Publications

2018

• Effective boundary condition for the reflection of shear waves at the periodic rough boundary of an elastic body
  
  • Maurel Agnes
  • Marigo Jean-Jacques
  • Pham Kim
  Vietnam Journal of Mechanics, Viện Hàn Lâm Khoa học và Công nghệ Việt Nam, 2018, 40 (4), pp.303-323. (10.15625/0866-7136/13497)
  DOI : 10.15625/0866-7136/13497
• Modélisations stationnaires des voies ferrées : comportement et dégradation du ballast
  
  • Badinier Thibault
  , 2018. Le développement récent du transport ferroviaire a conduit à une forte augmentation du trafic durant la dernière décennie, augmentation qui devrait sepoursuivre dans la décennie à venir avec les futurs développements de ce mode de transport. L'augmentation du trafic se traduit pour l'infrastructure par une augmentation des sollicitations subies par les voies ferrées. La qualité des voies ferrées est garante de la performance du mode de transport ferroviaire,mais également de la sécurité des matériels roulants et des usagers de l'infrastructure. Conserver la qualité du réseau ferré est donc une priorité pour les gestionnaires d'infrastructures ferroviaires. Le ballast ferroviaire a pour rôle de répartir les efforts induits par la circulation des trains et d'assurer la bonne géométrie de l'infrastructure. La surveillance de la dégradation du ballast est donc primordiale pour assurer la qualité del'infrastructure.L'objectif de cette thèse est de proposer un outil numérique permettant d'anticiper la dégradation et le comportement d'une infrastructure ferroviaire sous trafic. Cet outil doit permettre de simuler efficacement lecomportement du ballast ferroviaire sous un grand nombre de cycles de chargements mobiles.Une première partie détaille la composition des infrastructures ferroviaires, précise les rôles du ballast et identifie les grandes lignes de son comportement.Il est fait le choix d'utiliser une méthode de représentation du ballast par élément fini et un modèle de comportement élastoplastique. Le ballast est alors traité comme un géomatériau continu répondant à des lois de comportementélastoplastique.Dans une seconde partie, les bases de la modélisation élastoplastique sont rappelées. Puis, plusieurs modèles de comportement issus de la littérature et comportant des éléments intéressants sont identifiés et étudiés.Dans une troisième partie, un nouveau modèle de comportement frottant compactant est proposé. Il est composé d’un critère nouveau et d'une loi d'écoulement originale. Enfin, le modèle est complété par la prise encompte, de la dégradation du matériau via une diminution de l'angle de frottement interne.Dans une quatrième partie, les méthodes stationnaires sont rappelées. Ces méthodes sont spécifiquement développées pour la modélisation des problèmes incluant des charges en mouvement. Les différents algorithmes sont implémentés àl'aide d'un code de calcul développé dans le logiciel Matlab et à l'aide du logiciel d'éléments finis COMSOL Multiphysics. En particulier, la méthode stationnaire à double échelle de temps, qui est un développement nouveau, permet la modélisation rapide d'un grand nombre de cycles de chargements et la prise en compte des effets d'usure du matériau.Dans une dernière partie, les deux principaux modèles tridimensionnels utilisés sont présentés. Sur un faible nombre de cycles de chargements, divers résultats sont établis selon les différents modèles de comportement utilisé. Sur un très grand nombre de cycles de chargements, les résultats obtenus montrent l'évolution des déformations irréversibles de la structure et de la dégradation du matériau. (10.70675/31426946zce33z4bf7zbef4zc658814e336f)
  DOI : 10.70675/31426946zce33z4bf7zbef4zc658814e336f
• The childhood of turbulent spot in shear flows
  
