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Fusion of heterogeneous data for robust degradation prognostics
No full textInternational audienceAssessing the degradation state of an industrial asset first requires evaluating its current condition and then to project the forecast model trajectory to a predefined prognostic threshold, thereby estimating its remaining useful life (RUL). Depending on the available information, two primary categories of forecasting models may be used: physics-based simulation codes and datadriven (machine learning) approaches. Combining both modelling approaches may enhance prediction robustness, especially with respect to their individual uncertainties. This paper introduces a methodology for fusion of heterogeneous data in degradation prognostics. The proposed approach acts iteratively on a computer model's uncertain input variables by combining kernel-based sensitivity analysis for variable ranking with a Bayesian framework to inform the priors with the heterogeneous data. Additionally, we propose an integration of an aggregate surrogate modeling strategy for computationally expensive degradation simulation codes. The methodology updates the knowledge of the computer code input probabilistic model and reduces the output uncertainty. As an application, we illustrate this methodology on a toy model from crack propagation based on Paris law as well as a complex industrial clogging simulation model for nuclear power plant steam generators, where data is intermittently available over time.</div
Characterization of the aquifer's hydraulic properties using different pumping test modes: From oscillatory hydraulic tomography to steady state hydraulic tomography
No full text(IF 5.9;Q1)The characterization of aquifers hydraulic properties (e.g., transmissivity and storativity) and understanding its hydrodynamics are very important for groundwater management. Hydraulic tomography (HT) is one widely used tool to achieve it. In this paper, we use the principal components geostatistical approach (PCGA) to map the transmissivity and the storativity of an aquifer by using oscillatory pumping tests, pumping tests (transient) and steady state data. Firstly, through a synthetic case study, we investigate the differences between HT results using different observation data obtained from different hydraulic tests. Moreover, we explore how sensitive are T and S estimates obtained using different observation data to changes in the hydraulic properties of a buffer area surrounding the inversion domain. Then, the synthetic case study is repeated using a real field configuration and a field application is performed. Results show that the heterogeneous area surrounding the inversion domain have a significant effect on Hydraulic Tomography results. Results also show that high frequency oscillatory pumping tests provide the best hydraulic tomography results especially for the storativity fields. Such effect becomes more pronounced when using transient and steady state observations of constant flow-rate pumping tests. Surrounding heterogeneity has a considerable effect on T field which in return affects the solution of S field as well
Altérations thermiques induites par les éclusées
No full textInternational audienceThe rapid flow variations induced downstream of hydropower plants by the release of turbined water can be associated with temperature variations. Given the multiplicity of plant configurations and the diversity of structure characteristics, these temperature variations linked to hydropeaking are potentially highly variable from one site to another. The aim of our work was therefore firstly to review the state of the art of thermal alterations linked to hydropeaking and their impact on biological communities. Secondly, using our knowledge of the characteristics of the French hydropower fleet and representative case studies, we sought to define the different types of alteration possible, depending on the characteristics of the facilities. For most facilities, warming in winter and cooling in summer are generally observed, with widely varying amplitudes.. The most likely impacts on organisms are those linked to temperature gradients and the frequency of events. Changes in temperature regimes induced by hydropeaking are highly dependent on site configuration. Nevertheless, whatever the type of configuration, the temperature deviations induced are not systematic and concern a limited number of hydropeaking events. These results highlight the need to acquire knowledge about the effects of high temperature gradients on the physiology and behavior of individuals, and their indirect impacts at population or community level.Les variations rapides de débit induites à l’aval des centrales hydroélectriques par les lâchers d’eau turbinées peuvent être accompagnées de variations de température. Etant donné la multiplicité de configurations d’aménagements et la diversité de caractéristiques des ouvrages, ces écarts de température liées aux éclusées sont potentiellement très variables d’un site à un autre. Aussi, l’objectif de nos travaux a été d’une part de faire un état de l’art des altérations thermiques liées aux éclusées et de leurs impacts sur les communautés biologiques. D’autre part, à l’aide de la connaissance des caractéristiques du parc hydroélectrique français et de cas d’étude représentatifs, nous avons cherché à définir les différents types d’altérations possibles en fonction des caractéristiques des aménagements. Pour la plupart des aménagements, un réchauffement en hiver et un refroidissement en été sont généralement observés, avec des amplitudes très variées. Les incidences les plus probables sur les organismes sont celles liées aux gradients de baisse ou de hausse de température et la fréquence des évènements. Les écarts de température induits par les éclusées dépendent fortement de la configuration du site. Néanmoins, quel que soit, le type de configuration, les écarts de température induits ne sont pas systématiques et concernent un nombre restreint d’éclusées. Ces résultats mettent en avant le besoin d’acquérir des connaissances sur les effets de gradients de température élevés sur la physiologie et le comportement des individus et leurs impacts indirects à l’échelle des populations ou des communautés
Modeling of low alloy steels cleavage with an explicit local approach to fracture
