Liste des publications
Caractérisation et étude thermique et morphologique de la diatomite Algérienne
L’utilisation des poudres de coulée continue dans les aciéries a montré le manque d’information sur les propriétés de ces poudres. Dans cette étude, nous avons déterminé les différentes caractéristiques de la diatomite du dépôt de Sig de Mascara (ouest d’Algérie) ; qui est utilisée comme une poudre d’isolation thermique dans l’aciérie. Plusieurs techniques de caractérisation ont été utilisées pour expliquer la morphologie et la composition de cette poudre. La diffraction des rayons X montre que 91% de la composition minéralogique était de la silice amorphe, l’analyse par FRX montre que la poudre contient plus de 70% SiO2. Les résultats de DSC (Differential Scanning Calorimetry) montrent qu’entre 1461,6 et 1484,2°C la transformation est exothermique et la chaleur spécifique est estimée à 2324J/kg.K. La structure poreuse de la diatomite est clairement observée par le MEB, dont on a obtenu une porosité de 80% et une densité apparente de 400 Kg/m3. La surface spécifique a été mesurée par la méthode de Sears, dont le résultat obtenu est de l’ordre de 349m2/g. La structure, la composition, la résistance thermique et la surface spécifique de la diatomite nous permet d’utiliser cette poudre dans plusieurs domaines à savoir le traitement des eaux usées (filtration, adsorption, support catalytique) et l’isolation thermique. Voir les détails
Mots clés : diatomite, Caractérisation thermique, Morphologie du matériau, isolation thermique
Semi-implicit operator splitting Padé method for vector HNLS solitons
We use in this paper the semi-implicit finite difference operator splitting Padé (OSPD) method for solving the coupled higher-order nonlinear Schrödinger equation, which describes the propagation of vector solitons in optical fibers. This method having a fourth order accuracy in space shows good stability and efficiency for the coupled HNLS equations describing vector solitons. We have tested this method for analyzing the behavior of optical pulses in birefringent fibers verifying that the third order dispersion TOD has different effects on the two polarizations and the asymmetric oscillation is significant only in one polarization. Voir les détails
Mots clés : Birefringence, vector solitons, optical fibers, Operator Splitting Padé Method, coupled higher-order nonlinear Schrodinger equation, third order dispersion.
Analysis of HNLS Solitons with Quintic Nonlinearity Using Semi Implicit Operator Splitting Padé Method
In this communication, we use the semi-implicit finite difference operator splitting Padé method to solve the higher-order nonlinear Schrödinger equation with higher order linear and nonlinear effects such as the third order dispersion (TOD), Kerr dispersion, stimulated Raman scattering and the quintic nonlinearity. The role of quintic nonlinearity on the propagation characteristics of optical solitons is investigated for standard fibers. This method is readily generalized for nonlinear management fibers it’s found that the quintic nonlinearity has no significant role on the propagation of single solitons. Voir les détails
Mots clés : Optical solitons, Padé method, quintic nonlinearity. HNLS equation
Thermo-hydrodynamic study of the journal bearing under static load
A number of studies have been carried out on the hydrodynamic lubrication of journal bearings. This articleseeks to summarize this work, presenting it in the form of a flow chart. The treatment of rupture andreformation of the film fluid in the contact region, for a steady loaded circular journal bearing, areaccomplished using the Reynolds and the Jakobsson–Floberg and Olsson (JFO) boundary conditions.A flow chart taking into account the resolution of some of the hydrodynamic lubrication problems is elaborated.A computer code is carried out for solving the Reynolds equation and for calculating the most importantparameters relating to a hydrodynamic contact. The obtained results for a finite-length bearing are comparedwith those obtained from the short-bearing hypothesis. In addition, a global thermal study is carried out in orderto evaluate the effect of temperature. Voir les détails
Mots clés : hydrodynamic bearing, static load, thermal effect, Jakobsson–Floberg and Olsson, Elrod, Reynolds
Hydrodynamic effects of texture geometries on journal bearing surfaces
Lately, the expanding range of tribological applications to the microscopic levels has revived interest in this field. Actually, little is understood about the subtle effects of variations of a journal bearing’s profile upon its performance. The surface texturing is expected to make an important contribution to future technologies of bearing.Numerical study based on finite difference methods is used to find the tendency of important tribological properties of a journal bearing such as minimum film thickness, maximum pressure, axial oil flow and friction torque.The present work is a comparative study of the hydrodynamic effects of a few deterministic texture shapes in a journal bearing application. The geometry and the size of textures affect load capacity and friction torque. The parallelepipedic textures show advantages compared to the other geometries for the improvement of the performances of the bearing. In general, the impact of shapes is more visible for higher asperity area in accordance with the geometrical differences. Voir les détails
Mots clés : texture, lubrication, hydrodynamic, journal bearing
Thermal Simulation and Experimental Characterizations of Aeronautic Stainless Steel Welded by TIG process.
