5 research outputs found
Emission acoustique et traitement du bruit : cas de signaux expérimentaux en contexte nucléaire
No full textNational audienc
Emission Acoustique et Traitement du Bruit : Cas de signaux Expérimentaux en Contexte Nucléaire
No full textInternational audienceEn contrôle par Emission Acoustique (EA), il n’est pas rare d’observer une pollution du signal reçu par desbruits d’origines diverses, ce qui oblige souvent les expérimentateurs à augmenter le seuil d’acquisitiondes signaux, avec comme conséquence une perte de sensibilité. Cette perte de sensibilité peut parfoisconduire à une non détection de certains phénomènes (notamment les moins énergétiques) et/ou à unmanque de précision en terme de localisation. Il est alors préférable de préserver la sensibilité à traversle maintien du seuil d’acquisition et ensuite d’avoir recours à des méthodes de traitement du bruit.Dans ce travail, nous expérimentons des méthodes de soustraction spectrale (SS) dans le cadre dutraitement de signaux expérimentaux d’EA obtenus suite à des essais de sûreté nucléaire de type RIA(Reactivity Initiated Accident). Les résultats obtenus permettent de conclure à une très bonne adéquationdes méthodes de type SS en termes d’amélioration du rapport signal sur bruit (SNR) et de préservationde la forme d’onde pour les segments du signal reçu correspondant à des phénomènes physiques d’intérêt
Impact of the Test Device on Acoustic Emission Signals From Nuclear Safety Experiments: Contribution of Wave Propagation Modeling to Signal Processing
No full textInternational audienceA strongly energetic spectral component has been observed in the operating noise of a research reactor before the beginning of reactivity-initiated accidents (RIAs). We identify the source of this component by means of analytical derivations of torsional wave propagation in the test device. Numerical simulations, performed with a spectral-element method, confirm that this component is a resonant frequency of the device, and allow to evaluate the impact of wave travelpath in the test device on the acoustic emission (AE) signals recorded during RIA experiments. The transfer function of the test device is strongly dependent on both the source and the receiver locations, which precludes signal processing by deconvolution when the location of the AE source mechanism is unknown. Moreover, the geometry and the configuration of the test device may not influence the signals in the low-frequency range and hence the signals generated by source mechanisms located on the fuel clad such as clad failures. Finally, replacing the heat transfer fluid (pressurized water) by sodium leads to an increase in the recorded signal amplitude and a small shift of the frequency content toward the high frequencies. The results obtained in this paper may be useful to improve the design of future RIA experiments. They are also useful to understand wave propagation in the core of the reactor and to choose appropriate signal processing tools for recovering the source of AE signals generated during RIA experiments
Impact of the Test Device on the Behavior of the Acoustic Emission Signals: Contribution of the Numerical Modeling to Signal Processing
No full textIn a context of nuclear safety experiment monitoring with the non destructive testing method of acoustic emission, we study the impact of the test device on the interpretation of the recorded physical signals by using spectral finite element modeling. The numerical results are validated by comparison with real acoustic emission data obtained from previous experiments. The results show that several parameters can have significant impacts on acoustic wave propagation and then on the interpretation of the physical signals. The potential position of the source mechanism, the positions of the receivers and the nature of the coolant fluid have to be taken into account in the definition a pre-processing strategy of the real acoustic emission signals. In order to show the relevance of such an approach, we use the results to propose an optimization of the positions of the acoustic emission sensors in order to reduce the estimation bias of the time-delay and then improve the localization of the source mechanisms
Rivers and landscape ecology of a plant virus, Rice yellow mottle virus along the Niger Valley
No full textInternational audienceTo investigate the spread of Rice yellow mottle virus (RYMV) along the Niger River, regular sampling of virus isolates was conducted along 500 km of the Niger Valley in the Republic of Niger and was complemented by additional sampling in neighbouring countries in West Africa and Central Africa. The spread of RYMV into and within the Republic of Niger was inferred as a continuous process using a Bayesian statistical framework applied previously to reconstruct its dispersal history in West Africa, East Africa, and Madagascar. The spatial resolution along this section of the Niger River was the highest implemented for RYMV and possibly for any plant virus. We benefited from the results of early field surveys of the disease for the validation of the phylogeographic reconstruction and from the well-documented history of rice cultivation changes along the Niger River for their interpretation. As a prerequisite, the temporal signal of the RYMV data sets was revisited in the light of recent methodological advances. The role of the hydrographic network of the Niger Basin in RYMV spread was examined, and the link between virus population dynamics and the extent of irrigated rice was assessed. RYMV was introduced along the Niger River in the Republic of Niger in the early 1980s from areas to the southwest of the country where rice was increasingly grown. Viral spread was triggered by a major irrigation scheme made of a set of rice perimeters along the river valley. The subsequent spatial and temporal host continuity and the inoculum build-up allowed for a rapid spread of RYMV along the Niger River, upstream and downstream, over hundreds of kilometres, and led to the development of severe epidemics. There was no evidence of long-distance dissemination of the virus through natural water. Floating rice in the main meanders of the Middle Niger did not contribute to virus dispersal from West Africa to Central Africa. RYMV along the Niger River is an insightful example of how agricultural intensification favours pathogen emergence and spread
