Parameter uncertainties quantification for finite element based subspace fitting approaches

International audienceThis paper addresses the issue of quantifying uncertainty bounds when updating the finite element model of a mechanical structure from measurement data. The problem arises as to assess the validity of the parameters identification and the accuracy of the results obtained. In this paper, a covariance estimation procedure is proposed about the updated parameters of a finite element model, which propagates the data-related covariance to the parameters by considering a first-order sensitivity analysis. In particular, this propagation is performed through each iteration step of the updating minimization problem, by taking into account the covariance between the updated parameters and the data-related quantities. Numerical simulations on a beam show the feasibility and the effectiveness of the method

Embedded subspace-based modal analysis and uncertainty quantification on wireless sensor platform PEGASE

International audienceOperational modal analysis is an important step in many methods for vibration-based structural health monitoring. These methods provide the modal parameters (frequencies, damping ratios and mode shapes) of the structure and can be used for monitoring over time. For a continuous monitoring the excitation of a structure is usually ambient, thus unknown and assumed to be noise. Hence, all estimates from the vibration measurements are realizations of random variables with inherent uncertainty due to unknown excitation, measurement noise and finite data length. Estimating the standard deviation of the modal parameters on the same dataset offers significant information on the accuracy and reliability of the modal parameter estimates. However, computational and memory usage of such algorithms are heavy even on standard PC systems in Matlab, where reasonable computational power is provided. In this paper, we examine an implementation of the covariance-driven stochastic subspace identification on the wireless sensor platform PEGASE, where computational power and memory are limited. Special care is taken for computational efficiency and low memory usage for an on-board implementation, where all numerical operations are optimized. The approach is validated from an engineering point of view in all its steps, using simulations and field data from a highway road sign structure

Phased and synchronous sampling between multiple smart network sensors for modal assessment of large structures

International audienc

Emergence of mega-regional trade agreements and the imperative for African economies to strategically enhance trade-related South-South Cooperation

Over the last fifteen years, the number of regional trade agreements have multiplied tremendously and largely as a result of slow progress made in the multilateral trade negotiations. The latest trend towards increased regionalism is the emergence of mega-regional trade agreements (MRTAs). Currently three major MRTAs (i.e. Trans-Atlantic Trade and Investment Partnership (TTIP), Trans-Pacific Partnership (TPP) and Regional Comprehensive Economic Partnership (RCEP)) are envisaged and expected to greatly modifying trading relationships worldwide. Whereas there are developing countries–essentially from Asia and Latin America– amongst the MRTA members, African nations are not part of any of the three rising trade configurations. Relying on a Computable General Equilibrium analysis this paper aims at not only assessing the trade impacts that MRTAs are expected to produce on African economies but most importantly exploring various trade arrangements that could help mitigating any possible negative effect on Africa which are expected to arise as a result of the formation of MRTAs. Findings from the analysis indicate that deepening continental trade integration–by establishing the Continental Free Trade Are (CFTA)– should be seen as a key priority for Africa; it would allow to offset harmful impacts MRTAs would cause on African economies and strongly stimulating intra-African trade. However, results suggest that Africa needs to also start looking beyond its own, and still relatively small, Continental market to expand its trade. Explicitly, African countries should not wait until the CFTA is running up to speed to strategically enhance trade-related South-South Cooperation as the analysis demonstrates that it could clearly offer evident opportunities to support Africa’s structural transformation agenda

Les industries lithiques de la grotte Comarque

National audienc

Variance analysis for model updating with a finite element based subspace fitting approach

International audienceRecently, a subspace fitting approach has been proposed for vibration-based finite element model updating. The approach makes use of subspace-based system identification, where the extended observability matrix is estimated from vibration measurements. Finite element model updating is performed by correlating the model-based observability matrix with the estimated one, by using a single set of experimental data. Hence, the updated finite element model only reflects this single test case. However, estimates from vibration measurements are inherently exposed to uncertainty due to unknown excitation, measurement noise and finite data length. In this paper, a covariance estimation procedure for the updated model parameters is proposed, which propagates the data-related covariance to the updated model parameters by considering a first-order sensitivity analysis. In particular, this propagation is performed through each iteration step of the updating minimization problem, by taking into account the covariance between the updated parameters and the data-related quantities. Simulated vibration signals are used to demonstrate the accuracy and practicability of the derived expressions. Furthermore, an application is shown on experimental data of a beam

The last Lateglacial and Early Holocene societies in France (abridged version)

