Liste des publications

Nombre total de résultats : 418
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SIMULATION STUDY OF SUPER-RESOLUTION IN HYDROPHONE MEASUREMENTS OF PULSED ULTRASONIC FIELDS

Wahiba Djerir, Tarek Boutkedjirt (2018)
Article de journal

In order to carry out reliable measurements of pulsed ultrasonic fields, the use of a piezoelectric hydrophone as receiver is recommended. However, due the finite size of the receiver aperture the measured acoustic pressure is affected by spatial averaging on the surface active face. The aim of this work is to deconvolve the spatial effects of the receiver hydrophone in order to reconstruct the pulsed ultrasonic field with a better spatial resolution. Hereby, the linear pulsed pressure field radiated in water by wideband planar transducers of 19 mm diameter, with central frequencies fc=2.25 MHz and fc=15 MHz are considered. The receivers are PVDF membrane hydrophones of 25 µm - thickness with rectangular and circular apertures. The results of this study show the strong dependency of the reconstruction quality upon the signal-to-noise ratio (SNR). Generally, the quality of the reconstruction decreases with decreasing SNR. Good reconstruction quality has been obtained with correlation coefficient larger than 0.9936 when the “acquired” signals are not too much noisy (SNR=60dB). In this case, improvement of the spatial resolution by a factor of 5 and 9 respectively could be reached. The reconstruction quality depends also upon the hydrophone dimensions, the axial distance to the source, the central frequency and the spectral frequency bandwidth of the pressure pulse.Voir les détails

Mots clés : Super-resolution, spatial inverse filter, spatial Wiener filter, PVDF hydrophone, pulsed ultrasonic field, ultrasonic field reconstruction.

Spatially Varying Weighting Function-BasedGlobal and Local Statistical Active Contours.Application to X-Ray Images

Aicha Baya Goumeidane, Nafaa Nacereddine (2016)
Article de journal

Image segmentation is a crucial task in the image processingfield. This paper presents a new region-based active contour whichhandles global information as well as local one, both based on the pixelsintensities. The trade-off between these information is achieved by aspatially varying function computed for each contour node location. Theapplication preliminary results of this method on computed tomographyand X-ray images show outstanding and efficient object extractionVoir les détails

Mots clés : image segmentation, Active contour, Averaged Shifted, histogram, pressure forces, statistics, Spatially varying function

Electroless copper deposition on epoxy glass substrate for electrocatalysis of formaldehyde

C. Dehchar, I. CHIKOUCHE, R. KHERRAT, A. Sahari, A. Zouaoui, A. MERATI (2018)
Article de journal

In this paper, we investigated the characteristics of a structured copper (Cu) ?lm deposited on the surface of an insulating epoxy glass (EG) substrate via a facile electroless plating process. The ?lm produced by this method was found to be of high purity and has a homogeneous microstructure consisting of an assembly of numerous aggregates that vary in size from 1 to 5 mm depending on the electroless deposition time. The electrocatalytic activity of the prepared electrode was investigated for the electrooxidation of formaldehyde using cyclic voltammetry in 0.1 M NaOH solution. Results show that formaldehyde oxidation takes place at a low potential of -0.34 V with large anodic current densities.Voir les détails

Mots clés : copper, electroless plating, Formaldehyde, Oxidation, Thin films

Numerical simulation study of a high efficient AlGaN-based ultraviolet photodetector

F. Bouzid, L. Dehimi, F. Pezzimenti, M. HADJAB, A. HADJ LARBI (2018)
Article de journal

In this paper, a two-dimensional (2D) numerical simulation study of a p+-n-n+ AlGaN-based ultraviolet (UV) photodetector, which is designed to achieve true solar blindness with a cutoff wavelength of 0.31 µm, is presented. The device performance is evaluated by investigating both the current density-voltage characteristics and the spectral response (SR). The proposed structure is optimized in terms of the fundamental geometrical and doping parameters. During the simulations, it was found that the detector is sensitive to the UV rays in the 0.155-0.37 µm wavelength range and the spectral response can reach 0.156 AW-1 under a light intensity of 1 Wcm-2 at zero-bias voltage and room temperature. This SR peak value increases further under reverse bias conditions. The temperature effect on the detector SR and the impact of an explicit trap concentration located into the p+ and n-region are also investigated. The spectral response decreases for a temperature exceeding 420 K. At the same time, the SR reference values begin to be affected only for acceptor and donor trap densities that are much higher than the local (total) doping concentration.Voir les détails

Mots clés : AlGaN, Numerical simulation, Photodetector, Spectral response, Trap Density

Correlation between defect depth and defect length through a reliability index when evaluating of the remaining life of steel pipeline under corrosion and crack defects.

Djamel Zelmati, Oualid GHELLOUDJ, Abdelaziz AMIRAT (2017)
Article de journal

Despite the various engineering models existing for lifetime investigation of hydrocarbon steel pipelines under localized corrosion and crack defects there is still a lack of information about the correlation between the two main parameters characterizing the geometrical defect model, depth and length. So the aim of the present work is a contribution in evaluating the remaining life of the pipeline using reliability analysis in order to correlate the two parameters through one common parameter, the reliability index. As a first step, the investigation is carried out on four standard and well established engineering models; Irwin, SINTAP, ASME B31G and Modified ASME B31G methods, aiming to coordinate results given by each of the four models. The potential defect depth and length correlation through a reliability index can be used as a decision-making tool to give realistic answers for replacing and/or repairing a tube subjected to internal pressure and on which flaws of different depths and lengths have been detected from inspection of a pipeline after few years of service.Voir les détails

Mots clés : corrosion, Defect, Reliability, Correlation, Sensitivity

Reliability estimation of pressurized API 5L X70 pipeline steel under longitudinal elliptical corrosion defect.

