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Computing a flow within a congested solid medium is still nowadays an important scientific problematics in multiple research fields, such as nuclear engineering. Indeed, methods classically used in Fluid-Structure Interaction (FSI), which rely on an explicit representation of all interfaces, would in such a case result in cumbersome computations. Thus, in order to bypass on the one hand the numerous interfaces with the solid medium microstructure, and on the other hand the smallest spatial scales contained within the flow, more mesoscopic approaches have been proposed in literature. A porous medium modeling [1] has for instance been developed to study the interaction between an incompressible viscous turbulent flow and nuclear fuel assemblies, in the framework of a seismic loading on a Pressurized Water Reactor (PWR). The current PhD thesis aims at extending such a modeling to account for the propagation of compressible pressure waves within the flow and solid medium. Such a phenomenon can result from a sudden depressurization of a PWR primary loop. In literature, the interaction between such a pressure wave and the solid medium is based on a simplified representation of the latter, through for instance an acoustic impedance [2]. The aim is thus to develop a multiscale and homogenized modeling for a compressible flow within a congested solid medium, able on the one hand to take into account (without any interface meshing) the structure geometry, and on the other hand, to reconstruct, from the homogenized fluid, the force applied to the underlying microstructure. This new modeling shall also bypass the classical limitations encountered in homogenization and multiscale methods literature (micromechanics and RVE, asymptotic homogenization, spatial filtering, Variational Multi-Scale method, Multi-Resolution Analysis…), such as : scale separation assumption, periodicity, boundary conditions, linearity assumption, closure modeling between resolved and unresolved scales...To this end, in the spirit of [3], Continuous Wavelet Transform (CWT) is applied directly on the Partial Differential Equations (PDEs) governing the compressible flow. Such a process allows to derive spatially filtered PDEs governing an equivalent homogenized flow. Furthermore, this use of CWT allows to properly take into account the real fluid boundary conditions, and to connect microscopic (real fields) and mesoscopic (homogenized) variables with an analytical closure expression (i.e. no closure modeling). Thus, the computation of the homogenized pressure field opens the way to the reconstruction of the microscopic pressure field and the force applied by the fluid to the solid medium microstructure. This is a first major step in the design of a homogenized solver for Fluid-Structure Interaction (FSI). First results of this ongoing work have been published in [4]. [1] Ricciardi, G. Fluid-structure interaction modelling of a PWR fuel assembly subjected to axial flow. J. Fluids Struct., (2016), 62 :15–171 [2] Faucher, V. ; Crouzet, F. ; Debaud, F. Mechanical consequences of LOCA in PWR : Full scale coupled 1D/3D simulations with fluid-structure interaction. Nucl. Eng. Des., (2014), 270 :359–378. [3] Rouby, C. ; Rémond, D. ; Argoul, P. Orthogonal polynomials or wavelet analysis for mechanical system direct identification. Ann. Solid Struct. Mech., (2009), 1 :41–58. [4] Mokhtari, S. ; Ricciardi, G. ; Faucher, V. ; Argoul, P. ; Adélaide, L. Multiscale Filtering of Compressible Wave Propagation in Complex Geometry through a Wavelet-Based Approach in the Framework of Pressurized Water Reactors Depressurization Transient Analysis. Fluids, (2020), 5 :64, La simulation de l’écoulement d’un fluide au sein d’un milieu solide très congestionné constitue encore aujourd'hui une problématique scientifique importante dans certains domaines de recherche, notamment l’ingénierie nucléaire. En effet, les méthodes classiques d’interaction fluide-structure, reposant sur une prise en compte explicite de l’ensemble des interfaces fluide-solide, induiraient dans un tel cas un coût de calcul prohibitif. Ainsi, afin de s’affranchir d’une part des nombreuses interfaces avec la micro-structure, et d’autre part des plus petites échelles contenues dans l’écoulement, des approches plus mésoscopiques ont été développées dans la littérature. Une modélisation milieu poreux [1] a notamment été proposée pour simuler l’interaction entre un écoulement incompressible, visqueux, et turbulent, et les assemblages combustibles d’un réacteur nucléaire à eau pressurisée, dans le cas d’un transitoire lent de type séisme. Cette thèse a vocation à étendre ces travaux à la propagation d’une onde de pression (i.e. écoulement compressible supposé non visqueux) au travers des assemblages combustibles, phénomène résultant d'un transitoire rapide de dépressurisation du circuit primaire d'un réacteur (accident de référence). Actuellement, l’impact du milieu solide sur l’onde de pression repose sur une modélisation simplifiée de la structure, via notamment une impédance acoustique [2]. L’objectif est donc de développer une modélisation homogénéisée et multi-échelles d’un écoulement compressible au sein d’un milieu solide congestionné, capable d’une part de prendre en compte (sans maillage des interfaces) la géométrie réelle de la structure, et d’autre part, de reconstruire, à partir du fluide homogénéisé, l’effort appliqué sur la structure sous-jacente. Cette modélisation doit également s’affranchir des limitations classiquement rencontrées dans la vaste littérature de l’homogénéisation ou des méthodes multi-échelles (micromécanique et VER, homogénéisation asymptotique, filtrage spatial, méthode variationnelle multi-échelles, analyse multi-résolution. . .), telles que : l’hypothèse de séparation d’échelles, la périodicité de la micro-structure, le traitement des conditions aux limites, l’hypothèse de linéarité, la nécessité d’un modèle de fermeture micro-macro. . .Dans cette perspective, nous proposons, dans l’esprit des travaux [3], d’appliquer la transformée en ondelettes continue (TOC) directement sur les équations aux dérivées partielles gouvernant l’écoulement. Ce processus analytique aboutit en effet à l’obtention d’équations filtrées décrivant un fluide homogénéisé. Cette utilisation de la TOC nous permet par ailleurs de prendre en compte les conditions aux limites du fluide réel, mais également de relier les grandeurs micros (réelles) et macros (homogénéisées) avec une expression analytique. Dès lors, il est possible, à partir de la résolution du champ de pression homogénéisé, de reconstruire un champ de pression micro et ainsi l’effort appliqué sur la micro-structure, ouvrant dès lors la voie à un solveur homogénéisé de l’interaction fluide-structure. Les premiers résultats de ces travaux sont disponibles dans [4]. [1] Ricciardi, G. Fluid-structure interaction modelling of a PWR fuel assembly subjected to axial flow. J. Fluids Struct., (2016), 62 :15–171 [2] Faucher, V. ; Crouzet, F. ; Debaud, F. Mechanical consequences of LOCA in PWR : Full scale coupled 1D/3D simulations with fluid-structure interaction. Nucl. Eng. Des., (2014), 270 :359–378. [3] Rouby, C. ; Rémond, D. ; Argoul, P. Orthogonal polynomials or wavelet analysis for mechanical system direct identification. Ann. Solid Struct. Mech., (2009), 1 :41–58. [4] Mokhtari, S. ; Ricciardi, G. ; Faucher, V. ; Argoul, P. ; Adélaide, L. Multiscale Filtering of Compressible Wave Propagation in Complex Geometry through a Wavelet-Based Approach in the Framework of Pressurized Water Reactors Depressurization Transient Analysis. Fluids, (2020), 5 :64

