Publications

2021

• On structural finite element modeling strategies and their influence on the optimization of final constructability of reinforced concrete structures
  
  • Hervé-Secourgeon Guillaume
  • Hervé-Secourgeon Estelle
  • Bottoni Marina
  • Voldoire François
  • Razafimbelo Mihaja
  • Gatuingt Fabrice
  • Oliver-Leblond Cécile Oliver
  • Honorio Tulio
  • Kameh Ahmad
  • Habib Souheil
  • Escoffier Florian
  Nuclear Engineering and Design, Elsevier, 2021, 385, pp.111541. The design of nuclear civil structures based on rules in European standards makes extensive use of the Finite Element Method (FEM). The size and complexity of the models are continuously increasing. Lately, the post-processing of the FEM results has centered the engineers' contribution on analyzing the reinforcement density produced using automated methods dealing with shell or plate models, which often leads to excessive plate use even in D-regions (discontinuity or disturbance region). This practice is particularly problematic for nuclear structures, which exhibit a large set of massive parts due to radiation protection requirements in many areas such as the reactor pit, the raft, or the (10.1016/j.nucengdes.2021.111541)
  DOI : 10.1016/j.nucengdes.2021.111541
• The interplay between Fano and Fabry–Pérot resonances in dual-period metagratings
  
  • Zhou Hagström Joar
  • Maurel Agnès
  • Pham Kim
  Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, Royal Society, 2021, 477 (2255). We study theoretically and numerically the occurrence of Fano resonances in a metagrating made of slits with some symmetry breaking resulting in a dual period. At low frequency, a grating composed of long enough slits supports Fabry–Pérot resonances on which Fano resonances superimpose when the grating acquires dual period. The resulting spectrum exhibits flat-banded peaks interrupted by sharp dips with successions of perfect and zero transmissions. To model these scattering properties, homogenization theory is used resulting in an effective problem governing the solutions in the two, non-identical, slits, which are coupled through jump conditions at the grating interfaces. These jumps efficiently encode the effect of the evanescent field able to resonate in the radiative region due to the folding of the spoof plasmon polaritons branches. The model is validated with direct numerics and a local analysis allows us to characterize the resonant mechanisms. (10.1098/rspa.2021.0632)
  DOI : 10.1098/rspa.2021.0632
• Toughening induced by the formation of facets in mode I+III brittle fracture: experiments versus a two-scale Cohesive Zone model
  
  • Hattali M.L. L
  • Cambonie T.
  • Lazarus V.
  Journal of the Mechanics and Physics of Solids, Elsevier, 2021, 156, pp.104596. When subjected to some anti-plane shear mode III loading, segmentation of the crack front frequently occurs during propagation: even if the crack is initially planar, propagation produces facets/segments rotated toward the shear free direction. Here, we examine, both experimentally and theoretically, the effect of this microstructure on the effective macroscale brittle fracture toughness. Experiments performed on PMMA beams reveal that the critical load leading to abrupt rupture increases with mode III to mode I ratio. This apparent macroscopic toughening is usually taken into account by invoking a specific mode III toughness in addition to the mode I one. By applying thoroughfully a micro/macroscale Cohesive Zone (CZ) model that we have recently developed, we demonstrate that an additional material constant is useless here since this toughness increase can be attributed mainly to the presence of the facets at the microscale, whose geometry can be anticipated to depend on the classical mode I material constants. More precisely, two related physical mechanisms are generated due to the formation of a disconnected crack front: (i) changes in fractured surface area in comparison to a straight propagation, and (ii) crack shielding caused by the facets that reduce the effective crack opening. While the first effect is obvious to quantify, we show that the second plays an essential role but is more complex to take into account: it depends on the solution of the three-dimensional elasticity problem in presence of the facets, that is considered in the CZ model. We illustrate on the experiments how to use this approach in practice to determine the critical fracture threshold. (10.1016/j.jmps.2021.104596)
  DOI : 10.1016/j.jmps.2021.104596
• The interplay between Fano and Fabry–Pérot resonances in dual-period metagratings
  