  • Couliou Marie
  • Monchaux R.
  Physical Review Fluids, American Physical Society, 2018. We numerically investigate the temporal aspects of turbulent spot spreading in a plane Couette flow for transitional Reynolds numbers between 300 and 450. We focus our study on the spreading along the streamwise direction and on the shape of turbulent spots. Studying the topology of turbulent spots and the associated large-scale flows, we suggest a decomposition of the streamwise growth rate. On one hand, the quadrupolar large-scale flow heads for the spot along the streamwise direction and act against the growth. The associated growth rate is negative. On the other hand, we also define a positive growth rate associated to inside large-scale flow which enables the convection of the streaks. The sum of these two growth rates is compared to the spot streamwise growth rate and shows good agreement. The resulting shape of the spot is then discussed. A scenario gathering all these elements provides a better understanding of the growth dynamics and of the shape of a turbulent spot in a plane Couette flow. This scenario should be relevant to other shear flows. (10.1103/PhysRevFluids.3.123901)
  DOI : 10.1103/PhysRevFluids.3.123901
• 3D coupled HM-XFEM modeling with cohesive zone model and applications to non planar hydraulic fracture propagation and multiple hydraulic fractures interference
  
  • Paul Bertrand
  • Faivre Maxime
  • Massin P.
  • Giot Richard
  • Colombo Daniele
  • Golfier F.
  • Martin Alexandre
  Computer Methods in Applied Mechanics and Engineering, Elsevier, 2018, 342, pp.321 - 353. A 3D fully coupled hydromechanical model for the simulation of fluid-driven fracture propagation through poroe-lastic saturated media is presented and compared to several analytical or numerical benchmarks. The hydromechanical coupling in the porous matrix is derived within the framework of the generalized Biot theory and the fluid flow in the fractures satisfies the lubrication equation. The presence and propagation of fluid-driven fractures is handled with the extended finite element method and the propagation of the fluid-driven fractures is governed by a mixed linear cohesive law relying on a stable mortar formalism. A comparison between numerical results and a semi-analytical solution for plane fluid-driven fractures in porous media assess the validity of the proposed model. Then, a procedure for the propagation of fluid-driven fractures on non predefined paths is detailed. In particular, the fracture reorientation angle is computed exclusively from cohesive quantities. Various numerical experiments are performed to study the interferences between neighboring fluid-driven fractures as well as the reorientation of fluid-driven fractures under complex stress conditions. Finally, the model is extended to discontinuity junctions and an application to arrays of vertical fractures initiated from horizontal wells is presented. (10.1016/j.cma.2018.08.009)
  DOI : 10.1016/j.cma.2018.08.009
• Defect nucleation modelling
  
  • Stolz Claude
  Journal of Micromechanics and Molecular Physics, World Scientific Publishing, 2018, 3 (3). The purpose of this article is to compare concepts of defect nucleation based on bifurcation of equilibrium solution and on damage modelling. The nucleation criterion is defined as a bifurcation of the equilibrium solutions of the perfect body and of the imperfect one when the size of the defect vanishes. The defect is considered as a small volume which evolves as a damaged zone. To study the in uence of geometry of the defect on the critical loading governing its initiation, we consider the particular cases of a linear elastic composite sphere and of a linear elastic composite cylinder, for which the equilibrium solutions are known when the radial distribution of elastic bulk modulus is given simultaneously with an uniform shear modulus. The initial defect is a small sphere or a small cylinder respectively, it can be a cavity or a kernel made with an elastic material with lower mechanical properties. (10.1142/S2424913018400106)
  DOI : 10.1142/S2424913018400106
• Numerical simulation of two-phase flow induced vibration
  
  • Benguigui William
  , 2018. In nuclear power plants, steam generator tubes vibrate because of steam/water cross-flows. In order to understant this phenomenon, reduced-scale experiments are performed. Numerical simulations have shown their ability to accurately reproduce the vibration induced by a single phase flow in a tube bundle. The aim of the present work is to do the same with two-phase flow and to characterize the effect of the mixture physical properties on vibration.To do so, a CFD code based on a two-fluid approach is used. A "discrete forcing" method is implemented in order to allow solid body motion in a two-phase flow. The validation is performed with simple and industrial cases using experimental and theoretical results.Using an existing implicit algorithm, a fluid-structure coupling based on the developed interface tracking method is implemented. Validated for single and two-phase flows, it is now possible to have solid motion induced by fluid forces.The different numerical models dedicated to two-phase flows are then evaluated on a freon/freon flow across an inclined tube bundle. The use of a multi-regime model is required. In order to investigate the role of the different physical properties on the vibration, three simple studies are performed.Finally, the industrial application, a freon/water flow across a square pitch tube bundle, is performed. First, it is compared to a steam/water flow in order to characterize the discrepancies when we are using a modeling mixture. Then, the vibration induced by single- and two-phase flows is reproduced by the developed method on feasibility test cases. (10.70675/11534e0dz82dez4280zbcc6z1d0fe7461c97)
  DOI : 10.70675/11534e0dz82dez4280zbcc6z1d0fe7461c97
• Forces fluides stationnaires exercées sur un cylindre déformé en écoulement axial et confiné - application au dimensionnement sismique des assemblages combustibles
  
