Liste des documents
Performance evolution of fully and partially textured hydrodynamic journal bearings lubricated with two lubricants
This study investigates the evolution of the main bearing performance of partiallyand fully textured hydrodynamic journal bearing. The viscosity effect is also analysed by themean of numerical simulations for two types of oil: the oil 1 (ISO VG 32, 31.3 cSt at 40 °C)has a lower viscosity than oil 2 (ISO VG 100, 93 cSt at 40 °C). Reynolds equation is solved byfinite difference and Gauss-Seidel methods with over-relaxation for various operatingconditions. It is shown that, under hydrodynamic lubrication regime, the improvement of themost important characteristics (the friction coefficient and minimum film thickness) of atextured journal bearing depend strongly on the lubricant viscosity and the journal rotationalspeed. The fully textured journal bearing is highly favorable at very low speeds while thepartially textured journal bearing is more suitable for slightly higher speeds. The gain inbearing performance due to the texturing of the bushing disappears at a critical speed of thejournal and then, for higher rotational speeds, the presence of textures becomes detrimental. Voir les détails
Mots clés : journal bearing, texture, hydrodynamic, lubrication
Effect of Immersion Time and Cooling Mode on the Electrochemical Behavior of Hot-Dip Galvanized Steel in Sulfuric Acid Medium
In this work, we investigated the influence of galvanizing immersion time and cooling modes environments on the electrochemical corrosion behavior of hot-dip galvanized steel, in 1 M sulfuric acid electrolyte at room temperature using potentiodynamic polarization technique. In addition, the evolution of thickness, structure and microstructure of zinc coatings for different immersion times and two cooling modes (air and water) is characterized, respectively, by using of Elcometer scan probe, x-ray diffraction and metallography analysis. The analysis of the behavior of steel and galvanized steel, vis-a-vis corrosion, by means of corrosion characteristic parameters as anodic (βa) and cathodic (βc) Tafel slopes, corrosion potential (Ecorr), corrosion current density (icorr), corrosion rate (CR) and polarization resistance (Rp), reveals that the galvanized steel has anticorrosion properties much better than that of steel. More the immersion time increases, more the zinc coatings thickness increases, and more these properties become better. The comparison between the two cooling modes shows that the coatings of zinc produced by hot-dip galvanization and air-cooled provides a much better protection to steel against corrosion than those cooled by quenching in water which exhibit a brittle corrosive behavior due to the presence of cracks. Voir les détails
Mots clés : cooling mode, hot-dip galvanization, Metallography, Potentiodynamic polarization, steel, X-ray diffraction, zinc coating
Control of Matrix Converter Fed Induction Motor Drive
This paper presents a variable speed control of the squirrel induction machine fed by a three-phase matrix converter. Principle of vector control for induction motor and vector control strategy in synchronous reference frame are described. The use of matrix converter allows the availability of better switching devices, bi-directional power flow and sinusoidal input and output waveform. Also, the advantages of matrix converter are combined with the advantages of the field oriented control technique where Venturini algorithm is applied. We study the operation of the motor in the four regions of speed-torque plane. At this effect, the simulation results of the whole system are carried out with four quadrants of motor operations and the performance results obtained are presented and analyzed. A good performance of induction motor fed by a matrix converter is proved. Voir les détails
Mots clés : matrix converter, induction motor, vector control, modelling, Simulation.
A new time–frequency method for identificationand classification of ball bearing faults
In order to fault diagnosis of ball bearing that is one of the most critical components ofrotating machinery, this paper presents a time–frequency procedure incorporating a newfeature extraction step that combines the classical wavelet packet decomposition energydistribution technique and a new feature extraction technique based on the selection ofthe most impulsive frequency bands. In the proposed procedure, firstly, as a pre-processing step, the most impulsive frequency bands are selected at different bearing conditionsusing a combination between Fast-Fourier-Transform FFT and Short-Frequency Energy SFEalgorithms. Secondly, once the most impulsive frequency bands are selected, the measured machinery vibration signals are decomposed into different frequency sub-bands byusing discrete Wavelet Packet Decomposition WPD technique to maximize the detectionof their frequency contents and subsequently the most useful sub-bands are representedin the time-frequency domain by using Short Time Fourier transform STFT algorithm forknowing exactly what the frequency components presented in those frequency sub-bandsare. Once the proposed feature vector is obtained, three feature dimensionality reductiontechniques are employed using Linear Discriminant Analysis LDA, a feedback wrappermethod and Locality Sensitive Discriminant Analysis LSDA. Lastly, the Adaptive NeuroFuzzy Inference System ANFIS algorithm is used for instantaneous identification andclassification of bearing faults. In order to evaluate the performances of the proposedmethod, different testing data set to the trained ANFIS model by using different conditionsof healthy and faulty bearings under various load levels, fault severities and rotatingspeed. The conclusion resulting from this paper is highlighted by experimental resultswhich prove that the proposed method can serve as an intelligent bearing fault diagnosissystem. Voir les détails
Mots clés : Vibration signal processing Bearing fault diagnosis Bearing faults LDA, LSDA, ANFIS, WPD
Power Control of DFIG Driven by Matrix ConverterUnder Super and Sub Synchronous OperationModes
In this paper, we present the modeling and control of the wind energy conversion systemsbased on the doubly fed induction generator fed by AC/AC matrix converter. Firstly, wedeveloped the models of the different elements of the conversion chain. After, we consider thevector control strategy of the active and reactive powers in order to ensure an optimum operation.Finally, the dynamic model of a doubly fed induction generator and wind turbine grid connectedsystem is determined in the d-q synchronous reference frame.Therefore, the powers control isverified using software Matlab/Simulink. The behaviours of the sub-synchronous and supersynchronous operation modes is presented and discussed. The results prove that the power controlstrategy is well adapted to this kind of system. Voir les détails