Djamel Zelmati, Oualid GHELLOUDJ, Abdelaziz AMIRAT (2017)
Article de journal

The probabilistic approach is the best way to give realistic answers for design and maintenance and it is considered as a powerful decision-making tool. In the present paper, assessment of the failure probability of corroded pipeline subjected to internal pressure is estimated by using the first order reliability method (FORM). Measurements of defect dimensions have been achieved changed into collected by using ultra sound inspection probe through a 75-km pipeline portion on one of the main Algerian high pressure gas transportation that has been in service for 30 years. The sensitivity analyses have been carried out on random variables to identify the importance of the parameters within the reliability mechanical model. The modified B31G code has been coupled as a mechanical model, with Rackwitz optimization algorithm by using PHIMECA Software. The limit state function resumes the difference between the pipeline burst pressure and the pipeline operating pressure. The aim of the present work is to make in evidence the competitive importance of pressure service, wall thickness and the defect depth with regards to defect length and to determine the influence of the coefficients of variation on the failure probability and the remaining life of the pipeline. A diagram based on the reliability index results is proposed to predict the pipeline degradation and it can be used as a decision tool for maintenance program.Voir les détails

Mots clés : corrosion, Failure probability, Coefficient of variation, Modified ASME B31G

Engineering modeling of wear profiles in tooth flank of polyamidespur gears

Oualid GHELLOUDJ, Djamel Zelmati, Abdelaziz AMIRAT (2017)
Article de journal

The present paper is a contribution in developing an engineering model expressing the evolution of tooth flank wear in polyamide spur gears as a function of number of cycles. The method is based on first observing the behavior of wear on tooth flanks in real test conditions. Then progressive flank wear profiles are plotted in order to sort out the corresponding fitting curves together with the associated mathematical equations. The general engineering model controlling the evolution of wear profile is found of the form of quadratic equation where the variable is the circular thickness of a tooth at a given depth from the top land of the tooth. The respective parameters of the engineering wear equation are determined as a function of number of revolutions of the spur gear. A wear correction parameter kw is added in order to catch up the measuring errors when plotting the wear profile curves using the proposed engineering wear model for spur gears. The data are in good agreement with that obtained from experimental measurements.Voir les détails

Mots clés : polyamide, Spur gear, wear, Tooth flank, lubrication

Structure, magnetic and microwave studies of mechanically alloyed powders Fe45Ni35Co20

Ahmed HADDAD, Insaf Ouldbrahim, Mohamed Azzaz (2018)
Article de journal

Nanocrystalline Fe-35 wt%Ni-20 wt%Co has been prepared by using a high-energy planetary ball mill with increasing milling time from 4 to 36 h. Microstructural characterisations showed the development of an face-centred cubic nanostructured Fe-35 wt%Ni-20 wt%Co alloy with an average crystallite size of 8 nm. The magnetic investigation revealed that the nanostructures obtained from a milling time of 36 h have the highest magnetic saturation and the lowest coercive field. In addition, the hardness and the electromagnetic absorption of the Fe-35 wt%Ni-20 wt%Co alloy were found to increase with the milling time. These evolutions could be attributed to the crystallite size and the strain variations in the samples during milling.Voir les détails

Mots clés : nanostructure, magnetic, nanocristalline, Mechanical Alloying, Fe, Co

EFFECT OF ELECTRICAL CURRENT ON FRICTION AND WEAR BEHAVIOR OF COPPER AGAINST GRAPHITE FOR LOW SLIDING SPEEDS

Abdeldjalil BENFOUGHAL, Ali BOUCHOUCHA, Youcef MOUADJI (2018)
Article de journal

Copper-graphite is an important tribological material used in the applications of electrical sliding contact like generators and electrical brushes. A series of experimental tests were conducted on a pin-disc tribometer in air and dry sliding condition. The pair of material was subjected to electric current ranging from 0 to 10A, normal loads of 5 to 30N and sliding speed of 0.5m/s. The duration of each test was 30 minutes. Experimental results indicated that the friction coefficient decreases and wear rate increases with increasing load with and without applied electric current. The changes in surface chemistry and topography of the tribo-surfaces were characterized using Raman spectroscopy, scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). This later technique was used to analyze the transfer of pin materials to the counterface, and also to understand how copper and graphite influence the tribological properties. Results indicated that, electric current and normal load have more or less significant influence on the tribological behavior of the pair of materials and the effect of oxide layer created at interface of the pairs in contact.Voir les détails

Mots clés : friction, wear, Contact temperature, load, Electric current.

Estimated life time in an HDPE pipe with a semi-elliptical defect under internal pressure

L. Alimi, K. Chaoui, M. HASSANI, A. Azzi (2017)
Article de journal

High density polyethylene has been widely used in marine and gas transportation, storm sewers, culverts and city drainage system. Compared with other conventional pipes, it has its own advantages, such as, chemical and corrosion resistance, toughness, flexibility, easy splicing and consequent easy handling and installation. In this paper, and in order to predict the remaining lifetime of a pipe having a defect and subjected to internal pressure, it is necessary to estimate KI stress intensity factor during the propagation of the crack. The finite element method is used to assess the values of the stress intensity factor of an axially oriented semi-elliptical crack located at the inner surface of an HDPE pipe. The crack configuration is described by the relative wall thickness (t/R), the relative crack depth (a/t) and the crack aspect ratio (a/c). The lifetimes presented are discussed according to the size of the crack and the stress intensity factor in each case.Voir les détails

Mots clés : HDPE pipe, Crack, rupture, Finite Element Method FEM, stress intensity factor, Lifetime