Liste des documents
Répartition de champ électrique dans un système pointe-plan avec barrière isolante
The objective of our work is the study by numerical simulation of the distribution of the electric field according to geometric measurements of the insulating barrier and its position in the inter-electrodes gap Voir les détails
Mots clés : Electrical discharge, insulating barrier, finite element, electrical field
Adaptive backstepping control using combined direct and indirect adaptation for a single-link flexible-joint robot
In this paper, a new tuning functions based adaptive backstepping controller using combined direct and indirect adaptation for a single-link flexible-joint robot is presented. In this approach, the parameter estimation is driven by a weighted combination of tracking and identification errors. At first, the x-swapping filter identifier with a gradient-type update law is presented for a class of parametric strict-feedback nonlinear systems. Then, the main steps of the controller design for a single-link flexible-joint robot manipulator model are described. The closed-loop error dynamics is shown to be globally stable by using the Lyapunov stability approach. Finally, simulation results are given to illustrate the tracking performance of a single-link flexible-joint robot manipulator with the proposed adaptive control scheme Voir les détails
Mots clés : Backstepping control, direct and indirect adaptive control, combined adaptation, Lyapunov stability, flexible joint manipulators
Hybrid Shape Descriptors for an Improved Weld Defect Retrieval in Radiographic Testing
In this paper, four region-based shape descriptors well reported in the literature are used to characterize weld defect types of crack, lack of penetration, porosity and solid inclusion, usually encountered in radiographic testing of welds. The rectangularity and the roundness in the geometric descriptor (GEO) are used in order to propose an hybridization algorithm so that the hybrid descriptor issued from GEO and each of the other descriptors becomes more discriminant in such application where, due to bad radiographic image quality and weld defect typology, the human film interpretation is often inconsistent and labor intensive. According to the results given in the experiments, the efficiency of the proposed hybrid descriptors is confirmed on the weld defects mentioned above where, the retrieval scores are significantly improved compared to the original descriptors used separately. Voir les détails
Mots clés : Radiographic film, weld defects, shape descriptors, hybridization algorithm
A Quantitative Comparative Study of Back Projection, Filtered Back Projection, Gradient and Bayesian Reconstruction Algorithms in Computed Tomography (CT)
Images of the inside of the human body can be obtained noninvasively using tomographic acquisition and processing techniques. In particular, these techniques are commonly used to obtain X-ray images of the human body. The reconstructed images are obtained given a set of their projections, acquired using reconstruction techniques. A general overview of analytical and iterative methods of reconstruction in computed tomography (CT) is presented in this paper, with a special focus on Back Projection (BP), Filter Back Projection (FBP), Gradient and Bayesian maximum a posteriori (MAP) algorithms. Projections (parallel beam type) for the image reconstruction are calculated analytically by defining two phantoms: Shepp-Logan phantom head model and the standard medical image of abdomen with coverage angle ranging from 0 to ± 180° with rotational increment of 10°. The original images are grayscale images of size 128 × 128, 256 × 256, respectively. The simulated results are compared using quality measurement parameters for various test cases and conclusion is achieved. Through these simulated results, we have demonstrated that the Bayesian (MAP) approach provides the best image quality and appears to be efficient in terms of error reduction. Voir les détails
Mots clés : Computed tomography, Bayesian approach, Reconstruction techniques, Filter Back Projection (FBP), Gradient algorithm
Similarity Transformation Parameters Recovery based on Radon Transform. Application in Image Registration and Object Recognition
The Radon transform, since its introduction in the beginning of the last century, has been studied deeply and applied by researchers in a great number of applications, especially in the biomedical imaging fields. By using the Radon transform properties, the issue is to recover the transformation parameters regarding the rotation, scaling and translation, by handling only the image projections assuming no access to the spatial domain of the image. This paper proposes an algorithm using an extended version of the Radon transform to recover such parameters relating to two unknown images, directly from their projection data. Especially, our approach deals with the problem of the estimation accuracy of the rotation angle and its finding in one step instead of two steps as it is reported in the literature. This method may be applied in image registration as well in object recognition. The results are, for the first time, exploited in object recognition where comparison with powerful descriptors shows the outstanding performance of the proposed paradigm. Moreover, the influence of additive noise on registration and recognition experiments is discussed and shows the efficiency of the method to reduce the effect of the noise. Voir les détails
Mots clés : radon transform, 2π-Based Radon transform, Rotation, Scaling and translation transforms, Parameters recovery algorithm, Additive image noise
Theoretical estimation of the production of biogasfrom the landfill of Batna city and its electricalconversion by a SOFC
