Publications

2019

• Comparison of pseudo-static and modal spectral seismic analyses of motor-driven pump units: is 1.5 security coefficient of pseudo-static method relevant?
  
  • Audebert Sylvie
  • Rousseu Damien
  , 2019. In the framework of the seismic verification of plant equipments, the determination of the seismic loads applied to motor-driven pump anchorages is optimised. A rough justification is usually first performed using the 1 degree-of-freedom pseudo-static analysis, including a 1.5 multi-mode factor. The question is asked about the opportunity to decrease the multi-mode factor value, by comparison to response spectrum analysis, here considered as the reference method. Comparative seismic analyses are performed on more and more complex dynamical systems and excitations; seismic responses of a thin square plate, motor, pump, motor-driven pump unit, connected or not to suction and delivery pipes, are thus successively determined, under 1D and 3D excitations. Two different motor-driven pump units are studied: flexible with vertical axis and stiff with horizontal axis. The quantities of interest are the shearing and tearing loads, deduced from seismic loads at anchorage points.
• A thin layer approach model based on polynomial expansion for coated bodies in contact
  
  • Tiirats Tauno
  • Chevaugeon Nicolas
  • Moes Nicolas
  • Stolz Claude
  • Marouf Nabil
  , 2019.
• Modélisation multi-échelle du comportement multi-physique des batteries lithium ion : application au gonflement des cellules.
  
  • Masmoudi Moez
  , 2019. La batterie lithium ion est la technologie de stockage d’énergie la plus répandue dans l'industrie automobile. Assurer sa haute efficacité, sa puissance, sa capacité, sa sécurité et son endurance présente un défi pour plusieurs chercheurs et industriels. En effet, une batterie est un système complexe renfermant plusieurs composants et soumis à divers risques de dégradations d’origines chimiques, mécaniques et électriques, se manifestant même dans les conditions normales de fonctionnement. Cependant, la batterie devrait assurer ses fonctions pour un grand nombre de cycles de charge et de décharge et continuer à servir sans que ces dégradations influencent sa performance globale. L’une des dégradations principales et inévitables est son gonflement qui induit une discontinuité électrique et une perte de sa capacité.En effet, le gonflement est un phénomène multi-physique qui fait intervenir l’électrochimie, la mécanique et la thermique. D’une part, une batterie lithium-ion est basée sur l’échange réversible de l’ion lithium entre une électrode positive et une électrode négative. Le processus d’insertion de l’ion dans les particules de l’électrode aboutit à un changement volumique significatif réversible de la batterie pour chaque cycle de charge/décharge. Cette variation de volume mène à la formation de contraintes quand la batterie est maintenue dans un pack rigide empêchant ou limitant sa déformation. D’autre part, la formation d’une couche à l’interface particule-électrolyte (SEI) suite aux réactions parasites se produisant à l’échelle de l’électrode constitue une cause principale d’un gonflement supplémentaire irréversible et de vieillissement de la batterie.Ainsi, le gonflement doit être pris en compte pendant la phase du dimensionnement mécanique de la batterie. Il est donc indispensable d’avoir un outil numérique fiable capable de prédire ce comportement mécanique pendant toutes les phases de fonctionnement de la batterie et de permettre aux concepteurs d’améliorer sa structure.Ce travail rentre dans le cadre d’une collaboration entre l’ENSTA ParisTech et le constructeur automobile Renault suite à un besoin industriel de comprendre et de maîtriser le gonflement des batteries utilisées dans les véhicules électriques et hybrides. Pour répondre à ce besoin, un modèle multi-physique et multi-échelle fondé sur la théorie de la thermodynamique des processus irréversibles, sur l’endommagement et sur la théorie de l’homogénéisation est développé. Il permet de décrire et de prédire la déformation d’une batterie lithium ion pendant son fonctionnement. Le modèle tient compte des phénomènes mécaniques, électrochimiques et thermiques qui se produisent à l’échelle locale des électrodes afin de calculer la déformation mécanique au niveau macroscopique de la batterie. (10.70675/b53f0a28z0ed8z4a22zbd43z04d9203a5854)
  DOI : 10.70675/b53f0a28z0ed8z4a22zbd43z04d9203a5854
• Multiaxial fatigue under complex non-relaxing loads
  