Since the middle of the 1980s, a lot of research has focused on the end of the Upper Palaeolithic in France. This article presents an overview of these thirty years of research, organized around four main geographic units which structure our knowledge of these societies. However, this overview aims to bring to light the main dynamics driving the composition of the technical, economic, symbolic and probably socio-cultural systems in France as a whole. Between the end of the Magdalenian and the first stages of the Mesolithic, the history of the hunter-gatherers on this territory underwent three major changes. The rhythms of these changes are still unclear and understanding the forces driving these changes is still difficult, although scenarios based on the very unstable climatic and environmental context are often advanced. This Lateglacial is no longer merely considered to be the antechamber of the Mesolithic –an “EpiPalaeolithic”, as it was called– studied in particular to contextualize the emergence of complex societies, wrongly solely attributed to the Neolithic. These last Pleistocene periods, with their abundant cultural changes and complex evolutionary techno-complexes and traditions, comprise their own research issues and constitute a subject in their own right.Depuis le milieu des années 1980, une importante dynamique de recherche bénéficie aux derniers temps du Paléolithique supérieur en France. Cet article propose un bilan de cette trentaine d’années de recherche. Bien qu’organisée autour des quatre grandes unités géographiques, chacune structurante dans la connaissance de ces sociétés, cette synthèse vise à mettre en lumière, à l’échelle de la France, les grandes dynamiques de recomposition des systèmes techniques, économiques, symboliques et probablement socioculturels. Entre la fin du Magdalénien et les premiers temps du Mésolithique, l’histoire des chasseurs-collecteurs évoluant sur ce territoire connaît en effet trois grandes inflexions dont les rythmes restent flous. La compréhension des moteurs à l’origine de ces basculements demeure très délicate, même si plusieurs scénarios mobilisant le contexte climatique et environnemental, très instable de cette période, sont régulièrement avancés. Quoi qu’il en soit, ce Tardiglaciaire ne constitue plus aujourd’hui l’antichambre du Mésolithique – un « Épipaléolithique » disait-on – surtout étudié pour contextualiser l’avènement des sociétés complexes, attribuées à tort au seul Néolithique. Ces derniers temps du Pléistocène, du fait de nombreuses transformations culturelles des techno-complexes et traditions aux schémas évolutifs complexes, sont en réalité particulièrement riches en problématiques de recherches propres

Les dernières sociétés du Tardiglaciaire et des tout débuts de l’Holocène en France : bilan d’une trentaine d’années de recherche

International audienceSince the middle of the 1980s, a lot of research has focused on the end of the Upper Palaeolithic in France. This article presents an overview of these thirty years of research, organized around four main geographic units which structure our knowledge of these societies. However, this overview aims to bring to light the main dynamics driving the composition of the technical, economic, symbolic and probably socio-cultural systems in France as a whole. Between the end of the Magdalenian and the first stages of the Mesolithic, the history of the hunter-gatherers on this territory underwent three major changes. The rhythms of these changes are still unclear and understanding the forces driving these changes is still difficult, although scenarios based on the very unstable climatic and environmental context are often advanced. This Lateglacial is no longer merely considered to be the antechamber of the Mesolithic –an “EpiPalaeolithic”, as it was called– studied in particular to contextualize the emergence of complex societies, wrongly solely attributed to the Neolithic. These last Pleistocene periods, with their abundant cultural changes and complex evolutionary techno-complexes and traditions, comprise their own research issues and constitute a subject in their own right.Depuis le milieu des années 1980, une importante dynamique de recherche bénéficie aux derniers temps du Paléolithique supérieur en France. Cet article propose un bilan de cette trentaine d’années de recherche. Bien qu’organisée autour des quatre grandes unités géographiques, chacune structurante dans la connaissance de ces sociétés, cette synthèse vise à mettre en lumière, à l’échelle de la France, les grandes dynamiques de recomposition des systèmes techniques, économiques, symboliques et probablement socioculturels. Entre la fin du Magdalénien et les premiers temps du Mésolithique, l’histoire des chasseurs-collecteurs évoluant sur ce territoire connaît en effet trois grandes inflexions dont les rythmes restent flous. La compréhension des moteurs à l’origine de ces basculements demeure très délicate, même si plusieurs scénarios mobilisant le contexte climatique et environnemental, très instable de cette période, sont régulièrement avancés. Quoi qu’il en soit, ce Tardiglaciaire ne constitue plus aujourd’hui l’antichambre du Mésolithique – un « Épipaléolithique » disait-on – surtout étudié pour contextualiser l’avènement des sociétés complexes, attribuées à tort au seul Néolithique. Ces derniers temps du Pléistocène, du fait de nombreuses transformations culturelles des techno-complexes et traditions aux schémas évolutifs complexes, sont en réalité particulièrement riches en problématiques de recherches propres