Liste des documents
Multi-objective GA optimization of fuzzy penalty for image reconstruction from projections in X-ray tomography
This paper concerns X-ray tomography image reconstruction of an object function from few projections in Computed Tomography (CT). The problem is so ill-posed that no classical method can give satisfactory result. We have investigated a new combined method for penalized-likelihood image reconstruction that combines the fuzzy penalty function (FP) and GA (genetic algorithm) optimization. The proposed algorithm does not suffer from the same problem as that of ML EM (maximum likelihood expectation maximization) algorithm, and it converges rapidly to a low noisy solution even if the iteration number is high, and gives global estimation not a local one like in classical algorithm such as gradient, to the problem of determining object parameters. The method was tested and validated on datasets of synthetic and real image. Voir les détails
Mots clés : Computed tomography, Non-Destructive testing, Analytic estimation, Bayesian inference and estimation, Fuzzy inference, Genetic optimization
A Comparative Study of Analytical,Iterative and Bayesian Reconstruction Algorithms in Computed Tomography(CT)
These Images of the inside of the human body can be obtained using tomographic acquisition and processing techniques. In particular, these techniques are commonly used to obtain X-ray images of the human body. The reconstructed images are obtained given a set of their projections, acquired using reconstruction techniques. A general overview of analytical and iterative methods of reconstruction in computed tomography (CT) is presented in this paper, with a special focus on Bayesian algorithms. The simulated results are compared using quality measurements for various test cases and conclusion is achieved. Through these simulated results, we have demonstrated that the Bayesian approach provides the best image quality and the small values of the quality measurements. Voir les détails
Mots clés : Computed tomography, Bayesian approach, reconstruction techniques.
Object recognition using Radon transform based RST parameter estimation
In this paper, we propose a practical parameter recovering approach, for similarity geometric transformations using only the Radon transform and its extended version on [0, 2π]. The derived objective function is exploited as a similarity measure to perform an object recognition system. Comparison results with common and powerful shape descriptors testify the effectiveness of the proposed method in recognizing binary images, RST transformed, distorted, occluded or noised. Voir les détails
Mots clés : RST parameters, radon transform, object recognition
Improving the sensitivity of Raman signal of ZnO thin films deposited on silicon substrate
Raman spectroscopy results of DC reactive sputtering of ZnO thin films deposited on silicon substrates are reported. Monocrystalline silicon wafers are frequently used as substrates for thin film deposition, and when working on thin films materials of rather low Raman cross-sections such as ZnO, it is difficult and even sometimes hopeless to extract the Raman information relevant to the film from the silicon signal.In this paper, we show that using a 457 nm wavelength of the laser excitation combined with the effect of silicon Raman selection rules through convenient orientation of the silicon substrate, the 520 cm-1 Si signal can be sufficiently attenuated to give access to the ZnO Raman information, whatever the important difference of intensity between them. Voir les détails
Mots clés : Raman spectroscopy, Thin films, Silicon, Zinc oxide, DC reactive sputtering deposition
Segmentation of welding defects using level set methods
Non-destructive testing (NDT) is a technique used in science and industry to evaluate the properties of a material without causing damage. In this paper we propose a method for segmenting radiographic images of welding in order to extract the welding defects which may occur during the welding process. We study different methods of level set and choose the model adapted to our application. The methods presented here take the property of local segmentation geodesic active contours and have the ability to change the topology automatically. The computation time is considerably reduced after taking into account a new level set function which eliminates the re-initialisation procedure. Satisfactory results are obtained after applying this algorithm both on synthetic and real images. Voir les détails
Mots clés : image segmentation, Level set, weld defects, Radiographic image
Application of Wavelet Transform for Fault Diagnosis in Rotating Machinery
Vibration analysis is essential in improving condition monitoring and fault diagnostics of rotating machinery. Many signal analysis methods are able to extract useful information from vibration data. Currently, the most of these methods use spectral analysis based on Fourier Transform (FT). However, these methods present some limitations; it is the case of non-stationary signals. In the present work, we are interested to the vibration signal analysis by the Wavelet Transform (WT). The WT is one of the most important methods for signal processing; it is especially suitable for non-stationary vibration measurements obtained from accelerometer sensors. The monitoring results indicate that the WT can diagnose the abnormal change in the measured data. Voir les détails
Mots clés : Vibration analysis, Fault Diagnosis, Rotating machinery, Spectral analysis, Wavelet transform
Welding Quality Evaluation Using Residual – Based Reference Temperature Distribution Model and Fuzzy Reasoning
A method for welding quality evaluation, which combines model identification and fuzzy sets methods, is proposed. To account for welding quality variations, the proposed approach is based on an optimal reference Gauss distribution temperature along of the welding line in order to take into account the eventual process changes. Fuzzy analysis is then applied to the generated residual data to give an evaluation of the welding condition. This approach is applied to welding process for constructing a complementary condition monitoring system which permits an online quality evaluation. The temperature measurement is carried out using an infrared camera. Simulation results based on the measured surface temperature and generated residual data show that the new approach is easily implementable and gives good evaluation online. Voir les détails
Mots clés : Heat Affected zone of Welding Process, Infrared temperature measurement, Gauss distribution model, Residual generation, intelligent modeling, Fuzzy reasoning, Quality evaluation.
