Electronique
Local and Global Statistics-Based Explicit Active Contour for Weld Defect Extraction in Radiographic Inspection
Welding is a process of utmost importance in the metal industry. With the advances in computer science and artificial intelligence techniques, the opportunity to develop computer aided technique for radiographic inspection in Non Destructive Testing arose. This paper deals with the weld defects detection in radiographic films. A greedy active contour model is used exploiting global and local statistics to drive the model to the boundaries. Moreover, and to decrease the computation cost, the local statistics computation is done only for pixels in a selected band. Results seem to be promising ones. Voir les détails
Mots clés : Radiographic inspection, weld defects, Active contours
Adaptive B-Spline Model Based Probabilistic Active Contour for Weld Defect Detection in Radiographic Imaging
This paper describes a probabilistic region-based deformable model using a new adaptive scheme for B-spline representation. The idea is to adapt the number of spline control points which are necessary to describe an object with complex shape. For this purpose, the curve segment length (CSL) is used as criterion. The proposed split and merge strategy on the spline model consists in: adding a new control point when CSL is greater than a certain splitting threshold so that the contour tracks all the concavities and, removing a control point when CSL is less to a certain merging threshold so that the contour aspect maintains its smoothness. Noise on synthetic and real weld radiographic images is assumed following Gaussian or Rayleigh distribution. The experiments carried out confirm the adequacy of this approach, especially in tracking pronounced concavities contained in images. Voir les détails
Mots clés : weld defect, Active contour, adaptive B-spline, split and merge operations
Piezoelectric transformer: Comparison between a model and an analytical verification
In this paper, a study comparing a model of a composite piezoelectric transformer, based on the corresponding electrical equivalent circuit, and the direct calculation solving the mechanical fundamental equations constrained by the appropriate boundary conditions is presented. The approach is simplified considering vibrations only along one direction, neglecting the coupling phenomena existing along the other directions. The electrical equivalent circuit of the transformer is obtained from the equivalent circuit referred for the isolated piezoelectric oscillators. In this paper, each electrical equivalent circuit is placed on a cascade in order to conserve the continuity of dis- placements and stress at the junction. Voir les détails
Mots clés : Piezoelectricity, Transformer, Modeling; Equivalent circuit, Analytical verification, Voltage gain, Boundary conditions
A comparison of 1D analytical model and 3D Finite Element Analysis with experiments for a Rosen-type piezoelectric transformer
This article is dedicated to the study of Piezoelectric Transformers (PTs), which offer promising solutions to the increasing need for integrated power electronics modules within autonomous systems. The advantages offered by such transformers include: immunity to electromagnetic disturbances; ease of miniaturisation for example, using conventional micro fabrication processes; and enhanced performance in terms of voltage gain and power efficiency. Central to the adequate description of such transformers is the need for complex analytical modeling tools, especially if one is attempting to include combined con- tributions due to (i) mechanical phenomena owing to the different propagation modes which differ at the primary and secondary sides of the PT; and (ii) electrical phenomena such as the voltage gain and power efficiency, which depend on the electrical load. The present work demonstrates an original one-dimensional (1D) analytical model, dedicated to a Rosen-type PT and simulation results are successively compared against that of a three-dimensional (3D) Finite Element Analysis (COMSOL Multiphysics software) and experimental results. The Rosen-type PT studied here is based on a single layer soft PZT (P191) with corresponding dimensions 18 mm x 3 mm x 1.5 mm, which operated at the second harmonic of 176 kHz. Detailed simulational and experimental results show that the presented 1D model predicts experimental measurements to within less than 10% error of the voltage gain at the second and third resonance frequency modes. Adjustment of the analytical model parameters is found to decrease errors relative to experimental volt- age gain to within 1%, whilst a 2.5% error on the output admittance magnitude at the second resonance mode were obtained. Relying on the unique assumption of one-dimensionality, the present analytical model appears as a useful tool for Rosen-type PT design and behavior understanding. Voir les détails
Mots clés : Piezoelectric transformer, Rosen-type transformer, 1D analytical modelling, 3D FEA simulations, Experimental characterisation
Linear Fractional Order System Identification using Adjustable Fractional Order Differentiator
In previous decades, it has been observed that many physical systems are well characterised by fractional order models. Hence, their identification is attracting more and more interest of the scientific community. However, they pose a more difficult identification problem, which requires not only the estimation of model coefficients but also the determination of fractional orders with the tedious calculation of fractional order derivatives. This study focuses on an identification scheme, in the time domain, of dynamic systems described by linear fractional order differential equations. The proposed identification method is based on the recursive least squares algorithm applied to an ARX structure derived from the linear fractional order differential equation using adjustable fractional order differentiators. The basic ideas and the derived formulations of the identification scheme are presented. Illustrative examples are presented to validate the proposed linear fractional order system identification approach. Voir les détails
Mots clés : Adjustable fractional order differentiator, Least squares method, Linear fractional differential equation, Recursive identification.
