Liste des documents
Swarm Optimization Algorithm Inspired in the Behavior of the Social-Spider for Microwave Filters Optimization
In this paper, a recent swarm optimization algorithm on the simulation of the cooperative behavior of social spiders, called the Social Spider Optimization (SSO) is proposed for the optimization of microwave filters. In order to illustrate the proficiency and robustness of this optimization, it iscompared to other literature of evolutionary algorithms, particle swarm optimization (PSO) and teachingl earning-based optimization (TLBO). The outcome shows a high performance of the proposed method. Voir les détails
Mots clés : optimization, microwave filter, social spider optimization
Dielectric Characterization of Thermally Aged XLPE High Voltage Cable Insulation
The widespread use of crosslinked polyethylene (XLPE) as insulation in high voltage power cables may be attributed to its excellent electrical, thermal and mechanical characteristics. However, this insulation may undergo crucial degradations when exposed to the various constraints, which leadto its general weakness. During its operating under service conditions, the cable is in permanence subjected to thermal aging which can provokes an irreversible alteration of the cable insulation properties. This work presents an investigation on the changes induced in the dielectric and electrical properties of athermally aged XLPE cables insulation. Voir les détails
Mots clés : Crosslinked polyethylene (XLPE), insulation, thermal aging, dielectric properties.
Ultrasonic attenuation in trabecular bone: Theoretical approach and experimental measurement
The aim of this paper is to determine how different parameters such as porosity, scatter size and frequency affect the ultrasonic attenuation process during the acoustic wave propagation through the trabecular bone. In this study, a theoretical model combining absorption and scattering is proposed to predict attenuation in trabecular bones. The total theoretical attenuation coefficient is computed as the sum of the contributions of scattering and absorption. The obtained results have been compared with experimental data achieved on bovine cancellous bone samples filled by water. The porosity of the used samples varies between 40 % and 75 %. A transmission technique is used. This method only requires the measurement of the specimens thickness and recording of two pulses: one without and one with the specimen inserted between the transmitting and receiving transducers. The theoretical model used in this paper appears to give appropriate results compared with experimental measurements. The obtained results show that viscous losses are not sufficient to describe the attenuation intrabecular bone. This study indicates that scattering is the primary mechanism responsible for attenuation in trabecular bone and confirms the strong dependence of the attenuation of the size of the scatterer, the bone porosity and of the ultrasound frequency. Voir les détails
Mots clés : Cancellous bone, Ultrasound, Attenuation, Scattering, Propagation modeling
Modeling and Simulation of the Defect Form Effect on Mechanical Behaviour of Shrink-Fit Assemblies.
The calculation methods of shrink fit assemblies remain traditional and have hardly changed for several years. They consider that the contact surfaces are perfectly smooth and do not take into account their geometrical defects (shape,roughness ....). The models created impose too high manufacturing costs to make consistent assumptions of calculations with the operational conditions of realization. To reduce manufacturing costs, the study of the influence of defect form on assemblies resistance characteristics is essential. The objective of this work is to study the influence of the defect form on the strength characteristics of shrink fit assemblies. It is shown that the defect form is not prejudicial to the strength of the assembly: the mean pressures are almost equivalent to the conventional case of surfaces without defects. Various finite element simulations were performed. The influence of the amplitude and of the default period was studied for different types of tightening. Voir les détails
Mots clés : shrink-fit, finite element, modeling of contact, machining, behavior
Testing the setting and hardening of concrete using the prism technique
In non-destructive testing of concrete, the ultrasonic pulse-echo technique has proven to be a reliable method for locating cracks and other internal defects. An electro-mechanical transducer is used to generate a short pulse of ultrasonic stress waves that propagate into the object being inspected. Reflection of the stress pulse occurs at boundaries separating materials with different densities and elastic properties. The reflected pulse travels back to the transducer that also acts as a receiver. The received signal can give many insights to the properties of materials under test.The question arises how the setting and hardening of cement paste, mortar, and concrete can be measured continuously. Continuous measurement ask sfor non destructive methods. The current testing method such as the vicat needle for cement paste and penetration resistance test for concrete methods measure at intervals.These methods can be applied before the end of setting. All these methods do not allow continuous measurements and are partly destructive. In this paper a special pulse-echo technique called prism technique is used to evaluate the evolution of proprieties of concrete over time. For that, an automatic system has been developed with labview program in order to monitor the time of flight of the reflected p-wave. Two mixtures of mortar are made using different proportions, of water, cement, and sand. The mortar is poured into a mould that has a form of a prism. Measurements are taken every 10 minutes over a period of 24 hours. This enabled us to plot the evolution of p-wave velocities over time for the samples and compare the results. Voir les détails
Mots clés : hardening of concrete, p-wave velocity, prism technique, ultrasonic system, Setting of concrete
Theoretical investigation of damage detection in composite structures using harmonic response technique