This PhD thesis takes place in the Fond Unique Interministériel (FUI) HydroSafeTire project, dedicated to the study of the hydroplaning phenomenon. During a previous PhD thesis regarding this topic in the lab., the hydroplaning phenomenon has been investigated via a fluid/structure SPH/FE coupling, using the FE solver Abaqus developed by Simulia. Physical effects such as the water height, the velocity of the vehicle and the tire wear have been studied, showing that the tendencies experimentally observed were retrieved in the simulations. Therefore, it has been decided to use the FE structure solver specifically developed by Michelin for their tire applications, in order to take benefits of this solver for the specific hydroplaning problem. Then, in the present PhD thesis, the first step is the validation of the SPH/FE coupling, using this FE code, on academic test cases. The compromise between the accuracy of the results and the restitution time of the simulations is of paramount importance, particularly in an industrial context. Thus, three main topics are investigated in this work. Firstly, the consistency of SPH schemes using a Particle Shifting Technique (PST) is studied, in addition to a work on the PST itself. Then, a model of flow separation is proposed, compatible with suction effects. Finally, different coupling schemes SPH/FE using differed time-steps are studied, with an hydroplaning application.; Cette thèse s’inscrit dans le projet Fond Unique Interministériel (FUI) HydroSafeTire, dédié à l’étude du phénomène de l’hydroplanage. Au cours d’une précédente thèse sur le sujet au sein du laboratoire, l’étude de ce phénomène a été réalisée via un couplage fluide/structure SPH/FE en utilisant le solveur FE Abaqus développé par Simulia. Des effets tels que la hauteur d’eau, la vitesse du véhicule ou encore l’usure du pneumatique ont ainsi été investigués, montrant que les tendances observées durant les expérimentations étaient retrouvées numériquement. A l’issue de ces travaux, il a donc été décidé d’utiliser le solveur structure FE développé spécifiquement par Michelin (en collaboration avec le GIREF) pour ses applications, afin de tirer profit des avantages de ce solveur pour le problème spécifique de l’hydroplanage. Ainsi dans cette thèse, la première étape est la validation du couplage SPH/FE avec ce code structure sur des cas tests académiques. L’obtention d’un bon compromis précision des résultats / temps de restitution des simulations constitue un enjeu majeur, en particulier dans un contexte industriel. Ainsi, cette thèse s’articule autour de trois axes. Premièrement, un travail sur la consistance des schémas SPH utilisant une méthode de désorganisation particulaire est effectué, en parallèle d’un travail sur la méthode de désorganisation en elle même. Ensuite, un modèle de décollement de jets de surface libre est proposé, compatible avec la prise en compte des effets de succion. Enfin, différents schémas de couplage SPH/FE à pas de temps différés sont étudiés, avec une application à l’hydroplanage.

An efficient method to capture an arbitrary number of fluid/structure interfaces in a level-set framework is built, following ideas introduced for contour capturing in image analysis. Using only three label maps and two distance functions we succeed in locating and evolving the bodies independently in the whole domain and get the distance between the closest bodies in order to apply a collision force whatever the number of cells is. The method is applied to rigid solid bodies in order to compare to the results available in the literature. In that case, a global penalization model uses the label maps to follow the solid bodies all together without a separate computation of each body velocity. Numerical simulations are performed in two- and three- dimensions. An application to immersed vesicles is also proposed and shows the capability and efficiency of the method to handle numerical contacts between elastic bodies at low resolution. Two-dimensional simulations of vesicles under various flow conditions are presented.