  • Warneboldt I.
  • Szmytka F.
  • Raoult I.
  • Marco Yann
  • Le Saux V.
  • Charrier P.
  • Champy C.
  • Hervouet W.
  , 2019, XI. Automotive anti-vibration parts undergo complex and multi-directional fatigue loadings, which must be considered and finally validated in their design phase. Some parts have to endure Road Load Data (RLD) test-loads (i.e. stochastic signals, representative for the actual service conditions of a part), meanwhile being already pre-charged by a constant load e.g. by the engine mass or by swaging. These conditions might result in positive minimal load values. For natural rubber, it is well known that this leads to material reinforcement which is usually related to strain induced crystallization. The reinforcement effect is well studied and illustrated in the so-called Haigh diagram by various previous studies of uni-axial tension tests Cadwell et al. 1940, Champy et al. 2015). However, to be able to determine a mean-load correction factor for a part or a specimen under complex stochastic loads, the concept of the Haigh diagram must be extended to various complex and multi-axial test conditions. It is crucial for its fundamental understanding to perform a dedicated experimental test campaign on specimens under different complex periodic loading cycles. Such fatigue tests are conducted on hourglass-shaped natural rubber specimens, loaded by coupled and aligned tension and torsion actuators, which permits to induce numerous complex load states. Finite Element Analysis (FEA) is used to determine the respective local mechanical state in the rubber specimens. Different strain, biaxiality ratio and critical plane orientation histories over a loading cycle are achieved in different test series. Finally, the number of cycles to crack-initiation and the final fracture surfaces are carefully analyzed using an optical microscope and a Scanning Electron Microscope (SEM). The results are then compared with the outcomes of non-relaxing fatigue tests in simple tension and torsion with the same specimens. (10.1201/9780429324710-74)
  DOI : 10.1201/9780429324710-74
• Experimental characterisation and numerical modeling of wall)slab junctions in reinforced concrete structures
  
  • Hervé-Secourgeon Estelle
  • Voldoire François
  • Banci Fabien
  • Gatuingt Fabrice
  • Oliver-Leblond Cécile Oliver
  • Guilloux Adrien
  , 2019. The contribution of Reinforced Concrete (RC) wall-slab junctions to both dynamical behaviour and strength of nuclear buildings subjected to seismic loadings is investigated. An experimental program has been defined jointly by EDF and CEA, in order to improve the knowledge of the junctions' behaviour. As it has already been proposed in the literature for beam-column joints, our aim is to define a constitutive model of reinforced concrete wall-slab junctions fit to be integrated in a structural FE plate or shell model of a RC building. The objective is to represent the specific contribution of the junction to stiffness, forces redistribution and strength, under representative in-plane and out-of-plane seismic loading components. The experimental campaign, carried out on a series of 2 times 2 representative RC mockups, includes alternate static loading conditions and increasing seismic loading on Azalée shaking table, at CEA, up to high intensity ground motions. We discriminate the respective contributions of the slabs and the wall on one hand and of the junction on the other hand on the stiffness degradation and the dynamical response. We present the first steps achieved in the definition of the numerical model: kinematics, constitutive relation, by reference to experimental observations.
• Impact of 3D seismic input motion definition from physics-based simulations for soil-structure interaction studies
  
  • Michail Korres
  • Gatti F
  • Alves Fernandes Vinicius
  • Lopez‐caballero Fernando
  • Irmela Zentner
  • Voldoire François
  , 2019.
• A homogenization technique applied to periodic buildings.
  
