFexO3−δ (x = 0, 0.3, 0.5, and 0.7) ceramics were prepared using the classical solid-state reaction method. The investigated system presented properties that were derived from composition, microstructure, and oxygen deficiency. The phase investigations indicated that all of the samples were well crystallized, and the formation of a cubic structure with small traces of impurities was promoted, in addition to a tetragonal structure, as Fe3+ concentration increased. The scanning electron microscopy (SEM) images for PbTi1−xFexO3−δ ceramics revealed microstructures that were inhomogeneous with an intergranular porosity. The dielectric permittivity increased systematically with Fe3+ concentration, increasing up to x = 0.7. A complex impedance analysis revealed the presence of multiple semicircles in the spectra, demonstrating a local electrical inhomogeneity due the different microstructures and amounts of oxygen vacancies distributed within the sample. The increase of the substitution with Fe3+ ions onto Ti4+ sites led to the improvement of the magnetic properties due to the gradual increase in the interactions between Fe3+ ions, which were mediated by the presence of oxygen vacancies. The PbTi1−xFexO3−δ became a multifunctional system with reasonable dielectric, piezoelectric, and magnetic characteristics, making it suitable for application in magnetoelectric devices. Voir les détails
Mots clés : dielectric response, Fe-doped PbTiO3, Magnetic Properties, multiferroic ceramics, piezo- electric properties
Slug length and frequency upstream a sudden expansion in gas– liquid intermittent flow
The purpose of this work is to analyze the influence of a sudden expansion on the upstream behavior of the horizontal gas–liquid slug flow. Measurements were made on a 40 mm ID pipe with and without a sudden enlargement of aspect ratio σ = 0.444. The experiments were carried out with two-phase air–water mixture. The slug lengths and frequencies were measured using a non-intrusive video technique. Upstream the sudden enlargement, it was observed that the mixture velocity has no influence on slug length. The variation of slug frequency is found proportional to the liquid superficial velocity for the two cases within this study. It was also observed that the behavior of the slug length and frequency was affected by the presence of the sudden enlargement. The comparison of the results obtained with various empirical correlations available in the literature showed that the latter are not worthwhile in the case where singularity is installed. Voir les détails
Mots clés : slug flow, sudden expansion, slug length, slug frequency
Heat Transfer Mode and Effect of Fluid Flow on the Morphology of the Weld Pool
In this work, the heat transfer by conduction and convection mode, effect of the fluid flow on the morphology of the weld pool and the welding properties are investigated during Tungsten Inert Gas (TIG) process. In the first part, a computation code under Fortran was elaborated to solve the equations resulting from the finite difference discretization of the heat equation, taking into account the liquid-solid phase change with the associated boundary conditions. In order to calculate the velocity field during welding, the Navier-Stokes equations in the melt zone were simplified and solved considering their stream-vorticity formulation. A mathematical model was developed to study the effect of the melted liquid movement on the weld pool. The evolution of the fraction volume of the liquid and the thermal fields promoted the determination of the molten zone (MZ) and the Heat Affected Zone (HAT) dimensions, which seems to be in good agreement with literature. Voir les détails
Mots clés : Thermal and flow modeling, TIG welding, Heat affected zone, molten zone
Tamanrasset’s Clay Characterization and Use as Low Cost, Ecofriendlyand Sustainable Material for Water Treatment: Progress and Challengein Copper Cu (II)
In this study, the adsorption of copper Cu (II) from aqueous solution, on Tamanrasset’sclay which is low cost adsorbent, was studied using batch experiments. The adsorption study includesboth equilibrium adsorption isotherms and kinetics. The characterization of the adsorbent necessitatedseveral methods such as X-Ray Diffraction, Scanning Electron Microscopy coupled with EnergyDispersive X-ray, BET for specific surface area determination, Fourier transform infraredspectroscopy and thermogravimetric analysis. Indeed, various parameters were investigated such ascontact time, initial metal ion concentration, mass of solid, pH of the solution and temperature. Theadsorption process as batch study was investigated under the previews experimental parameters. Theresults revealed that the adsorption capacity of Cu2+ is maximized at naturel pH of metal 5.5. Removalof copper by the clay of Tamanrasset (kaolinite) achieved equilibrium within 50 minutes; the resultsobtained were found to be fitted by the pseudo-second order kinetics model. The equilibrium processwas well described by the Langmuir model and the maximum adsorption capacity was found to be26.59 mg/g. Voir les détails
