Szerző szerinti böngészés "Khamlichi, Abdellatif"
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Tétel Szabadon hozzáférhető Application of viscoelastic dampers for reducing dynamic response of high-speed railway bridges(Akadémiai Kiadó, 2020-08-01) Tahiri, Mohamed; Khamlichi, Abdellatif; Bezzazi, Mohammed; nemDue to the extensive development of high-speed railway lines which are operating at increasing velocities, the dynamic performance of railway bridges has become an important issue of scientific research. The aim of this study is to investigate the possibility of reducing the vertical acceleration and displacement of pre-stressed reinforced concrete bridges beams by using passive nonlinear viscoelastic dampers to retrofit them. The proposed solution is based on connecting the dampers directly to the abutments and the bottom surface of the bridge deck with an eccentricity between the neutral axis of the bridge and the contact point of the viscoelastic dampers. First, the dampers are modeled through the concept of linearized fractional derivatives to obtain energetic equivalent linear viscoelastic dampers. Optimization of the configuration of these dampers was performed then as function of the orientation angle and the eccentricity. Considering two bridges having different length that were studied in the literature with other systems of damping, it was found that the best orientation angle of dampers is close to 60°. It was found also that, in order to satisfy Eurocode 1 requirements, the total equivalent damping coefficient for the actual damping system is less than half of that required for systems using auxiliary beam to fix dampers, which indicates higher efficiency of the proposed solution.Tétel Szabadon hozzáférhető Force-displacement relationships for NiTi alloy helical springs by using ANSYS: Superelasticity and shape memory effect(Akadémiai Kiadó, 2022-10-27) El Mtili, Chayma; Khamlichi, Abdellatif; Hessissen, Loubna; Badar, Hafiz Muhammad Waqas; nemShape memory alloys are smart materials which have remarkable properties that promoted their use in a large variety of innovative applications. In this work, the shape memory effect and superelastic behavior of nickel-titanium helical spring was studied based on the finite element method. The three-dimensional constitutive model proposed by Auricchio has been used through the built-in library of ANSYS® Workbench 2020 R2 to simulate the superelastic effect and one-way shape memory effect which are exhibited by nickel-titanium alloy. Considering the first effect, the associated force-displacement curves were calculated as function of displacement amplitude. The influence of changing isothermal body temperature on the loading-unloading hysteretic response was studied. Convergence of the numerical model was assessed by comparison with experimental data taken from the literature. For the second effect, force-displacement curves that are associated to a complete one-way thermomechanical cycle were evaluated for different configurations of helical springs. Explicit correlations that can be applied for the purpose of helical spring’s design were derived.Tétel Szabadon hozzáférhető Inspection of transverse flaws for railways using phased array ultrasonic technique(Akadémiai Kiadó, 2021-08) Benzer, Hajar; Khamlichi, Abdellatif; Zakriti, Alia; nemRail monitoring is an important activity which aims to preserve the safety and availability of railways. According to statistics, the primary cause of railway accidents is due to transverse defects that occur in the rail head. These special defects develop generally in a plane orthogonal to the rail running direction. The detection of these defects is a priority to increase the safety of rail transportation. Rail control monitoring techniques mostly rely on infrared thermography, eddy currents, air-coupled acoustic sensors, and ultrasounds. The present research studies the rail diagnosis by means of a non-contact device. The focus is on ultrasonic based methods where excitation is generated by thermal elastic coupling following laser irradiation of the rail head. For the reception of echoes, a special ultrasound sensor was used. In order to sense defects, phased array elements, which use multiple transducers and electronic time delays, are used to increase and to focalise the signal intensity. Flaws that have a moderate extension are better detected by the proposed method than with laser irradiation consisting of a single spot.Tétel Szabadon hozzáférhető Low cycle fatigue behavior of circumferentially notched specimens made of modified 9Cr–1Mo steel at elevated temperature(Akadémiai Kiadó, 2021-10-13) Abarkan, Ikram; Khamlichi, Abdellatif; Shamasss, Rabee; nemDuring service, notched designed components such as steam generators in the nuclear power plant usually experience fatigue damage at elevated temperatures, due to the repeated cyclic loadings during start-up and shut-down operations. Under such extreme conditions, the durability of these components is highly-affected. Besides, to assess the fatigue life of these components, a reliable determination of the local stress-strain at the notch-tips is needed. In this work, the maximum strains of circumferentially notched cylindrical specimens were calculated using the