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International audience; In this work, we establish a link between recent investigations on bending-to-shear conversion phenomena in sandwich structures, and the existence of a local group velocity plateau in the near-cut-on bandwidth of high-order guided resonances. The resulting non-dispersiveness allows the actuation and propagation of these elastic waves over a long range, which is unusual for such structures in the low acoustic bandwidth. The experimental setup involves an array of piezoelectric patches, designed to produce a custom wave shape displacement field as predicted by Floquet-Bloch theory.

International audience; The present work shows many aspects concerning the use of a numerical wave-based methodology for the computation of the structural response of periodic structures, focusing on cylinders. Taking into account the periodicity of the system, the Bloch-Floquet theorem can be applied leading to an eigenvalue problem, whose solutions are the waves propagation constants and wavemodes of the periodic structure. Two different approaches are presented, instead, for computing the forced response of stiffened structures. The first one, dealing with a Wave Finite Element (WFE) methodology, proved to drastically reduce the problem size in terms of degrees of freedom, with respect to more mature techniques such as the classic FEM. The other approach presented enables the use of the previous technique even when the whole structure can not be considered as periodic. This is the case when two waveguides are connected through one or more joints and/or different waveguides are connected each other. Any approach presented can deal with deterministic excitations and responses in any point. The results show a good agreement with FEM full models. The drastic reduction of DoF (degrees of freedom) is evident, even more when the number of repetitive substructures is high and the substructures itself is modelled in order to get the lowest number of DoF at the boundaries.

International audience; To predict the wave characteristics of the periodic media in the presence of fuzzy uncertainties, the wave finite element method in conjunction with fuzzy logic and algebra has been applied. For one-dimensional wave propagation, firstly, the most significant input parameters such as Young's modulus and mass density are identified and then fuzzified using the membership functions. Then, the fuzzy variable is propagated through the numerical model of interval analysis. The dispersion curves for flexural and longitudinal waves with fuzzy parameters have been used to illustrate the generality of the proposed approach also looking at the possibility to have frequency region in which those waves cannot propagate (frequency band gaps). The triangular membership functions have been used in the numerical examples and the obtained results are compared against the classical Monte Carlo simulations (MCS). The approach was presented for very simplified test-cases but it is found to be more efficient when compared with the conventional MCS approach in terms of computational cost.

International audience; In the last decades, the main issue concerning structures is related to weight constraint. Many solutions are available as composites or sandwich panels. Nevertheless, it seems that metamaterials such periodic structures focus a specific attention nowadays. In this field, honeycomb structures remain wide used solutions especially in the aerospace industry, but they exhibit a high stiffness-to-weight ratio leading to poor acoustic properties. Consequently, some new designs are created to obtain better acoustic indicators. In this context, this paper proposes to study a new kind of periodic structures using multi-layer core topology systems consisting on stacking layers made of different geometry of cores (auxetic, hexagonal, rectangular…). Several new parameters should be considered to fully understand the dynamic and acoustic behaviour. In this paper we will limit the study to rectangular core combined with a random core located in between. Consequently, we will stack 3 kind of cores: Rect-Random-Rect. The main objective of this study is to analyse the results of the parametric survey. All configurations are constraint to have the same surface density. The chosen acoustic indicator is the Sound Transmission Loss (STL). The transition frequency will be also investigated as well as the compression and shear modulus and the bending waves. Modelling these structures is possible using either Wave Finite Element Method (WFEM) only or combining WFEM and the Transfer Matrix Method (TMM). We assume an infinite panel, real wavenumbers and that the structure is excited by plane waves with the angles of incidence and reflection equal. The model is implemented using MATLAB and ANSYS apdl. Because such structures are made using a 3D printer, the ABS is used as the material for the study. From the parametric study, it turned out that multi-layer core systems correspond to relevant solutions to highly improve the STL. Moreover, it is possible to find out an optimized design giving the best STL. However, as it will be shown, it goes along with less efficiency in terms of mechanical properties and thus should be relevant for some specific applications.

This paper investigates the broadband vibro-acoustic and dynamic behavior of different structures, such as flat and curved panels and cylindrical shells. The aim of this work is to investigate propagation and dispersion features through the analysis of the wavenumber domain. The technique used to investigate the vibro-acoustic behavior is a wave propagation based technique, implemented to obtain the propagative and evanescent waves using a harmonic force excitation. The employed techniques are used to obtain the harmonic displacement field, given as primary input for the wavenumber domain analysis. To deeply investigate the dispersion features, a Discrete Fast Fourier Transform (DFFT) technique is used. The whole displacement field could be obtained by experimental tests or by numerical simulations; in our case, it is calculated using a classical Finite Element Analysis (FEA), by a commercial Finite Element package, or by an in-home algorithm, developed in a commercial numerical computing software. no ISSN ispartof: pages:4627-4636 ispartof: Proceedings of the International Conference on Noise and Vibration Engineering (ISMA) / International Conference on Uncertainty in Structural Dynamics (USD) pages:4627-4636 ispartof: International Conference on Noise and Vibration Engineering (ISMA 2018) location:Leuven, Belgium date:17 Sep - 19 Sep 2018 status: Published online

International audience; In this paper, we focus on multi-layer core topology systems which consists in piling up layers made by different kind of cores and offers innovative solutions to periodic structures design. The main objective of this study is to analyze the phenomena occurring in these multilayer core topologies, and then compare the numerical models with experimental measurements while the effects of the phase shift on the STL will be investigated. The model is implemented using MATLAB and ANSYS apdl. The mass of the unit cell is taken as constraints to eliminate its influence on the STL and the compression modulus is calculated to verify the mechanical properties. To perform the experimental measurements, the samples are designed with CATIA and then made by an industrial 3D printer using the fused deposed model technic. An impedance tube is used to measure the STL and compare with the vibroacoustic phenomena.

International audience; A better knowledge of the structural response of periodic structures can be achieved through the classification of possible uncertainty, to be included in the predictive models. Nowadays, the wave finite element approach is used for the simulation of periodic structures to reduce the computational cost. On the contrary, it introduces a higher complexity in the model formulation. Recently, the spectral approach has shown its relevance in the uncertainty analysis of structures. This paper presents the literature on uncertainty effect on vibroacoustic of periodic media. The present work is an initial literature study on available analytical and numerical approaches for capturing the parametric and non-parametric uncertainties.

The main aim of the present paper is to describe the issues and aspects related to the flow induced noise and vibrations, as well as the original features and the expected results of the ongoing research, mainly focused to a specific use of periodic structures for vibro-acoustic purposes. A literature review both on the flow excitation and on the induced response is reported. Some Early-stage research steps are then expressed to give a complete overview of the project.