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Bayesian sequential design of computer experiments for quantile set inversion
No full textInternational audienceWe consider an unknown multivariate function representing a system—such as a complex numerical simulator—taking both deterministic and uncertain inputs. Our objective is to estimate the set of deterministic inputs leading to outputs whose probability (with respect to the distribution of the uncertain inputs) of belonging to a given set is less than a given threshold. This problem, which we call Quantile Set Inversion (QSI), occurs for instance in the context of robust (reliability-based) optimization problems, when looking for the set of solutions that satisfy the constraints with sufficiently large probability. To solve the QSI problem we propose a Bayesian strategy, based on Gaussian process modeling and the Stepwise Uncertainty Reduction (SUR) principle, to sequentially choose the points at which the function should be evaluated to efficiently approximate the set of interest. We illustrate the performance and interest of the proposed SUR strategy through several numerical experiments
A physics-based multi-regime approach for estimation of head losses in operating hydropower plants
No full textInternational audienceIn this paper, the problem of estimating head losses in the hydraulic feeding system of a hydropower plant is considered. Accurate head loss assessment is crucial for performance monitoring, efficiency optimization, and predictive maintenance of these critical energy infrastructures. To this end, a nonlinear state-space model based on fundamental physical principles is first established. Recognizing the challenges of observability with a full complex model, this paper proposes a multi-regime modelling strategy, where the full model is particularized into simplified forms suitable for different operational scenarios (normal operation, quasi-static conditions, and plant shutdown). This approach facilitates the estimation of specific head loss coefficients or their combinations. Various estimation techniques are then explored and applied to these models, primarily based on Kalman filters for state-observer approaches and direct least squares for regression-based methods, all integrating real-time measurements. The efficacy of these methods is validated through comprehensive simulations and tests using operational data collected from an industrial hydropower facility
Une approche par observateur d’état pour Jumeau Numérique enproduction hydroélectrique : l’exemple des pertes de charge
No full textInternational audienceCet article met en avant la notion d’observateur d’état, issue du domaine de l’Automatique,comme outil pouvant directement servir les enjeux de jumeau numérique, en plein essor ces dernièresannées. Une application au suivi des pertes de charge dans les galeries d’amenée / conduites forcées decentrale hydroélectrique est présentée comme illustration possibl
Considérations physiques sur le développement et la validation des modèles de partition du flux de chaleur : application à la simulation des écoulements bouillants ascendants"
No full textInternational audienceAs part of a critical assessment of wall boiling modeling through Heat Flux Partitioning approach, a new model dedicated to vertical boiling flows is proposed, with a revisited partitioning including a boiling heat flux related to bubble coalescence.Closure laws include a recent model for bubble dynamics, a new correlation for the bubble maximum lift-off diameter, and comprehensive selection of existing models for nucleation site density and bubble wait time.Each formulation are compared to relevant existing data from the literature in order to emphasize the importance of separate validation in such a modeling framework.The whole model is then confronted to detailed wall boiling experiments to simultaneously compare boiling curve predictions along other physical parameters such as boiling time scales (bubble growth, transient conduction, bubble wait), nucleation frequency, or nucleation site density.Finally, validation against wall heat flux measurements in various conditions are used to assess the model accuracy and further discuss the limits of the Heat Flux Partitioning approach.Une évaluation critique de la modélisation de l’ébullition pariétale via l’approche de partition du flux de chaleur est proposée au travers du développement d'un nouveau modèle dédié aux écoulements bouillants ascendants, incluant une partition du flux revisitée incluant notamment des effets de coalescence des bulles en paroi.Les lois de fermeture comprennent un modèle récent pour la dynamique des bulles, une nouvelle corrélation pour le diamètre maximal de détachement des bulles, ainsi qu’une sélection attentive de modèles existants pour des paramètres clés tels que la densité de sites de nucléation et le temps d’attente entre deux