No full textNational audienceAs a nuclear power plant operator, EDF aims to acquire the technical and scientific knowledge to predict the mechanical properties of large forged components made of low alloy steel. EDF R&D and its partners are thus engaged in a skill development on the experimental characterization tools and simulation of the whole manufacturing process, from solidification to mechanical properties after heat treatments. The aim of this work focuses on the last step of a so-called "knowledge chain", and knowing the microstructure resulting from a given manufacturing process, being able to predict its mechanical fracture properties. This is done by expliciting the link between the brittle fracture properties and the combined effects of (i) stress heterogeneities in polycrystalline structures and (ii) the presence of defects inside microstructures.En tant qu'exploitant de centrales nucléaires, EDF ambitionne de se donner les moyens techniques et scientifiques de prévoir les propriétés mécaniques des gros composants forgés en aciers faiblement alliés des centrales nucléaires. Dans cette optique, EDF R&D et ses partenaires sont engagés dans une démarche de montée en compétences au niveau des outils de caractérisation expérimentale et de simulation de l'ensemble des étapes du procédé de fabrication des composants forgés, de la solidification aux propriétés de rupture après traitements thermiques. Le présent travail vise à développer la dernière brique de cette chaîne de prévision en proposant d'expliciter le lien entre, les propriétés de rupture d'une part, et d'autre part l'effet croisé des hétérogénéités de contraintes dans les structures polycristallines et la présence de défauts au sein des microstructures
Improved cycling stability of ferrocene intercalated layered double hydroxides electrodes in aqueous electrolytes
No full textInternational audienceThrough two redox molecules, mono- and dicarboxylic ferrocene anions (FcMono and FcDi, respectively), interleaved between the lamellae of a layered double hydroxide Mg2Al(OH)6 (LDH), have been synthesized and investigated as electrode materials inwater in salt electrolyte using lithium bis-(trifluoromethanesulfonyl)-imide Li+[N(SO2CF3)2]- (LiTFSI) mixed in different amount of H2O. The redox activities of the composite electrode materials including Mg2Al(OH)6[FcMono]1.0 and Mg2Al(OH)6[FcDi]0.5 suffer from the dissolution of the active redox species migrating out of the host structure in water based electrolyte when low molalities are used. However, while increasing the molality of the electrolyte solution Mg2Al(OH)6[FcDi]0.5 electrode material performs better than Mg2Al(OH)6[FcMono]1.0 ones according to the cycling stability For Mg2Al(OH)6[FcDi]0.5, an optimum behavior is observed for a concentration of LITFSI of at least of 10 m. The electrode exhibits a stable capacity of 25 mAh g-1 which is maintained after more than 100 cycles with 100 % coulombic efficiency. Such stability during cycling is explained by two complementary processes: the preservation of the lamellar structure of Mg2Al(OH)6[FcDi]0.5, FcDi molecule being tethered by its two ends (unlike FcMono tethered at one end only), in connection with the high concentration of the electrolyte in LiTFSI, which helps slowing down the migration of the interleaved redox species out of the structure. This opens the route to re-evaluate LDH-based hybrid materials for water-based energy storage devices
Experimental investigations addressing steam release in the water pool through a multi-hole sparger and spray water activation in the gas space
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Duality between polyhedral approximation of value functions and optimal quantization of measures
No full textInternational audienceApproximating a convex function by a polyhedral function that has a limited number of facets is a fundamental problem with applications in various fields, from mitigating the curse of dimensionality in optimal control to bi-level optimization. We establish a connection between this problem and the optimal quantization of a positive measure. Building on recent stability results in optimal transport, by Delalande and Mérigot, we deduce that the polyhedral approximation of a convex function is equivalent to the quantization of the Monge-Ampère measure of its Legendre-Fenchel dual. This duality motivates a simple greedy method for computing a parsimonious approximation of a polyhedral convex function, by clustering the vertices of a Newton polytope. We evaluate our algorithm on two applications: 1) A high-dimensional optimal control problem (quantum gate synthesis), leveraging McEneaney's max-plus-based curse-of-dimensionality attenuation method; 2) A bi-level optimization problem in electricity pricing. Numerical results demonstrate the efficiency of this approach
Végétalisons nos cours d’eau : les ripisylves, un habitat aux multiples bénéfices
No full textInternational audienceRiparian forests are all forest stands and linear woodlands located alongside watercourses, where the aquatic and terrestrial environments meet. In recent decades, an increasing number of scientific studies have emphasised the ecological, social and economic advantages of preserving and restoring riparian forests. The first part of this article summarises the associated benefits. The second part presents reasons for preserving and restoring riparian forests as a strategy for mitigating climate change and adapting to its effects on rivers, biodiversity and humans. These characteristics mean that the restoration of riparian vegetation is a management measure that should be developed within a well-thought-out, locally adapted framework.La ripisylve désigne l’ensemble des peuplements forestiers et boisements linéaires situés aux abords des cours d'eau, à l’interface entre les milieux aquatique et terrestre. Ces dernières décennies, un nombre croissant d’études scientifiques ont mis en lumière les intérêts écologiques, sociétaux et économiques de la préservation et de la restauration des ripisylves. Dans la première partie de cet article, nous synthétisons les bénéfices associés aux ripisylves. Nous présentons, dans une seconde partie, les éléments soutenant la préservation et la restauration des ripisylves comme des stratégies d’atténuation du changement climatique et d'adaptation à ses effets sur les rivières, la biodiversité et les humains. Ces caractéristiques font de la restauration de la végétation des berges des cours d’eau une mesure de gestion à développer dans les années à venir, dans un cadre réfléchi et adapté aux contraintes locales
Non-Destructive Ultrasonic Evaluation of Asphalt Concrete Waterproofing in Hydraulic Structures: Experimental and Numerical Study
No full textInternational audienceSome hydraulic structures use a multi-layer asphalt concrete coating to ensure waterproofing. Over time, defects may appear in this coating due to ageing of the materials or environmental conditions. In order to prevent further degradation phenomena that could eventually compromise the stability of the structure, we aim to develop a non-destructive monitoring system based on mechanical waves propagation for early detection of such defects. A first step of this study consists in characterizing the presence of defects in terms of measurable mechanical parameters. To this end, six coating samples taken from both healthy and degraded areas of a real embankment dam are considered. They are analysed using a ultrasound acquisition system. The initial results are promising, showing a difference in dynamic modulus between healthy and degraded areas