Liste des documents
UPFC Device: Optimal Location and Parameter Settingto Reduce Losses in Electric-Power Systems Using a Genetic-algorithm Method
Ensuring the secure operation of power systems has become an important and critical matter during the present time, along with the development of large, complex and load-increasing systems. Security constraints such as the thermal limits of transmission lines and bus-voltage limits must be satisfed under all of a system’s operational conditions. An alternative solution to improve the security of a power system is the employment of Flexible Alternating-Current Transmission Systems (FACTS). FACTS devices can reduce the flows of heavily loaded lines, maintain the bus voltages at desired levels, and improve the stability of a power network. The Unifed Power Flow Controller (UPFC) is a versatile FACTS device that can independently or simultaneously control the active power, the reactive power and the bus voltage; however, to achieve such functionality, it is very important to determine the optimal location of the UPFC device, with the appropriate parameter setting, in the power system. In this paper, a genetic algorithm (GA) method is applied to determine the optimal location of the UPFC device in a network for the enhancement of the power-system loadability and the minimization of the active power loss in the transmission line. To verify our approach, simulations were performed on the IEEE 14 Bus, 30 Bus, and 57 Bus test systems. The proposed work was implemented in the MATLAB platform. Voir les détails
Mots clés : FACTS, UPFC, GA, loadability, Matlab
An experimental analysis of fracture mechanisms by acousticemission of woven composite bolted assembly
This work is focused on the study of the evolution of damage mode and failure mechanisms of woven composite bolted assembly carbon fiber/epoxy. In the present paper three configurations are studied [0°,45°,0°,45°], [0°,45°,0°,45°]s and [0°,45°,0°,45,0°]s. In order to analyze a global mechanical behavior of the assembly, monotonous tensile tests are performed. The damage evolution is followed simultaneously by acoustic emission (A.E) and digital image correlation (D.I.C). Acoustic signatures of four modes of damage are identified, matrix cracking, fiber-matrix debonding, delaminating and fiber breakage, then confirmed by microscopic observations in scanning electron microscopy (SEM).Composite woven, émission acoustique, assemblage boulonné, corrélation d'image numérique, endommagement. Voir les détails
Mots clés : Woven composite, acoustic emission, bolted assembly, digital image correlation, Damage.
Oi and Cs Impurities Study on the Edge of Si-mc Ingot for Photovoltaic Applications
The objective of this work is determining the substitutional carbon ([Cs]) and interstitial oxygen ([Oi]) concentrations in the edge of the multicrystalline silicon ingot (mc-Si) for photovoltaic applications obtained by the heat exchanger method (HEM). Some calculations of [Cs] and [Oi] was obtain by the Fourier Transform InfraRed spectroscopy (FTIR). The results obtained for [Cs] give an increase of bottom-up of the ingot: 130 ppm to 150 ppm. The results obtained for the [Oi] give constant concentrations throughout the edge of the ingot with an author of concentration 325 ppm. Voir les détails
Mots clés : Crystallization, mc-Si, HEM, FTIR, [Cs], [Oi]
A Comparative Study of Various Methods of Bearing Faults Diagnosis Using the Case Western Reserve University Data
Bearing is probably one of the most critical components of rotating machinery. They are employed to guide and support the shafts in rotating machinery. Therefore, any fault in the bearings can lead to losses on the level of production and equipments as well as potentially unsafe. For these reasons, the bearing fault diagnosis has received considerable attention from the research and engineering communities in recent years. The purpose of this study is to review the vibration analysis techniques and to explore their capabilities, advantages, and disadvantage in monitoring rolling element bearings. Voir les détails
Mots clés : Vibration analysis, bearing Fault diagnosis, Temporal analysis, Cepstrum analysis, Envelope analysis, Wavelet transform
Contribution to Reconfigured Multi-Level Inverter FedDouble Stator Induction Machine DTC-SVM Control
The Dual Stator Induction Machine (DSIM) meets well with the need for high power applications. In the recent years, it has been increasingly used for variable speed drives. However, its control strategy is still a subject of research due to its complex structure, though it offers more reliable application in use due to the presence of double stators. The fault detection and localization in an inverter are profitable for better diagnosis and the inverter reconfiguration is the most required process to ensure acceptable service continuity. This paper tackles, on the one hand, a control strategy based on the Direct Torque Control combined with the Space Vector PWM of a DSIM (DTC-SVM-DSIM) and on the other hand, a three-level inverter fault detection and localization, reconfiguration of the inverter when operating under open-circuit IGBT switch faults. Several results are presented to illustrate the enhancement of torque and flux quality owed to the proposed control strategy and also to show the improvement of the open-circuit fault detection and localization method for better diagnosis as well as the inverter reconfiguration impact on the drive system service continuity. Voir les détails
Mots clés : DSIM, Multi-level Inverter, NPC, DTC, SVM, Reconfiguration
Numerical Simulation of Temperature Distribution and Material Flow During Friction Stir Welding 2017A Aluminum Alloys.