  • Zhou Hagström Joar
  • Pham Kim
  • Maurel Agnès
  Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, Royal Society, 2021, 477 (2255). We study theoretically and numerically the occurrence of Fano resonances in a metagrating made of slits with some symmetry breaking resulting in a dual period. At low frequency, a grating composed of long enough slits supports Fabry–Pérot resonances on which Fano resonances superimpose when the grating acquires dual period. The resulting spectrum exhibits flat-banded peaks interrupted by sharp dips with successions of perfect and zero transmissions. To model these scattering properties, homogenization theory is used resulting in an effective problem governing the solutions in the two, non-identical, slits, which are coupled through jump conditions at the grating interfaces. These jumps efficiently encode the effect of the evanescent field able to resonate in the radiative region due to the folding of the spoof plasmon polaritons branches. The model is validated with direct numerics and a local analysis allows us to characterize the resonant mechanisms. (10.1098/rspa.2021.0632)
  DOI : 10.1098/rspa.2021.0632
• MAESSTRO 1.0.0
  
  • Elie Benjamin
  • Cotté Benjamin
  • Boutillon Xavier
  • Chauvat Nicolas
  • Laxalde Denis
  • Bessou Frank
  • Nhu Viet-Hung
  • Trévisan Benjamin
  , 2021. MAESSTRO is a software for sound synthesis of piano tones based on a complete vibroacoustic modeling of the piano. The main goal is to provide piano makers a set of tools that allow them to predict the acoustic impacts of structural modifications of piano soundboards on the resulting sounds. The interest of the physical modeling that drives the numerical computations embedded in the software is to be able to reproduce the vibroacoustics of the piano in a realistic fashion: the acoustic variations between tones produced by different pianos faithfully reflect their structural differences. For that purpose, MAESSTRO gathers and coordinates several numerical and physical models that numerically simulate all of the physical phenomena involved in the production of piano tones, from the hammer impulsion upto the acoustic radiation. MAESSTRO includes several functionalities which are the following * entering the geometry and the materials of the virtual soundboard thanks to a Graphical User Interface (GUI), * feeding MAESSTRO with MIDI files to be synthesized, * simulating numerically the physical phenomena involved in the production of piano tones, * post-processing the software outputs, * creating audio files of synthesized piano tones. The package contains three subpackages : * maesstro-ihm contains the source codes of the GUI, implemented in TypeScript * maesstro-matlab is a Matlab toolbox that contains the source codes for the computation of the modal basis of the soundboard, including an automatic mesh generator using GMSH. Matlab is only needed to modify the source files and generate updated executables. In order to launch the executables, only Matlab Runtime is needed * maesstro-python contains the python modules which is used to call the different modules via a command line interface
• Geometric optimization of dielectric elastomer electrodes for dynamic applications
  
  • Garnell Emil
  • Aksoy Bekir
  • Shea Herbert
  • Doaré Olivier
  • Rouby Corinne
  Applied Acoustics, Elsevier, 2021, 181, pp.108120. (10.1016/j.apacoust.2021.108120)
  DOI : 10.1016/j.apacoust.2021.108120
• Analysis, improvement and limits of the multiscale Latin method
  
  • Oumaziz Paul
  • Gosselet Pierre
  • Saavedra Karin
  • Tardieu Nicolas
  Computer Methods in Applied Mechanics and Engineering, Elsevier, 2021, 384, pp.113955. This work studies the convergence properties of the mixed non-overlapping domain decomposition method (DDM) commonly named "Latin method". As all DDM, the Latin method is sensitive to nearinterface heterogeneity and irregularity. Using a simple yet fresh point of view, we analyze the role of the Robin parameters as well as of the second level (coarse space) correction-which are a characteristic of the method. In particular, we show how to build a spectrum-motivated coarse space aiming at ensuring fast convergence. 2D and 3D linear elasticity problems involving highly heterogeneous materials confirm the robustness of the spectral coarse space and provide evidence of the scalability of the multiscale Latin method. (10.1016/j.cma.2021.113955)
  DOI : 10.1016/j.cma.2021.113955
• On damage regularity defect nucleation modelling
  
  • Stolz Claude
  International Journal of Solids and Structures, Elsevier, 2021, 229, pp.111107. The purpose of this article is to model defect nucleation. The defect is considered as a small volume which evolves as a damaged zone. The damage is described by a transition zone which can be sharp or continuous. In the first case, discontinuities occur and the initiation of defect is based on bifurcation of an equilibrium state. When the transition is continuous, the initiation of the defect is continuous.The analysis is based on considering different models of damage, depending on the regularity imposed on mechanical field. For each model, the presence of discontinuities on mechanical fields is investigated. Consequences of each model on defect nucleation are illustrated on particular structures: bars under extension and spheres under radial loading. (10.1016/j.ijsolstr.2021.111107)
  DOI : 10.1016/j.ijsolstr.2021.111107
• Direct computation of nonlinear mapping via normal form for reduced-order models of finite element nonlinear structures
  
