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Flexible Optimization for Cyber-Physical and Human Systems
No full text13 pages, 2 figuresInternational audienceCan we allow humans to pick among different, yet reasonably similar, decisions? Are we able to construct optimization problems whose outcome are sets of feasible, close-to-optimal decisions for human users to pick from, instead of a single, hardly explainable, do-as-I-say ``optimal'' directive? In this paper, we explore two complementary ways to render optimization problems stemming from cyber-physical applications flexible. In doing so, the optimization outcome is a trade off between engineering best and flexibility for the users to decide to do something slightly different. The first method is based on robust optimization and convex reformulations. The second method is stochastic and inspired from stochastic optimization with decision-dependent distributions
Impact response of filament-wound structure with polymeric liner: Experimental and numerical investigation (Part-A)
No full textInternational audienceFilament wound pipelines and Type IV composite pressure vessels (CPVs) constitute polymeric liners and are extensively used to transport and store petroleum products, hydrogen, and compressed natural gas (CNG). The polymeric liner does not share much pressure load; hence, the composite layers share most of the load. The situation gets worse under transverse impact loads on such structures. For the polymeric liner to be effectively used in pipelines and CPVs, it is crucial to study impact response through testing and computational methods. This article presents experimental and numerical investigations of the transverse low-velocity impact response of filament wound samples. High-density polyethylene (HDPE) liner was adopted, and carbon fiber (T700) continuous filaments with epoxy resin were wound over the liner with several layers. A drop-weight impact loading with 40 J energy has been applied to the fabricated samples. The development of impact damage was assessed using the finite element method, and the damage modes have been discussed. The specimen remains unperforated at the chosen energy level. Though HDPE is ductile, however at impact loads liner damage was encountered, displaying a brittle fracture. At higher strain rates, the material reaches its brittle fracture point sooner, leading to failure. The material breaks as brittle due to its inability to dissipate impact energy quickly, resulting in fracturing instead of deformation. Fiber damage was scarcely seen; however, matrix damage has been the dominant failure mode at the chosen impact energy. Comparisons between the simulation and test findings were made, and they agreed on force-time and force-displacement histories
Comprendre et générer des distributions de commandes réalistes
No full textInternational audienceIn the real world, the sequences of commands encountered by a user are complex, whereas studies in HCI (empirical, intelligent systems simulations) dealing with commands generally use simplified stimuli: for example, independent sequences distributed according to a uniform or Zipf distribution. In this article, we first describe the characteristics of real commands, studying the dependencies between commands using Markov models. We then propose an algorithm for generating Zipf sequences with dependencies, which we evaluate and discuss.Dans le monde réel, les séquences de commandes exécutées par un utilisateur sont complexes, alors même que les études (empiriques, simulations de systèmes intelligents) utilisées en IHM sont fortement simplifiées : par exemple des séquences indépendantes distribuées selon une loi uniforme ou de Zipf. Dans cet article, on décrit d'abord les caractéristiques des distributions de commandes réelles, en étudiant les dépendances entre commandes à travers des modèles de Markov. On propose ensuite un algorithme pour générer des séquences de Zipf avec des dépendances dont les performances sont évaluées puis discutées
A Survey for Unmanned Aerial Vehicles in Smart Agriculture: Types and Modelling Perspectives
No full textInternational audienceDespite its major role in economic growth and development, the agriculture sector is facing many challenges globally. More significant problems have been continuously induced over the years, such as desertification, lack of infrastructure over vast agriculture areas, environmental pollution, excessive use of pesticides, lack of water resources, land fertility decline, and many more. As a solution, the idea of smart agriculture started pervading the world with the ability of transforming traditional farming sector to modern automated one for better crop field management. This can be done by using the technology of Wireless Sensor Networks (WSNs) where diverse agriculture sensors are located on the ground to measure different crop field parameters. However, as the number of