Mots clés : wind systems, doubly fed induction generator, Bidirectional DC-DC Converter, Variable Speed Wind Turbine
Rational Function Approximationof a Fundamental Fractional OrderTransfer Function
This paper introduces a rational function approximation of thefractional order transfer function ; for 0 to 0:5. Thisfractional order transfer function is one of the fundamental functions of thelinear fractional system of commensurate order corresponding to pure complexconjugate poles or eigenvalues, in sa. Hence, the proposed approximation willbe used in the solution of the linear fractional systems of commensurate order.Illustrative examples are given to show the exactitude and the efficiency of theapproximation method. Voir les détails
Mots clés : Fractional power zero Linear fractional system Irrational transfer function Rational transfer function
The solution of state space linear fractionalsystem of commensurate order withcomplex eigenvalues using regularexponential and trigonometric functions
In a previous work, we have derived the generalsolution of the state space linear fractional system of commensurate order for real simple and multiple eigenvalues ofthe state space matrix. The obtained solutions of the homogeneous and non-homogeneous cases have been expressed as alinear combination of introduced fundamental functions. Inthis paper, the above work has been extended to solve thestate space linear fractional system of commensurate orderfor complex eigenvalues of the state space matrix. First, suitable fundamental functions corresponding to the differenttypes of complex eigenvalues of the state space matrix areintroduced. Then, the derived formulations of the resolutionapproach are presented for the homogeneous and the nonhomogeneous cases. The solutions are expressed in terms ofa linear combination of the proposed fundamental functionswhich are in the form of exponentials, sine, cosine, dampedsine and damped cosine functions depending on the commensurate fractional order. The results are validated by solving anillustrative example to demonstrate the effectiveness of theproposed analytical tool for the solution of the state spacelinear fractional system of commensurate order. Voir les détails
Mots clés : Complex eigenvalues · Fractional differential equation · Fundamental functions · Modal decomposition · Rational function · State space representation
Study of physico-chemical properties of diatomiteAlgeria: Application to the thermal insulation ofliquid steel bath
The purpose of this paper is to characterize and to evaluate the diatomite powder of Sig region (West Algeria) withoutfluorine by powder generally used in tundish to thermal insulation of steel bath contain fluorine, that affecting the environment andhealth of workers. Thermal and physicochemical characterization showed different endothermic and exothermic peaks. Thescanning microscopy method was used and a large porosity was observed, which is very beneficial for improving the thermalconductivity of the product. The trial industrial in steelwork with diatomite powder, showed a weak loss temperature of steel (10 °Cmax), and filled fully function in thermal insulation of the steel bath. Voir les détails
Mots clés : diatomite, fluorine, Tundish, steelwork, thermal insulation, DSC
Fuzzy monitoring of stator and rotor winding faultsfor DFIG used in wind energy conversion system
According to its high robustness, the use of doubly-fed induction generators in thewind energy conversion takes an important place in the world of production of electrical energy.This type of conversion became very attractive because of its manufacturing environments,low cost and operation with an easily available power supply. The increase interest in windenergy conversion has been accompanied by efforts to improve reliability, effective conditionmonitoring and better efficiency. In this work, a new technique is proposed for monitoring anddetection of inter-turn short-circuit ITSC and open phase circuits in the stator or rotor windingsof wind turbines based on doubly-fed induction generator The principle of the suggestedtechnique is based on the acquisition of the stator and the rotor currents of a doubly-fed inductiongenerator with the aim to calculate the values of root mean square amplitude, in addition to theknowledge expressed in rules and membership function. This technique is verified usingsimulations performed via the model of doubly-fed induction generators built in MATLAB ®Simulink. Voir les détails
Mots clés : doubly-fed induction generator, DFIG, Fuzzy logic, Monitoring, Detection, faults, RMS
Spatio-temporal aspects of the domain propagation in a spin-crossover lattice with defect
the collective spatiotemporal dynamics of the metastable high-spin state (HS) upon relaxation towards the low-spin (LS) is investigated using an electro-elastic model which includes the change of the spin states and the lattice volume at the transition. The present work focusses on the case of a lattice in which is embedded a structural defect in the center, represented here by a hole with a fixed size. The simulations are made on a 2D rectangular-shaped and compared to those of an ideal system. To account for the volume change, we set the distances between the sites as spin-dependent which requires the use of Monte Carlo simulations on spin states and atomic positions to solve the present problem. It is found that the presence of the defect affects the dynamics of the spin-crossover transformations which starts stochastically from a corner of the lattice, then propagates in the first stage along the width (shortest distance to the surface), before to proceed via a second longitudinal regime whose velocity slows down significantly at the vicinity of the defect, which plays the role of a pining center. After a while, the interface leaves the defect, and accelerates when it approaches the lattice's border. We have also investigated the spatial dependence of the displacement field, from which we derived the distribution of the divergence and rotational of the displacement field, which directly connects to the trace of the strain tensor and to shear strains respectively. Valuable information on the relaxation process of the elastic field are derived and discussed in direct relation with the presence of the defect. Voir les détails
Mots clés : Spin Crossover, Phase transition;, Interface propagation;, Spatiotemporal effects, elasticity