  • Joly Aurélien
  , 2018. Les phénomènes d’interaction fluide-structure jouent un rôle important dans le calcul de tenue au séisme des assemblages combustibles. Afin de quantifier les marges de dimensionnement, le modèle de forces fluides utilisé doit être validé et affiné. Pour cela, des campagnes d’essais à l’échelle industrielle ont été réalisées en amont de la thèse. L’objectif ici est de contribuer à l’interprétation des essais industriels pour le cas stationnaire, et de valider les méthodes numériques permettant de simuler ce type d’écoulement. La problématique industrielle s'inscrit dans la tradition de l'étude des structures élancées sous écoulement axial. Le modèle de force fluide locale généralement utilisé, que nous appelons modèle de Taylor-Lighthill-Païdoussis (TLP), consiste en stationnaire à combiner un terme de force fluide potentielle, proportionnel à la courbure, et un terme de force fluide visqueuse, proportionnel à la pente. Des versions dynamiques de ce modèle ont été employées avec succès pour prédire le comportement vibratoire de cylindres flexibles en écoulement axial. Néanmoins, la littérature propose très peu de données de validation directe de cette représentation des forces fluides. Afin d’acquérir de telles données, pour le cas particulier d’un cylindre confiné dans un réseau de cylindres, un nouveau banc d’essai a été conçu et mis en place au laboratoire. Il s’agit d’un faisceau de 3x3 cylindres disposé dans une veine de soufflerie. Le cylindre central possède trois degrés de liberté : rotation, translation, flexion. Les efforts fluides résultants sont mesurés à l’aide d’une balance. Un modèle numérique similaire à la maquette est aussi réalisé et donne accès aux forces fluides locales. Les forces globales obtenues numériquement et expérimentalement sont comparables. Les forces locales obtenues dans les simulations numériques s’expliquent bien à l’aide du modèle TLP, en ignorant les effets de bord à l’entrée et à la sortie du faisceau. La transposition au cas industriel, de géométrie plus complexe, est réalisable par recalage des coefficients du modèle. (10.70675/137fff60z25f6z4e05za2bfz6108a91d9fc7)
  DOI : 10.70675/137fff60z25f6z4e05za2bfz6108a91d9fc7
• Coexistence and compatibility of martensite reorientation and phase transformation in high-frequency magnetic-field-induced deformation of Ni-Mn-Ga single crystal
  
  • Zhang Shaobin
  • Chen Xue
  • Moumni Ziad
  • He Y. J.
  International Journal of Plasticity, Elsevier, 2018, 110, pp.110 - 122. (10.1016/j.ijplas.2018.06.010)
  DOI : 10.1016/j.ijplas.2018.06.010
• Effect of strong static magnetic field on the microstructure and transformation temperature of Co–Ni–Al ferromagnetic shape memory alloy
  
  • Bu Fan
  • Xue Xiangyi
  • Wang Jun
  • Kou Hongchao
  • Li Chao
  • Zhang Pingxiang
  • Beaugnon Eric
  • Li Jinshan
  Journal of Materials Science: Materials in Electronics, Springer Verlag, 2018, 29 (22), pp.19491-19498. (10.1007/s10854-018-0079-9)
  DOI : 10.1007/s10854-018-0079-9
• A new approach of graded damage modelling
  
  • Stolz Claude
  Mathematics and Mechanics of Solids, SAGE Publications, 2018. To prevent the problem of spurious localisation in damage mechanics, it is necessary to control the damage gradient amplitude. The body is decomposed in three domains: the undamaged body where (d=0), the transition zone (0+ łdł1) and the totally broken body (d=1). For the thick level set (TLS) model, damage is a function of the signed distance to the surface d=0+. In this article, we propose to control the damage gradient using a convex internal constraint. This point of view produces a new description of graded damage. Analytical solutions on spheres and cylinders under radial loading are given and discussed. For particular internal constraints, the TLS results are recovered. (10.1177/1081286518810068)
  DOI : 10.1177/1081286518810068
• Numerical investigations of water-hammer with column-separation induced by vaporous cavitation using a one-dimensional Finite-Volume approach
  