In nuclear industry, simulating accidental transient sequences at full reactor scale is becoming an increasingly important feature of the safety demonstration towards national agencies. It thus allows limiting the number of complex and costly experiments, while simplifying and accelerating the evaluation of mitigation strategies. However, the implemented numerical models are inevitably heavy to build and maintain, with a global modelling scale making it difficult to account for local geometric details yet able to significantly influence the physical solution. To provide an answer to these problems, this PhD work is dedicated to multi-model approaches designed to integrate such details into bigger models with no modification at the global level (techniques often designated as numerical zoom techniques). Some methods are proposed for both structures and fluids, with special care given to the accuracy and stability of the coupled multi-scale solution compared to a single-scale reference solution. This work handles two very specific topics, namely its compatibility with numerical features imposed by fast transient dynamics with explicit time integration, and the general objective of simultaneously dealing with superimposed models and fluid-structure interaction., Dans l’industrie nucléaire, la simulation de transitoires accidentels à l’échelle d’un réacteur devient une composante d’importance croissante de la démonstration de sûreté à destination des agences de surveillance nationales. Elle permet ainsi de limiter le recours à des expériences complexes et coûteuses tout en facilitant l’évaluation des stratégies de mitigation. Cependant, les modèles mis en jeu sont inévitablement volumineux et construits avec une finesse de modélisation rendant difficile la prise en compte de détails géométriques locaux pourtant susceptibles d’influencer significativement la solution globale. Dans ce travail de thèse, on propose ainsi des approches multi-modèles pour l’intégration de tels détails dans un modèle global sans modification du maillage initial (on parle aussi de zoom numérique). Des techniques sont proposées aussi bien pour les structures que pour les fluides, avec un souci de démontrer la précision et la stabilité de la solution multi-modèles couplée comparée à une solution de référence à une seule échelle. Ce travail intègre deux spécificités propres, à savoir son adéquation avec les contraintes de la dynamique rapide avec intégration temporelle explicite et l’objectif de traiter simultanément la superposition de modèles et l’interaction fluide-structure.

In this work, we propose a method to efficiently capture an arbitrary number of fluid/solid or fluid/fluid interfaces, in a level-set framework. This technique, borrowed from image analysis, is introduced in the context of the interaction of several bodies immersed in a fluid. A configuration of the bodies in the fluid/structure domain is described by three label maps providing the first and second neighbours, and their associated distance functions. Only one level set function captures the union of all interfaces and is transported with the fluid velocity or with a global velocity field which takes into account the velocity of each structure. A multi-label fast marching method is then performed in a narrow-band around the interfaces allowing to update the label and distance functions. Within this framework, the numerical treatment of contacts between the structures is achieved by a short-range repulsive force depending on the distance between the closest bodies.The method is validated through the simulation of a dense suspension of rigid bodies immersed in an incompressible fluid. A global penalization model uses the label maps to follow the solid bodies altogether without a separate computation of each body velocity. Consequently, the method shows its efficiency when dealing with a large number of rigid bodies. We also investigate the numerical simulation of vesicle suspensions for which a computation of elastic and bending forces on membranes is required. In the present model, only one elastic and bending force is computed for the whole set of membranes according to the level set function and the label maps., Dans ce travail, nous nous sommes intéressés à la simulation numérique de suspensions denses d'objets immergés dans un fluide. En s'inspirant d'une méthode de segmentation d'image, nous avons développé une méthode efficace de capture d'interface permettant d'une part de localiser les structures immergées et d'autre part de gérer les contacts numériques entre les structures.Le domaine fluide/structure est représenté à l'aide de trois fonctions labels et deux fonctions distances qui permettent de localiser chaque structure et son plus proche voisin.Les interfaces sont capturées par une seule fonction level set, celle-ci est ensuite transportée par la vitesse du fluide ou par la vitesse de chaque structure. Un algorithme de multi-label fast marching permet de réinitialiser à chaque pas de temps les fonctions labels et distances dans un périmètre proche des interfaces.La gestion des contacts numériques est effectuée grâce à une force répulsive à courte portée prenant en compte l'interaction entre les objets les plus proches.Dans un premier temps, la méthode est appliquée à l'évolution de solides rigides immergés.Un modèle de pénalisation global couplé aux fonctions labels permet de calculer en une seule fois l'ensemble des vitesses des structures rigides. Les résultats obtenus montrent l'efficacité de la méthode à gérer un grand nombre de solides.Nous avons ensuite appliqué la méthode des suspensions de vésicules immergées. Ce type de simulation requiert le calcul des forces élastiques et de courbures exercées sur les membranes. Grâce au modèle proposé, seulement une force élastique et une force de courbure sont calculées pour l'ensemble des membranes à l'aide de la fonction level set et des fonctions labels.