Mots clés : adsorption, Clay, copper, kinetic, Isotherms
Segmentation of x-ray image for welding defects detection using an improved Chan-Vese model
The welding defects detection in industries is becoming an important area and is attracting the attention of many researchers. Radiography is one of the most widely used techniques for inspecting weld defects. X-ray images are generally characterized by low contrast, poor quality and uneven illumination, so the extraction of weld defects could become a difficult task. Among the techniques most used in this field, it is the active contour and the main problem of this technique is the initial contour selection. To solve this problem and obtain reliable and efficient detection of welding defects, we propose in this work a new approach for welding defects detection from x-ray image based on an improved Chan-Vese model. This improved model is based on three stages. The first stage is the detection the region of interest. In the second stage, we apply the Fuzzy C-Mean (FCM) algorithm to select one of the clusters as the initial contour. In the third stage, we use the Chan-Vese model and the selected initial contour to segment the acquired images and obtain the boundaries of the weld defects. Experiments are carried out on different x-ray welding images of the GDxray database in order to extract the characteristics of the welding defects. The results obtained show the effectiveness of the proposed approach compared to conventional techniques. Voir les détails
Mots clés : Chan-Vese model Fuzzy, C-means clustering, X-ray image, Welding defects
Scale space Radon transform
An extension of Radon transform by using a measure function capturing the user need isproposed. The new transform, called scale space Radon transform, is devoted to the casewhere the embedded shape in the image is not ?liform. A case study is brought on a straightline and an ellipse where the SSRT behaviour in the scale space and in the presence of noiseis deeply analyzed. In order to show the effectiveness of the proposed transform, the exper-iments have been carried out, ?rst, on linear and elliptical structures generated syntheticallysubjected to strong altering conditions such blur and noise and then on structures imagesissued from real-world applications such as road traf?c, satellite imagery and weld X-rayimaging. Comparisons in terms of detection accuracy and computational time with well-known transforms and recent work dedicated to this purpose are conducted, where theproposed transform shows an outstanding performance in detecting the above-mentionedstructures and targeting accurately their spatial locations even in low-quality images. Voir les détails
Mots clés : radon transform, line, ellipse, scale space, noise
Investigation ?n Dry Sliding Wear Performance and Corrosion Resistance of 13Cr5Ni2Mo Supermartensitic Stainless Steel
This work aimed to study the microstructure, wear and corrosion resistance of supermartensitic stainless steel (SMSS). Heat treatment applied to samples consists of quenching after austenitization at elevated temperature (1250 °C) followed by a double tempering at 650 °C. Conventional mechanical properties, scanning electron microscopy (SEM/EDS) analysis and X-ray diffraction methods (XRD) are used to analyze the microstructure and to evaluate the wear mechanisms. The potentiodynamic polarisation and the electrochemical impedance spectroscoopy (EIS) methods are used to evaluate the corrosion resistance in both the 0.5M H2SO4 and 0.5M NaCl aggressive media. The microstructure is mainly composed with tempered lath martensite, small quantity of retained austenite and carbides. Oxidative and abrasive wear dominated the wear process in dry condition. During the corrosion process, the same mechanism of degradation was found in both the 0.5M NaCl and 0.5M H2SO4. Voir les détails
Mots clés : Supermartensitic steel, microstructure, friction, Wear Corrosion