  • Vizzaccaro Alessandra
  • Shen Yichang
  • Salles Loïc
  • Blahoš Jiří
  • Touzé Cyril
  Computer Methods in Applied Mechanics and Engineering, Elsevier, 2021, 384, pp.113957. The direct computation of the third-order normal form for a geometrically nonlinear structure discretised with the finite element (FE) method, is detailed. The procedure allows to define a nonlinear mapping in order to derive accurate reduced-order models (ROM) relying on invariant manifold theory. The proposed reduction strategy is direct and simulation free, in the sense that it allows to pass from physical coordinates (FE nodes) to normal coordinates, describing the dynamics in an invariant-based span of the phase space. The number of master modes for the ROM is not a priori limited since a complete change of coordinate is proposed. The underlying theory ensures the quality of the predictions thanks to the invariance property of the reduced subspace, together with their curvatures in phase space that accounts for the nonresonant nonlinear couplings. The method is applied to a beam discretised with 3D elements and shows its ability in recovering internal resonance at high energy. Then a fan blade model is investigated and the correct prediction given by the ROMs are assessed and discussed. A method is proposed to approximate an aggregate value for the damping, that takes into account the damping coefficients of all the slave modes, and also using the Rayleigh damping model as input. Frequency-response curves for the beam and the blades are then exhibited, showing the accuracy of the proposed method. (10.1016/j.cma.2021.113957)
  DOI : 10.1016/j.cma.2021.113957
• Dynamic response of shallow foundations on reinforced soil with rigid inclusions
  
  • Shen Yuxiang
  • Pérez-Herreros Jesús
  • Cuira Fahd
  • Semblat Jean-François
  • Burlon Sébastien
  , 2021.
• Dynamic response of shallow foundations on reinforced soil with rigid inclusions
  
  • Shen Yuxiang
  • Pérez-Herreros Jesús
  • Cuira Fahd
  • Semblat Jean-François
  • Burlon Sébastien
  , 2021. The soil-improvement technique by rigid inclusions represents today a practical, economical and time-saving solution that allows the use of shallow foundations on compressible soils. Several studies have recently focused on the static behavior of this reinforcement system (i.e. ASIRI French national project), however, its seismic performance has not yet received the same amount of attention. This paper presents a state of the art in the dynamic soil-structure interaction (SSI) analysis of structures supported on shallow foundations on reinforced soil with rigid inclusions. Special attention is given to the calculation methods that are currently being used in design offices. A parametric study is conducted by means of 3D numerical models and the hybrid BEM-FEM method in order to highlight the possibilities and limitations of these methods, especially for the study of inertial and kinematic interaction effects. Different configurations of rigid inclusions are studied, including several lengths, spacing and foundation layout. The results of this parametric study are compared to those obtained for equivalent shallow and deep foundations in terms of impedance functions and kinematic interaction factors. Finally, a discussion on different aspects that may control the dynamic linear and non-linear response of these foundation systems is undertaken.
• Deep mean-field modeling for successive bifurcations exemplified for the fluidic pinball
  