Identification of Linear Fractional Systems of Commensurate Order
The identification of fractional order systems is a more difficult problem than the integer order systems because it requires not only the estimation of the model coefficients but also the determination of the fractional orders with the tedious calculation of fractional order derivatives. This paper addresses the identification of linear fractional systems of commensurate order. The proposed identification method is based on the recursive least squares algorithm applied to a linear regression equation derived from the linear fractional order differential equation using adjustable fractional order differentiator. The proposed technique does not require a prior knowledge of the commensurate order of the fractional linear differential equation. The derived formulations of the identification scheme are presented. Illustrative examples are also presented to validate the proposed linear fractional systems of commensurate identification approach. Voir les détails
Mots clés : Least squares method, Linear fractional differential equation, Recursive identification.
MULTI-OBJECTIVE PREDICTIVE CONTROL: A SOLUTION USING METAHEURISTICS
The application of multi objective model predictive control approaches is significantly limited with computation time associated with optimization algorithms. Metaheuristics are general purpose heuristics that have been successfully used in solving difficult optimization problems in a reasonable computation time. In this work , we use and compare two multi objective metaheuristics, Multi-Objective Particle swarm Optimization, MOPSO, and Multi-Objective Gravitational Search Algorithm, MOGSA, to generate a set of approximately Pareto-optimal solutions in a single run. Two examples are studied, a nonlinear system consisting of two mobile robots tracking trajectories and avoiding obstacles and a linear multi variable system. The computation times and the quality of the solution in terms of the smoothness of the control signals and precision of tracking show that MOPSO can be an alternative for real time applications. Voir les détails
Mots clés : Model predictive control, Metaheuristcis, Multiobjective Optimization
Analog Circuit Implementation of FractionalOrder Damped Sine and Cosine Functions
This paper introduces for thefirst time analog circuitimplementations of two fundamental linear fractional order systems whose impulse responses called fractional order damped sineand cosine functions are the inverse Laplace transform of their irrational transfer functions. These analog circuit implementationsare derived through rational function approximations of their irrational transfer functions. Voir les détails
Mots clés : Analog circuit, fractionalorder differential equation, fractional order system, irrational function, rational function.
Automatic Crack Detection and Characterization During Ultrasonic Inspection
The creation of a non-destructive technique that enables the automatic detection of defects is desirable, and TOFD (Time-Of-Flight Diffraction) technique is gaining rapid prominence due to its high accuracy in detecting, positioning and sizing flaws in steel structures. In this type of imaging, cracks are characterized using sets of hyperbolas, where summit positions correspond to crack tip positions.However, ultrasonic diffracted signals are often too low and difficult to distinguish from noise, and when large structures are inspected, the quantity of data can be extremely large, with the area of interest being very small in comparison to the image size. This paper describes a method that avoids the image formation, replacing it with a sparse matrix (as there is no reason to store and operate on an excessive number of zeros), and automates crack detection by analyzing the curve formed by the sparse matrix elements.The sparse matrix is formed using Split-Spectrum Processing, which enhances the signal-to-noise ratio. The Randomized Hough transform is then applied on the sparse matrix elements to detect the hyperbolas that characterize the crack defects. Voir les détails
Mots clés : Automated inspection, Ultrasonic imagery, Sparse matrix, Defect characterization
Méthodes de traitement des signaux ultrasonores basées sur la déconvolution dans la détection des défauts
Ce travail de thèse concerne l’étude et l’implémentation des méthodes de traitement des signaux ultrasonores basées sur la déconvolution, appliquées à la détection des défauts de délaminage présents dans un matériau composite multicouches du type CFRP. Le signal ultrasonore mesuré est modélisé sous la forme d'un produit de convolution entre une fonction représentative de la forme d'onde émise par le traducteur ultrasonore et une fonction appelée réflectivité. Le problème de l'échographie ultrasonore consiste à essayer de reconstruire le plus précisément possible la séquence de réflectivité. Compte tenu de la définition du modèle direct, le problème inverse spécifique traité dans cette thèse est celui de la déconvolution. La résolution de cette classe de problèmes se heurte à deux difficultés liées d'une part à la présence de bruit et d'autre part à la perte d'informations due à la convolution. Le problème de la déconvolution est donc de remonter à la "bonne" solution, c'est-à-dire celle qui est physiquement significative. Dans cette thèse, les méthodes de déconvolution qui sont divisées en trois grandes catégories : déterministe, semi aveugle et aveugle, ont été étudiées, implémentées, adaptées aux signaux ultrasonores et appliquées au contrôle des matériaux composites. Les résultats obtenus sur divers signaux ultrasonores synthétiques et expérimentaux attestent de la robustesse et des performances de ces méthodes. Voir les détails
Mots clés : contrôle non destructif, ultrason, traitement de signal, déconvolution