Nowadays the fiber-reinforced composite materials have used widely in the construction of aircraft structures; these structures are subjected to different excitations which may cause serious failure. For this reason our research presents a technique aimed to identify the damage in fiber-reinforced composite beam subjected to harmonic load using analytical model. The presence of a crack in structural elements leads to an energy concentration near to the crack region and introduce a local flexibility which affects its dynamical characteristic. Due to this fact, the harmonic response technique assumed to be reasonable technique for damage identification in cracked beam through the evaluating of its dynamic response to harmonic excitation. The discrete spring model has been used for modeling the crack, including the stress intensity factors, in which the composite beam is assumed to be divided into two sub-beams at the crack position, connected together by the additional equivalent spring. Euler-Bernoulli beam and the modal expansion theories are used in this study for solving the differential equation related to forced vibration. A parametric study has been carried out in order to investigate the influence, of crack depth and crack location on the transverse displacement of cracked composite beam under harmonic excitations. The obtained results show that the response amplitudes of a cracked beam changes with the varying of crack depth and location, and therefore, it can be used as a crack detection criterion. The dynamical behavior of composite beam with a lower flexural rigidity is more sensitive to presence of a crack. The vibration amplitudes are more sensitive when the crack depth increases. As aconsequence, the evaluation of dynamical response of cracked beam subjected to moving harmonic excitation can be used as an appropriate technique for damage detection in composite structures Voir les détails
Mots clés : Composite beam, Damage detection, harmonic excitation, Transverse displacement
The technique enabling to measurement the dispersion influence of the phase velocity Lamb wave A0 mode
The application of ultrasonic guided waves (UGW) is one of the latest methods of non-destructive testing (NDT) and structural health monitoring (SHM). Nowadays, it is widely used in various industrial fields to inspect and screenm any structures by exploring the properties of its waves which can propagate long distances with high sensitivity to structural changes. In this paper a technique based on the zero crossing approach combined with the spectrum decomposition methodis proposed. In general, according to the spectrum decomposition technique, the frequency spectrum of the signal is multiplied by special filter and the signal is reconstructed using inverse Fourier transform. Using this filtered signal, further signal processing is performed applying the zero crossing method. This technique has been investigated using simulated and modelled signals of the Lamb wave asymmetric A0 mode propagating in the higher dispersion zone. In order to obtain Lamb wave signals for analysis aluminium plates having thickness of 2 mm are used. The excitation signal was 3 periods, 300 kHz burst with the Gaussian envelope. The obtained measurement results are compared with the theoretical dispersion curves obtained by SAFE method. The results have shown that the proposed measurement technique enables not only to reconstruct the phase velocity dispersion curve of the Lamb wave A0 mode, but also to choose in what precision limits and in what extent of the frequency ranges the dispersion curve of the phase velocity can be reconstructed. Voir les détails
Mots clés : Lamb waves, phase velocity, dispersion, Frequency Spectrum
Rectangular Dielectric Resonator Antenna with Stacked BaxSr1-xTiO3 Ceramic film
In this communication, we propose a new dielectric resonator antenna loaded with rectangular ceramic of the BST material. The high permittivity of the material allows the shifting of the antenna resonant frequency from 10.77 GHz to 8 GHz, achieving a size reduction of the resonator antenna about 67% compared to an ordinary DRA for the same resonant frequency. The numerical analysis was carried out using two electromagnetic simulators including the CST Microwave Studio in the time domain and the HFSS (High-frequency Structure Simulator) in the frequency domain. The numerical results issued from simulations are presented and compared in terms of the resonant frequency, antenna size, reflection coefficient, and radiation patterns. Voir les détails
Mots clés : Dielectric resonator antenna DRA, BST ceramic, Numerical analysis.
The finite element method and the Infrared Thermography principle applied to the control of homogeneity between a weld and the structure to weld
The main purpose of this work is to investigate by a numerical method the effect of the thermophysical nature of solder, used to connect two pipe elements, on the distribution of the surface temperature of a considered structure. The analysis of the obtained thermograms can reveal the thermophysical quality of the used solder. The finite element method is used to calculate the temperature distribution on the welded region. The thermal response of the structure, which is subjected to a thermal flux step, is presented and analyzed. The simulations results are presented in the form of surface thermographic images, to show the contrast in temperature due to the presence of the weld zone.To better quantify the contrast induced by the presence of welding on temperature distribution we present the spatial variation of the temperature along a surface axis of the pipe. Voir les détails
Mots clés : thermographical images, finite element, Infrared thermography, surface temperature, Pipe, welding
Investigating Applicability of Discontinuous Galerkin Methods Towards Structural Health Monitoring in Transportation
Ultrasonic guided waves offer an efficient means of rapid non-destructive inspection over long distances. Several researches has been conducted to study and modelise efficiently the propagation of these waves in large structures with arbitrary cross-sections like rails, bars, tubes, and plates. Classical numerical methods such as the finite element method (FEM), the semi-analytical finite element method (SAFE), the hybrid method FEM-SAFE, etc. have proved successful in this regard, but still have a major drawback: the high consumption of resources (memory and CPU time). Recently,the discontinuous Galerkin finite element method (DG-FEM) has revolutionised computations in the time domain through its potential in terms of applications and facilities it provides. In this work, the potential benefits of a class of discontinuous methods namely the interior penalty discontinuous Galerkin methods (IPDG) in the frequency domain are investigated by performing a modal analysis of a finite structure. The natural frequencies and vibration modes are searched via the eigenvalue problem derived from the discretisation of the Helmholtz problem with free boundaries, in one dimension of space. In line with the work of literature, it was foundthat the resulting solutions are correct and free of spurious modes. In addition, the discontinuous formulation provides an interesting algebraic system with a block tridiagonal stiffness matrix and a diagonal block mass matrix. Therefore, the eigenproblem can be reduced from a generalised problem to a standard one. For large size problems, this can lead to a significant gain in computation time. Moreover, it retains its block-tridiagonal form for which effective and well suited for parallel implementation block algorithms are developed. Thus, the DG-FEM allows a double gain strategy in computation time/memory consumption and achieving high order accuracy. Voir les détails
Mots clés : Structural health monitoring (SHM), Interior penalty discontinuous Galerkin methods (IPDG), Eigenvalue problem.