  • Deng Nan
  , 2021. Artificial intelligence becomes increasingly important in solving problems that are difficult to handle with traditional mathematical methods. Reduced-order modelling (ROM) is no exception. In this thesis, we pave the way to automatable ROM in flow dynamics using first principles and machine learning techniques. The aim is to establish a benchmark problem for the most important dynamical features of wake flows.The chosen benchmark configuration is the two-dimensional incompressible wake flow around the fluidic pinball, a cluster of parallel cylinders whose axis are located at the vertices of an equilateral triangle pointing upstream. At low Reynolds numbers, this configuration has a stable steady state satisfying the reflectional symmetry. With increasing Reynolds numbers, it undergoes two supercritical bifurcations of Hopf and pitchfork types, associated with the Bénard-von Kármán instability and a symmetry-breaking instability, respectively. A secondary Hopf bifurcation leads to quasi-periodic asymmetric shedding, before finally bifurcating into a chaotic regime. From numerical investigations of the periodic regimes, the asymmetric periodic shedding is characterized by three steady solutions and three limit cycles, which evidently poses a challenge to automated modelling.Before modelling, a comprehensive understanding of the underlying mechanisms is pursued, including linear stability analysis of steady solutions, Floquet analysis of periodic solutions, and nonlinear analysis of asymptotic dynamics. These analyses, together with the Galerkin method, are the starting point of our mean-field modelling strategy. A five-dimensional least-order mean-field model is proposed, resolving the six invariant sets induced by the first two successive bifurcations. In addition, we derive an aerodynamic force model associated with the mean-field Galerkin model. Sparse calibration is applied to balance the accuracy and complexity of the model. These efforts culminate in a sparse human interpretable model for the flow dynamics and a predictive model for the unsteady forces. The mean-field models proposed above provide a challenging benchmark example for automatable ROM, combining data-driven modelling with physical constraints for a better understanding of complex flow dynamics.For quasi-periodic and chaotic regimes, we propose a hierarchical cluster-based network modelling (HiCNM), adapting to more complex dynamics with multi-scale, multi-frequency, multi-attractor behaviours. The only assumption about the model structure is the mean-field assumption. The HiCNM enables identifying the transient and post-transient dynamics between multiple invariant sets in a self-supervised manner and steps towards automated ROM of complex dynamics. (10.70675/45410851z474dz498czb443z27be66015e4a)
  DOI : 10.70675/45410851z474dz498czb443z27be66015e4a
• Coinciding local bifurcations in the Navier-Stokes equations
  
  • Deng Nan
  • Pastur Luc
  • Tuckerman Laurette
  • Noack Bernd
  EPL - Europhysics Letters, European Physical Society / EDP Sciences / Società Italiana di Fisica / IOP Publishing, 2021, 135 (2), pp.24002. Generically, a local bifurcation only affects a single solution branch. However, branches that are quite different may nonetheless share certain eigenvectors and eigenvalues, leading to coincident bifurcations. For the fluidic pinball, two supercritical pitchfork bifurcations, of the equilibrium and the periodic solutions, occur at nearly the same Reynolds number. The mechanism of this kind of non-generic coincidence is modelled and explained. (10.1209/0295-5075/ac182a)
  DOI : 10.1209/0295-5075/ac182a
• Reduced-order models for geometrically nonlinear vibrations of thin structures
  
  • Shen Yichang
  , 2021. When vibrating with large amplitudes, thin structures experience geometric nonlinearity due to the nonlinear relationship between strains and displacements. Because full-order nonlinear analysis on geometrically nonlinear models are computationally very expensive, the derivation of efficient reduced-order models (ROMs) has always been a topic of interest.In this thesis, nonlinear reduction methods for building ROMs with geometric nonlinearity in the framework of the Finite Element (FE) procedure, are investigated. Three non-intrusive nonlinear reduction methods are specifically investigated and systematically compared. They are: implicit condensation and expansion (ICE), modal derivatives (MD), and the reduction to invariant manifold. Theoretical analysis shows that the first two methods can give reliable results only if a slow/fast assumption between slave and master coordinates holds. On the other hand, reduction to invariant manifolds allows proposing a simulation-free reduction method that can be applied without restricting assumptions on the frequencies of the slave modes.Numerical comparisons and numerous applications to continuous structures discretized with the FE procedure, are given subsequently. For application of the invariant manifold-based method, the computation is based on a direct application of the normal form to the physical space and hence to the nodes of the FE mesh, a method recently developed. The examples show the advantages and drawbacks of each reduction method when deriving ROM, and the results of the theoretical comparison are validated.Finally, the analysis of the dynamics of a system with 1:2 internal resonance and cubic nonlinearity is given in the last part of the thesis. The real normal form of the problem is first derived. Then the solution branches of the problem are investigated and compared to simpler solutions with the dynamics truncated at order two. The divergent behaviour of the hardening/softening characteristics for single-mode reduction is investigated with this more complete model. (10.70675/f6a2e953z8f74z47b7za716zee01303e79b8)
  DOI : 10.70675/f6a2e953z8f74z47b7za716zee01303e79b8
• Existence and Nonexistence of Nontrivial Doubly Periodic Solutions of Nonlinear Telegraph Equations
  