Amongst the interests in fuel cells is exploring the possibility of using different fuel types;one of them is biogas or Landfill gas (LFG) from landfills or from controlled digesters.Biogas; a gas produced by an anaerobic digestion of organic waste represents an environmentalproblem that could turn to a renewable energy source. The valorization ofbiogas into energy (electricity, heat, fuel) will save other sources of energy. The authors ofthe study are interested in evaluating three technologies: fuel cells, micro turbines andinternal combustion engine.In this paper, we discussed the conversion of biomass into electricity in two steps: thefirst step (biomass-to-biogas) is based on an evaluation of biogas potential generated bysolid waste of landfill the Batna city (Algeria) by the kinetic model (U.S.EPA, 1993). In thesecond step (biogas-to-electricity), the paper considers the technology of a stack of standardsolid oxide fuel cells (Ni-YSZ/YSZ/LSM) SOFC; this allowed us to determine the besttemperature, hydrogen concentration and electrolyte thickness for maximum powerdensity in the fuel cell SOFC. At a temperature T = 1273 K and thickness of electrolyte of theorder of 0.1 mm and at higher hydrogen concentration, a maximum power density ofP = 1.4 W/cm2 was obtained. Voir les détails
Mots clés : LFG, Biogas, Anaerobic digestion, Electricity, SOFC
An advanced control approach for current harmonic cancellation using shunt active power filter
Generally, low harmonic frequencies such as the harmonic of the order 5 and 7 have agreat influence to deteriorate the network current and interim the grid power factor. The objectiveis; to cancel out the selected harmonic order from the network current. The shapes of waves andthe values of the THD of the network current before and after applying the proposed techniqueare introduced. The system is simulated and investigated using MATLAB/Simulink. The resultsprove the effectiveness of the design and control strategy (α-β). This paper deals with design,analysis and simulation of a three phase three wire shunt selective active power filter. Itcompensates the harmonic currents selectively under balanced power network. In order toimprove, the power factor of the supply network, an advanced control approach based on amultivariable filter is adopted. The novelty of the proposed control approach developed in thispaper is to use a multi-variable filter (MVF), which can extract the harmonics content of loadcurrent reference, according to the axis of Concordia. Voir les détails
Mots clés : harmonic, shunt selective active power filter control, power factor, multi-variable filter, MVF, axis of Concordia, THD
A comparison of 1D analytical model and 3D Finite Element Analysis with experiments for a Rosen-type piezoelectric transformer
This article is dedicated to the study of Piezoelectric Transformers (PTs), which offer promising solutions to the increasing need for integrated power electronics modules within autonomous systems. The advantages offered by such transformers include: immunity to electromagnetic disturbances; ease of miniaturisation for example, using conventional micro fabrication processes; and enhanced performance in terms of voltage gain and power efficiency. Central to the adequate description of such transformers is the need for complex analytical modeling tools, especially if one is attempting to include combined con- tributions due to (i) mechanical phenomena owing to the different propagation modes which differ at the primary and secondary sides of the PT; and (ii) electrical phenomena such as the voltage gain and power efficiency, which depend on the electrical load. The present work demonstrates an original one-dimensional (1D) analytical model, dedicated to a Rosen-type PT and simulation results are successively compared against that of a three-dimensional (3D) Finite Element Analysis (COMSOL Multiphysics software) and experimental results. The Rosen-type PT studied here is based on a single layer soft PZT (P191) with corresponding dimensions 18 mm x 3 mm x 1.5 mm, which operated at the second harmonic of 176 kHz. Detailed simulational and experimental results show that the presented 1D model predicts experimental measurements to within less than 10% error of the voltage gain at the second and third resonance frequency modes. Adjustment of the analytical model parameters is found to decrease errors relative to experimental volt- age gain to within 1%, whilst a 2.5% error on the output admittance magnitude at the second resonance mode were obtained. Relying on the unique assumption of one-dimensionality, the present analytical model appears as a useful tool for Rosen-type PT design and behavior understanding. Voir les détails
Mots clés : Piezoelectric transformer, Rosen-type transformer, 1D analytical modelling, 3D FEA simulations, Experimental characterisation
Numerical study of thermal Effects in the hydrodynamic Behavior of textured journal bearings
The journals bearing characteristics with texture presence on the bearing surface are investigated. The thermaleffect has been studied. The used numerical approach in this analysis is Finite Difference Method. The textured bearingperformance enhancement passes essentially by a minimum film thickness and a friction torque improvement through anappropriate surface texture geometry and right texture distribution on the bearing surface. It is found that the simulationresults are in good concordance with those issued from the litterature. The obtained results by considering thetemperature effect are more realistic. Voir les détails
Mots clés : Hydrodynamic lubrication, journal bearing, texturation, dimple
Surface texturing effect comparative analysis in the hydrodynamic journal bearings
The journal bearing is a complex system with high film convergence and with cavitation hydrodynamicphenomena. The surface texturation influence study on journal bearing performances requiresunavoidably experimental investigations followed by a numerical modelling of the problem. This work consistsin modellization and understanding of the journal bearing characteristics in both cases of presence orabsence of textures onto the bearing surface. The finite difference method is used as numerical approachin the analysis. The textured bearing performance enhancement passes essentially by an improvement of aminimum film thickness, a maximum pressure and a friction torque through an appropriate surface texturegeometry and appropriate texture distribution on the contact surface. It is found that the simulationsresults are in good concordance with litteratures. The texture area position on the bearing surface is theprimary endpoint for journal bearing performance enhancement. The best design of textured area dependsstrongly on the geometrical parameters and the journal bearing operating conditions. Voir les détails
Mots clés : Journal bearings, Reynolds equation, Hydrodynamic lubrication, Stribeck curve, texture