  • Franco Ariza Graciela Carolina
  • Chesnais Céline
  • Desprez Cedric
  • Semblat Jean François
  • Giry Cédric
  , 2019, pp.1 p.. The homogenization technique consists in describ-ing the global behavior of the structure with an 'equivalent beam' model according to the following process : (i) Static analysis of only a story for the determination of the mechanical properties of the global model, (ii) Dynamic analysis of the equivalent beam, which is a 1D analytical model, (iii) Application of the macroscopic deformation on the model of a story in order to compute the internal forces of the structural elements.
• Impact of the Green function in acoustic analogies for flow noise predictions at low Mach number
  
  • Trafny Nicolas
  • Serre Gilles
  • Cotté Benjamin
  • Mercier Jean-François
  , 2019. It is known that hydrodynamic noise can be a major contribution to the total sound radiated by a ship. It is in part attributed to the interaction between turbulent eddies with appendages and marine propeller blades. Because hydrodynamics is associated with very low Mach numbers, direct noise computation methods are too expensive. Other approaches must be chosen, based on acoustic analogies which consist first in modeling the incompressible turbulent flow and then in computing the noise radiated by this flow. We focus on Lighthill's wave equation, solved using the free space Green function or a tailored Green's function in presence of an arbitrary geometry. Unlike many studies from the literature where the impact of the chosen turbulent model is evaluated over a semi-infinite plate, the objective of this study is to evaluate the impact of the chosen Green function on the predicted broadband flow noise for a fixed semi-empirical turbulence model. The impact of the chosen tailored Green function on the radiated noise spectra and directivity diagrams is evaluated considering various analytical and numerical tailored Green's functions.
• Only thickness is essential in the Thick Level Set approach
  
  • Valoroso Nunziante
  • Stolz Claude
  , 2019. Regularized damage formulations have become increasingly popular in the last decades for dealing with problems in Mechanics suffering from spurious mesh sensitivity induced by strain softening [1]. In short, the idea underlying almost all such models is that of using some extended constitutive equations in which a length scale parameter brings to the macro level information about material microstructure.
• Fluid-structure interaction in two-phase flow using a discrete forcing method
  
  • Laviéville J.
  • Mérigoux N.
  • Benguigui W
  International Journal for Numerical Methods in Fluids, Wiley, 2019. The numerical simulation of interaction between structures and two-phase flows is a major concern for many industrial applications. Using a discrete forcing method (see the work of Benguigui et al) (implemented in a multiphase CFD code based on a two-fluid approach) to track the solid motion in two-phase flow, an iterative fluid-structure coupling is developed to allow free-motion of multiple solids (with any kind of geometry) due to two-phase fluid forces. As the fluid-structure interface is located thanks to a time and space dependent porosity on a cartesian grid, the fluid force computation is accommodated to the interface tracking method. A Newmark algorithm is used to estimate the solid motion. The iterative coupling is addressed in detail going from the algorithm to the determination of its convergence parameter. Three application cases are proposed to validate the method from motion under a single-to a two-phase flow. (10.1002/fld.4753)
  DOI : 10.1002/fld.4753
• A Hybrid High-Order method for finite elastoplastic deformations within a logarithmic strain framework
  
  • Abbas Mickaël
  • Ern Alexandre
  • Pignet Nicolas
  International Journal for Numerical Methods in Engineering, Wiley, 2019. We devise and evaluate numerically a Hybrid High-Order (HHO) method for finite plasticity within a logarithmic strain framework. The HHO method uses as discrete unknowns piecewise polynomials of order k 1 on the mesh skeleton, together with cell-based polynomi-als that can be eliminated locally by static condensation. The HHO method leads to a primal formulation, supports polyhedral meshes with non-matching interfaces, is free of volumetric locking, the integration of the behavior law is performed only at cell-based quadrature nodes, and the tangent matrix in Newton's method is symmetric. Moreover, the principle of virtual work is satisfied locally with equilibrated tractions. Various two-and three-dimensional benchmarks are presented, as well as comparison against known solutions with an industrial software using conforming and mixed finite elements. (10.1002/nme.6137)
  DOI : 10.1002/nme.6137
• Simulation of the failure of quasi-brittle specimen with defects using the TLS damage model: Scale effect analysis
  