International audience; Characterizing the path of a hydraulic fracture in a heterogeneous/jointed medium is one of the challenges of current research on hydraulic fracturing. We present here a 2D lattice hydro-mechanical model for this purpose. Natural joints are represented by introducing elements with a new plastic-damage behaviour. The action of the fluid pressure on the skeleton is represented by using Biot’s theory. The interactions of cracks on the fluid flow are represented by considering a Poisueille’s flow between two parallel plates. Numerical coupling is achieved with a staggered coupling scheme.

The aim of this work is to characterize the influence of two kinds of obstacles, sills and macro-roughnesses, on the flow inside a vertical slot fishway (VSF) and the behavior of several species of fish. Another objective is to study a technical solution to allow the passage of small fish species, which take the form of flexible cylinders placed in the jet at the entrance of each pool of the VSF. A hydraulic characterization is made by experimental measurements of the water level in each pool with acoustic sensors and by measurements of three-dimensional velocity components with an acoustic Doppler velocimeter (ADV). The data acquired by these measurements are then used to define a predictive law that takes into account the presence of sills or macro-roughnesses, to help the design of devices that are as efficient as possible. Unsteady RANS and LES three-dimensional numerical simulations of the flow allow performing a careful volume analysis of the turbulence characteristics inside the pools when obstacles are presents in the flow. By obstructing a part of the slot, sills enhance the three-dimensionality of the flow while macro-roughnesses generate a low velocity layer and shelters for benthic species. Flexible elements produce a better dissipation of the energy of the jet and reduce the turbulent kinetic energy in a part of the volume of the pools. The effect of the modification of the flow kinematic properties, by the presence of obstacles, on the behavior of various fish species is evaluated. It provides important insights on how to adapt the flow in existing fishways to fish species with low swimming capacity.; L'objectif de cette thèse est de caractériser l'influence de la présence d'obstacles dans les passes à poissons à fentes verticales. Deux types d'éléments sont couramment insérés, à l'heure actuelle, dans les passes : les seuils et les macro-rugosités. Dans un premier temps, l'effet de ces deux dispositifs à la fois sur l'écoulement et sur le comportement des poissons est étudié. Dans le but de favoriser le passage des petites espèces à travers le dispositif de franchissement, une solution technique est ensuite proposée, sous la forme de plusieurs rangées de cylindres flexibles placées en sortie de fente. La caractérisation du comportement hydraulique d'une passe à poissons équipée de ces obstacles est effectuée par des mesures expérimentales de niveau d'eau à l'aide de sondes acoustiques et des mesures de vitesses tridimensionnelles avec un vélocimètre acoustique à effet Doppler (ADV). La base de données générée par ces mesures est ensuite utilisée pour définir une loi de dimensionnement, qui prend en compte les paramètres influençant le fonctionnement hydraulique de l'ouvrage en vue d'améliorer sa conception. Les simulations numériques 3D instationnaires URANS et LES de l'écoulement permettent une analyse volumique fine des grandeurs caractéristiques de la turbulence qui règne dans les bassins en fonction du type d'obstacle inséré. En obstruant une partie de la fente, la présence d'un seuil accentue la tridimensionnalité de l'écoulement tandis que les macro-rugosités créent une zone de plus faible vitesses et des abris utilisables par les espèces de fonds. L'insertion des structures souples permet une meilleure dissipation de l'énergie du jet et réduit l'énergie cinétique turbulente dans une partie du volume des bassins. Les manipulations réalisées avec différentes espèces de poissons, permettent de mieux comprendre l'effet de la modification des grandeurs cinématiques de l'écoulement, par l'insertion d'obstacles, sur le comportement des poissons pour pouvoir adapter les passes à poissons existantes aux espèces dotées de faibles capacités de nage.

This work presents experimental studies on fluid/structure interaction in supersonic flows, performed in the test sections TMK and L3K of the German Aerospace Center in Cologne. The generic model for the investigation of the mechanical aspect is an elastic panel clamped at two sides and hit by an oblique shock wave. The flow field is surveyed with schlieren photography, pressure probes and oil-film technique. Displacement sensors and strain gauges measure the panel deflection. The shock wave/boundary layer interaction and the vibration characteristics of the structure are also analysed separately. The thermal aspect is studied with flat and curved panels of fibre-reinforced ceramics in high enthalpy flows. Configurations with and without back plane insulation were tested at two angles of attack. The panel heating is documented with the help of infrared thermography, pyrometers and thermocouples. The analysis includes heat transfer via radiation and catalysis on the surface. The interpretation of the experimental data is supported by simulations conducted with the numerical flow solver TAU and the finite element solver ANSYS® as well as coupled simulations.

