Publications

2020

• Combining nonlinear vibration absorbers and the Acoustic Black Hole for passive broadband flexural vibration mitigation
  
  • Li Haiqin
  • Touzé Cyril
  • Pelat Adrien
  • Gautier François
  International Journal of Non-Linear Mechanics, Elsevier, 2020, pp.103558. The Acoustic Black Hole (ABH) effect refers to a special vibration damping technique adapted to thin-walled structures such as beams or plates. It usually consists of a local decrease of the structure thickness profile, associated to a thin viscoelastic coating placed in the area of minimum thickness. It has been shown that such structural design acts as an efficient vibration damper in the high frequency range, but not at low frequencies. This paper investigates how different types of vibration absorbers, linear and nonlinear, added to the primary system can improve the low frequency performance of a beam ABH termination. In particular, the conjugated effects of the Acoustic Black Hole effect and a Tuned Mass Damper (TMD), a Nonlinear Energy Sink (NES), a bi-stable NES (BNES), and a vibro-impact ABH (VI-ABH) are investigated. Forced response to random excitation are computed in the time domain using a modal approach combined with an energy conserving numerical scheme. Frequency indicators are defined to characterize and compare the performance of all solutions. The simulation results clearly show that all the proposed methods are able to damp efficiently the flexural vibrations in a broadband manner. The optimal tuning of each proposed solution is then investigated through a thorough parametric study, showing how to optimize the efficiency of each solution. In particular, TMD and VI-ABH show a slight dependence on vibration amplitude, while the performance of NES and BNES have a peak of efficiency for moderate amplitudes. (10.1016/j.ijnonlinmec.2020.103558)
  DOI : 10.1016/j.ijnonlinmec.2020.103558
• Low-dimensional Flow Models from high-dimensional Flow data with Machine Learning and First Principles
  
  • Nan Deng
  • Pastur Luc R.
  • Noack Bernd R.
  , 2020. Reduced-order modelling and system identification can help us figure out the elementary degrees of freedom and the underlying mechanisms from the high-dimensional and nonlinear dynamics of fluid flow. Machine learning has brought new opportunities to these two processes and is revolutionising traditional methods. We show a framework to obtain a sparse humaninterpretable model from complex high-dimensional data using machine learning and first principles.
• Thermo-magneto-mechanical coupling dynamics of magnetic shape memory alloys
  
  • Chen Xue
  • He Yongjun
  International Journal of Plasticity, Elsevier, 2020, 129, pp.102686. (10.1016/j.ijplas.2020.102686)
  DOI : 10.1016/j.ijplas.2020.102686
• A low-diffusion self-adaptive flux-vector splitting approach for compressible flows
  
  • Iampietro David
  • Daude Frédéric
  • Galon Pascal
  Computers and Fluids, Elsevier, 2020, 206(C). A low-diffusion self-adaptive flux-vector splitting method is presented for the Euler equations. The flux-vector is here split into convective and acoustic parts following the formulation recently proposed by the authors. This procedure is based on the Zha-Bilgen (or previously Baraille et al. for the Euler barotropic system) approach enriched by a dynamic flow-dependent splitting parameter based on the local Mach number. As a consequence, in the present self-adaptive splitting, the convective and acoustic parts decouple in the low-Mach number regime whereas the complete Euler equations are considered for the sonic and highly subsonic regimes. The low diffusive property of the present scheme is obtained by adding anti-diffusion terms to the momentum and the energy components of the pressure flux in the acoustic part of the present splitting. This treatment results from a formal invariance principle preserving the discrete incompressible phase space through the pressure operator. Numerical results for several carefully chosen one- and two-dimensional test problems are finally investigated to demonstrate the accuracy and robustness of the proposed scheme for a wide variety of configurations from subsonic to highly subsonic flows. (10.1016/j.compfluid.2020.104586)
  DOI : 10.1016/j.compfluid.2020.104586
• Quadrupolar flows around spots in internal shear flows
  