  • Zghal Jihed
  • Moes Nicolas
  • Leguillon Dominique
  • Stolz Claude
  , 2019, pp.1-1. Predicting the maximum load that a (quasi-)brittle specimen can sustain is an important scientific and practical issue. A natural approach is to search for a criterion. Strength and toughness criteria are well suited for simple specimen having either no defect or an existing crack. When defects (notches, or cavities, …) are present, the criterion is more complex to set up. Two approaches are considered in this work: the first is the coupled criterion which is introduced by [1]. It could be qualified as semi-analytical since it starts from analytical consideration finalized by (simple) numerical treatment. The second one is pure numerical approach which allow us to perform a full numerical quasi- static analysis of the specimen with an increasing loading. The failure load is defined as the maximum load above which no quasi-static solution may be found (and the specimen goes into dynamics). Since we are discussing quasi-brittle failure, we use a damage model. It is well known that regularization is needed when addressing failure with such a model, otherwise failure may be reached for infinitely small loading. Here we consider the TLS (Thick Level Set) approach of graded damage modeling. A material length scale is introduced explicitly, and the model is closely connected to the cohesive zone model (CZM) [2]. Note that the coupled criterion contains a length scale since it is written in terms of toughness, strength and Young modulus from which a characteristic length may be extracted. In this work, failure load is determined using the two approaches which is then compared to ones obtained experimentally. Then the influence of scale effect is investigated. More precisely, we analyze the role played by length ratio (notch or cavity size over characteristic length) on the predicted failure load.
• A vibro-impact acoustic black hole for passive damping of flexural beam vibrations
  
  • Li Haiqin
  • Touzé Cyril
  • Pelat Adrien
  • Gautier François
  • Kong Xianren
  Journal of Sound and Vibration, Elsevier, 2019, 450, pp.28-46. Nonlinear flexural vibrations of slender beams holding both an Acoustic Black Hole termination and a contact non-linearity are numerically studied. The Acoustic Black Hole (ABH) effect is a passive vibration mitigation technique, which has shown attractive properties above a given cut-on frequency. In this contribution, a vibro-impact acoustic black hole (VI-ABH) is introduced, the contact nonlinearity being used as a mean to transfer energy from low to high frequencies. A numerical model of a VI-ABH is derived from an Euler-Bernoulli beam. The contact law is handled with a penalization approach, the visco-elastic layer with a Ross-Kerwin-Ungard model and the problem is solved with a modal approach combined with an energy-conserving time integration scheme. Numerical results show that the VI-ABH brings about important modifications, and changes the nature of more traditional black holes, by redistributing all the vibrational energy. It can lead to a strong decrease of the resonance magnitude at low frequencies. Under steady state noise excitation, parametric studies are realised in the cases of a single contact, a grid of contacts and bilateral contacts layouts, in order to find some optimal designs. Transient dynamics is also studied through the analysis of displacement signal envelope and energy decay time. All the numerical results constantly show that the combination the ABH effect and an energy transfer provided by contact nonlinearity leads to very attractive mitigation template including low frequencies. (10.1016/j.jsv.2019.03.004)
  DOI : 10.1016/j.jsv.2019.03.004
• Extended equivalent linear model (X-ELM) to assess liquefaction triggering: Application to the City of Urayasu during the 2011 Tohoku earthquake
  
  • Kteich Ziad
  • Labbé Pierre
  • Javelaud Emmanuel
  • Semblat Jean-François
  • Bennabi Abdelkrim
  Soils and Foundations, Japanese Geotechnical Society, 2019, 59 (3), pp.750-763. (10.1016/j.sandf.2019.02.002)
  DOI : 10.1016/j.sandf.2019.02.002
• Reduced-order modeling of the fluidic pinball
  