Mechanical properties study in extruded HDPE-80 pipe wall used fornatural gas distribution
Polymers represent a remarkable family of materials becauseof the variety of products that it is possible to design with and the different implementationprocesses offered. The use of these materials allowed to acheive substantial gains onassociated costs, service times and repair. Despite the acceptance of polyethylene as an economicalternative for pipes networks, safety remains a fundamental issue, and it requiresthe ability to determine intrinsic properties as a function of the service conditions requiredby the design and the use. This study deals with the determination of the mechanical behaviourof an HDPE resin through the entire pipe wall thickness. Standard testing specimenshave been manufactured under specific conditions in the longitudinal direction accordingto ISO-527. The mechanical properties are measured in traction using a computer-driventesting machine. The results indicate that there is a clear evolution of the mechanical propertiesthrough the pipe wall, which confirms the bahaviour observed in other studies ofpolyethylene filaments tested under the same conditions. These variations are attributed tomorphological gradients and the evolution of internal stresses imparted by the extrusionprocess. Voir les détails
Mots clés : Mechanical caracterization; polyethylene pipe; elastic modulus; extrusion; traction
Combining RBF-PCA-ReliefF Filter for a better diagnosis performances in rotating machines
Monitoring and faults diagnosis in rotating machinery is a current research field. In this direction the use of pattern recognition combined with non-destructive testing techniques such as' vibration analysis and signal processing can be very useful. In this paper was proposed, a diagnosis method of rotating machinery using vibration signatures with a Radial Basis Function classifier. The recorded signals were preprocessed with a Wavelet Decomposition and indicators were extracted both in temporal and frequency domain. To improve diagnosis performance, two techniques for dimension reduction of indicators space are combined; Principal Component Analysis and the filter ReliefF. The method was tested on real signatures from a vibration test bench, operating under several conditions, the results showed the interest to look closely at the choice of indicators in order to have best diagnosis performance. Voir les détails
Mots clés : diagnosis, Rotating machinery, principal component analysis, radial basis function
STYDY OF MECHANICAL PROPERTIES OF MOLYBDENUM COATINGS DEPOSITED BY THERMAL FLAME SPARYING ON GRAY CAST IRON
Thermal spraying coatings are used to meet the most stringent industrial requirements in the wider of application. The molybdenum coatings present a good wear resistance which used several mechanical applications. In this work, we studied the mechanical properties of molybdenum coating deposited using thermal flame spraying on gray cast iron with lamellar graphite. After optimization of the spraying parameters, the microstructure was investigated using optical microscopy, scanning electron microscopy and X-ray diffraction. The mechanical properties obtained by microhardness and nanoindentation tests were evaluated on a polished cross section. The mass loss was measured using the abrasive wear test at varying the normal load. The results showed an improvement the mechanical properties of gray cast iron after deposition of molybdenum with wire-flame spraying. Voir les détails
Mots clés : Thermal Spraying, Molybdenum Coating, mechanical properties, Nanoindentation, wear.