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New Methods of Isochrone Mechanics
No full text17 pages, 1 figuresInternational audienceIsochrone potentials, as defined by Michel H\'enon in the fifties, are spherically symmetric potentials within which a particle orbits with a radial period that is independent of its angular momentum. Isochrone potentials encompass the Kepler and harmonic potential, along with many other. In this article, we revisit the classical problem of motion in isochrone potentials, from the point of view of Hamiltonian mechanics. First, we use a particularly well-suited set of action-angle coordinates to solve the dynamics, showing that the well-known Kepler equation and eccentric anomaly parametrisation are valid for any isochrone orbit (and not just Keplerian ellipses). Second, by using the powerful machinery of Birkhoff normal forms, we provide a self-consistent proof of the isochrone theorem, that relates isochrone potentials to parabolae in the plane, which is the basis of all literature on the subject. Along the way, we show how some fundamental results of celestial mechanics such as the Bertrand theorem and Kepler's third law are naturally encoded in the formalism
Optimization of wireless sensor networks deployment with coverage and connectivity constraints
No full textInternational audienceWireless sensor networks have been widely deployed in the last decades to provide various services, like environmental monitoring or object tracking. Such a network is composed of a set of sensor nodes which are used to sense and transmit collected information to a base station. To achieve this goal, two properties have to be guaranteed: (i) the sensor nodes must be placed such that the whole environment of interest (represented by a set of targets) is covered, and (ii) every sensor node can transmit its data to the base station (through other sensor nodes). In this paper, we consider the Minimum Connected k-Coverage (MCkC) problem, where a positive integer k ≥ 1 defines the coverage multiplicity of the targets. We propose two mathematical programming formulations for the MCkC problem on square grid graphs and random graphs. We compare them to a recent model proposed by (Rebai et al 2015). We use a standard mixed integer linear programming solver to solve several instances with different formulations. In our results, we point out the quality of the LP-bound of each formulation as well as the total CPU time or the proportion of solved instances to optimality within a given CPU time
Dispositifs de formation au numérique en primaire : usages des rôles modèles et redistribution des rôles.: Retours d’expérience des acteurs et actrices
No full textInternational audienceDes dispositifs de formation tentent de contrer les stéréotypes. À l’appui d’une démarche compréhensive, l’article montre comment les acteurs et actrices s’emparent d’un dispositif œuvrant à l’égalité entre les femmes et les hommes dans le domaine du numérique. Le terrain de recherche, “Les filles qui”, est celui d’ateliers de médiation numérique créés dans des écoles primaires de Bretagne. L’expérience redéfinit le rôle de l’identité professionnelle et la fait évoluer. Les étudiantes expérimentent une place entre la grande sœur et la sachante scientifique. Le corps enseignant identifie chez les élèves des potentialités non mobilisées par l’école traditionnelle. Son identité professionnelle évolue d’une logique de qualification vers une logique de compétence, sans que l’une annihile l’autre. Les participants dessinent une alternative : un partenariat sur des dispositifs qui viennent combler des manques en leur apportant des bénéfices en termes d’image et de représentations du métier
Control of the Swell by an Array of Helmholtz Resonators
No full textInternational audienceWe present a theoretical and experimental study of a resonator of the Helmholtz type for the control of the swell. An experimental demonstration of the shielding effect by a belt made of evenly distributed resonators is given. We then provide in-depth analysis of the Fano resonance resulting from the interference between the dock scattering (the background) and the resonant cavity scattering. This is done thanks to space–time resolved experiments which provides the complex-valued scattering coefficients and amplitude within the resonator. We provide a one-dimensional model derived in the shallow water regime owing to asymptotic analysis. The model contains the two ingredients of the Fano resonance and allows us to exhibit the damping due to leakage. When adding heuristically the damping due to losses, it reproduces the main features of the resonance observed experimentally
Analytical and numerical simplified modeling of a single-lap joint
No full textInternational audienceThis paper is devoted to the theoretical modeling of the mechanical response of bonded structures and particularly focuses on the single-lap joint which corresponds to the simplest and most fundamental bonding configuration. Such a geometry brings into play all the features of any bonded assembly in terms of mechanical response (stress/strain heterogeneities, singularities, adhesion at the interfaces,...). It can especially be used to characterize the mechanical behavior of new adhesives within an assembly. In all cases, an accurate description of the stress/strain distribution (specifically in the adhesive layer) is required both for the calibration of an adhesive behavior and for dimensioning purposes. Accordingly, the present study aims at developing a specific 1D enriched finite element devoted to the numerical modeling of single-lap joints, especially of the overlap region. First, analytical solutions for a single-lap joint under tensile forces are investigated in the framework of elasticity. They are particularly based on the choice of a 2D representation of the adhesive layer with polynomial displacement fields in terms of the thickness coordinate. Such a preliminary study allows one to identify optimally the appropriate kinematics for each layer (adhesive but also substrates) and highlights the importance of non-linear terms in the polynomial expressions of both longitudinal and transverse displacements within the adhesive. A three-layer finite element model is then formulated for the overlap region, based on the retained kinematics, and involving an elastoplastic constitutive law for the adhesive material. The numerical integration through the adhesive thickness and the assembly of the three layers lead to the definition of a very low-cost 1D finite element, which provides nevertheless a complete and accurate description of the stress fields, especially within the adhesive layer. This new finite element (used simultaneously with a more classical beam finite element for the unbonded parts of the adherends) is finally validated by comparison with 2D reference results computed using Abaqus software