most commonly known analytical methods, namely Neuber's rule, modified Neuber's rule, Glinka's rule, and linear rule, with notch root radius of 1.25, 2.5, and 5 mm, made of modified 9Cr–1Mo steel at 550 °C, and subjected to nominal stress amplitudes of ±124.95, ±149.95, and ±174.95 MPa. The calculated local strains were compared to those obtained from Finite Element Analysis (FEA). It was found that all the analytical approximations provided unreliable local strains at the notch-tips, resulting in an overestimation or underestimation of the fatigue life. Therefore, a mathematical model that predicts the fatigue lives for 9Cr–1Mo steel at elevated temperature was proposed in terms of the applied stress amplitude and the fatigue stress concentration factor. The calculated fatigue lifetimes using the proposed model are found to be in good agreement with those obtained experimentally from the literature with relative errors, when the applied stress amplitude is ±149.95 MPa, are of 1.97%,–8.67%, and 13.54%, for notch root radii of 1.25, 2.5, and 5 mm, respectively.Tétel Szabadon hozzáférhető Optimizing linear phased array transducers for non-destructive evaluation of thin layers(Akadémiai Kiadó, 2020-08-01) Achbal, Mariam; Khamlichi, Abdellatif; El Khannoussi, Fadoua; nemIn this work, a numerical method is proposed in order to achieve design optimisation of phased array (PA) probes for the special application of defects detection in thin films. This approach relies on an extended Fourier-based model that was adapted to predict the two-dimensional ultrasonic displacement field taking place in a thin plate under individual excitation of PA probe elements which have arbitrary orientation with respect to the examined part surface. Excitation is applied through a fluid couplant and is operated at scheduled delays that are managed to enable emission of constructive pulses. This gives the possibility to steer sound waves towards a direction and to focalize the beam in a selected point. An optimisation algorithm based on the concept of pattern search that does not require evaluation of a gradient was used to find the best match in the multidimensional analysis space of possibilities including the elements orientation angles, the elements lengths, the inter-elements distances and work frequency. Optimisation was performed with the objective to maximize the displacement amplitude at the focal point while minimizing simultaneously the effect of beam side lobes. The results obtained by this approach reveal that focalisation can be achieved with enhanced features in comparison with previous algorithms assuming linear elements that are parallel to the surface of the plate.Tétel Szabadon hozzáférhető Reliability analysis of slope stability in earthen dams following rapid drawdown(Akadémiai Kiadó, 2019-06-01) Kahot, Zakariae; Dkiouak, Rachid; Khamlichi, Abdellatif; nemThis work was dedicated to assessing reliability of slope stability in earthen dams following rapid drawdown. Modeling of the problem physics was based on saturated-unsaturated seepage flow through the nonlinear Richards equation, under the assumption of two-dimensional approximation in steady state and transient state. The modeling of seepage taking place inside the earth dam infill materials included soil parameters, the negative pore water pressure-hydraulic conductivity relationship as well as the negative pore water pressure-volumetric water content. Slope stability was analyzed by using safety factor as evaluated by the Bishop's simplified method. Solution of the governing equations in terms of pore water pressure and fluid flow velocity was performed by using the modules SEEP/W and SLOPE/W of the Finite Element based software package GeoStudio. The drawdown phenomenon was then analyzed and its influence on dam stability assessed by using surface response method and Monte Carlo simulation. A design formula was proposed in order to bound the probability of failure associated to slope stability.Tétel Szabadon hozzáférhető Simulation aided design of a high efficient GaSb based single-junction solar cell(Akadémiai Kiadó, 2023-05-09) Kharchich , Fatima Zahra; Khamlichi, Abdellatif; nemOwing to their elevated absorption coefficient, superior resistance to radiation and reduced effective electron mass, gallium antimonide (GaSb) semiconductors were documented to be suitable for photovoltaic systems applications. However, they were found to suffer from low efficiency. This work has been dedicated to enhance the design of GaSb based single-junction solar cells having window and back surface field made from AlGaAsSb material. The purpose is to maximize their electrical performance by considering doping and thickness of layers as design variables. A methodology of optimization was proposed. It is based on computer aided design through simulations performed under SILVACO-ATLAS software and a numerical procedure that was developed to achieve optimal design of this particular solar cell. The approach encompasses analysis of variance and derivation of response surface models to get explicit expression of the objective function corresponding to efficiency. The obtained results have shown an efficiency which is higher than all the previous known values established in literature.