  • Pastur Luc R
  • Deng Nan
  • Morzyński Marek
  • Noack Bernd R.
  , 2019, pp.205-213. The fluidic pinball is a geometrically simple flow configuration with three rotating cylinders on the vertex of an equilateral triangle. Yet, it remains physically rich enough to host a range of interacting frequencies and to allow testing of control laws within minutes on a laptop. The system has multiple inputs (the three cylinders can independently rotate around their axis) and multiple outputs (downstream velocity sensors). Investigating the natural flow dynamics, we found that the first unsteady transition undergone by the wake flow, when increasing the Reynolds number, is a Hopf bifurcation leading to the usual time-periodic vortex shedding phenomenon, typical of cylinder wake flows, in which the mean flow field preserves axial symmetry. We extract dynamically consistent modes from the flow data in order to built a reduced-order model (ROM) of this flow regime. We show that the main dynamical features of the primary Hopf bifurcation can be described by a non-trivial lowestorder model made of three degrees of freedom. (10.1007/978-3-030-15297-0_19)
  DOI : 10.1007/978-3-030-15297-0_19
• Invariant integrals and asymptotic fields of a planar crack
  
  • Stolz Claude
  , 2019.
• Airfoil Noise Numerical Simulations with Direct Noise Computation and Hybrid Methods Using Inflow Synthetic Turbulence
  
  • Rigall T
  • Cotté B
  • Lafon P.
  , 2019. The interaction of inflow turbulence with an airfoil is significant for low Reynolds number applications, as it generates leading edge noise, but also strongly modifies the airfoil boundary layer properties and thus the produced noise. Inflow turbulence impact still demands to be better understood and is also a numerical challenge. Large Eddy Simulations are here carried out with both incompressible and compressible solvers. The Synthetic Eddy Method and the Random Fourier Modes method, used to generate synthetic turbulence, are studied in this work. In order to eventually perform airfoil simulations, the second method is modified to take into account spanwise periodic boundary conditions, to reduce spurious noise level in compressible simulations. First, properties of the methods are studied with a spatially decaying turbulence academic case. Even if the decay is not well represented, the methods show satisfactory properties in terms of isotropy, homogeneity and one-dimensional spectra. Furthermore, spurious noise levels are reduced thanks to the modified method. Preliminary airfoil simulations are then carried out with inflow turbulence for flow validation in presence of a laminar separation bubble. The drag coefficient is in very good agreement with experimental results. However, there are some discrepancies between simulations and experiments on the lift coefficient, which is extremely sensitive to perturbations. These discrepancies are attributed to a lack of experimental turbulence characteristic information, such as isotropy or integral length scale and to too short simulations at high angles of attack. (10.2514/6.2019-2721)
  DOI : 10.2514/6.2019-2721
• Liaisons convexes et endommagement à variation graduée
  
  • Valoroso Nunziante
  • Stolz Claude
  , 2019. On propose une modélisation de l'endommagement fondée sur l'introduction de liaisons convexes en complément d'une une loi locale. On retrouve ainsi un modèle d'endommagement à variation graduée dont la formulation est proche de celle dite Thick Level Set. Cependant, la modélisation présente s'affranchit complètement des level sets, d'où les performances numériques améliorées pour la simulation de l'initiation, la coalescence et la propagation des défauts dans les matériaux quasi-fragiles.
• Intégrale J et champs asymptotiques le long d'une fissure plane
  
  • Stolz Claude
  • Le Cren Mathieu
  • Martin Alexandre
  , 2019. La méthode G − θ est une méthode de détermination du taux de restitution d'énergie et des facteurs d'intensité de contrainte (FICs) répandue. Dans cette contribution, nous étudions l'influence de la courbure du front de fissure sur la précision de l'évaluation des FICs. Le rôle de la courbure du front de fissure sur la valeur de l'intégrale J de Rice est quantifié. De nouveaux champs de déplacements admissibles, tenant compte de la courbure, sont proposés. Le gain en précision est évalué sur des cas-tests admettant une solution analytique, dans le cas des fissures planes sollicitées en mode I. Mots clés-Mécanique de la rupture, Taux de restitution d'énergie, FICs, Fissures planes à front courbe.
• Dynamique et rayonnement acoustique d'une membrane d'élastomère diélectrique
  
  • Garnell Emil
  • Doaré Olivier
  • Rouby Corinne
  , 2019. Les membranes d’élastomère diélectrique sont des matériaux actifs capables de grandes déformations sous l’action d’une tension électrique. Une telle membrane, préalablement gonflée sur une cavité, peut être utilisée comme haut-parleur. Un modèle non-linéaire en grandes transformations est établi et résolu par éléments finis. La dynamique linéaire forcée autour d’un état d’équilibre est ensuite étudiée. Les fonctions de transfert entre tension électrique, vitesse de la membrane et pression acoustique rayonnée sont calculées. L’étude numérique est validée par une comparaison expérimentale.
• Méthode G−θ en 3D : interpolation des facteurs d'intensité de contraintes.
  