Analyzing Uncertain Dynamical Systems after State-Space Transformations into Cooperative Form: Verification of Control and Fault Diagnosis
No full textInternational audienceWhen modeling real-life applications, uncertainty appears in the form of, for example, modeling approximations, measurement errors, or simply physical restrictions. Those uncertainties can either be treated as stochastic or as bounded, with known limits in the form of intervals. The latter is considered in this paper for a real-life application in the form of an electrical circuit. This is reasonable because the electrical circuit is subject to uncertainties, mainly due to circuit element tolerances and variable load conditions. Since conservative worst-case limits for such parameters are commonly known, interval methods can be applied. The aim of this paper is to demonstrate a possible overall handling of the given uncertain system. Firstly, this includes a control and a reliable computation of the states’ interval enclosures. On the one hand, this can be used to predict the system’s behavior, and on the other hand to verify the control numerically. Here, the implemented feedback control is based on linear matrix inequalities (LMIs) and the states are predicted using an interval enclosure technique based on cooperativity. Since the original system is not cooperative, a transformation is performed. Finally, an observer is implemented as a diagnosis tool regarding faulty measurements or component failures. Since adding a state-of-the-art observer would destroy this structure, a cooperativity-preserving method is applied. Overall, this paper combines methods from robust control design and interval-based evaluations, and presents a suitable observer technique to show the applicability of the presented methods
Predicting file lifetimes for data placement in multi-tiered storage systems for HPC
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Multi-objective Optimization of Data Placement in a Storage-as-a-Service Federated Cloud
No full textInternational audienceCloud federation enables service providers to collaborate to provide better services to customers. For cloud storage services, I/O performance and network latency are important to ensure end-to-end QoS. Therefore, effectively placing customer objects for a cloud that is a member of a federation is a real challenge. In order to optimize data placement, storage, migration and latency costs need to be considered. These costs are contradictory in some cases. In this paper, we modeled object placement as a multi-objective optimization problem. The proposed model takes into account parameters related to the local infrastructure, the federated environment, customer workloads and their SLAs. For resolving this problem, we propose CDP-NSGAII , a Constraint Data Placement matheuristic based on NSGAII with injection and repair functions. The objective of the injection function is to enhance the solutions' quality. It consists to calculate some solutions using an exact method then inject them into the initial population of NSGAII. The repair function was designed to ensure that the solutions obey the problem constraints in term of storage and so prevents from exploring large sets of infeasible solutions. It allows to reduce the execution time of NSGAII. Our experimental results show that, the injection function improves the HV of NSGAII and the exact method by up to 94% and 60% respectively while the repair function reduces the execution time by an average of 68%. CCS Concepts: • Federated cloud → Hybrid storage system; • Data placement → Cost optimization
Experimental characterization of the noise generated by an airfoil oscillating above stall
No full textInternational audienceThe present work investigates the noise emitted by an airfoil oscillating above stall, thanks to synchronized surface pressure and far-field acoustic measurements in an anechoic open-jet wind tunnel. Both NACA0012 and a NACA633418 airfoils are tested in order to investigate the effects of the airfoil shape on the static and dynamic stall noise. For static configurations, a smoother transition to stall noise is obtained for the cambered NACA633418 airfoil, with a gradual increase and shift of the noise spectra at low frequencies as the separation point moves closer to the leading edge of the airfoil. Phase-averaged time-frequency analysis of the oscillating airfoil noise reveals that the light-stall noise and deep-stall noise regimes commonly observed for static airfoils also take place during the oscillations. Increasing the frequency of the oscillations leads to an increase of the duration and amplitude of the stall onset broadband noise, and a delay of the dynamic stall noise to greater angles of attack. In the same way, the dynamic stall noise is delayed for the NACA633418 compared to the NACA0012, causing the stalled phase to be shorter for the NACA633418. For the NACA0012, the noise does not depend on the angle of attack before the onset on stall. For the NACA633418, the noise gradually increases in the pre-stall regime and the stall noise is preceded by a high amplitude separation noise