  • Deng Nan
  Asian Research Journal of Mathematics, SCIENCEDOMAIN international, 2021, 17 (6), pp.70-80. Aims/ Objectives: We discuss the existence and nonexistence of nontrivial nonnegative doubly periodic solutions for nonlinear telegraph equations utt-uxx+cut+a(t,x)u=λf (t,x,u) , where c > 0 is a constant, λ > 0 is a positive parameter, a ∈ C(R2,R+), f ∈ C(R2 × R+,R+), and a, f are 2π-periodic in t and x. The proof is based on a known xed point theorem due to Schauder. In previous articles, a single telegraph equation or telegraph system have been widely studied, but there is relatively little research on nonlinear telegraph equations with a parameter and the nonlinearities are nonnegative. We would like do some research on this topic. We give new conclusions on the existence and nonexistence of nontrivial nonnegative doubly periodic solutions for nonlinear telegraph equations under sublinear assumptions. Study Design: Study on the existence and nonexistence of nontrivial nonnegative doubly periodic solutions. Place and Duration of Study: School of Applied Science, Beijing Information Science & Technology University, September 2020 to present.Methodology: We prove the existence and nonexistence of nontrivial nonnegative doubly periodic solutions by the results of Schauder's xed point theorem. Results: We give new conclusions of existence and nonexistence of nontrivial nonnegative doubly periodic solutions for the equations. Conclusion: We prove the existence and nonexistence of nontrivial nonnegative doubly periodic solutions for nonlinear telegraph equations utt − uxx + cut + a(t, x)u = λf (t, x, u), and give new conclusions. (10.9734/arjom/2021/v17i630311)
  DOI : 10.9734/arjom/2021/v17i630311
• The relation between martensitic phase transformation and martensite reorientation in single crystal Ni-Mn-Ga magneticshape memory alloy
  
  • Qin Guoshun
  , 2021. Ferromagnetic shape memory alloy (FSMA) is a promising candidate for actuators because of its high-frequency Magnetic-Field-Induced-Strain (MFIS) property. Compared to other types of FSMAs, Ni2MnGa single crystal is the most popular one because of its much lower twinning stress (σtw < 2 MPa). Ni2MnGa single crystal has two important microstructure processes: martensite reorientation and phase transformation, which give it various potential engineering applications. In literature, the martensite reorientation and phase transformation were usually studied separately. Their interaction (coupling) has not yet been systematically studied. In this thesis, I demonstrate in two typical situations (magnetic-field-induced martensite reorientation and stress-free temperature-induced phase transformation) that both martensite reorientation and phase transformation can take place simultaneously, leading to some special performances.The first set of the systematic experiments investigates the thermal effect on the magnetic-field-induced strain oscillation of Ni2MnGa single crystal by stepwise gradually changing thermal boundary condition (from still ambient air to strong airflow). The results show that the extremely weak or extremely strong ambient heat transfer can only have small strain oscillation amplitude while the maximum strain amplitude can be achieved only at a mild heat transfer condition (i.e., non-monotonic dependence of the strain amplitude on the ambient heat.) Particularly at weak ambient heat transfer, the energy dissipation of the high-frequency martensite reorientation can trigger the temperature increase of the specimen, leading to the phase transformation to austenite phase, which can in turn modulate the strain oscillation amplitude by the phase-fraction adjustment of the martensitic phase transformation.The second set of the systematic experiments investigates the martensitic phase transformation of the Ni2MnGa single crystal bars of different geometric sizes under different heating-cooling cycles without stress or magnetic-field. The experimental results show that the cooling-induced austenite  martensite phase transformation in Ni2MnGa single crystal slim bar takes place via two steps: (1) austenite  martensite twin(s); (2) detwinning into single martensite variant (the major martensite variant in the twin frows at the expense of the minor martensite variant; i.e., the reorientation from the minor martensite variant to the major martensite variant takes place). This new phenomenon demonstrates that the martensite reorientation indeed occurred during the cooling-induced phase transformation without any directional driving force (without stress or magnetic field), which can have a large global shape change. It breaks the usual idea about the self-accommodation martensite formation in the one-way shape memory effect. This finding promotes the SMA applications such as the stress-free two-way shape memory effect. But the accurate prediction/control on the performance is still a challenging task, demanding further experimental and theoretical research. (10.70675/f482455czbc52z47fbza2caze10b51bbf426)
  DOI : 10.70675/f482455czbc52z47fbza2caze10b51bbf426
• Mixing nanostructured Ni/piezoPVDF composite thin films with e-beam irradiation: A beneficial synergy to piezoelectric response
  