  • Daude Frédéric
  • Tijsseling A.S.
  • Galon P.
  Journal of Fluids and Structures, Elsevier, 2018, 83, pp.91 - 118. Water-hammer with column-separation induced by cavitation is investigated numerically. The vapor–water flow is modeled using the Homogeneous Equilibrium Model in conjunction with the 1984 NBS/NRC Steam Tables. The discretization is done with the quasi 1-D Finite-Volume approach recently developed by the authors for compressible flows in pipelines. The ability of the present approach to tackle cavitating flows is first assessed. Then, comparisons with experimental results of water-hammer with column-separation demonstrate consistency with the present computations. Based on the obtained numerical results, focus is given to the dynamics of the liquid column-separation and to the associated physics such as cavitation, vapor growth and collapse, generation of the secondary water-hammer peak and the interaction of the primary and secondary pressure waves. The influence of the initial flow velocity before valve closure on the duration and size of the cavity and on the magnitude of the secondary water-hammer is examined. (10.1016/j.jfluidstructs.2018.08.014)
  DOI : 10.1016/j.jfluidstructs.2018.08.014
• Dynamics of the unstable wake modes in automotive aerodynamics : from simplified models to real vehicles
  
  • Bonnavion Guillaume
  , 2018. Since the recent discovery of asymmetric modes in the wake of a simplified vehicle geometry, reminiscent from a bifurcation at low Reynolds numbers, some questions related to the aerodynamic development of ground vehicles such as the influence of lateral wind, pitch and afterbody boat-tail classically used during shape optimization remain unanswered. Our work is devoted to assess those questions experimentally for simplified but also real geometries. The tests are conducted in an industrial wind-tunnel, at the 2/5-scale for the academic body and at the full scale for the minivans. We show that the vehicle's misalignment only modifies the asymmetric mode's orientation without affecting its intensity. We build a model predicting not only this orientation but also the consequences on the cross-flow aerodynamic loading. The contribution of the instability to the lift or side force coefficients is of the order of 0,02 independently of lateral wind or of the vehicle's pitch. Afterbody boat-tails also impact the wake dynamics and its orientation but the instability is never suppressed. These results are retrieved for real vehicles such as minivans, whose wake is then subjected to the same asymmetric mode as well, revealed unambiguously with pitch sensitivity experiments. Our results indicate that, for all considered vehicles, the asymmetric wake mode is systematically present in the driving envelope. The control or the suppression of this mode should offer new optimization's perspectives for blunt based vehicles such as minivans or SUVs. (10.70675/e2a313d8z58aez4eb8z8f23zf0a3ef39f5fd)
  DOI : 10.70675/e2a313d8z58aez4eb8z8f23zf0a3ef39f5fd
• Transition from hypereutectic to hypoeutectic for rapid solidification in an undercooled Co-B alloy
  
  • He Yixuan
  • Li Jinshan
  • Wang Jun
  • Beaugnon Eric
  Journal of Crystal Growth, Elsevier, 2018, 499, pp.98-105. (10.1016/j.jcrysgro.2018.07.032)
  DOI : 10.1016/j.jcrysgro.2018.07.032
• Conversion of Love waves in a forest of trees
  
  • Maurel Agnes
  • Marigo Jean-Jacques
  • Pham Kim
  • Guenneau Sebastien
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2018, 98 (13), pp.134311. We inspect the propagation of shear polarized surface waves akin to Love waves through a forest of trees of the same height atop a guiding layer on a soil substrate. An asymptotic analysis shows that the forest behaves like an infinitely anisotropic wedge with effective boundary conditions. We discover that the foliage of trees brings a radical change in the nature of the dispersion relation of these surface waves, which behave like spoof plasmons in the limit of a vanishing guiding layer, and like Love waves in the limit of trees with a vanishing height. When we consider a forest with trees of increasing or decreasing height, this hybrid “spoof Love wave” is either trapped within the trees or converted into a downward propagating bulk (shear) wave. These mechanisms of wave trapping and wave conversion appear to be robust with respect to perturbations of height or position of trees in the metawedge and with respect to three-dimensional effects such as regarding a potential change of elastic wave polarization. (10.1103/PhysRevB.98.134311)
  DOI : 10.1103/PhysRevB.98.134311
• Characterization of dissipative behaviour of a reinforced concrete mock-up after soft impact tests through wavelet analysis
  
