283 research outputs found
Couplage non-intrusif: réanalyse locale et calcul haute performance
Le couplage non-intrusif permet de prendre en compte efficacement des modifications locales (non-linĂ©aritĂ©s, conditions limites, gĂ©omĂ©trie) dans un modĂšle initial linĂ©aire prĂ©-existant sans que ce dernier ne soit affectĂ©. Ce concept est Ă©tendu au cas des non-linĂ©aritĂ©s apparaissant de maniĂšre gĂ©nĂ©ralisĂ©e Ă lâĂ©chelle globale. Dans ce cas un ensemble de patchs recouvre lâintĂ©gralitĂ© du domaine, et le couplage peut ĂȘtre assimilĂ© Ă une mĂ©thode de dĂ©composition de domaine non-linĂ©aire sâappuyant sur un logiciel industriel sĂ©quentiel
Local enrichment of NURBS patches using a non-intrusive coupling strategy: Geometric details, local refinement, inclusion, fracture
International audienceIn this work, we apply a non-intrusive global/local coupling strategy for the modelling of local phenomena in a NURBS patch. The idea is to consider the NURBS patch to be enriched as the global model. This results in a simple, flexible strategy: first, the global NURBS patch remains unchanged, which completely eliminates the need for costly re-parametrization procedures (even if the local domain is expected to evolve); then, easy merging of a linear NURBS code with any other existing robust codes suitable for the modelling of complex local behaviour is possible. The price to pay is the number of iterations of the non-intrusive solver but we show that this can be strongly reduced by means of acceleration techniques. The main development for NURBS is to be able to handle non-conforming geometries. Only slight changes in the implementation process, including the setting up of suitable quadrature rules for the evaluation of the interface reaction forces, are made in response to this issue. A range of numerical examples in two-dimensional linear elasticity are given to demonstrate the performance of the proposed methodology and its significant potential to treat any case of local enrichment in a NURBS patch simply
Microfabrication directe de liens sacrificiels au sein de fibres polymériques par manipulation d'une instabilité fluidique
RĂSUMĂ
Une instabilitĂ© fluidique est mise Ă contribution dâun procĂ©dĂ© de microfabrication modifiĂ© afin de permettre la production de fibres directement structurĂ©es de liens sacrificiels durant la dĂ©position, amĂ©liorant ainsi leurs propriĂ©tĂ©s mĂ©caniques. En effet, lorsquâun filament visqueux tombe sur une plateforme, les forces de compression axiales induisent un flambement poussant le filament Ă boucler sur lui-mĂȘme. Lorsque lâon donne Ă la plateforme de dĂ©position un mouvement de translation, lâĂ©coulement du filament adopte diffĂ©rents patrons rĂ©sultant en une dĂ©position pĂ©riodique et bouclante sur elle-mĂȘme. Le procĂ©dĂ© est adaptĂ© Ă un fluide polymĂ©rique de telle sorte que le filament visqueux durcisse. Les fibres ainsi obtenues possĂšdent des liens solides au noeud de chaque boucle, formĂ©s lors de la solidification. Lorsque les fibres sont soumises Ă des forces de traction, les noeuds brisent en premier, jouant le rĂŽle de liens sacrificiels, tandis que les longueurs contenues dans les boucles se dĂ©plient, jouant le rĂŽle de longueurs cachĂ©es. Les mĂ©canismes de liens sacrificiels et longueur cachĂ©e sont connus pour amĂ©liorer la tĂ©nacitĂ© de plusieurs matĂ©riaux naturels. Le but final du projet est dâimplĂ©menter un procĂ©dĂ© fournissant aux fibres une structure amĂ©liorant leur tĂ©nacitĂ© dĂšs leur production.
En plus de la crĂ©ation de nombreuses microfibres, cette maitrise a donnĂ© lieu Ă la participation Ă une confĂ©rence (IMECE MontrĂ©al 2014), Ă un article de confĂ©rence et Ă un article format lettre (soumis Ă Nature Materials), prĂ©sentĂ© dans le ce mĂ©moire. La soumission a Ă©tĂ© accompagnĂ©e dâune vidĂ©o de prĂ©sentation de lâarticle. Les contributions ont aussi Ă©tĂ© une vidĂ©o dĂ©crivant le procĂ©dĂ© de fabrication et remportant la seconde place au concours vidĂ©o « Gallery of Mechanics » de la confĂ©rence NewMech 2013, ainsi quâune photographie dĂ©montrant la prĂ©cision microscopique du procĂ©dĂ©, remportant le concours GĂ©nie en image, Polytechnique 2014, visible en annexe. Lâarticle soumis Ă Nature Materials est prĂ©sentĂ© Ă la suite dâune revue de littĂ©rature dĂ©taillĂ©e et de la mĂ©thodologie. Lâarticle de confĂ©rence ainsi que la video candidate au concours NewMech sont prĂ©sentĂ©s en Annexe.----------ABSTRACT
A fluidic instability is involved in a microfabrication process to allow the direct manufacture of sacrificial bonds into polymeric fibers. As soon as a fluid falls onto a solid platform, it coils onto itself as a result of axial compressive forces and forms a pile of loops. If the solid platform is now translated at a given speed, the pattern of the deposition is affected, resulting in the creation of squiggly fibers with periodic patterns. As the extruded solution is polymeric, it dries and the filament becomes a removable fiber. During solidification, solid bonds are formed at the node of each loop. If the fiber is loaded in tension, bonds have to break first, playing the role of sacrificial bonds, and the loops are extended, playing the role of hidden length. Such mechanisms have been shown to enhance toughness of many natural materials. The purpose of this study is thus to produce fibers directly structured with mechanical toughing mechanisms.