  • Potrzebowska Natalia
  • Cavani Olivier
  • Oral Ozlem
  • Doaré Olivier
  • Melilli Giuseppe
  • Wegrowe Jean-Eric
  • Clochard Marie-Claude.
  Materials Today Communications, Elsevier, 2021, 28, pp.102528. (10.1016/j.mtcomm.2021.102528)
  DOI : 10.1016/j.mtcomm.2021.102528
• Numerical modeling of liquid sloshing in flexible tank with FSI approach
  
  • Khouf Lydia
  • Benaouicha Mustapha
  • Seghir Abdelghani
  • Guillou Sylvain S
  World Journal of Engineering, Emerald Publishing Limited, 2021, 20 (1), pp.131-142. Purpose The paper aims to present a numerical modeling procedure for the analysis of liquid sloshing in a flexible tank subjected to an external excitation, with taking into account the effects of fluid–structure interaction (FSI). Design/methodology/approach A numerical model based on coupling a two-phase flow solver and an elastic solid solver is developed in OpenFOAM code. The Arbitrary Lagrangian–Eulerian formulation is adopted for the two-phase Navier–Stokes equations in a moving domain. The volume of fluid (VOF) method is applied for the air–liquid interface tracking. The finite volume method is used for the spatial discretization of both the fluid and the structure dynamics equations. The FSI coupling problem is solved by an explicit coupling scheme. The model is validated for linear and nonlinear sloshing cases. Then, it is used to analyze the effects of the liquid sloshing on the dynamic response of the tank and the effects of the tank flexibility on the liquid sloshing. Findings The obtained results show that the flexibility of the tank walls amplifies the amplitude of the sloshing and increases the fluctuation period of the air–liquid interface. Furthermore, it is found that the bending moment acting on the tank walls may be underestimated when rigid walls assumption is adopted as usually done in sloshing tank modeling. Also, tank walls flexibility causes a phase shift in the free surface dynamic response. Originality/value A review of previous studies on liquid sloshing in flexible tanks revealed that FSI effects have not been clearly and comprehensively analyzed for large-amplitude liquid sloshing. Many physical and numerical aspects of this problem still require clarifications and enhancements. The added value of the present work and its originality lie in the investigation of large-amplitude liquid sloshing in flexible tanks by using a staggered coupling approach. This approach is carried out by an original combination of a linear solid solver with a two phase fluid solver in OpenFOAM code. In addition, FSI effects on some response quantities, identified and analyzed herein, have not been found in the previous works. (10.1108/WJE-03-2021-0125)
  DOI : 10.1108/WJE-03-2021-0125
• Numerical modeling of liquid sloshing in flexible tank with FSI approach
  
  • Khouf Lydia
  • Benaouicha Mustapha
  • Seghir Abdelghani
  • Guillou Sylvain S.
  World Journal of Engineering, Emerald Publishing Limited, 2021, 20 (1), pp.131-142. Purpose The paper aims to present a numerical modeling procedure for the analysis of liquid sloshing in a flexible tank subjected to an external excitation, with taking into account the effects of fluid–structure interaction (FSI). Design/methodology/approach A numerical model based on coupling a two-phase flow solver and an elastic solid solver is developed in OpenFOAM code. The Arbitrary Lagrangian–Eulerian formulation is adopted for the two-phase Navier–Stokes equations in a moving domain. The volume of fluid (VOF) method is applied for the air–liquid interface tracking. The finite volume method is used for the spatial discretization of both the fluid and the structure dynamics equations. The FSI coupling problem is solved by an explicit coupling scheme. The model is validated for linear and nonlinear sloshing cases. Then, it is used to analyze the effects of the liquid sloshing on the dynamic response of the tank and the effects of the tank flexibility on the liquid sloshing. Findings The obtained results show that the flexibility of the tank walls amplifies the amplitude of the sloshing and increases the fluctuation period of the air–liquid interface. Furthermore, it is found that the bending moment acting on the tank walls may be underestimated when rigid walls assumption is adopted as usually done in sloshing tank modeling. Also, tank walls flexibility causes a phase shift in the free surface dynamic response. Originality/value A review of previous studies on liquid sloshing in flexible tanks revealed that FSI effects have not been clearly and comprehensively analyzed for large-amplitude liquid sloshing. Many physical and numerical aspects of this problem still require clarifications and enhancements. The added value of the present work and its originality lie in the investigation of large-amplitude liquid sloshing in flexible tanks by using a staggered coupling approach. This approach is carried out by an original combination of a linear solid solver with a two phase fluid solver in OpenFOAM code. In addition, FSI effects on some response quantities, identified and analyzed herein, have not been found in the previous works. (10.1108/WJE-03-2021-0125)
  DOI : 10.1108/WJE-03-2021-0125
• Time domain modelling of a Helmholtz resonator analogue for water waves
  