  • Wang Zhe
  • Guet Claude
  • Monchaux Romain
  • Duguet Yohann
  • Eckhardt Bruno
  Journal of Fluid Mechanics, Cambridge University Press (CUP), 2020, 892, pp.A27. Turbulent spots occur in shear flows confined between two walls and are surrounded by robust quadrupolar flows. Although the far-field decay of such large-scale flows has been reported to be exponential, we predict a different algebraic decay for the case of plane Couette flow. We address this problem theoretically, by modelling an isolated spot as an obstacle in a linear plane shear flow with free-slip boundary conditions at the walls. By seeking invariant solutions in a co-moving Lagrangian frame and using geometric scale separation, a set of differential equations governing large-scale flows is derived from the Navier–Stokes equations and solved analytically. The wall-normal velocity turns out to be exponentially localised in the plane, while the quadrupolar in-plane velocity field, after wall-normal averaging, features a superposition of algebraic and exponential decays. The algebraic decay exponent is −3. The quadrupolar angular dependence stems from (i) the shearing of the streamwise velocity and (ii) the breaking of the spanwise homogeneity. Near the spot, exponentially decaying solutions can generate reversed quadrupolar flows. Eventually, by noting that the algebraically decaying in-plane flow is two-dimensional and harmonic, we suggest a topological origin to the quadrupolar large-scale flow (10.1017/jfm.2020.190)
  DOI : 10.1017/jfm.2020.190
• Self-heating behavior during cyclic loadings of 316L stainless steel specimens manufactured or repaired by Directed Energy Deposition
  
  • Balit Yanis
  • Joly Louis-Romain
  • Szmytka Fabien
  • Durbecq Sylvain
  • Charkaluk Eric
  • Constantinescu Andrei
  Materials Science and Engineering: A, Elsevier, 2020, 786, pp.139476. The purpose of this article is to assess a self-heating testing method for the characterization of fatigue properties of single-track thickness additively manufactured specimens. It also evaluates the impact of the microstructure orientation with respect to the loading direction on the dissipative behavior and the initiation of microcracks. The 316L stainless steel specimens under scrutiny were manufactured by Directed Energy Deposition in two configurations: (i) fully printed specimens (2 orientations) and (ii) repaired specimens. The paper first presents a morphologic and crystallographic texture analysis and second, a series of self-heating tests under cyclic loading. The mi-crostructural analysis revealed elongated grains with their sizes, shapes and preferred orientations controlled by process parameters. The self-heating measurements under cyclic tensile loading proved that the dissipation estimation through infrared measurements can be performed on small scale, thin specimens. The self-heating curves could successfully be represented by the Munier model. Moreover, several links between the printing parameters and self-heating results could be established. For example, a smaller vertical increment between successively deposited layers leads to higher mean (10.1016/j.msea.2020.139476)
  DOI : 10.1016/j.msea.2020.139476
• Combination of Hexahedral and Prismatic Solid-shell Finite Elements
  
  • Dia Mohamadou
  • Gravouil Anthony
  • Hamila Nahiene
  • Abbas Mickaël
  , 2020, 47, pp.1424-1428. In most papers with solid-shell finite elements for non-linear calculation of thin structures, only one type of element is presented. Either prismatic solid-shell or hexahedral solid-shell element. However, it is well known that in industrial studies, where complex geometries are involved, it is very difficult to model with only hexahedral type of finite element. We will therefore propose a study where two recently formulated solid-shell finite elements (SB7 and SB9) are combined to solve a practical industrial problem. The SB7 and SB9 are two solid-shell finite elements of prismatic and hexahedral topologies. They contain respectively 6 and 8 vertex nodes plus one additional central node. This central node acts as an EAS parameter, but not only. From this additional degree of freedom (DOF), a new distribution is made on the applied pressure forces, generating a volume contribution. This allows to go beyond the EAS method, allowing to improve considerably the pinch stresses. These two elements work with three dimensional constitutive laws and are under integrated (reduced integration). The ANS method is also used to reduce transverse shear and trapezoidal locking. (C) 2020 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 23rd International Conference on Material Forming. (10.1016/j.promfg.2020.04.304)
  DOI : 10.1016/j.promfg.2020.04.304
• Hybridized Love Waves in a Guiding Layer Supporting an Array of Plates with Decorative Endings
  