  • Vacca Nicolas
  • Rouzaud Christophe
  • Herve-Secourgeon Guillaume
  • Galan Mathieu
  • Argoul Pierre
  • Rospars Claude
  , 2018, pp.8 p.. The objectives of this communication is to characterize the soft impact response behaviour of a reinforced concrete mock-up (OECD/NEA IRIS Phase 3 mock-up, part of a benchmark), and to evaluate the ability of some mechanical models to represent the energy dissipation during and after the impact. Results from the benchmark show insufficient dissipation in numerical models. Using time-frequency analysis, the dissipative behaviour of the mock-up under impact is evaluated. The stiffness and dissipation associated with the first mode are shown to be amplitude-dependent. This non-linear effect seems to be of a different nature than damage or plastic deformation. A simple rheological model with friction exhibits a similar behaviour.
• Oscillations auto-entretenues et instabilités centrifuges dans un écoulement de cavité ouverte
  
  • Pastur Luc R.
  • Douay Christelle
  • Basley Jérémy
  • Lusseyran François
  , 2018. Dans cette contribution, nous nous intéressons aux structures et instabilités d’écoulements de cavité ouverte expérimentalement observées en régime incompressible
• An empirical study to determine the optimal k in Ek-NNclus method
  
  • Zhang Yiru
  • Bouadi Tassadit
  • Martin Arnaud
  , 2018. Ek-NNclus is a clustering algorithm based on the evidential k-nearest-neighbor rule. It has the advantage that the number of clusters can be detected unlike a c-means for example. However, the parameter k has crucial influence on the clustering results, especially for the number of clusters and clustering quality. Thus, the determination of k is an important issue to optimize the use of the Ek-NNclus algorithm. The authors of Ek-NNclus only give a large interval of k, which is not precise enough for real applications. In traditional clustering algorithms such as c-means and c-medoïd, the determination of c is a real issue and some methods have been proposed in the literature and proved to be efficient. In this paper, we borrow some methods from c determination solutions and propose a k determination strategy based on an empirical study.
• High frequency magnetic field-induced strain of ferromagnetic shape memory alloys
  
  • Zhang Shaobin
  , 2018. Ferromagnetic Shape Memory Alloys (FSMAs) have ability to provide large high-frequency reversible strain via magnetic field-induced martensite reorientation. But, the high-frequency frictional twin boundary motion of the martensite reorientation can induce a rapid accumulation of dissipation heat and cause a significant temperature rise in the material, which poses instability problems about the dynamic performance of FSMA. Particularly, the output strain amplitude would be reduced significantly when the temperature increases to be high enough to trigger the Martensite-Austenite phase transformation. However, such thermal effect on the dynamic responses of FSMA has not yet been investigated in literature where most existing dynamic experiments were performed only for a short-time period (a few seconds) to avoid the temperature variation. In this thesis, multi-scale experimental and theoretical analyses of the long-time performance of FSMA under high-frequency magnetic actuation are performed. Systematic experiments of the long-time magnetic actuation (> 100 seconds) on a Ni-Mn-Ga single crystal bar are conducted at various levels of magnetic field frequency, initial compressive stress and ambient airflow (ambient heat-exchange efficiency) to investigate their influences on the stable state of the high-frequency FSMA-actuator. A one-dimensional heat-transfer model is developed and the new experimental phenomena of the thermal effects are well understood. Based on the experimental results and theoretical analysis, critical conditions to achieve the large and stable output strain amplitude in the high-frequency actuation are derived. Moreover, to understand the heat-exchange dependence of the output nominal-strain from a microscopic view, the local strain distribution/evolution and the associated transformation/reorientation among the different phases/variants during the high-frequency actuation under various heat-exchange efficiencies are demonstrated via the in-situ Digital Image Correlation observations. A novel mechanism is revealed: the temperature-driven phase boundary motion (phase transformation) and the magnetic field-driven twin boundary motion (martensite reorientation) can be activated at the same time under the magneto-thermal-mechanical actuation (i.e., the high-frequency magnetic field, the mechanical spring force and the varying ambient airflow) as the material can self-organize its volume fractions of the different phases/variants to satisfy all the thermo-magneto-mechanical boundary conditions. Further, the self-organized morphology/pattern composed of various variants and phases during cyclic deformation (with the moving habit plane and twin boundaries) can be explained by microstructure compatibility analyses. (10.70675/f682a5f0z9911z4026za5b7zbd4eab5d969a)
  DOI : 10.70675/f682a5f0z9911z4026za5b7zbd4eab5d969a
• A clustering model for uncertain preferences based on belief functions
  