  • Euvé Leo-Paul
  • Pham Kim
  • Petitjeans Philippe
  • Pagneux Vincent
  • Maurel Agnès
  Journal of Fluid Mechanics, Cambridge University Press (CUP), 2021, 920. In the context of water waves, we consider a resonator with deep subwavelength resonance, analogue to the Helmholtz resonator in acoustics. In the shallow water regime, using asymptotic analysis, a one-dimensional model is derived in which the effect of the resonator is reduced to effective transmission conditions. These conditions clearly highlight two contributions. The first is associated with the dock on its own and it is responsible for a jump of the potential at the free surface. The second is due to the resonant cavity and it is responsible for a jump in the horizontal velocity. It involves as well the uniform amplitude within the resonant cavity with a transient dynamics explicitly given by the equation of a damped oscillator forced by the incident waves. The one-dimensional model is validated in the harmonic regime by comparison to direct two-dimensional numerics. It is shown to reproduce accurately the scattering coefficients and the amplitude within the resonator; interestingly, this remains broadly true for finite water depths. We further inspect the spatio-temporal behaviour of different types of wave packets interacting with the resonating and radiating cavity. (10.1017/jfm.2021.450)
  DOI : 10.1017/jfm.2021.450
• Experimental characterization of the noise generated by an airfoil oscillating above stall
  
  • Raus David
  • Sicard Lisa
  • Cotté Benjamin
  • Monchaux Romain
  • Jondeau Emmanuel
  • Souchotte Pascal
  • Roger Michel
  , 2021. The present work investigates the noise emitted by an airfoil oscillating above stall, thanks to synchronized surface pressure and far-field acoustic measurements in an anechoic open-jet wind tunnel. Both NACA0012 and a NACA633418 airfoils are tested in order to investigate the effects of the airfoil shape on the static and dynamic stall noise. For static configurations, a smoother transition to stall noise is obtained for the cambered NACA633418 airfoil, with a gradual increase and shift of the noise spectra at low frequencies as the separation point moves closer to the leading edge of the airfoil. Phase-averaged time-frequency analysis of the oscillating airfoil noise reveals that the light-stall noise and deep-stall noise regimes commonly observed for static airfoils also take place during the oscillations. Increasing the frequency of the oscillations leads to an increase of the duration and amplitude of the stall onset broadband noise, and a delay of the dynamic stall noise to greater angles of attack. In the same way, the dynamic stall noise is delayed for the NACA633418 compared to the NACA0012, causing the stalled phase to be shorter for the NACA633418. For the NACA0012, the noise does not depend on the angle of attack before the onset on stall. For the NACA633418, the noise gradually increases in the pre-stall regime and the stall noise is preceded by a high amplitude separation noise. (10.2514/6.2021-2291)
  DOI : 10.2514/6.2021-2291
• Galerkin force model for transient and post-transient dynamics of the fluidic pinball
  
  • Deng Nan
  • Noack Bernd
  • Morzyński Marek
  • Pastur Luc
  Journal of Fluid Mechanics, Cambridge University Press (CUP), 2021, 918, pp.A4. We propose an aerodynamic force model associated with a Galerkin model for the unforced fluidic pinball, the two-dimensional flow around three equal cylinders with one radius distance to each other. The starting point is a Galerkin model of a bluff-body flow. The force on this body is derived as a constant-linear-quadratic function of the mode amplitudes from first principles following the pioneering work of Noca (On the evaluation of time-dependent fluid-dynamic forces on bluff bodies. PhD thesis, California Institute of Technology, 1997), Noca et al. (J. Fluids Struct., vol. 13, issue 5, 1999, pp. 551–578) and Liang & Dong (Virtual force measurement of POD modes for a flat plate in low Reynolds number flows. AIAA Paper 2014-0054). The force model is simplified for the mean-field model of the unforced fluidic pinball (Deng et al., J. Fluid Mech., vol. 884, 2020, p. A37) using symmetry properties and sparse calibration. The model is successfully applied to transient and post-transient dynamics in different Reynolds number regimes: the periodic vortex shedding after the Hopf bifurcation and the asymmetric vortex shedding after the pitchfork bifurcation comprising six different Navier–Stokes solutions. We foresee many applications of the Galerkin force model for other bluff bodies and flow control. (10.1017/jfm.2021.299)
  DOI : 10.1017/jfm.2021.299
• Direct measurement of steady fluid forces upon a deformed cylinder in confined axial flow
  