We study experimentally a fluid/structure interaction between an elastic fiber and a dense granular medium near the jamming transition. In our horizontal setup, a bidimensionnal and dense random packing is interacting with a clamped elastic fiber. The clamped end of the fiber is in translation relative to the the grains while the free end faces initially the grain flux in a penetration geometry before being deflected by grain/fiber interactions. The control parameters of our system are the packing fraction of the medium, the length and the rigidity of the fiber. Our setup allows us to measure the deflected shape of the fiber, the forces exerted by the grains on the fiber (including the drag force) and to follow the reorganizations of the granular medium. Under some experimental conditions, we observed that this system exhibits several regimes of evolution. For low and large fiber deflections, the system evolves stochastically as a consequence of the random nature of the granular medium : respectively small fluctuations of the fiber around its equilibrium position and sudden events of unlozding of the fiber in flexion associated to granular avalanches. The transition between those two regimes is associated with a symmetry breaking that affects the granular medium as well as the fiber. In a first part, we study how the fiber deflection is influenced by the control parameters, particularly by the distance to jamming. In a second part, we show that a packing fraction asymmetry appears in the granular medium when the fiber is deflected enough. In a third part, we try to understand the evolution of the measured forces using numerical simulations of the Elastica on a constrained beam. Finally, we propose a model of compaction of the grains by the fiber that is in a good aggreement with the experimental evolution of the system. An application of this thesis is the understanding of the mechanisms involved in the penetration of a root or a beam in a granular soil., Nous étudions de manière expérimentale un cas d’interaction fluide/structure entre une fibre élastique et un milieu granulaire dense proche du jamming. Dans notre dispositif expérimental horinzontal, un milieu granulaire bidimensionnel, aléatoire et dense est en interaction avec une fibre élastique encastrée. L'extrémité encastrée de cette fibre est en translation par rapport aux grains tandis que son extrémité libre fait initialement face au flux de grains dans une géométrie de pénétration, avant de se défléchir par interaction avec les grains. Les paramètres de contrôle de notre système sont la compacité du milieu granulaire, la longueur et la rigidité de la fibre. Notre dispositif nous permet de mesurer la déformée de la fibre, les efforts que les grains exercent sur la fibre, notamment la force de traînée et de suivre les réorganisation du milieu granulaire. Sous certaines conditions expérimentales, nous avons observé que ce système présente plusieurs régimes d'évolution. A faible et à forte déflexions de la fibre, le système connaît une évolution stochastique, liée à la nature aléatoire du milieu granulaire : respectivement de petites fluctuations de la fibre autour de sa position d'équilibre et des événements brusques de balayage de la fibre en flexion associés à des avalanches granulaires. La transition entre ces deux régimes est associée à une brisure de symétrie qui affecte tant la fibre que le milieu granulaire. Dans une première partie, nous étudions comment la déflexion de la fibre est influencée par les paramètres de contrôle, en particulier par l'écart au jamming. Dans une seconde partie, nous montrons qu'une asymétrie de densité se développe dans le milieu granulaire lorsque la fibre est suffisamment défléchie. Dans une troisième partie, nous tentons de comprendre l'évolution des forces mesurées à l'aide de simulations numériques de l'Elastica sur une poutre sous chargement. Enfin, nous proposons un modèle de compaction des grains par la fibre qui est en bon accord avec l'évolution expérimentale du système. Une application de cette thèse est la compréhension des mécanismes de pénétration d'une racine ou d'une tige dans un sol granulaire.

International audience; Immersed granular flows a re p resent w idely i n d ifferent d omains u nder d ifferent f orms (at various s cales) s uch a s i n nature (rivers, muds, atmosphere, blood...), and in many industrial applications (detergents, cosmetics, etc...). Studying such flows properly requires one to represent well the physics behind their dynamics: the fluid/solid interactions (FSI), the solid/solid interactions (SSI) and the coupling mechanisms at various scales. In this work, a new coupling framework to simulate immersed granular flows has been developed. The FSI has been modeled using a direct-forcing immersed boundary method (DF-IBM) and implemented in the parallelized " PELICANS " C++ library. In this DF-IBM, all the mathematical equations, including the direct-forcing term, are discretized, both in space and time, and solved iteratively via a finite-volume a nd p rojection methods o n E ulerian G rids. A sharp-edge i nterface, that c an b e s moothed, i s used to represent the fluid/solid transition. The modeling of the multiple SSI at the grain's scale is based on the Non-Smooth Contact Dynamics (NSCD) approach developed in the " LMGC90 " open-source library. The coupling of the two softwares " PELICANS " and " LMGC90 " , called Xper, provides an efficient framework to simulate and study dense immersed granular flows by taking into account, both advanced contact laws between grains, and hydrodynamic interactions. We address in this paper the effects of imposing a fluid-ring numerically (or fluid-mesh-cells) around two settling solid disks on modifying their dynamics. The DF-IBM approach implemented in Xper is validated, on a 2D flow over a stationary rigid cylinder benchmark, and on the settling of a rigid buoyant sphere in an incompressible laminar fluid at different Reynolds numbers. The numerical results are in good agreement with experimental and numerical data from the literature.

International audience; We propose a numerical method to capture an arbitrary number of fluid/solid interfaces in a level-set framework, following the ideas introduced for image segmentation. Using only three label maps and two distance functions it is possible to get the distance between the closest cellsand to apply the collision force whatever the number of cells is. Consequently, the method is very efficient when dealing with a large number of cells. Numerical simulations are performed in two- and three-dimensions under gravity force.

