Modeling Shallow Over-Saturated Mixtures on Arbitrary Rigid Topography

In this paper a system of depth-integrated equations for over-saturated debris flows on three-dimensional topography is derived. The lower layer is a saturated mixture of density preserving solid and fluid constituents, where the pore fluid is in excess, so that an upper fluid layer develops above the mixture layer. At the layer interface fluid mass exchange may exist and for this a parameterization is needed. The emphasis is on the description of the influence on the flow by the curvature of the basal surface, and not on proposing rheological models of the avalanching mass. To this end, a coordinate system fitted to the topography has been used to properly account for the geometry of the basal surface. Thus, the modeling equations have been written in terms of these coordinates, and then simplified by using (1) the depth-averaging technique and (2) ordering approximations in terms of an aspect ratio ϵ which accounts for the scale of the flowing mass. The ensuing equations have been complemented by closure relations, but any other such relations can be postulated. For a shallow two-layer debris with clean water in the upper layer, flowing on a slightly curved surface, the equilibrium free surface is shown to be horizonta

Bayesian Programming: life science modeling and robotics applications

International audienceHow to use an incomplete and uncertain model of the environment to perceive, infer, decide and act efficiently? This is the challenge both living and artificial cognitive systems have to face. Logic is by nature unable to deal with this question. The subjectivist approach to probability is an alternative to logic specifically designed to face this challenge. In this paper we introduce Bayesian Programming, a methodology, a for- malism and an inference engine to build and compute probabilistic models. The principles are illustrated with two examples: modeling human perception of structure from motion and playing to train a video game avatar

Development and Optimization of Motion Cueing for Flight Simulation of Maritime Helicopter Operations

Maritime helicopter operations such as helicopter ship deck landings are highly demanding for both the pilot and the helicopter. In the absent of potential safety risks during an offshore mission a maritime simulation environment offers a benefit for pilot training and development of new systems and procedures. Such a maritime simulation environment requires a specific optimized motion system. In the recent past years new methods have been developed to tune the motion system in an easier, faster and objective way. Unfortunately, these methods are not sufficiently validated because however suitable validation methods are still missing. This master thesis presents a methodology to implement a Classical Washout Algorithm (CWA) in the simulator. To develop suitable motion parameter sets for a helicopter ship deck landing procedure the fitness function is used as a novel optimization method. The validation is conducted with piloted simulator flight test trials that are new developed. Additionally, an unpiloted validation is carried out with the Objective Motion Cueing Test (OMCT). The results of both validation methods are compared to each other

Caractérisation des mécanismes d'usure par tribocorrosion d'alliages modèles Ni-Cr

