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Modeling dynamic formability of porous ductile sheets subjected to biaxial stretching: Actual porosity versus homogenized porosity
No full textInternational audienceThis paper investigates the effect of porous microstructure on the necking formability of ductile sheets subjected to dynamic in-plane stretching. We have developed an original approach in which finite element calculations which include actual void distributions obtained from additively manufactured materials are compared with simulations in which the specimen is modeled with the Gurson-Tvergaard continuum plasticity theory (Gurson, 1977; Tvergaard, 1982) which considers porosity as an internal state variable. A key point of this work is that in the calculations performed with the continuum model, the initial void volume fraction is spatially varied in the specimen according to the void distributions included in the simulations with the actual porous microstructure. The finite element computations have been carried out for different loading conditions, with biaxial strain ratios ranging from 0 (plane strain) to 0.75 (biaxial tension) and loading rates varying between 10000s-1 and 60000s-1. We have shown that for the specific porous microstructures considered, the necking forming limits obtained with the Gurson-Tvergaard continuum model are in qualitative agreement with the results obtained with the calculations which include the actual void distributions, the quantitative differences for the necking strains being generally less than ≈25% (the calculations with actual voids systematically predict greater necking strains). In addition, the spatial distribution of necks formed in the sheets at large strains is very similar for the actual porosity and the homogenized porosity models. The obtained results demonstrate that the voids promote plastic localization, acting as preferential sites for the nucleation of fast growing necks. Moreover, the simulations have provided individualized correlations between void volume fraction, maximum void size and necking formability, and highlighted the influence of the heterogeneity of the spatial distribution of porosity on plastic localization
New Methods for Fast Detection for Embedded Cognitive Radio
No full textInternational audienceSpectrum Sensing is an important part of Cognitive Radio (CR) process. It can be used to determine if a Primary User (PU) (i.e. a licensed user) is emitting or not in the communication channel. This paper presents and compares three types of FFT-based detection algorithms for LTE-Advanced (LTE-A) cellular network at Orthogonal Frequency Division Multiple Access (OFDMA) level. These detectors sense the usage of the minimum time-frequency called Resource Block (RB). They are also low latency detectors and they only need one particular Orthogonal Frequency Division Multiplexing (OFDM) symbol to detect the usage of one RB. The three new detectors are based respectively on energy, correlation, and one what will be called eogration which combines energy and correlation. We analyze them with the Fisher's ratio and simulations of hypothesis test. The computing complexity of these detectors is also theoretically analyzed to provide guidance for future implementations
Developing flow photo-thiol–ene functionalizations of cinchona alkaloids with an autonomous self-optimizing flow reactor
No full textInternational audienceContinuous flow photo-thiol–ene reactions on cinchona alkaloids with a variety of organic thiols have been developed using enabling technologies such as a self-optimizing flow photochemical reactor
Montrer l'exemple pour plus d'égalité entre les femmes et les hommes dans et par le numérique
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Hybrid Interval-Probabilistic Localization in Building Maps
No full textInternational audienceWe present a novel online capable hybrid interval-probabilistic localization method using publicly available 2D building maps. Given an initially large uncertainty for the orientation and position derived from GNSS data, our novel interval-based approach first narrows down the orientation to a smaller interval and provides a set described by a minimal polygon for the position of the vehicle that encloses the feasible set of poses by taking the building geometry into account using 3D Light Detection and Ranging (LiDAR) sensor data. Second, we perform a probabilistic Maximum Likelihood Estimation (MLE) to determine the best solution within the determined feasible set. The MLE is converted into a least-squares problem that is solved by an optimization approach that takes the bounds of the solution set into account so that only a solution within the feasible set is selected as the most likely one. We experimentally show with real data that the novel interval-based localization provides sets of poses that contain the true pose for more than 99% of the frames and that the bounded optimization provides more reliable results compared to a classical unbounded optimization and a Monte Carlo Localization approach
Model order reduction for geometrically nonlinear beams featuring internal resonance and centrifugal effect