  • Martin Alexandre
  • Le Cren Matthieu
  • Stolz Claude
  , 2019. La méthode G−θ est une méthode de calcul du taux de restitution d’énergie et des facteurs d’intensité de contrainte (FICs) répandue. Dans cette contribution, nous rappelons les fondements de la méthode et discutons sa mise en œuvre dans le cas tridimensionnel. Une analyse de convergence réalisée sur des cas-tests admettant une solution analytique montre que la méthode est précise. Les erreurs issues de choix de mise en œuvre naïfs sont également discutés. L’analyse est restreinte au cas des fissures planes à front droit.
• Modélisation des effets de site multidimensionnels par le calcul haute-performance avec code_aster
  
  • Tardieu Nicolas
  • Alves Fernandes Vinicius
  • Devésa Georges
  , 2019. Les effets de site influencent la propagation des ondes sismiques du substratum rocheux vers la surface, engendrant une modification de l’amplitude et de la durée du signal sismique. Des développements récents sur l’architecture de code_aster permettent de démontrer sa capacité à l’utilisation de la méthode des éléments finis pour l’estimation des effets de site multidimensionnels pour des études industrielles.
• Modélisation des effets des fluides externes et internes sur le comportement dynamique des dirigeables déformables
  
  • Le Mestre Robin
  • Doaré Olivier
  • Schotté J.S.
  , 2019. Pendant le vol d’un dirigeable, le couplage entre les petites déformations de la structure, le fluide interne et le fluide externe en écoulement conduit à des phénomènes de masse, amortissement et raideur ajoutés (pour des nombres de Stokes élevés). On présente ici une méthode de calcul de la masse ajoutée par les fluides internes et externes dont la performance est testée en comparant les résultats numériques obtenus à des formules analytiques présentes dans la littérature. Le domaine de validité du modèle potentiel supposé ici est déterminé expérimentalement sur une maquette de taille réduite en oscillation dans un bassin d’eau.
• Analyse de la méthode G−θ en 3D : cas des fissures planes à front droit
  
  • Martin Alexandre
  • Le Cren Mathieu
  • Stolz Claude
  , 2019. La méthode G−θ est une méthode de calcul du taux de restitution d'énergie et des facteurs d'intensité de contrainte (FICs) répandue. Dans cette contribution, nous rappelons les frontements de la méthode et discutons sa mise en œuvre dans le cas tridimensionnel. Une analyse de convergence réalisée sur des cas-tests admettant une solution analytique montre que la méthode est précise. Les erreurs issues de choix de mise en œuvre naïfs sont également discutés. L'analyse est restreinte au cas des fissures planes à front droit.
• Problème grossier spectral pour une méthode de décomposition de domaine mixte
  
  • Oumaziz Paul
  • Saavedra K
  • Gosselet Pierre
  • Tardieu N
  , 2019. Nous proposons ici une construction spectrale de l'espace grossier d'une méthode de décomposition de domaine mixte non-intrusive. Ceci est l'adaptation naturelle des travaux de N.Spillane [9, 10] sur les méthodes de Schwarz, BDD et FETI. En particulier l'implémentation non-intrusive permet de se rapprocher des approches type Schwarz et définir aisément un problème aux valeurs propres généralisé afin de construire notre espace grossier. Nous montrons ici leur application dans un cadre mixte et non-intrusif. Cette nouvelle robustesse est illustrée sur des cas fortement hétérogènes et élancés. Mots clés-Décomposition de domaine, problème aux valeurs propres généralisé, non intrusif, approche spectrale, méthode mixte