nucléations.Chaque sous-modèle est comparé à des données expérimentales issues de la littérature, mettant en évidence l’importance d’une procédure de validation à effets séparés.Le modèle de partition du flux obtenu est ensuite confronté à des expériences d’ébullition pariétale récentes afin de comparer des prédictions de courbe d'ébullition en parallèle d’autres grandeurs physiques telles que les échelles de temps caractéristiques de l’ébullition (temps de croissance de bulle, conduction transitoire, temps d’attente), la fréquence de nucléation ou encore la densité de sites de nucléation actifs.Enfin, une validation par comparaison à des mesures de flux de chaleur pariétaux permet d’évaluer la précision du modèle et de discuter les limites de l’approche par partition du flux de chaleur
Spurious resonances for substructured FEM-BEM coupling
No full textWe are interested in time-harmonic acoustic scattering by an impenetrable obstacle in a medium where the wavenumber is constant in an exterior unbounded subdomain and is possibly heterogeneous in a bounded subdomain. The associated Helmholtz boundary value problem can be solved by coupling the Finite Element Method (FEM) in the heterogeneous subdomain with the Boundary Element Method (BEM) in the homogeneous subdomain. Recently, we designed and analyzed a new substructured FEM-BEM formulation, called Generalized Optimized Schwarz Method (GOSM). Unfortunately, it is well known that, even when the initial boundary value problem is well-posed, the variational formulation of classical FEM-BEM couplings can be ill-posed for certain wavenumbers, called spurious resonances. In this paper, we focus on the Johnson-Nédélec and Costabel couplings and show that the GOSM derived from both is not immune to that issue. In particular, we give an explicit expression of the kernel of the local operator associated with the interface between the FEM and BEM subdomains. That kernel and the one of classical FEM-BEM couplings are simultaneously non-trivial
From algorithm to activities: towards a situated definition of AI explainability
No full textThis document explores the concept of explainability in artificial intelligence (AI) by proposing a definition that is situated and centered on human activity, going beyond the traditional view focused solely on the algorithm. It draws on a practical case study in the nuclear industry to illustrate this approach.It was presented at the annual workshop of the Foncsi Fundation in decembre 202
Enhancing Open-Circuit Voltage in Infrared PbS Quantum Dot Heterojunction Solar Cells Using ZnO Nanowires Passivated by Atomic Layer Deposition of Al 2 O 3
No full textInternational audienc
Orchestrating an interoperable sovereign federated Multi-vector Energy data space built on open standards and ready for GAia-X D6.1 Use Cases Implementation Plan
No full textThe primary goal of this document is to outline a practical plan for carrying out pilot activitiesin the four OMEGA-X use case families. These plans will serve as the basis for subsequentwork in tasks T6.2 "Renewable Use Case Family", T6.3 "Energy Communities and SectorIntegration Use Case Family", T6.4 "Collaboration among Electromobility Actors Use CaseFamily", and T6.5 "Flexibility Use Case Family". By detailing the specific steps and strategiesfor implementing pilots, this deliverable aims to ensure a smooth and coordinated effort,aligning with the broader project timeline. In essence, it's a roadmap that guides the practicalexecution of pilot initiatives, contributing significantly to the overall success of OMEGA-X
Simulations of Richtmyer-Meshkov instabilities using a stochastic front tracking method
No full textInternational audienceThis paper is dedicated to Richtmyer-Meshkov simulations. The strategy adopted here is not classical. It is based on a two-fluid Euler model, whose approximated solutions are computed using a first-order scheme coupled with a pseudo-random front-tracking algorithm. This new method has been tested satisfactorily, demonstrating good accuracy, with an effective convergence rate close to 0.9 even on linearly degenerate fields. This first application to the Richtmyer-Meshkov instability shows satisfactory agreement with experiments and exhibits appreciable properties: no spurious velocity/pressure oscillations show up near the interface, and the interface is maintained sharp
Global solutions and uniform convergence stability for compressible Navier-Stokes equations with oldroyd-type constitutive law
No full textInternational audienceWe consider one dimensional isentropic compressible Navier-Stokes equations withOldroyd-type constitutive law. By establishing uniform a priori estimates (with respect to relaxation time), we show global existence of smooth solutions with small initial data. Moreover, we get global-in-time convergence of the system towards the classical isentropic compressible Navier-Stokes equations