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Abdelkader Nour,Samir Lecheb,Nouredine Chikh,M. Ouali Si-Chaïb 대한기계학회 2011 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.25 No.7
This work concerns the characterization of the thermodynamic behavior of the superalloy Airsist 215 (PN 3601669-7) containing cobalt. Such superalloys are used in aeronautical construction, in the hot parts of the turbine. They are frequently used for the production of the paddles. The parts in service are subjected to dynamic solicitations and thermal fluctuations over the course of time. They are responsible for modification and degradation of material properties. This can lead to the appearance of cracks and, in the long term, to the rupture of these parts. In this paper, a preliminary physical study is made on the appearance of the cracks, followed by experiments using shocks at ambient temperature and under a heating situation which simulates combustion. It is found that these dynamic loads have a significant impact on the development of the cracks that appear on the segments of the turbine nozzle. The study is devoted to the elastic shock of Hertz-Boussinesq extended to viscoelastic bodies by direct convolution of Riemann-Stielges. The interest resides in the local convolution and the distribution of stresses in the contact zone. The shock excitation method includes a deduced force in the load and disload phases. This force is an impulse which approaches a Dirac function. The sample can be modeled approximately by a system of one degree of freedom for natural frequency, damping and transfer function. The spectral response of the specified shock allows calculation of the damping. Every point of this spectrum gives the response for the linear system of the transfer function. Then, viscoelastic shock parameters are deduced.
GMM-Based Maghreb Dialect Identification System
( Lachachi Nour Eddine ),( Adla Abdelkader ) 한국정보처리학회 2015 Journal of information processing systems Vol.11 No.1
While Modern Standard Arabic is the formal spoken and written language of the Arab world; dialects are the major communication mode for everyday life. Therefore, identifying a speaker’s dialect is critical in the Arabic-speaking world for speech processing tasks, such as automatic speech recognition or identification. In this paper, we examine two approaches that reduce the Universal Background Model (UBM) in the automatic dialect identification system across the five following Arabic Maghreb dialects: Moroccan, Tunisian, and 3 dialects of the western (Oranian), central (Algiersian), and eastern (Constantinian) regions of Algeria. We applied our approaches to the Maghreb dialect detection domain that contains a collection of 10-second utterances and we compared the performance precision gained against the dialect samples from a baseline GMM-UBM system and the ones from our own improved GMM-UBM system that uses a Reduced UBM algorithm. Our experiments show that our approaches significantly improve identification performance over purely acoustic features with an identification rate of 80.49%.
Dynamic prediction fatigue life of composite wind turbine blade
Samir Lecheb,Abdelkader Nour,Ahmed Chellil,Hamza Mechakra,Hicham Ghanem,Hocine Kebir 국제구조공학회 2015 Steel and Composite Structures, An International J Vol.18 No.3
In this paper we are particularly focusing on the dynamic crack fatigue life of a 25 m length wind turbine blade. The blade consists of composite materiel (glass/epoxy). This work consisted initially to make a theoretical study, the turbine blade is modeled as a Timoshenko rotating beam and the analytical formulation is obtained. After applying boundary condition and loads, we have studied the stress, strain and displacement in order to determine the critical zone, also show the six first modes shapes to the wind turbine blade. Secondly was addressed to study the crack initiation in critical zone which based to finite element to give the results, then follow the evolution of the displacement, strain, stress and first six naturals frequencies a function as crack growth. In the experimental part the laminate plate specimen with two layers is tested under cyclic load in fully reversible tensile at ratio test (R = 0), the fast fracture occur phenomenon and the fatigue life are presented, the fatigue testing exerted in INSTRON 8801 machine. Finally which allows the knowledge their effect on the fatigue life, this residual change of dynamic behavior parameters can be used to predicted a crack size and diagnostic of blade.
Forced transverse vibration of composite sandwich beam with magnetorheological elastomer core
Salah Aguib,Abdelkader Nour,Toufik Djedid,Georges Bossis,Nourddine Chikh 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.1
We studied, experimentally and numerically, the vibrational response of a magnetorheological elastomer sandwich beam, clampedfree,delimited by two skins aluminum 7075T6, first subjected to a variable magnetic field perpendicular to the skin of the beam, andsecond to a harmonic excitation by magnetic force applied at the free end. Our main objective was to predict the effect of the intensity ofthe current flowing through a coil on several dynamic factors. The maximum amplitude of resonance and the variation of the loss factoras a function of structural stiffness are adjusted simultaneously by the application of different magnetic fields. The results of bothmethods are compared.