The aim of this study is to develop a new numerical cutting model that includes fluid structure interaction and to take into account heat transfer between the water-jet, the workpiece and the chip. This has been achieved using a CEL (Coupled–Eulerian–Lagrangian) technique, an algorithm has been developed to ensure heat exchange between the fluid and the structure. This new model allows decoupling of the mechanical and the thermal effects of the water-jet on chip formation and fragmentation. It has been demonstrated that fragmentation of the chip is ensured by the combination of the thermal and the mechanical effects of the water-jet. Moreover, the tool rake temperature is reduced by more than 400 °C, the tool/chip contact length is also decreased by about 30%.; International audience; The aim of this study is to develop a new numerical cutting model that includes fluid structure interaction and to take into account heat transfer between the water-jet, the workpiece and the chip. This has been achieved using a CEL (Coupled–Eulerian–Lagrangian) technique, an algorithm has been developed to ensure heat exchange between the fluid and the structure. This new model allows decoupling of the mechanical and the thermal effects of the water-jet on chip formation and fragmentation. It has been demonstrated that fragmentation of the chip is ensured by the combination of the thermal and the mechanical effects of the water-jet. Moreover, the tool rake temperature is reduced by more than 400 °C, the tool/chip contact length is also decreased by about 30%.

Birds and aquatic animals exploit the surrounding fluid to propel themselves in air or water. In inertial regimes, the mechanisms of propulsion are based on momentum transfer; by flapping wings or fins, animals accelerate fluid in their wake, creating a jet that propels them forward. The structures used to move can be flexible, and are thus likely to experiment large bending. Literature showed that those passive deformations can improve propulsive performance, when exploited in a constructive way. The mechanisms at play however remain poorly understood. In the present thesis, we aim at studying how a flapping elastic structure generates thrust, using two experimental biomimetic models. The first setup is a simplified mechanical insect with flexible wings, and the second one is a swimmer whose elastic body mimics the undulating motion of an eel. We show that propulsive performance is significantly influenced by the way the systems passively bend, and that their elastic response can be described by simplified theoretical models of forced oscillators. Those models also bring forward the crucial role of the quadratic fluid damping that resists the flapping motion. This result introduces the counter-intuitive idea that it is sometimes desirable to dissipate part of the energy in the fluid, in order to improve performance.; Les oiseaux et poissons se déplacent dans leur environnement fluide en interagissant avec l'air/eau qui les entoure. Pour des régimes inertiels, les mécanismes de propulsion se basent sur un transfert de quantité de mouvement au fluide; les battements d'ailes ou de nageoires générant un jet dans le sillage de l'animal qui le propulse vers l'avant. Pour les oiseaux comme pour les poissons, les structures utilisées possèdent une certaine flexibilité, et sont donc susceptibles de plier de façon importante. La littérature montre que ces déformations passives peuvent améliorer les performances de propulsion lorsqu'elles sont exploitées de façon constructive. Le détail des mécanismes en jeu reste cependant mal compris. L'objectif de cette thèse est d'étudier, à travers deux modèles biomimétiques, la façon dont une structure battante déformable génère des forces de propulsion. Le premier modèle est une version mécanique simplifiée d'insecte dotée d'ailes flexibles, tandis que le deuxième est un nageur dont le corps élastique reproduit le mouvement d'ondulation d'une anguille. Nous montrons que la façon dont ces systèmes se déforment passivement est déterminante pour leurs performances, et que leur réponse élastique peut être décrite par des modèles théoriques simplifiés d'oscillateurs forcés. Ces modélisations mettent par ailleurs en avant le rôle crucial joué par le frottement fluide quadratique qui s'oppose aux mouvements de battements de la structure. Ce résultat introduit l'idée, un peu contre-intuitive, qu'il peut s'avérer avantageux de dissiper une part de son énergie dans le fluide pour améliorer ses performances.

Birds and aquatic animals exploit the surrounding fluid to propel themselves in air or water. In inertial regimes, the mechanisms of propulsion are based on momentum transfer; by flapping wings or fins, animals accelerate fluid in their wake, creating a jet that propels them forward. The structures used to move can be flexible, and are thus likely to experiment large bending. Literature showed that those passive deformations can improve propulsive performance, when exploited in a constructive way. The mechanisms at play however remain poorly understood. In the present thesis, we aim at studying how a flapping elastic structure generates thrust, using two experimental biomimetic models. The first setup is a simplified mechanical insect with flexible wings, and the second one is a swimmer whose elastic body mimics the undulating motion of an eel. We show that propulsive performance is significantly influenced by the way the systems passively bend, and that their elastic response can be described by simplified theoretical models of forced oscillators. Those models also bring forward the crucial role of the quadratic fluid damping that resists the flapping motion. This result introduces the counter-intuitive idea that it is sometimes desirable to dissipate part of the energy in the fluid, in order to improve performance.; Les oiseaux et poissons se déplacent dans leur environnement fluide en interagissant avec l'air/eau qui les entoure. Pour des régimes inertiels, les mécanismes de propulsion se basent sur un transfert de quantité de mouvement au fluide; les battements d'ailes ou de nageoires générant un jet dans le sillage de l'animal qui le propulse vers l'avant. Pour les oiseaux comme pour les poissons, les structures utilisées possèdent une certaine flexibilité, et sont donc susceptibles de plier de façon importante. La littérature montre que ces déformations passives peuvent améliorer les performances de propulsion lorsqu'elles sont exploitées de façon constructive. Le détail des mécanismes en jeu reste cependant mal compris. L'objectif de cette thèse est d'étudier, à travers deux modèles biomimétiques, la façon dont une structure battante déformable génère des forces de propulsion. Le premier modèle est une version mécanique simplifiée d'insecte dotée d'ailes flexibles, tandis que le deuxième est un nageur dont le corps élastique reproduit le mouvement d'ondulation d'une anguille. Nous montrons que la façon dont ces systèmes se déforment passivement est déterminante pour leurs performances, et que leur réponse élastique peut être décrite par des modèles théoriques simplifiés d'oscillateurs forcés. Ces modélisations mettent par ailleurs en avant le rôle crucial joué par le frottement fluide quadratique qui s'oppose aux mouvements de battements de la structure. Ce résultat introduit l'idée, un peu contre-intuitive, qu'il peut s'avérer avantageux de dissiper une part de son énergie dans le fluide pour améliorer ses performances.