Les alliages à base nickel sont utilisés dans les centrales nucléaires pour la fabrication des tubes générateurs de vapeur, parce qu ils présentent une bonne résistance aux sollicitations mécaniques élevées dans un milieu corrosif à haute température. La résistance au milieu corrosif est attribuée à une couche protectrice très fine de Cr2O3 qui se forme à la surface de l alliage. Les tubes générateurs de vapeur comptent parmi les composants les plus délicats à entretenir, d une part, du fait de leur importance pour la sûreté et, d autre part, parce que les tubes d échange sont soumis à de nombreux mécanismes de dégradation à cause de conditions sévères de fonctionnement.. L objectif de cette étude a été d évaluer et de comparer le comportement en tribocorrosion de deux alliages modèles Ni 15%Cr et Ni 30%Cr. Ces alliages ont été utilisés pour mettre en évidence, évaluer et comparer l influence de la teneur en chrome sur la formation de la couche d'oxyde superficielle et le rôle de cette dernière sur les mécanismes et cinétiques d'usure par tribocorrosion. L étude de la tribocorrosion a été effectuée à l aide d un tribomètre pion disque par application d un frottement unidirectionnel, en régime continu et intermittent en milieu aqueux boré lithié à la température ambiante. La dégradation de la couche protectrice formée à la surface des deux alliages a été suivie en mettant en œuvre un protocole expérimental en trois étapes. Dans la première étape du protocole, le suivi de l évolution du potentiel libre et l enregistrement des diagrammes d impédance électrochimique ont été utilisés pour analyser le comportement électrochimique des deux alliages en absence de frottement. Lors de la deuxième étape, les mêmes techniques électrochimiques ont été employées en présence d un frottement continu et pour différentes pressions de contact. Durant l étape trois du protocole, des essais de tribocorrosion en régime de frottement intermittent ont été réalisés pour mettre en évidence la capacité d auto cicatrisation de la surface des deux alliages modèles. Pour les deux alliages Ni - Cr, les essais de tribocorrosion ont mis en évidence une augmentation de l usure totale avec la pression de contact appliquée. Quel que soit la force normale appliquée, la principale composante de l usure totale est l usure mécanique du substrat mis à nu. L usure purement corrosive du substrat diminue avec l augmentation de la teneur en chrome. Du point de vue qualitatif, le principal mécanisme d usure identifié a été l usure abrasive par micro - labourage. Dans cette étude a été effectuée une étude de l usure d alliages modèles Ni Cr, dans les conditions de tribocorosion, ainsi que une analyse du mécanisme et la cinétique d usure. Le comportement de la couche superficielle d oxyde de chrome et son effet sur la résistance à la tribocorrosion ont été évalués. Ces résultats peuvent servir de base à la compréhension de l origine des problèmes qui peuvent apparaître pendant la vie d un alliage inoxydable à base nickel soumis à des efforts mécaniques en milieu agressifs et permettre une sélection plus pertinente des matériaux métalliques pour diverses applications industrielles, particulièrement dans le domaine nucléaire.Some components of nuclear power plants, as steam generator tubes are made from Ni base alloys. These components are exposed to severe environment of high temperature and high pressure and submitted to contact mechanical stresses. These Ni based alloys properties are determined by their ability to form on their surface an inner protective barrier film mainly composed of Cr2O3. The steam generator tubes are among the most difficult components to maintain, on the hand, because of their safety importance and secondly, the exchange tubes are subject to various degradation mechanisms, because of the harsh conditions of work. Wear by tribocorrosion is a physicochemical aging mechanism which occurs in the management of the nuclear power plants life time.Tribocorrosion is an irreversible process which involves mechanical and chemical / electrochemical interactions between surfaces in relative motion, in the presence of a corrosive environment. The goal of this study was to quantify in terms of quantity and quality the wear generated by tribocorrosion process on Ni Cr model alloys. Two model alloys: Ni -15Cr and Ni -30Cr were used to highlight, evaluate and compare the influence of the chromium content on the formation of the protective oxide layer and the role played by the latter one on the kinetics and mechanisms of wear by tribocorrosion. The tribocorrosion experiments were performed by using a pin -on disc tribometer under controlled electrochemical conditions in LiOH H3BO3 solution. The corrosion wear degradation of the protective layer during continuous and intermittent unidirectional sliding tests was investigated by a three-stage tribocorrosion protocol. In the first stage, electrochemical techniques (open circuit potential measurements and electrochemical impedance measurements) were used without applying unidirectional sliding to monitor and evaluate the characteristics of protective oxide layer formed on the surface of the two model alloys. In the second stage, the same electrochemical techniques were employed during the application of the unidirectional sliding test to evaluate the total material loss for different applied contact pressures. In the last stage of the experimental procedure the self healing process was investigated by intermittent unidirectional sliding tests.The total material loss after a tribocorrosion experiment, determined by profilometric measurements, is the sum of two components: the material loss due to corrosion of active material in the wear track, which can be calculated fro, the corrosion current values given by impedance measurements; applying Faraday s law, and the material loss due to mechanical wear, the difference between total material loss and the material loss due to corrosive wear. Experiments proved that the total material loss increases with the increase of the contact pressure in both cases of Ni Cr model alloys. The prevailing contribution in the total volumetric material loss is the material loss due to mechanical wear of active material in the sliding track. Nevertheless, the increase of the chromium content improves the resistance to the corrosive wear of active material in the sliding track. From qualitative viewpoint, a mechanism of abrasive wear by micro-ploughing was revealed in the sliding tracks.CHATENAY MALABRY-Ecole centrale (920192301) / SudocSudocFranceF

Atlas-Centaur VI flight path and its determination from tracking data

Atlas Centaur spacecraft trajectory in earth orbit and tracking data reduction metho