Abstract.This study describes the use of fluid dynamic code, FLUENT to model the flow of metal in the AA2017A case around the welding tool pin (FSW). A standard threaded tool profile is used for the analysis of phenomena during welding such as heat generation and flow of the material are included. The main objective is to gain a better understanding of the flow of material around a tool. The model showed a large number of phenomena similar to those of the real process. The model has also generated a sufficient amount of heat, which leads to a good estimate of the junction temperature. These results were obtained using a viscosity which is near the solidus softening. Voir les détails
Mots clés : Friction Stir Welding, 2017A aluminum alloy, Temperature distribution
Finite volume modeling of laser assisted friction stir welding of 2017A-T451 aluminum alloy for enhanced sustainability of welded joints.
This study focuses on a new welding modification friction stir welding, using a preheating during the welding phase. This method utilizes laser energy to pre-heat the workpiece to a localized area at the front of the FSW tool, thereby reducing the temperature gradient over a localized area in advance of the tool. The amount of heat generated during welding determines the quality of the weld. Therefore the understanding of the temperature distribution is required to determine the optimal method of welding parameters. In this study, a two-dimensional model of an aluminum alloy plate coupled to a circular laser source is developed, using FLUENT software that is based on the finite volume method, also the geometry of the pin of the FSW tool was modified in several configurations to highlight the effect of the geometry of the tool on the temperature distribution in the welded plate. The model developed can be used to better understand the process, predict process performance and to determine the optimal parameters of the process. Voir les détails
Mots clés : riction stir welding, 2017A-T451 aluminum alloy, Finite volume modeling
Residual stresses of a magnesium alloy (AZ31) welded by the friction stir welding processes.
Abstract. The objective of this study was to evaluate the residual stresses of FSW welding magnesium alloys (AZ31). The results show that the FSW processes lead to the formation of several distinct zones with differing mechanical properties. The residual stresses evolution have been explained by the heterogeneous modifications of the microstructure particularly a marked decrease in the grain size, a high modification of the crystallographic texture and the different anisotropic properties resulting from plasticity induced by the FSW process. Voir les détails
Mots clés : AZ31 magnesium alloy, Friction Stir Welding, residual stresses
Gap states density measurement in copper oxide thin films
The density of gap states near the Fermi level have been measured in copper oxide (CuO) thin ?lms deposited by spray pyrolysis technique. The measurement method is based on the exploitation of the current–voltage characteristics of the space charge limited current (SCLC) measured in a sandwich Au/CuO/Au structure. The measured gap states density is equal to 1.5x1014cm-3 and 2.0 x1014 ev-1 respectively in films prepared at 300 and 400 °C substrate temperature, while the defect position are located at 16 and 20meV above Fermi level. The carriers mobility and concentration are also determined from SCLC, the obtained results are in good agreement with Hall effect measurement ones. Voir les détails
Mots clés : Density of states Thin ?lms Spray pyrolysis Solar cells
Sulfide precursor concentration and lead source effect on PbS thin flms properties
Lead sul?de (PbS) thin ?lms were synthesized using chemical bath deposition (CBD). Bath solutions are formed of various concentrations of thiourea, sul?de source, ranged from 0.6 to 1.2 M and two different salts as Pb source (lead acetate and lead nitrate). From the growth mechanism, we inferred that PbS is formed through the ion by ion process when using acetate lead source, while, using nitrate source yields to ?lms growth through the complex decomposition process. Due to the difference in the involved growth process, lead acetate produces ?lms with larger crystallite size (from 4 to 16 nm), smooth and dense ?lms. However, lead nitrate produces rough ?lms with smaller crystallite size (from 1 to 4 nm).Increasing the thiourea concentration results in crystallinity improvement when using lead acetate and, oppositely, in crystallinity degradation when using lead nitrate. Due to the quantum effect caused by the small crystallite sizes, the ?lms optical gap is varied from 0.5 to 0.9 eV. Voir les détails
Mots clés : Thin ?lms Lead sul?de Chemical bath deposition