  • Zhang Yiru
  • Bouadi Tassadit
  • Martin Arnaud
  , 2018. Community detection is a popular topic in network science field. In social network analysis, preference is often applied as an attribute for individuals' representation. In some cases, uncertain and imprecise preferences may appear in some cases. Moreover, conflicting preferences can arise from multiple sources. From a model for imperfect preferences we proposed earlier, we study the clustering quality in case of perfect preferences as well as imperfect ones based on weak orders (orders that are complete, reflexive and transitive). The model for uncertain preferences is based on the theory of belief functions with an appropriate dissimilarity measure when performing the clustering steps. To evaluate the quality of clustering results, we used Adjusted Rand Index (ARI) and silhouette score on synthetic data as well as on Sushi preference data set collected from real world. The results show that our model has an equivalent quality with traditional preference representations for certain cases while it has better quality confronting imperfect cases. (10.1007/978-3-319-98539-8_9)
  DOI : 10.1007/978-3-319-98539-8_9
• Thermal effects on high-frequency magnetic-field-induced martensite reorientation in ferromagnetic shape memory alloys: An experimental and theoretical investigation
  
  • Zhang Shaobin
  • Chen Xue
  • Moumni Ziad
  • He Y. J.
  International Journal of Plasticity, Elsevier, 2018, 108, pp.1 - 20. (10.1016/j.ijplas.2018.04.008)
  DOI : 10.1016/j.ijplas.2018.04.008
• Discrete element modelling of concrete structures under hard impact by ogive-nose steel projectiles
  
  • Antoniou Andria
  • Daudeville Laurent
  • Marin Philippe Maurice
  • Omar Ahmad
  • Potapov Serguei
  The European Physical Journal. Special Topics, EDP Sciences / Springer Verlag, 2018, 227 (1-2), pp.143-154. Concrete structures are widely used as shielding barriers to protect sensitive infrastructures. Accidental conditions such as aircraft impacts on nuclear containments lead to a designing demand under extreme loadings. A discrete element method (DEM) model is presented, able to predict damage of concrete structures under severe impacts. The original developments of Cundall and Strack for granular materials were extended in the proposed DEM model for cohesive materials such as concrete by introducing cohesive interactions in addition to contact ones. Spring-like interactions between discrete elements are based on phenomenological models inspired by observations at the macroscopic scale. Constitutive parameters are calibrated thanks to simulations of experiments performed under different states of loading (unconfined quasi-static tests, high confined compression, high strain rates). The DEM approach is validated with the simulation of three hard impact tests where numerical and experimental results are discussed. CEA Gramat performed the experiments on plain concrete targets with a passive confinement given by a steel jacket surrounding the cylindrical specimen and submitted to the impact of ogive-nosed steel projectiles. (10.1140/epjst/e2018-00059-y)
  DOI : 10.1140/epjst/e2018-00059-y
• Large Eddy Simulation of Fluid-Elastic Instability in Square Normal Cylinder Array
  
