Physique

1 Abstract-Electrical energy production based on wind power has become the most popular renewable resources in the recent years because it gets reliable clean energy with minimum cost. The major challenge for wind turbines is the electrical and the mechanical failures which can occur at any time causing prospective breakdowns and damages and therefore it leads to machine downtimes and to energy production loss. To circumvent this problem, several tools and techniques have been developed and used to enhance fault detection and diagnosis to be found in the stator current signature for wind turbines generators. Among these methods, parametric or super-resolution frequency estimation methods, which provides typical spectrum estimation, can be useful for this purpose. Facing on the plurality of these algorithms, a comparative performance analysis is made to evaluate robustness based on different metrics: accuracy, dispersion, computation cost, perturbations and faults severity. Finally, simulation results in MATLAB with most occurring faults indicate that ESPRIT and R-MUSIC algorithms have high capability of correctly identifying the frequencies of fault characteristic components, a performance ranking had been carried out to demonstrate the efficiency of the studied methods in faults detecting.

ESPRIT-TLS method appears a good choice for high resolution fault detection in induction machines. It has a very high effectiveness in the frequency and amplitude identification. Contrariwise, it presents a high computation complexity which affects its implementation in real time fault diagnosis. To avoid this problem, a Fast-ESPRIT algorithm that combined the IIR band-pass filtering technique, the decimation technique and the original ESPRIT-TLS method was employed to enhance extracting accurately frequencies and their magnitudes from the wind stator current with less computation cost. The proposed algorithm has been applied to verify the wind turbine machine need in the implementation of an online, fast, and proactive condition monitoring. This type of remote and periodic maintenance provides an acceptable machine lifetime, minimize its downtimes and maximize its productivity. The developed technique has evaluated by computer simulations under many fault scenarios. Study results prove the performance of Fast-ESPRIT offering rapid and high resolution harmonics recognizing with minimum computation time and less memory cost.

Résumé: Ce travail présente le comportement du radon émanant du sol dans quatre régions du Maroc (Tétouan, Khouribga, Ifrane et Berchid) vis à vis de deux tremblements de terre de magnitudes 5,2 et 5,3 et dont les épicentres se situent dans la province de Rachidia. La méthode de mesure du radon est basée sur la technique des détecteurs solides de traces nucléaires (DSTN). Cette étude a été précédée par des mesures, sur une longue durée, des taux d'émanation du radon en l'absence des séismes pour établir les niveaux de référence et avoir une idée sur l'influence des paramètres atmosphériques sur le radon. Les résultats obtenus mettent en évidence une bonne corrélation entre le radon et ces deux séismes bien que les distances épicentrales se situent entre 350 et 470 km.

Measurement of 7 Be depositional fluxes at Granada, Spain (37110 0 50 00 N-3135 0 44 00 W, altitude 670 m) in the period 1995 through 1998 indicates substantial variations between the four seasons and also between corresponding seasons in different years, ranging from 23.6 to 242 Bq m À2 per season. A strongly positive correlation with precipitation is shown, which explains about 70% of the variations in the 7 Be depositional fluxes over the 16 seasons studied. The depositional 7 Be flux is on the average highest in the fall and lowest in the summer. The study shows that precipitation primarily controls the 7 Be depositional flux and plays a dominant role in the removal of 7 Be from the troposphere. The average annual 7 Be depositional flux at Granada amounts to 469+145 Bq m À2 .

In the present work, we analyze the CREOLE experiment on the reactivity temperature coefficient (RTC) by using the three-dimensional continuous energy code (MCNP5) and the last updated nuclear data evaluations. This experiment performed in the EOLE critical facility located at CEA/Cadarache, was mainly dedicated to the RTC studies for both UO 2 and UO 2 -PuO 2 PWR type lattices covering the whole temperature range from 20 • C to 300 • C. We have developed an accurate 3D model of the EOLE reactor by using the MCNP5 Monte Carlo code which guarantees a high level of fidelity in the description of different configurations at various temperatures taking into account their consequence on neutron cross section data and all thermal expansion effects. In this case, the remaining error between calculation and experiment will be awarded mainly to uncertainties on nuclear data. Our own cross section library was constructed by using NJOY99.259 code with point-wise nuclear data based on ENDF-BVII, JEFF3.1 and JENDL3.3 evaluation files. The MCNP model was validated through the axial and radial fission rate measurements at room and hot temperatures. Calculation-experiment discrepancies of the RTC were analyzed and the results have shown that the JENDL3.3 and JEFF3.1 evaluations give the most consistent values; the discrepancy is less than 0.23 pcm/ • C. Whereas, when using ENDF-BVII evaluation for UOX configuration, this discrepancy reaches a value of 0.63 pcm/ • C. In order to specify the source of this relatively large discrepancy in the case of ENDF-BVII nuclear data evaluation, the k eff discrepancy between ENDF-BVII and JENDL3.3 was decomposed by using sensitivity and uncertainty analysis technique. The thermal energy range of 238 U(n,␥) absorption cross section was found to contribute to the major part of the observed k eff discrepancy between ENDFB-VII and JENDL3.3 evaluations.