In order to study the thermal behaviour of aeronautic stainless steel welded by TIG process, we have improved the energetic distribution formulation by adapting the geometric configuration into a bi-elliptic form with Gaussian surface heat flow distributions of the welding source. The Thermal transient fields and thermal cycles are evaluated to determine dimensions of the risky zones (Heat Affected Zone and Fusion Zone) and the welded joint is characterized by tension tests, micro-hardness (Hv) and micrographics. A metallographic analysis is prepared to differentiate all zones as well as the grain sizes, and to confirm theirs widths. Computations are carried out by finite volume method, where thermo-physic’s properties and boundary conditions are in function of temperature. The reliability of the model is evaluated by the comparison of the simulated results with those obtained by thermal cycle recordings to evaluate the size of the risky zones. Both, theoretical and experimental approaches have good agreement and give an enhancement of a previous work. Voir les détails
Mots clés : Aeronautic stainless steel, Mechanical and metallurgical characterization, TIG welding, Thermal simulation
Prediction of Bath Temperature Using Neural Networks
In this work, we consider an application of neuralnetworks in LD converter. Application of this approach assumes areliable prediction of steel temperature and reduces a reblow ratio insteel work.It has been applied a conventional model to charge calculation, theobtained results by this technique are not always good, this is due tothe process complexity. Difficulties are mainly generated by thenoisy measurement and the process non linearities.Artificial Neural Networks (ANNs) have become a powerful toolfor these complex applications. It is used a backpropagationalgorithm to learn the neural nets. (ANNs) is used to predict the steelbath temperature in oxygen converter process for the end condition.This model has 11 inputs process variables and one output.The model was tested in steel work, the obtained results by neuralapproach are better than the conventional model. Voir les détails
Mots clés : LD converter, bath temperature, neural networks
Effect of molybdenum and niobium on the wear behaviour of high chromium white cast iron
High chromium white cast irons are excellent wearable materials. Their wear resistance is due to the presence of high volume fraction of hard carbides in microstructure. Accordingly, this material is very suitable for many applications such as mineral processing, cement production and other industrial fields. Researchers have tried different alloying elements in order to improve wear resistance of this material. An investigation was conducted to determine the effect of alloying elements on the friction and wear behaviour of high chromium cast iron with various concentrations of molybdenum and niobium. The alloys used in this work were made in industrial induction furnace. Alloying elements were added in crucibles after pouring operation. Amounts of molybdenum and niobium were varied between 0 and 3%. A molybdenum and niobium combination of an amount of 0.5% was also studied in this work. Wear investigations were carried out on the as cast and heat treated state of a slightly hypoeutectic high chromium cast iron.Results showed that the studied alloy is composed of netted eutectic chromium carbides embedded in an austenitic matrix. Wear looses carried out on as cast and heat treated cast irons indicates that the best results were obtained by abrasion with 3% Mo alloy. Friction tests has also given good results but less important. Manganese comparing to niobium addition has much more facilitated the abrasion than the friction resistance. These results indicate that the alloying elements do not act similarly on the two type of studied wear. Voir les détails
Mots clés : high chromium cast iron, microstructure, wear, friction, carbide
Structural and magnetic studies of nanocrystalline Fe80Ni20 alloy prepared by high-energy ball milling
Mechanical alloying is a powder metallurgy processing technique involving the cold welding, fracturing and rewilding of powder particles in high energy. It has been used to obtain nanocrystalline alloys. Fe-20 wt. % Ni alloys were synthesised using a planetary ball mill (Retsch PM400). X-ray Diffraction (XRD) was used to identify and characterise various phases during the milling process. It is shown that the bcc Fe(Ni) solid solution was formed after 2 h of milling. The steady state grain size is about 12 nm. Many nanostructures' magnetic materials have exhibited excellent soft magnetic properties, which suit so many applications. We used electromagnetic methods (hysteresis) to characterise the variation of the residual magnetisation and the coercive field.r Voir les détails
Mots clés : nanostructure, nanocrystalline alloys, Magnetic Properties, microstructure, high-energy ball milling, mechanical alloying.
Theoretical description of the interactions between a mixture of vapors and a set of chemical sensors by variable temperature
A sensor system is expected to detect gas concentrations of interest within low-ranges. The interactions between a sensor array and mixture of vapors hang not only on mixture composition and temperature but also on the partial sensitivities of the array elements. The aim of this paper is to find a useful equation in differential form that relates the change of sensors partial sensitivities to mixture component concentrations and temperature. This kind of equations is known in the thermodynamic of miscellaneous as equations of Gibbs–Duhém Voir les détails
Mots clés : adsorption, chemical sensors, sensor array, mixture of vapors, functions of state, equations of Gibbs-Duhem