  • Pham Kim
  • Maurel Agnès
  • Félix Simon
  • Guenneau Sebastien
  Materials, MDPI, 2020, 13 (7), pp.1632. This study follows from Maurel et al., Phys. Rev. B 98, 134311 (2018), where we reported on direct numerical observations of out-of-plane shear surface waves propagating along an array of plates atop a guiding layer, as a model for a forest of trees. We derived closed form dispersion relations using the homogenization procedure and investigated the effect of heterogeneities at the top of the plates (the foliage of trees). Here, we extend the study to the derivation of a homogenized model accounting for heterogeneities at both endings of the plates. The derivation is presented in the time domain, which allows for an energetic analysis of the effective problem. The effect of these heterogeneous endings on the properties of the surface waves is inspected for hard heterogeneities. It is shown that top heterogeneities affect the resonances of the plates, hence modifying the cut-off frequencies of a wave mathematically similar to the so-called Spoof Plasmon Polariton (SPP) wave, while the bottom heterogeneities affect the behavior of the layer, hence modifying the dispersion relation of the Love waves. The complete system simply mixes these two ingredients, resulting in hybrid surface waves accurately described by our model. (10.3390/ma13071632)
  DOI : 10.3390/ma13071632
• Modèle de force basé sur les dynamiques transitoires de sillage dans le pinball fluidique
  
  • Deng Nan
  • Pastur Luc
  • Bernd R. Noack
  • Cornejo Maceda Guy
  • Lusseyran François
  • Loiseau Jean-Christophe
  • Morzyński Marek
  , 2020.
• Backbone curves of coupled cubic oscillators in one-to-one internal resonance: bifurcation scenario, measurements and parameter identification
  
  • Givois Arthur
  • Tan Jin-Jack
  • Touzé Cyril
  • Thomas Olivier
  Meccanica, Springer Verlag, 2020, 55 (3), pp.481-503. A system composed of two cubic nonlinear oscillators with close natural frequencies, and thus displaying a 1:1 internal resonance, is studied both theoretically and experimentally, with a special emphasis on the free oscillations and the backbone curves. The instability regions of uncoupled solutions are derived and the bifurcation scenario as a function of the parameters of the problem is established, showing in an exhaustive manner all possible solutions. The backbone curves are then experimentally measured on a circular plate, where the asymmetric modes are known to display companion configurations with close eigenfrequencies. A control system based on a Phase-Locked Loop (PLL) is used to measure the backbone curves and also the frequency response function in the forced and damped case, including unstable branches. The model is used for a complete identification of the unknown parameters and an excellent comparison is drawn out between theoretical prediction and measurements. (10.1007/s11012-020-01132-2)
  DOI : 10.1007/s11012-020-01132-2
• Perfect Brewster transmission through ultrathin perforated films
  
  • Pham Kim
  • Maurel Agnès
  • Mercier Jean-François
  • Félix Simon
  • Cordero Maria Luisa
  • Horvath Camila
  Wave Motion, Elsevier, 2020, 93, pp.102485. We address the perfect transmission of a plane acoustic wave at oblique incidence on a perforated, sound penetrable or rigid, film in two-dimensions. It is shown that the Brewster incidence θ * realizing so-called extraordinary transmission due to matched impedances varies significantly when the thickness e of the film decreases. For thick films, i.e. ke ≫ 1 with k the incident wavenumber, the classical effective medium model provides an accurate prediction of the Brewster angle independent of e (this Brewster angle is denoted θ B). However, for thinner films with ke < 1, θ * becomes dependent of e and it deviates from θ B. To properly describe this shift, an interface model is used (Marigo et al., 2017) which accurately reproduces the spectra of ultrathin to relatively thick perforated films. Depending on the contrasts in the material properties of the film and of the surrounding matrix, decreasing the film thickness can produce an increase or a decrease of θ * ; it can also produce the disappearance of a perfect transmission or to the contrary its appearance. (10.1016/j.wavemoti.2019.102485)
  DOI : 10.1016/j.wavemoti.2019.102485
• Coupled vibro-acoustic modeling of a dielectric elastomer loudspeaker
  