sensor nodes increases as the difficulty in managing the system network increases. Consequently, common limitations are to be considered such as energy management, communication interruption, bad connectivity, and difficulties in nodes localization. Therefore, the idea of using Unmanned Aerial Vehicle (UAV) along with WSN in smart agriculture becomes cruicial to improve the system capabilities. UAVs can help locate and identify sensors on the ground, ensure a correct delivery of data, and assist in every stage of the crop field cycle. With its ability to provide better solution for crop fields management, UAV grabbed researchers' attention and encouraged them to deeply study this area and try to develop innovative UAV-WSN based applications that can be integrated with the agriculture sector. Hence, it is important to study UAV in all its aspects as it becomes the heart of the smart agriculture system. This article focuses particularly on UAV's type and mathematical model selection. Therefore, to understand UAV's functionality, this paper surveys different mathematical modelling techniques to derive the UAV plant, examines parameters identification methods to numerically evaluate the model, and discusses existing UAV open-source simulators to verify the ability of the selected model in realistic scenarios. Furthermore, key challenges and future research directions are presented to continuously improve the WSN-UAV based applications in smart agriculture
Characterization and modelling of the compressible hyperelastic behaviour of polyurethane foams: influence of the density
No full textInternational audienceIn parts such as automotive jounce bumpers, microcellular polyurethane foams are subjected to multiaxial loading leading to very large deformations. The density of the material can vary from one part to another or within the same part. Thus, the numerical simulations used to design the parts require a model describing the mechanical behaviour of the material over a wide range of loading conditions, as a function of the material density. This paper presents an extensive experimental database of uniaxial tension and compression, simple shear and confined compression test results, obtained on elastomeric microcellular polyurethane foam samples with several densities between 380 and 600 kg.m-3. The model proposed by Landauer et al. (2019), based on invariants of the Henck’s strain tensor, is used to describe compressible hyperelasticity. The influence of the foam density is integrated in the model. A robust identification strategy is proposed. Once identified, the model is used to simulate the response of a jounce bumper under global axial compression. The results are compared to the experimental load-displacement curve and to the deformed shape of the jounce bumper obtained from X-ray tomography
Construction et analyse des signatures spectrales pour des défauts dans des milieux complexes
No full textConcrete is widely used in construction, particularly in the reactor building of nuclear power plants. Monitoring its evolution and identifying any defects that could compromise its proper functioning can be achieved through non-destructive testing. Concrete is composed of aggregates, but their high concentration and proximity pose challenges for classical methods, such as the Linear Sampling Method, which fail to produce quantitative results or exploitable images.The objective of this thesis is to build an imaging algorithm that can estimatethe density of the aggregates and recover the local distribution of those smallinhomogeneities.To address this challenge, inspiration was drawn from a monotonicity property of the Transmissioneigenvalues. They correspond to the frequencies for which an incident wave exists such that the scattered field is trivial outside the scatterers.Instead of comparing the scattered field to the vacuum, this thesis introduces a new approach: comparing it, at a fixed wavenumber, to a numerical scattering problem, referred to as the background. This led to the introduction of a new class of eigenvalues known as the f-averaged Steklov eigenvalues. Each of these eigenvalues is associatedwith an artificial background problem that contains a resonator and is solution to a simple spectral problem inside the resonator. In addition, each f-averaged Steklov eigenvalue is monotonically increasing with respect to the number of inhomogeneities inside that resonator. These spectral signatures can be recovered from the data. By computing theseeigenvalues for various positions of the resonator, we can estimate the variation ofthe local density of the inhomogeneities in an unknown medium.Le béton est largement employé dans le secteur de la construction, notamment dans les bâtiments réacteurs des centrales nucléaires. La surveillance de son évolution et la détection des défauts susceptibles de compromettre son bon fonctionnement peuvent être effectuées grâce à des