ERRORS IN QUANTITIES OF INTEREST IN THE LAMINATED PLATE BENDING PROBLEM USING HIERARCHIC SETS OF BASIS FUNCTIONS IN GFEM

A formulation for error estimation is developed for the bending problem of composite laminated plates based on the Mindlin-Reissner kinematic model discritized by the Generalized Finite Element Method (GFEM). The error estimation process starts with an upper bound in energy norm, which is obtained following the basic CRE (Constitutive Relation Error) framework of the Ladev`eze formulation, that is, the estimate is obtained from a statically admissible stress field computed at element level in a Neumann problem where the element boundary forces are equilibrated. The authors have previously shown that an accurate description of the in plane stresses in a laminate is essential to obtain an accurate approximation to the transverse shear stresses at the layers interfaces. Since important failure modes in laminated composite plates, like the delamination, are linked to the transverse stresses, it is essential to develop both, accurate post-processing procedures to compute improved transverse stresses, and also estimate techniques for the discretization errors. The first condition is adequately satisfied by GFEM. Therefore, the aim of the present work is to extend the general CRE technology to develop formulations to estimation of errors in Quantity of Interest (QI) identified preferably with the stress field in the laminated plate problem. One of the steps necessary in the CRE procedure is the computation of and admissible stress field in each element, in a Neumann problem where the boundary forces have been previously equilibrated. For a GFEM basis with high order enrichment, adequate procedures have to be sought. Here we use one single higher order finite element, based on displacement FEM, to obtain an approximation to the equilibrated field. The formulation is implemented for arbitrary degree of the basis, which allows an arbitrarily close approximation to the equilibrium condition. The sharpness of the QI’s error bounds is increased with the accuracy of the primal and dual global energy norm of errors. In the present work we investigate the effectiveness of a local GFEM p-enrichment as a tool to improve the approximability of the model in capturing the local gradients which characterizes response of the dual loading. The GFEM p-enrichment is implemented in a simple and straightforward way, as opposed to some other possible forms of enrichment, e.g. local h-refinement or a sub-domain approach. Numerical tests are performed to asses the effect of the different parameters in the modeling over the errors in the quantities of interest

Biodiversity post-2020: Closing the gap between global targets and national-level implementation

National and local governments need to step up efforts to effectively implement the post-2020 global biodiversity framework of the Convention on Biological Diversity to halt and reverse worsening biodiversity trends. Drawing on recent advances in interdisciplinary biodiversity science, we propose a framework for improved implementation by national and subnational governments. First, the identification of actions and the promotion of ownership across stakeholders need to recognize the multiple values of biodiversity and account for remote responsibility. Second, cross-sectorial implementation and mainstreaming should adopt scalable and multifunctional ecosystem restoration approaches and target positive futures for nature and people. Third, assessment of progress and adaptive management can be informed by novel biodiversity monitoring and modeling approaches handling the multidimensionality of biodiversity change

Damage tracking using distributed optic fiber sensors in structures

International audienceEarly detection of damage and monitoring helps improving the safety and durability of structures. The ability to model and simulate this phenomenon, along with measurements, facilitates system control.Various sensor types have been used in the context of structural health monitoring. Among them, Distributed Optic Fiber Sensors grant certain benefits which make them a convenient option for real-time monitoring of structures. This work comprises of using distributed strain sensors, based on Rayleigh backscattering and OFDR technology, in samples that bear loading up to their failure point. The collected data are then post-processed in the framework of modified constitutive relation error (mCRE) to perform damage model updating and estimate the material condition. Several damage models are presented and compared, and the most suitable model is also selected using mCRE.La détection précoce de l’endommagement et le suivi de sa progression contribuent à améliorer la sécurité et la durabilité des structures. La capacité à modéliser et simuler ce phénomène, en complément de mesures, facilite le contrôle du système. Différents types de capteurs ont été utilisés dans le cadre de la surveillance de l’état des structures. Parmi eux, les capteurs à fibre optique distribués offrent divers avantages qui en font une option pratique pour la surveillance en temps réel des structures. Ce travail consiste à utiliser des capteurs distribués de déformation, basés sur la rétrodiffusion de Rayleigh et la technologie OFDR, dans des échantillons qui supportent une charge jusqu’à leur point de rupture. Les données recueillies sont ensuite post-traitées dans le cadre de l’erreur en relation de comportement modifiée (mCRE) pour effectuer la mise à jour du modèle d’endommagement et estimer l’état du matériau.Plusieurs modèles d’endommagement sont présentés et comparés, et le modèle le plus adapté est aussi sélectionné au moyen de la mCRE

An educational review on distributed optic fiber sensing based on Rayleigh backscattering for damage tracking and structural health monitoring

International audienceThis paper is a review on distributed optic fiber sensing for structural health monitoring applications, with a focus on technologies relying on the Rayleigh backscattering phenomenon. It addresses the basic physical principles which are involved, the implementation and instrumentation of the measurement techniques, as well as recent practical applications, current performance, and remaining challenges. Being written at an elementary level and integrating relevant theoretical and technical details, we hope the document can be useful for researchers and engineers looking for an up-to-date overview on a field which currently undergoes significant development and increasing attractiveness, in particular for damage tracking in complex mechanical structures

Réduction du pouvoir absorbant de chènevottes par traitement imperméabilisant

Le béton de chanvre est utilisé comme matériau de remplissage non porteur associé à une ossature bois. C’est un matériau composite obtenu en mélangeant un liant minéral à base de chaux, du chanvre (chènevottes) et de l’eau. Afin de garantir une bonne mise en œuvre, le béton de chanvre a, en général, un besoin en eau de gâchage nettement supérieur à celui d’un mélange classique granulat/liant. Cette quantité d’eau est de plus liée au process de fabrication. Cette étude vise à montrer l’influence de la chènevotte sur le dosage en eau et à évaluer les effets d’un traitement visant à réduire la capacité d’absorption de la chènevotte tout en préservant au maximum les propriétés qui font du béton de chanvre un bon matériau isolant et perméable. Un banc expérimental est conçu pour réaliser les essais de mouillage. Différents protocoles de traitements par immersion avec un hydrofuge sont testés

Analysis of a subdomain-based error estimator for finite element approximations of elliptic problems

In this article we analyze a subdomain residual error estimator for finite element approximations of elliptic problems. It is obtained by solving local problems on patches of elements in weighted spaces and provides an upper bound on the energy norm of the error when the local problems are solved in sufficiently enriched discrete spaces. A guaranteed lower bound on the error is also derived by a simple postprocess of the solutions to the local problems. Numerical tests show very good effectivity indices for both the upper and lower bounds and a strong reliability of this estimator even for coarse meshes. © 2003 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 20: 165–192, 200

Influence de la formulation et du procédé de mise en oeuvre sur les propriétés thermique, mécanique et hydrique du béton de chanvre

Colloque Matériaux - Génie civil et habitat du futur, Nantes, Octobre 2010, communication oral