  • Garnell Emil
  • Doaré Olivier
  • Rouby Corinne
  Journal of the Acoustical Society of America, Acoustical Society of America, 2020, 147 (3), pp.1812-1821. (10.1121/10.0000930)
  DOI : 10.1121/10.0000930
• An energy-based strategy for fatigue analysis in presence of general multi-axial time varying loadings
  
  • Ma Zepeng
  • Maitournam Habibou
  • Le Tallec Patrick
  International Journal of Fatigue, Elsevier, 2020, 132, pp.105367. The purpose of this paper is to propose an energy based multi-scale fatigue approach which handles multidimensional time varying loading histories. Our fundamental thought is to assume that the energy dissipated at small scales governs fatigue at failure in a nonlinear additive way. We follow the Dang Van paradigm at macro scale. The structure is elastic at the macroscopic scale. At each material point, there is a stochastic distribution of weak points which will undergo strong plastic yielding, which contribute to energy dissipation without affecting the overall macroscopic stress. A kinematic hardening under the assumption of associative plasticity is also considered. Instead of using the number of cycles, we use the concept of multi-scale damage accumulation during the considered load history. A concise non-linear damage accumulation law is also proposed in our model. Fatigue will then be determined from the plastic shakedown cycle and from a phenomenological fatigue law linking lifetime and accumulated mesoscopic plastic dissipation. (10.1016/j.ijfatigue.2019.105367)
  DOI : 10.1016/j.ijfatigue.2019.105367
• Nonlinear delayed feedback model for incompressible open cavity flow
  
  • Tuerke F.
  • Lusseyran F.
  • Sciamarella Denisse
  • Pastur L.
  • Artana G.
  Physical Review Fluids, American Physical Society, 2020, 5 (2), pp.1-13. The dynamics of an oscillating shear layer when confined is enriched by retarded actions whose physical modeling is not trivial. We present a nonlinear delayed saturation feedback model, which allows us to correctly reproduce the complex shear layer spectra observed experimentally in open cavity flows in the incompressible limit. The model describes the evolution of the amplitude of the shear layer instabilities and considers two hydrodynamic feedback mechanisms directly related to the confinement introduced by the walls. One is associated with reflections of instability waves on the vertical cavity walls and the other to intracavity recirculation flow. These feedback mechanisms provide retarded actions with time lags that are used in the delay differential equation and allow the computation of the model parameters on physical grounds. The frequency components of six experimental cases in different flow regimes are well recovered by the dynamical model. The results show that the model with a single feedback mechanism produces monoperiodic oscillations of the amplitude, while the interplay of two purely hydrodynamic feedback mechanisms allow quasiperiodicity to develop. (10.1103/physrevfluids.5.024401)
  DOI : 10.1103/physrevfluids.5.024401
• A nine nodes solid-shell finite element with enhanced pinching stress
  
  • Dia Mouhamadou
  • Hamila Nahiene
  • Abbas Mickaël
  • Gravouil Anthony
  Computational Mechanics, Springer Verlag, 2020. In this paper we present a low-order solid-shell element formulation—having only displacement degrees of freedom (DOFs), i.e., without rotational DOFs. The element has an additional middle node, that allows efficient and accurate analyses of shell structures using elements at extremely high aspect ratio. The formulation is based on the Hu–Washizu variational principle leading to a novel enhancing strain and stress tensor that renders the computation particularly efficient, with improved inplane and out-of-plane bending behavior (Poisson thickness locking). The middle-node is endowed with only one degree of freedom, in the thickness direction, allowing the assumption of a quadratic interpolation of the transverse displacement. Unlike solid-shell finite elements reported previously in the literature and formulated under the hypothesis of plane stress or with enhanced assumed strain parameter, the new solid-shell element here mentioned uses a complete three-dimensional constitutive law and gives an enhanced pinching stress, thanks to the middle-node. Moreover, to handle the various locking problems that usually arise on solid-shell formulation, the reduced integration technique is used as well as the assumed shear strain method. Finally to assess the effectiveness and performance of this new formulation, a set of popular benchmark problems, involving geometric non-linear analysis as well as elastic-plastic behavior has been investigated. (10.1007/s00466-020-01825-1)
  DOI : 10.1007/s00466-020-01825-1
• Low-order model for successive bifurcations of the fluidic pinball
  