We study the deformation and transport of an elastic filament in a viscous cellular flow. We used a simple experimental model system consisting of a one centimeter long elastic filament with controlled geometry and elasticity and a viscous flow formed by a lattice of stagnation points.First, we characterized the buckling instability of the filament approaching a stagnation point. We have shown that this instability is controlled by the elasto-viscous number Sp which compares the relative intensity of the viscous forces deforming the filament and the elastic forces resisting the deformation.Then, we showed that the parameters related to the dynamics of the fiber transported are crucial in the prediction of the buckling probability. In parallel to the experimental analysis, numerical simulations were performed in collaboration with Michael Shelley. The characterization of the dynamical parameters and their influence on the buckling instability allows the prediction of a buckling event as a function of the elasto-viscous number Sp and the dynamical parameters linked to the transport of filament accros the lattice.Finally, we investigated how the deformation and the size of the filament affect its transport properties.; Ce travail porte sur l’étude de la déformation et le transport d’un filament élastique dans un écoulement cellulaire visqueux. Pour cette étude nous avons utilisé un système expérimental modèle simple constitué d’un filament élastique centimétrique de géométrie et d’élasticité contrôlées et d’un écoulement constitué d’un réseau de points de stagnation.Dans un premier temps, nous avons caractérisé l’instabilité de flambage du filament à l’approche d’un point de stagnation. Nous avons ainsi montré que cette instabilité est contrôlée par le nombre élasto-visqueux Sp qui compare l’intensité relative des forces visqueuses qui tendent à déformer le filament et des forces élastiques qui cherchent à le maintenir droit.Nous avons ensuite mis en évidence que les paramètres liés à la dynamique de la fibre évoluant librement à la surface de l’écoulement sont des paramètres cruciaux déterminant si le filament flambe ou pas à l’approche d’un point de stagnation. Cette analyse s’est aussi appuyée sur des simulations numériques modélisant le même système en collaboration avec Michael Shelley. La caractérisation de ces différents paramètres et de leur influence sur l’instabilité de flambage permet ainsi la prédiction de l’existence ou non d’un évènement de flambage à partir du nombre élasto-visqueux Sp et des paramètres dynamiques du filament.Enfin nous nous sommes intéressés à la manière dont la déformation du filament et sa taille influent sur ses propriétés de transport.

Hydroelasticity is a phenomenon occurring during the interaction between water and a deformable structure. Structural deformations can modify the fluid motion, introducing difficulties in the calculation of the impact-induced stresses. Predicting the structural deformations and stresses during the water entry of flexible structures is a major challenge and suitable computer-aided design tools are currently being developed and validated. This work investigates the water impact of deformable wedges. Experimental and numerical results on the parameters affecting hydroelasticity are evaluated for flexible plates with different boundary conditions. The occurrence of hydroelastic effects is shown to depend on the ratio between the natural frequency of the structure and the characteristic wetting time. The influence of the fluid–structure interactions is investigated by numerical simulations. The conditions for which fluid–structure interactions are significant and must be accounted for in the analysis are identified, while outside this range the structure can be modeled as a rigid body. Pressure at the fluid–structure interface is found not to be influenced by the structural deformation, unless fluid detaches from the structure due to cavitation or ventilation.

International audience; The hydrodynamic ram phenomenon generally referred to as HRAM, constitutes an important threat to modern aircraft, especially lightweight aircraft such as UAV that cannot be armoured due to the weight penalty. The aim of the present feasibility study is to determine whether an ALE solver using bi-material fluid permits a qualitative simulation of all the phases of the HRAM event, in particular the oscillations (growth and collapse) of the cavity created during the impact of a non-trivial geometry high speed projectile on a water filled tank. The present study examines the closure of the wake cavity, its shape and the deceleration of the projectile.

When a vessel sails in rough seas, its forefoot can rise above the water surface. As the vessel re-enters the water, impulsive pressures are imparted to the hull structure due to the relative motion of the sea and ship. In these cases the hull literally slams into the water surface. The duration of the slamming event is in the order of milliseconds. The hull slamming problem is of particular interest for shipbuilding industries due to the high impact load that is generated during the water entry. These loads might damage the entire ship or, because of their short duration, excite dynamic response of the local structure of the hull and cause the structure to vibrate. The aim of this work is to investigate the interaction between the fluid and the structure in case of a deformable wedge entering the water. In this case, the pressure at the fluid/structure interface and the fluid motion are influenced by the structural deformation; this phenomenon is known as hydroelasticity. Hydroelastic effects introduce diffculties in the calculation of the structural stresses. Being able of correctly predicting the structural deformations and stresses during the slamming phenomena is a major challenge, and suitable computer-aided design tools still have to be found. Experimental and numerical results on the parameter affecting hydroelasticity are evaluated for deformable wedges with different boundary conditions, showing a dependency of the hydroelasticity from the ratio between the structural natural frequency and the characteristic wetting time.

