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Concept

Uncertainty

Résumé

Uncertainty refers to epistemic situations involving imperfect or unknown information. It applies to predictions of future events, to physical measurements that are already made, or to the unknown. Uncertainty arises in partially observable or stochastic environments, as well as due to ignorance, indolence, or both. It arises in any number of fields, including insurance, philosophy, physics, statistics, economics, finance, medicine, psychology, sociology, engineering, metrology, meteorology, ecology and information science. Concepts Although the terms are used in various ways among the general public, many specialists in decision theory, statistics and other quantitative fields have defined uncertainty, risk, and their measurement as: Uncertainty The lack of certainty, a state of limited knowledge where it is impossible to exactly describe the existing state, a future outcome, or more than one possible outcome. ;Measurement of uncertainty: A set of possible stat

Source officielle

https://en.wikipedia.org/wiki/Uncertainty

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L'économie (ou économie politique, science économique) est une discipline qui étudie l'économie en tant qu'activité humaine, qui consiste en la production, la distribution, l'échange et la consommat

La méthode scientifique désigne l'ensemble des canons guidant ou devant guider le processus de production des connaissances scientifiques, qu'il s'agisse d'observations, d'expériences, de raisonnement

Le risque est la possibilité de survenue d'un événement indésirable, la probabilité d’occurrence d'un péril probable ou d'un aléa. Le risque est une notion complexe, de définitions multiples car d'

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Cours associés (88)

This course covers some theoretical and practical aspects of robust and adaptive control. This includes H-2 and H-infinity control in model-based and data-driven framework by convex optimization, direct, indirect and switching adaptive control. The methods are implemented in a hands-on lab.

L'ensemble des problématiques liées à l'eau est présenté afin d'avoir une vue globale de la gestion et de l'économie de cet élément essentiel à toute vie et toute activité. L'analyse des ressources et des besoins est présentée ainsi que les outils d'optimisation et d'évaluation économique.

This course introduces the theory and application of modern convex optimization from an engineering perspective.

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Although pedestrian crossings are supposed to guarantee safety, accidents are still frequent. Prior to implementing any measures to address this issue, the safety of the pedestrian crossing must be assessed. Various indices estimating the safety of pedestrian crossings have been developed. They quantify spatio-temporal distance, potential collision severity or kinetic energy on impact. Computing these indices requires accurate and reliable trajectory data which can be extracted from videos thanks to computer vision algorithms. Like any measurement technology, this process produces imperfections and uncertainty in its output. These errors and uncertainties are scarcely considered in the current index definitions. This project aims to integrate these different measurement uncertainties into the calculation of such indices. Instead of computing a single deterministic value for each index, we propose a methodology providing the index probability distribution under various uncertainties. Further- more, we investigate the influence of each uncertainty on the index distribution. The feasibility and reliability of this method are verified by applying it to an empirical data set. The methodology is validated by comparing the results to state-of-the-art conflict analysis. We observe that the outcome of the indices is strongly conditioned by the quality of the data, in particular the smoothness of the trajectories.

2020

Chargement

Improved methodology for analysis and design of Molten Salt Reactors

Rodrigo Gonzalez Gonzaga De Oliveira

Molten Salt Reactors is a class of advanced reactors that is typically characterised by the presence of a molten inorganic salt of a fissile material as fuel. At the moment, this class of reactors is considered one of the promising options in the long run of nuclear power.In the context of safety assessment of the MSFR, a task on analysis of selected transients was planned by the SAMOFAR project, to which this thesis should contribute. In addition, fluids with high melting temperature bring with them challenges regarding solidification of the fluid and possible flow blockage, to which a method was implemented during this thesis to evaluate the consequences. The open core cavity with curved shape adds another issue where the core is highly turbulent and requires the use of unstructured mesh codes for routine analysis, adding uncertainty and computational burden to the analytical workflow. Using ATARI, the tool developed during this thesis, we:1. Analyse the MSFR together with partners in support of a safety assessment task.2. Consider the impact and how to include solidification/melting in an analytical methodology.3. Evaluate options to manage/reduce uncertainties and the burden of routine use of high-fidelity codes.After a careful derivation of the conservation laws and assembling the code main algorithms, ATARI undergoes verification in a limited scope using the Stefan problem, manufactured solutions and energy balances.The nuclear cavity benchmark was performed between SAMOFAR partners showing equivalency of the codes within the scope of the benchmark. Then the participating institutions perform analysis of the MSFR for the safety assessment task, which ATARI is unable to followup with the transient analysis. The reason for failure is identified as the requirement of appropriate acceleration schemes by OpenFOAM-based multiphysics solvers, and the lack of one in ATARI.In the lack of accurate data regarding the heat exchangers, the impact of solidification is evaluated in a few simplified cases of a pipe with square cross-section and heat exchanger. For different salt compositions and different boundary conditions, the heat exchanger is found to recover from blockage if pump maintains its momentum and some cross-flow is allowed. The recovery of cases with abrupt solidification is questionable due to the required pressure head.The use of flow baffles is investigated as an option to structure the flow inside the reactor and reduce uncertainties originating from turbulence modelling while allowing the use of structured mesh codes for analysis. The concept is tested in a chloride based MSR, which retains its breed and burn mode while showing a quasi-1D flow appropriate for modelling with legacy codes.We recommend that the nuclear cavity benchmark should be expanded to include a more demanding transient case, representative of MSFR transient analysis requirements. A case is made for homogenised and economical models as used in ATARI to enable the practical use of coupling methods that promote the simultaneous solution of equations. A niche for ATARI is found as a special-mission code for analysis of challenging cases with deforming structure and flow field that justifies the use of unstructured meshes and the added computational burden. Due to design uncertainties and their nature, it is recommended to consider solidification implicitly when analysing the MSFR fuel circuit.

EPFL2021

Chargement

Ancient off-shore lighthouses have a phenomenal cultural significance. They were built as physical aid for navigation to guide mariners and to warn them from dangerous shallow rocky reefs. Understanding their structural response under waves loading is a challenging task. La Jument lighthouse, off the coast of Brittany, has sustained extreme environmental loading for more than 110 years. The main motivation of the present study is to characterize its structural response under extreme waves loading by 3D Finite Element Modeling using the commercial software DIANA. The model is calibrated based on the data collected from accelerometers and photographical documentations during a measurement campaign in winter 2018 in which the highest wave recorded with 19 meters height is considered for this study. The effect on the lighthouse’s structural response of slamming pressure magnitude, tide level, and slamming area is investigated in a parametric study. The predictions of the FE model were comparable to the actual measurements confirming the main hypothesis in this study. The tide level was proven to be an important factor contributing to the structural response parameters. The FE model suggested 230 kPa as the most likely pressure of the wave under consideration. Moreover, intervention methods using UHPFRC combined with a measurement campaign are proposed to preserve the outstanding cultural significance of La Jument lighthouse. Extending the life of off-shore lighthouses is essential to understand non-linear characteristics of extreme waves in future field measurements which helps validating numerical computations and removing uncertainties about their dynamic behavior.

2022

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Improved methodology for analysis and design of Molten Salt Reactors

Rodrigo Gonzalez Gonzaga De Oliveira

EPFL2021