  • Nan Deng
  • Noack Bernd R.
  • Morzyński Marek
  • Pastur Luc R.
  Journal of Fluid Mechanics, Cambridge University Press (CUP), 2020, 884, pp.A37. We propose the first least-order Galerkin model of an incompressible flow undergoing two successive supercritical bifurcations of Hopf and pitchfork type. A key enabler is a mean-field consideration exploiting the symmetry of the mean flow and the asymmetry of the fluctuation. These symmetries generalize mean-field theory, e.g. no assumption of slow growth-rate is needed. The resulting 5-dimensional Galerkin model successfully describes the phenomenogram of the fluidic pinball, a two-dimensional wake flow around a cluster of three equidistantly spaced cylinders. The corresponding transition scenario is shown to undergo two successive supercritical bifurcations, namely a Hopf and a pitchfork bifurcations on the way to chaos. The generalized mean-field Galerkin methodology may be employed to describe other transition scenarios. (10.1017/jfm.2019.959)
  DOI : 10.1017/jfm.2019.959
• Comparative investigation of the fatigue limit of additive-manufactured and rolled 316 steel based on self-heating approach
  
  • Cao Yinfeng
  • Moumni Ziad
  • Zhu Jihong
  • Zhang Yahui
  • You Yajun
  • Zhang Weihong
  Engineering Fracture Mechanics, Elsevier, 2020, 223, pp.106746. (10.1016/j.engfracmech.2019.106746)
  DOI : 10.1016/j.engfracmech.2019.106746
• Surface waves from flexural and compressional resonances of beams
  
  • Marigo Jean-Jacques
  • Pham Kim
  • Maurel Agnes
  • Guenneau Sébastien
  , 2020.
• Macroscopic model of fluid structure interaction in cylinder arrangement using theory of mixture
  
  • Gineau A
  • Longatte E.
  • Lucor D.
  • Sagaut P.
  Computers and Fluids, Elsevier, 2020, 202, pp.104499. In the framework of the theory of mixture, the dynamic behaviour of solid cylinder bundles submitted to external hydrodynamic load exerted by surrounding viscous fluid flow is described. Mass conservation and momentum balance formulated on an elementary domain made of a given volume of mixture give rise to a system of coupled equations governing solid space-averaged displacement, fluid velocity and pressure provided that near-wall hydrodynamic load on each vibrating cylinder is expressed as a function of both fluid and solid space-averaged velocity fields. Then, the ability of the macroscopic model to reproduce over time an averaged flow surrounding vibrating cylinders in a large array in the context of small magnitude displacements is pointed out. Numerical solutions obtained on a two-dimensional configuration involving an array of several hundreds of cylinders subjected to an impulsional load are compared to those provided by averaged well-resolved microscopic-scale solutions. The relative error is less than 3% in terms of displacement magnitude and 5% for frequency delay. The proposed macroscopic model does not include any assumption on relative effect contributions to mechanical exchanges occurring in the full domain. Therefore it features interesting properties in terms of fluid solid interaction prediction capabilities. Moreover it contributes to a significant gain in terms of computational time and resources. Further developments are now required in order to extent the formulation to large magnitude displacements including three-dimensional effects. This could be recommended for investigations on fuel assembly vibration risk assessment in Pressure Water, Fast Breeder reactors at a whole core scale or any other large-scale mechanical system involving some kind of periodic geometry. (10.1016/j.compfluid.2020.104499)
  DOI : 10.1016/j.compfluid.2020.104499
• Environmental parameters sensitivity analysis for the modeling of wind turbine noise in downwind conditions
  