The presented master led to the participation to a conference (IMECE MontrĂ©al 2014) and its corresponding technical paper, the redaction of a letter format submited to Extreme Mechanics, as well as a winner photography of the âGĂ©nie en imageâ contest organized by Ăcole Polytechnique de MontrĂ©al and a second place at the competition âGallery of Mechanicsâ organized at the conference NewMech2013. Papers and the photography are presented in this thesis, following a review of the literature and a description of the used methodology
Non-Intrusive model coupling: A flexible way to handle local geometric and mechanical details in FEA
Computer Aided Engineering (CAE) often involves structural mechanics analysis (most of the time using the finite element method). When dealing with nonlinear complex models on large 3D structures, the computational cost becomes prohibitive. In this paper, we present the recent developments linked to an innovative computing method: non-intrusive coupling. Such a method allows to efficiently taking into account local modifications on an initial existing model in a non-intrusive way: the previously computed analysis is left unchanged. Large scale linear models can thus be easily computed, then localised nonlinear complex models can be used to pinpoint the analysis where required on the structure. After a presentation of the scientific context and a description of non-intrusive coupling methods, we will present its application to crack growth simulation and parallel structure analysis
Local/global non-intrusive parallel coupling for large scale mechanical analysis
The permanent increase in available computing resources can achieve more and more ambitious numerical simulations (most of the time using the finite element method). When dealing with non-linear complex models on large 3D structures, the computational cost becomes prohibitive. In this paper, we present the recent developments linked to an innovative computing method: non-intrusive coupling. Such a method allows to efficiently take into account local modifiations on an initial existing model in a non-intrusive way: the previously computed analysis is left unchanged. Large scale linear models can thus be easily computed, then localised non-linear complex models can be used to pinpoint the analysis where required on the structure. After a presentation of the scientific context and a description of non-intrusive coupling methods, we will present its application to crack growth simulation and parallel structure analysis
3D digital image correlation applied to birdstrike tests
The development of new bird strike shielding materials for commercial aircrafts requires test campaigns. During these tests, measurement of the high speed deformation is needed to characterize and compare the mechanical response of the shielding samples and to correlate numerical simulations with experiments. In this work, 3D digital image correlation method is used with high speed (HSP) cameras to compute the displacement and strain fields on a large area (approximately 400mm wide) of the back side of impacted samples. Compromise on spatial resolution, frame rate of HSP camera and measurement error is discussed
Validation and Modeling of Aeronautical Composite Structures Subjected to Combined Loadings: the VERTEX Project. Part 1: Experimental Setup, FE-DIC Instrumentation and Procedures
The development and certification of aeronautical composite structures is still largely based on the pyramid of tests. This approach is extremely costly in terms of number of tests and design loops. Moreover, this is made up of uniaxial tests whereas the real structures are mostly subjected to combined forces. The aim of the collaborative research program "VERTEX" is to make progress towards Predictive Virtual Testing and to significantly reduce the development costs of aeronautical and space programs. In this first part, the specific methodology for multiaxial tests of aeronautical structures is presented. The concept of technical specimen and their size are justified. Then, the development of a specific test device is presented. Compression / traction, shear, internal pressure and any combination are possible. Since structural tests were complex to be instrumented, a specific method of field measurement was developed. It is based on multi-camera instrumentation and an original approach named Finite Element Stereo Digital Image Correlation (FE-SDIC). A mechanical regularization with the use of Finite Element (FE) of the optical field measurements allows to calculate the translation or rotation displacement field. Thus this measured field is used for boundary conditions of the VERTEX tests. The experimental procedure, the measurement methodologies and the calculation / test dialogue are validated on isotropic metal plates in this paper
Validation and modeling of aeronautical composite structures subjected to combined loadings: The VERTEX project. Part 2: Load envelopes for the assessment of panels with large notches
One of the important issues in the certification of composite aeronautical structures is large notches. In this paper, tests are carried out on technological specimens and under tensile, shear stresses and combined loadings using the VERTEX means presented in the first part of this publication. Strong interactions between postbuckling and propagation of cuts were observed. The FE-SDIC methodology developed specifically allows a first dialog between calculation / testing. The Discrete Ply Modeling method is able to compute the onset of failure of such complex tests. New tests responses called "envelop" are proposed and realized by following a load path that allows to validate the behavior of the notched structure for certification purposes. This methodology should eventually lead to a new vision of the tests pyramid by "Predictive Virtual Testing"
Non-intrusive Coupling: Recent Advances and Scalable Nonlinear Domain Decomposition
This paper provides a detailed review of the global/local non-intrusive coupling algorithm. Such method allows to alter a global ïŹnite element model, without actually modifying its corresponding numerical operator. We
also look into improvements of the initial algorithm (Quasi-
Newton and dynamic relaxation), and provide comparisons
based on several relevant test cases. Innovative examples
and advanced applications of the non-intrusive coupling
algorithm are provided, granting a handy framework for
both researchers and engineers willing to make use of such
process. Finally, a novel nonlinear domain decomposition
method is derived from the global/local non-intrusive cou-
pling strategy, without the need to use a parallel code or software. Such method being intended to large scale analysis, we show its scalability. Jointly, an efïŹcient high level Message Passing Interface coupling framework is also proposed, granting an universal and ïŹexible way for easy software coupling. A sample code is also given
Residual error based adaptive mesh refinement with the non-intrusive patch algorithm
This paper deals with the introduction of mesh refinement techniques within the non-intrusive patch process. For this, an ad hoc residual based explicit error estimator is built, which is adapted to a multi-scale solution, associated with those non-intrusive mesh refinement technique. Moreover, to reduce the global cost of the process, one introduces an estimate of the convergence error of the non-intrusive algorithm, which allows to reduce the number of iterations. This method is discussed and illustrated in various numerical examples
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