No full text[ENOC] Conférence internationale sur la dynamique non linéaire en ingénierieInternational audienceThe direct parametrisation of invariant manifold is used for model order reduction of large amplitude vibrations of clampedclamped and rotating cantilever beams. A particular emphasis is set on the computation of the backbone curve in case of internal resonance. For the clamped beam, the 1:5 resonance between first and third mode occuring at large amplitude, is reproduced with the model. For the rotating cantilever, a Campbell diagram is first used to detect the appearance of a 1:5 resonance, which is then computed with the reduction method
Analysis of Small Sea-Surface Targets Detection Performance According to Airborne Radar Parameters in Abnormal Weather Environments
No full textInternational audienceAlong with the rapid development of marine radar, and particularly those carried on aircraft, the detection of small-sized targets which pose an increasing threat has become one of the main areas of interest. However, by considering an observation chain from an aircraft (such as a drone) in a maritime environment, with the aim of detecting and tracking of low signal-to-clutter ratio (SCR) targets, one of the important points would be the analysis of the radar system performance according to the radar input parameters, the atmospheric propagation medium, the various sea clutter characterization, and the type of targets (RCS, speed, etc.) in this environment. Therefore, it is necessary to obtain the overall path loss including the anomalous atmospheric environment, gas attenuation, clouds attenuation, rainfall attenuation, and beam scanning loss. To consider atmospheric attenuations, ITU-R models are used. On another side, because of spikes and dynamic variation properties, sea clutter is generally described by the statistical distribution with long tail and by its wider Doppler spectrum. Conventional algorithms such as those based on statistical models, MTI, and MTD processing are often limited, especially for the target of low speed and low RCS. Therefore, sea clutter, including empirical and statistical models available, is considered to estimate and simulate the impact of radar input parameters, targets RCS, and sea state on detection performance. The Doppler frequency of target echo which can be exploited for coherent processing is described by assuming an adequate scenario of observation geometry
Hybrid Systems and Contracts with Zélus and DynIbexZeldyn: a Compilation and Verification Toolchain
No full textModeling cyber-physical systems is known to be a challenging task. Model-based programming frameworks for CPS are an appealing approach to tackle this challenge, by providing languages close to engineers. However, these tools usually lack formal semantics, causing simulation results to vary from one version to another. A second particularity in the design of CPS is the presence of uncertainties due to parameters not well known at design-time. Monte-Carlo methods are classically used to circumvent this issue but they do not provide a complete coverage. Another solution is to rely on set-based simulation methods. On the one hand, control command systems find an elegant programming solution in synchronous languages. Zélus is such a language extended to deal with CPS, with a well-defined semantics. On the other hand, many set-based simulation libraries exist with a lack of proper front-end to make them suitable for industrial use. We propose to bridge the gap between set-based simulation and development frameworks for CPS by designing a new backend and runtime for Zélus, using set-based methods and guaranteed arithmetic. This runtime is described by very simple set-based primitives in order to be implemented in any set-based simulation library. An instance of the runtime is given with the DynIbex library to prove the effectiveness of the proposed approach. Finally, a mechanism of contracts is added to state and verify properties on the simulated system
CRANDALL-LIONS VISCOSITY SOLUTIONS FOR PATH-DEPENDENT PDES: THE CASE OF HEAT EQUATION
No full textInternational audienceWe address our interest to the development of a theory of viscosity solutions à la Crandall-Lions for path-dependent partial differential equations (PDEs), namely PDEs in the space of continuous paths C([0, T ]; R^d). Path-dependent PDEs can play a central role in the study of certain classes of optimal control problems, as for instance optimal control problems with delay. Typically, they do not admit a smooth solution satisfying the corresponding HJB equation in a classical sense, it is therefore natural to search for a weaker notion of solution. While other notions of generalized solution have been proposed in the literature, the extension of the Crandall-Lions framework to the path-dependent setting is still an open problem. The question of uniqueness of the solutions, which is the more delicate issue, will be based on early ideas from the theory of viscosity solutions and a suitable variant of Ekeland's variational principle. This latter is based on the construction of a smooth gauge-type function, where smooth is meant in the horizontal/vertical (rather than Fréchet) sense. In order to make the presentation more readable, we address the path-dependent heat equation, which in particular simplifies the smoothing of its natural "candidate" solution. Finally, concerning the existence part, we provide a new proof of the functional Itô formula under general assumptions, extending earlier results in the literature