  • Kayser Bill
  • Cotté Benjamin
  • Ecotière David
  • Gauvreau Benoit
  Journal of the Acoustical Society of America, Acoustical Society of America, 2020, 148 (6), pp.3623--3632. (10.1121/10.0002872)
  DOI : 10.1121/10.0002872
• Wall‐slab joint parameter identification of a reinforced concrete structure using possibly corrupted modal data
  
  • Oliveira Hugo
  • Louf François
  • Hervé‐secourgeon Estelle
  • Gatuingt Fabrice
  International Journal for Numerical and Analytical Methods in Geomechanics, Wiley, 2020, 44 (1), pp.19-39. In numerical models, the connections among component members are crucial for the prediction of structural behaviour under different type of solicitations. In reinforced structures, the connections are often assumed rigid, what may not be realistic in many practical cases. As alternative, a semi-rigid behaviour depending on a set of independent parameters can be proposed. In this case, a new difficulty arises, which is finding the appropriate values for those parameters. The present study proposes a numerical strategy for identification of the connection parameters based on the Constitutive Relation Error (CRE). To include all available information, an augmented version (Modified CRE) is implemented. The parameters search is iterative and require large amount of system response analysis. To increase the computational efficiency, a reduced order model is adopted. The proposed approach shows low-sensitivity to limited lack of information and also to support condition variability, both of them verified numerically. In this work, experimental tests for a real 1:4 scale structure is utilized for finding the parameters corresponding to the first three modal shapes. A good agreement between numerical predictions and observations is verified, what highlights the accuracy and stability of the proposed numerical approach. The present study may also find applications in the domain of design of experiments. (10.1002/nag.2994)
  DOI : 10.1002/nag.2994
• Modeling place cells and grid cells in multi-compartment environments: Entorhinal–hippocampal loop as a multisensory integration circuit
  
  • Li Tianyi
  • Arleo Angelo
  • Sheynikhovich Denis
  Neural Networks, Elsevier, 2020, 121, pp.37-51. Hippocampal place cells and entorhinal grid cells are thought to form a representation of space by integrating internal and external sensory cues. Experimental data show that different subsets of place cells are controlled by vision, self-motion or a combination of both. Moreover, recent studies in environments with a high degree of visual aliasing suggest that a continuous interaction between place cells and grid cells can result in a deformation of hexagonal grids or in a progressive loss of visual cue control over grid fields. The computational nature of such a bidirectional interaction remains unclear. In this work we present a neural network model of the dynamic interaction between place cells and grid cells within the entorhinal-hippocampal processing loop. The model was tested in two recent experimental paradigms involving environments with visually similar compartments that provided conflicting evidence about visual cue control over self-motion-based spatial codes. Analysis of the model behavior suggests that the strength of entorhinal-hippocampal dynamical loop is the key parameter governing differential cue control in multi-compartment environments. Moreover, construction of separate spatial representations of visually identical compartments required a progressive weakening of visual cue control over place fields in favor of self-motion based mechanisms. More generally our results suggest a functional segregation between plastic and dynamic processes in hippocampal processing. (10.1016/j.neunet.2019.09.002)
  DOI : 10.1016/j.neunet.2019.09.002
• Influence of the variability of soil profile properties on weak and strong seismic response
  