tests non destructifs. Le béton est constitué d'agrégats. Ces derniers présentent des défis en raison de leur concentration élevée et de leur proximité. Ces caractéristiques rendent les méthodes classiques, telles que la Linear Sampling Method, inefficaces pour fournir des résultats quantitatifs ou des images exploitables.Cette thèse a pour objectif de développer un algorithme d'imagerie capable d'estimer la densité des agrégats et de retrouver la distribution locale de ces petites hétérogénéités.Pour résoudre ce problème, l'inspiration provient d'une propriété de monotonie des valeurs propres de transmission. Ces valeurs correspondent aux fréquences pour lesquelles il existe une onde incidente générant un champ diffracté trivial à l'extérieur des obstacles.Plutôt que de comparer le champ diffracté à celui du vide, cette thèse propose une nouvelle approche consistant à le comparer, à un nombre d'onde fixé, à un problème de diffraction numérique. Cela a conduit à l'introduction d'une nouvelle classe de valeurs propres, appelées f-averaged Steklov eigenvalues. Chacune de ces valeurs est associée à un problème artificiel contenant un résonateur et est la solution d'un problème spectral simple à l'intérieur de ce résonateur. En outre, chaque f-averaged Steklov eigenvalue croît de manière monotone en fonction du nombre d'hétérogénéités présentes dans le résonateur. Ces signatures spectrales peuvent être extraites des données. En calculant ces valeurs propres pour différentes positions du résonateur, il devient possible d'estimer les variations de densité locale des hétérogénéités dans un milieu inconnu
Sonder l'interaction laser-plasma et faisceau d’électrons-plasma à très haute précision
No full textThe interactions of plasmas with ultrahigh intensity lasers and relativistic particle beams are important for many different fields of research, such as high energy physics, medical physics, material science, and astrophysics. These interactions consist of small-scale fast-evolving processes, which require suitable and specialized diagnostics. This manuscript presents two novel diagnostics with unprecedented precision and sensitivity. They serve different purposes: one has been developed for studying the interaction of laser pulses with solid targets, and the other one for probing laser and electron beam interactions with gaseous plasma.The interaction of ultra-intense lasers with solid targets is known to provide one of the mechanisms of ion acceleration – target normal sheath acceleration (TNSA). It is capable of accelerating ions to multi-MeV per nucleon from thin solid targets. It is also considered as a model of astrophysical systems in laboratories due to the presence of very strong magnetic fields. However, the fact that the targets in these systems are opaque to optical diagnostics makes it more challenging to obtain information about the phenomena evolving inside of them. The diagnostic method presented in this manuscript uses laser-generated particle beams of micrometer size that are capable of locally measuring the very strong magnetic fields arising in the laser-solid interaction. They are also suitable for distinguishing between different physical phenomena occurring on a femtosecond timescale during the laser-solid interaction. This probing technique provides unprecedented spatial resolution and precision. It can furthermore be applied to study laser-solid interactions in various other contexts.The second method presented in this thesis is developed for plasma-based particle accelerators that use ultraintense lasers and relativistic electron beams as drivers for the acceleration process. These acceleration schemes are called laser wakefield acceleration (LWFA) and plasma wakefield acceleration (PWFA), and they offer acceleration gradients exceeding conventional accelerators by orders of magnitude. The acceleration in such systems happens in plasma on a micrometer scale and over millimeter distances, and a better characterization of the process allows a better understanding and control. The probing method developed in the scope of this work is a modification to a widely used diagnostic, which boosts the sensitivity by orders of magnitude. This allowed, for the first time, the observation of the interaction in plasma density ranges that are important for future large-scale accelerators, and to observe an important feature in the acceleration process that has so far only been predicted. The increased sensitivity alleviates other requirements, which makes it much more affordable and thus more available to other laboratories.L’interaction des plasmas avec des lasers d'intensité ultra-élevée et des faisceaux de particules relativistes est importante pour de nombreux domaines de recherche, tels que la physique des hautes énergies, la physique médicale, la science des matériaux et l'astrophysique. Cette interaction est siège de processus à petite échelle et à évolution