  • Shinde Vilas
  • Longatte Elisabeth
  • Baj Franck
  Journal of Pressure Vessel Technology, American Society of Mechanical Engineers, 2018, 140 (4), pp.041301. Large eddy simulations (LES) are performed at low Reynolds number (2000–6000) to investigate the dynamic fluid-elastic instability in square normal cylinder array for a single-phase fluid cross flow. The fluid-elastic instability is dominant in the flow normal direction, at least for all water-flow experiments (Price, S., and Paidoussis, M., 1989, “The Flow-Induced Response of a Single Flexible Cylinder in an in-Line Array of Rigid Cylinders,” J. Fluids Struct., 3(1), pp. 61–82). The instability appears even in the case of single moving cylinder in an otherwise fixed-cylinder arrangement resulting in the same critical velocity (Khalifa, A., Weaver, D., and Ziada, S., 2012, “A Single Flexible Tube in a Rigid Array as a Model for Fluidelastic Instability in Tube Bundles,” J. Fluids Struct., 34, pp. 14–32); Khalifa et al. (2013, “Modeling of the Phase Lag Causing Fluidelastic Instability in a Parallel Triangular Tube Array,” J. Fluids Struct., 43, pp. 371–384). Therefore, in the present work, only a central cylinder out of 20 cylinders is allowed to vibrate in the flow normal direction. The square normal (90 deg) array has 5 rows and 3 columns of cylinders with 2 additional side columns of half wall-mounted cylinders. The numerical configuration is a replica of an experimental setup except for the length of cylinders, which is of 4 diameters in numerical setup against about 8 diameters in the experiment facility. The single-phase fluid is water. The standard Smagorinsky turbulence model is used for the subgrid scale eddy viscosity modeling. The numerical results are analyzed and compared to the experimental results for a range of flow velocities in the vicinity of the instability. Moreover, instantaneous pressure and fluid-force profiles on the cylinder surface are extracted from the LES calculations in order to better understand the dynamic fluid-elastic instability. (10.1115/1.4040417)
  DOI : 10.1115/1.4040417
• Temperature dependent deformation mechanisms of Al 0.3 CoCrFeNi high-entropy alloy, starting from serrated flow behavior
  
  • Zhang Yu
  • Li Jinshan
  • Wang Jun
  • Wang William Yi
  • Kou Hongchao
  • Beaugnon Eric
  Journal of Alloys and Compounds, Elsevier, 2018, 757, pp.39-43. (10.1016/j.jallcom.2018.04.305)
  DOI : 10.1016/j.jallcom.2018.04.305
• Ductile fracture modelling using local approaches, application to steel welded joints in nuclear components
  
  • Kebiri S.
  • Maitournam H.
  • Bourgeois M.
  • Di Paola F.
  , 2018. The simulation of crack propagation in ductile materials using the finite element method requires appropriate models for describing the nucleation, growth and coalescence of voids in a robust way. Local models, such as Rousselier and Gurson-Tvergaard-Needleman are now available in the finite element softwares as Cast3m [3]. A large number of models of this kind can be found in the literature, but they suffer from numerical drawbacks. First, they often show a marked mesh dependency of the solution. Second, volumetric locking of the elements is common in elastoplastic damage models in near-incompressible conditions. These two major issues must be solved in order to insure the robustness of such approaches. Our goal is to propose a model which be able to handle these two problems. The mesh dependency can solved by using regularization techniques, such as implicit gradient enrichment of an internal variable [1]. The locking can be treated, either using selective integration techniques, or a mixed formulation [2], which adds the volume variation as a new variable in addition to the displacement.The proposed models, based on the existing Rousselier and GTN models in Cast3m [3], address both issues using an implicit-enriched gradient of damage, and include a mixed formulation in the local models to ensure the desired robustness. In this presentation, the new models and the implementation of the new models are first presented. In a second part, simulations of crack propagation using the proposed models for axisymmetric and compact-tensile specimens in 2D using the Cast3m finite element software [3] are used to illustrate the relevancy of the approach.
• Route to Chaos in the Fluidic Pinball
  
  • Deng Nan
  • Pastur Luc R
  • Morzyński Marek
  • Noack Bernd R
  , 2021. The fluidic pinball has been recently proposed as an attractive and effective flow configuration for exploring machine learning fluid flow control. In this contribution, we focus on the route to chaos in this system without actuation, as the Reynolds number is smoothly increased. The route was found to be of the Newhouse-Ruelle-Takens kind, with a secondary pitchfork bifurcation that breaks the symmetry of the mean flow field on the route to quasi-periodicity. (10.1115/FEDSM2018-83359)
  DOI : 10.1115/FEDSM2018-83359