  • Gobbi Stefania
  • Lenti Luca
  • Santisi D’avila Maria Paola
  • Semblat Jean-François
  • Reiffsteck Philippe
  Soil Dynamics and Earthquake Engineering, Elsevier, 2020, 135, pp.106200. Characterizing the potential effect of local site conditions on the amplification of ground motions is a critical aspect of seismic hazard and risk assessment. The aim of this study is to investigate the reliability and the limit of using the average shear wave velocity in the upper 30 m of the soil profile vs,30 , as single proxy, to characterize seismic site effects for weak and strong events. To this regard, a dataset of 300 one-dimensional soil profiles with a given vs,30 are generated through a Monte Carlo approach. Their seismic responses are computed for a set of 40 real accelerograms, with different seismic features. The vertical propagation from the bottom of the generated columns is modeled using a finite element spatial discretization, accounting for both linear and nonlinear soil behavior. The site dominant frequency f0 and the shear wave velocity gradient in the profile B30 are proposed as proxies to characterize seismic site effects and the variability of the response spectra for the numerical signals, at the free surface of the set of columns, is discussed. Correlations between site-specific amplification factors deduced using the numerical response spectra and the proposed site proxies are analyzed for different sub-ranges of periods. The obtained amplification factors are then compared to those proposed by different international and national design codes. The results, obtained under assumption of linear and nonlinear behavior of soil, emphasize the need to introduce complementary site parameters proxies, in addition to vs,30, to characterize the expected site effects in design response spectra. (10.1016/j.soildyn.2020.106200)
  DOI : 10.1016/j.soildyn.2020.106200
• Chemo-Hydro-Mechanical analysis of Bituminized Waste swelling due to water uptake: Experimental and model comparisons
  
  • Melot G
  • Dangla Patrick
  • Granet Sylvie
  • M'Jahad Sofia
  • Champenois Jean-Baptiste B
  • Poulesquen Arnaud
  Journal of Nuclear Materials, Elsevier, 2020, 536, pp.152165. This paper presents a numerical model developed to reproduce the behaviour of French simplified Bituminized Waste Products (BWP) during a leaching test. The model is calibrated on experimental data sets. BWP were mainly produced during industrial reprocessing of nuclear spent fuel and are classified as low or intermediate activity long lived radioactive waste. Geological disposal is the reference solution for intermediate level long-lived BWP. Under geological disposal facility conditions, and after a long period of time, BWP will undergo water re-saturation from the host rock. A chemo-hydro-mechanical numerical model has been implemented with a finite element scheme to model BWP behaviour under such conditions. The constitutive model takes into account the impact of dissolution, permeation, diffusion and osmosis. Original evolution laws of diffusion coefficient and permeability as a function of the porosity are proposed. Specific mechanical model is proposed including Mori-Tanaka homogenization law. To simulate the hydration of the material, an original and simple method is proposed, avoiding costly two-phase flow resolution and complex calibration of the related parameters. This model was mainly used to reproduce the evolution of the amount of both water absorbed and salt leached by the sample during unconfined water up-taking tests. The calibration is based on experimental data obtained on French simplified BWP containing one highly soluble salt. Water uptake could generate swelling mainly due to osmosis. (10.1016/j.jnucmat.2020.152165)
  DOI : 10.1016/j.jnucmat.2020.152165
• Non-intrusive reduced order modelling for the dynamics of geometrically nonlinear flat structures using three-dimensional finite elements
  
  • Vizzaccaro Alessandra
  • Givois Arthur
  • Longobardi Pierluigi
  • Shen Yichang
  • Deü Jean-François
  • Salles Loïc
  • Touzé Cyril
  • Thomas Olivier
  Computational Mechanics, Springer Verlag, 2020, 66 (6), pp.1293-1319. Non-intrusive methods have been used since two decades to derive reduced-order models for geometrically nonlinear structures, with a particular emphasis on the so-called STiffness Evaluation Procedure (STEP), relying on the static application of prescribed displacements in a finite-element context. We show that a particularly slow convergence of the modal expansion is observed when applying the method with 3D elements, because of nonlinear couplings occurring with very high frequency modes involving 3D thickness deformations. Focusing on the case of flat structures, we first show by computing all the modes of the structure that a converged solution can be exhibited by using either static condensation or normal form theory. We then show that static modal derivatives provide the same solution with fewer calculations. Finally, we propose a modified STEP, where the prescribed displacements are imposed solely on specific degrees of freedom of the structure, and show that this adjustment also provides efficiently a converged solution. (10.1007/s00466-020-01902-5)
  DOI : 10.1007/s00466-020-01902-5