rapide, nécessitant des diagnostics appropriés et spécialisés. Ce manuscrit présente deux diagnostics nouveaux avec une précision et une sensibilité sans précédent. Ils servent des objectifs différents : l'un a été développé pour étudier l'interaction des impulsions laser avec des cibles solides, et l'autre pour sonder les interactions des faisceaux laser et d'électrons avec un plasma gazeux.L'interaction des lasers ultra-intenses avec des cibles solides est connue pour fournir l'un des mécanismes d'accélération des ions – target normal sheath acceleration (TNSA). Elle est capable d'accélérer des ions à plusieurs MeV par nucléon à partir de cibles solides minces. Elle est également considérée comme un modèle de systèmes astrophysiques en laboratoire en raison de la présence de champs magnétiques très forts. Cependant, le fait que les cibles dans ces systèmes soient opaques aux diagnostics optiques rend plus difficile l'obtention d'informations sur les phénomènes qui évoluent à l'intérieur d'elles. La méthode de diagnostic présentée dans ce manuscrit utilise des faisceaux de particules générés par laser de taille micrométrique capables de mesurer localement les champs magnétiques très élevés qui se forment lors de l'interaction laser-solide. Ils sont également adaptés pour distinguer entre différents phénomènes physiques se produisant à une échelle de temps de la femtoseconde lors de l'interaction laser-solide. Cette technique de sondage offre une résolution spatiale et une précision sans précédent. Elle peut en outre être appliquée pour étudier les interactions laser-solide dans divers autres contextes.La deuxième méthode présentée dans cette thèse est développée pour les accélérateurs de particules basés sur les plasmas qui utilisent des lasers ultra-intenses et des faisceaux d'électrons relativistes pour créer la structure accélératrice. Ces schémas d'accélération sont appelés laser wakefield acceleration (LWFA) et plasma wakefield acceleration (PWFA), et ils offrent des gradients d'accélération dépassant de plusieurs ordres de grandeur ceux des accélérateurs conventionnels. L'accélération dans de tels systèmes se produit dans le plasma à une échelle micrométrique et sur des distances millimétriques, et une meilleure caractérisation du processus permet une meilleure compréhension et un meilleur contrôle. La méthode de sondage développée dans le cadre de ce travail est une modification d'un diagnostic largement utilisé, qui augmente la sensibilité de plusieurs ordres de grandeur. Cela a permis, pour la première fois, l'observation de l'interaction dans des gammes de densité de plasma particulièrement pertinentes pour les futurs accélérateurs plasma, ainsi que l'observation d'une caractéristique importante du processus d'accélération qui n'avait jusqu'à présent été que prédite. L’amélioration de la sensibilité réduit d'autres contraintes, ce qui rend cette méthode beaucoup plus abordable et donc plus accessible à d'autres laboratoires
Adaptive solution of the domain decomposition+ -jumps method applied to the neutron diffusion equation on structured meshes
No full textInternational audienceAt the core scale, neutron deterministic calculations are usually based on the neutron diffusion equation. Classically, this equation can be recast in a mixed variational form, and then discretized by using the Raviart-Thomas-Nédélec Finite Element. The goal is to extend the Adaptive Mesh Refinement (AMR) strategy previously proposed in [1] to the Domain Decomposition+ jumps which allows non conformity at the interface between subdomains. We are able to refine each subdomain independently, which eventually leads to a more optimal refinement. We numerically investigate the improvements made to the AMR strategy
Theoretical Cooperation in Decision Aid and System Engineering Technical decisions: decision distribution over time in constrained environment
No full textInternational audienceSystems engineering proposes methods to down select a set of decisions so as to create systems that perform specified capabilities in constrained time and resources. Tradeoffs in Architecture are decided by architects, with an approximation of the performance in terms of quality, resources and time <Q,R,T>. In the current context, in introducing robots on battlefield seen as system-of-systems, those decisions are taken based on a set of beliefs over data that is generated by approximate resolution of complex equations. In the time constraints, decisions should be taken on multiple levels, concurrently. In the end, government agencies in acquisition processes rely on both field experience and prospective performance of those systems. This article exposes relationships that could be built between decision aid and system engineering process yet to be solved in both domains, which could be mutually beneficial in helping large programs authorities to avoid violating <Q,R,T> constraints of those programs.</div