Hydroelasticity is a phenomenon occurring during the interaction between water and a deformable structure. Structural deformations can modify the fluid motion, introducing difficulties in the calculation of the impact-induced stresses. Predicting the structural deformations and stresses during the water entry of flexible structures is a major challenge and suitable computer-aided design tools are currently being developed and validated. This work investigates the water impact of deformable wedges. Experimental and numerical results on the parameters affecting hydroelasticity are evaluated for flexible plates with different boundary conditions. The occurrence of hydroelastic effects is shown to depend on the ratio between the natural frequency of the structure and the characteristic wetting time. The influence of the fluid-structure interactions is investigated by numerical simulations. The conditions for which fluid-structure interactions are significant and must be accounted for in the analysis are identified, while outside this range the structure can be modeled as a rigid body. Pressure at the fluid-structure interface is found not to be influenced by the structural deformation, unless fluid is detaching due to cavitation of ventilation.

The objective of this work is to understand the failure mechanism and evaluate the maximum hydroelastic loads during the slamming phenomena of a Wakeboard with the water surface, in order to provide an engineering basis for the design process. Wakeboards are built as a sandwich structure, with polyurethane foam and E-Glass fiber/Epoxy reinforcements. Several specimens were extracted from real boards and tested in three point bending to investigate the structural properties and the major failure mechanisms. These data are later used in a parametric full-scale numerical model investigation of the water-entry event. The numerical simulations consist in coupled Smoothed Particle Hydrodynamic (SPH) for the fluid domain and FEM model for the boards’ structure. The obtained results are of the major interest for the design considerations.

The aim of this paper is to analyze the aeroelastic processes developed during the starting phase of a rocket engine via a coupling fluid/structure code. This analysis gives a better understanding of the behavior of the structure as the shock waves propagate inside the engine nozzle. The gasdynamics Euler equations are solved for the fluid and constitutive linear elastic solid assuming large displacements and rotations with no material damping is adopted for the structure. The coupling of each subproblem is carried out with a Gauß-Seidel algorithm over the fluid andstructure states. For the fluid problem an ALE (Arbitrary Lagrangian-Eulerian) formulation is used. It allows us to define a reference system following the moving boundaries while the structure is deformed. The code is validated with a study of the flutter phenomena that may occur when a supersonic compressible fluid flows over a flat solid plate. Regarding the rocket engine ignition problem, a modal analysis of the structure is performed in order to analyze the eigenfrequency shifts when considering the coupling with the fluid flow. Fil: Garelli, Luciano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química (i); Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico. Centro de Investigación de Métodos Computacionales; Argentina. Universidad Nacional del Litoral; Argentina Fil: Paz, Rodrigo Rafael. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química (i); Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico. Centro de Investigación de Métodos Computacionales; Argentina. Universidad Nacional del Litoral; Argentina Fil: Storti, Mario Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico. Centro de Investigación de Métodos Computacionales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química (i); Argentina. Universidad Nacional del Litoral; Argentina

We model the interaction of one-dimensional moving structures with a surrounding three-dimensional fluid, physically close to a Newtonian liquid. The interaction is the adherence of the fluid to the immersed structures, which drag it while moving as rigid bodies. To get solutions of the dynamical problem, we need a model of viscous fluid slightly more general than the Newtonian one, in which the Cauchy stress tensor depends upon higher-order derivatives of the velocity field. Assuming reasonable hypotheses on the motion of the one-dimensional rigid bodies, existence and uniqueness of the solution for the dynamical problem can be proved. © 2010 Elsevier Ltd. All rights reserved.

International audience; This paper describes the usefulness of Lagrangian and arbitrary Lagrangian/Eulerian (ALE) methods in simulating the gun launch dynamics of a generic artillery component subjected to launch simulation in an air gun test. Lagrangian and ALE methods are used to simulate the impact mitigation environment in which the kinetic energy of a projectile is absorbed by the crushing of aluminum honeycomb mitigator. In order to solve the problem due to high impact penetration, a new fluid structure coupling algorithm is developed and implemented in LS-DYNA, a three dimensional FEM code. The fluid structure coupling algorithm used in this paper combined with ALE formulation for the aluminum honeycomb mitigator allows to solve problems for which the contact algorithm in the Lagrangian calculation fails due to high mesh distortion. The numerical method used for the fluid and fluid structure coupling is discussed. A new coupling method is used in order to prevent mesh distortion. Issues related to the effectiveness of these methods in simulating a high degree of distortion of Aluminum honeycomb mitigator with the commonly used material models (metallic honeycomb and crushable foam) are discussed. Both computational methods lead to the same prediction for the deceleration of the test projectile and are able to simulate the behavior of the projectile. Good agreement between the test results and the predicted projectile response is achieved via the presented models and the methods employed.