  • Joly Aurélien
  • de Buretel de Chassey Nicolas
  • Martin Alexandre
  • Cadot Olivier
  • Pastur Luc
  • Moussou Pierre
  Journal of Fluids and Structures, Elsevier, 2021, 104, pp.103326. This paper addresses the case of a cylinder array in axial flow at Reynolds numbers from 60 000 to 110 000. A comprehensive experimental and numerical study of the steady fluid forces arising from a geometrical perturbation in the array arrangement is carried out and compared with a semi-empirical model from the literature. The test rig consists of a 3x3 confined cylinder bundle with a pitch-to-diameter ratio equal to 1.33. The central cylinder can be rotated, translated or bent. Global forces and moments as well as pressure profiles at several sections are measured. Velocity profiles at both sides of the cylinder are also collected. Additionally, RANS simulations (Reynolds-averaged Navier–Stokes) are carried out. Pressure loss effects similar to the ones occurring in hydraulic pipes are found to play a major role on the velocity field. Rotation tests are in agreement with the literature: at low angles of incidence, the lift force is proportional to the angle. The supporting rod at the centre of the cylinder strongly disturbs the local lift force but does not change the global linear trend. In translation, the wake of the support generates a fluid stiffness effect. Bending tests allow to assess all terms of the semi-empirical model from the literature, which proves to be quite accurate at a sufficient distance from the ends and from the supports. In addition, the investigation provides refined quantitative measurements of local and global force coefficients of the statically deformed cylinder in rotation, translation and bending. (10.1016/j.jfluidstructs.2021.103326)
  DOI : 10.1016/j.jfluidstructs.2021.103326
• Liquefaction triggering in silty sands: effects of non-plastic fines and mixture-packing conditions
  
  • Gobbi Stefania
  • Reiffsteck Philippe
  • Lenti Luca
  • D’avila Maria Paola Santisi
  • Semblat Jean-François
  Acta Geotechnica, Springer Verlag, 2021, 17 (2), pp.391-410. During recent seismic events, such as 2010 Darfield and 2016 Ecuador earthquakes, widespread liquefaction has been observed in sand deposits with silt content. Nevertheless, the presence of non-plastic fines implies variable liquefaction resistance of sands. The goal of this research is the assessment of the influence of non-plastic fines and mixture-packing conditions on liquefaction triggering. A series of monotonic and cyclic consolidated undrained triaxial as well as resonant column tests is carried out on reconstituted soil specimens. The behavior of loose, medium and dense silty-sands is analyzed, using different fine contents and confining pressures. The results show that the behavior of mixtures strongly depends on the packing configuration of coarse and fine particles. The experimental results are analyzed in terms of equivalent intergranular void ratio, which is identified in the literature as an adequate state parameter to characterize the global effect of fine particles. The estimation of the equivalent intergranular void ratio requires the determination of the active fine fraction participating in the force transfer. An original formula is proposed for the parameter based on packing configuration. The validation of the proposed formula is undertaken through comparisons with the present experimental results but also with results reported in the literature. The proposed expression to estimate the active fine fraction allows a satisfactory prediction of liquefaction triggering in sand-fines mixtures independently from the fine content. (10.1007/s11440-021-01262-1)
  DOI : 10.1007/s11440-021-01262-1
• Model-based adaptive filtering of dielectric elastomer loudspeakers
  
  • Garnell Emil
  • Doaré Olivier
  • Rouby Corinne
  Journal of the Audio Engineering Society, Audio Engineering Society, 2021, 69 (6), pp.389-397. Dielectric elastomers are soft actuators that can reach deformations by more than 500% when a high voltage is applied. They have been considered for use as loudspeakers because of their quick response. One of their limitations is an inhomogeneous frequency response, due to the modal behavior of the membrane. In this study, we set up a sensor-free adaptive filtering strategy that relies on a finite element model of the loudspeaker, to improve the frequency response. (10.17743/jaes.2021.0010)
  DOI : 10.17743/jaes.2021.0010