On the low frequency acoustic properties of novel multifunctional honeycomb sandwich panels with micro-perforated faceplates

This paper explores further possibilities of structurally-efficient honeycomb sandwich panels by replacing one of the faceplates with the perforated faceplate from the viewpoint of sound absorption coefficient (SAC) as well as sound transmission loss (STL). An analytical model is presented to calculate both the STL and SAC, with the displacements of the two faceplates assumed identical at frequencies below the faceplate resonance frequency. Influences of core configuration are investigated by comparing different honeycomb core designs. Finite element (FE) models are subsequently developed to validate the proposed analytical model, with agreement achieved. Subsequently, parametric surveys, including the influences of perforation ratio, pore size and core configuration on STL and SAC, are conducted based on the analytical model. Unlike classical honeycomb sandwich panels which are poor sound absorbers, honeycomb sandwiches with perforated faceplates lead to high SAC at low frequencies, which in turn brings about increment in the low frequency STL. Moreover, sandwich panels with triangular cores are found to have the lowest peak frequency in the STL and SAC curves compared with the other kinds of sandwich panels having the same effective mass and perforations

Wireless sensor networks for active vibration control in automobile structures

International audienceWireless Sensor Network (WSN) are nowadays widely used in monitoring and tracking applications. This paper presents the feasibility of using Wireless Sensor Networks in active vibration control strategy. The active control method used is an active-structural acoustic control using piezoelectric sensors distributed on the car structure. This system aims at being merged in wireless sensor network whose head node collects data and process control law so as to command piezoelectric actuators wisely placed on the structure. We will study the feasibility of implementing WSN in active vibration control and introduce a complete design methodology to optimize hardware/software and control law synergy in mechatronic systems. A design space exploration will be conducted so as to identify the best Wireless Sensor Network platform and the resulting impact on control

Dispersion curves of infinite laminate panels through a modal analysis of finite cylinders

This work presents an approach for using a modal analysis on an equivalent finite cylindrical model, to predict the elastic waves in infinite, isotropic or composite, panels. In the description of the infinite paths, an analogy, between the classical topologies of a straight line and a circumference, is exploited and tested. Different aspects, concerning the wavemode duality and the discretization and the needed radii of curvature, are investigated to frame the problem and test the robustness of the methodology. The analysis presents a well conditioned problem and solution for any propagation wave angle by transforming the original problem into a simple modal analysis

Passive vibration control of tyres using embedded mechanical resonators

An investigation is carried out on structure-borne vibration and noise propagation of tyres’ models at low frequencies. The idea is to use embedded resonant meta-materials to damp the tyres’ vibrations and thus reduce the transferred energy to the main attached structures. A simplified tyre model is used, being the investigation of the effects of the embedded substructures the main target of the work; internal pressure and tyre rotation effects are neglected at this stage. Different configurations are tested targeting different natural modes of the tyre, while mechanical excitation is assumed on one section of the tyres. The results show how the proposed designs are a feasible solution for vibration control

Investigations about periodic design for broadband increased sound transmission loss of sandwich panels using 3D-printed models

International audienceTwo types of sandwich panels are designed by using the periodic structure theory. A double-wall panel with mechanical links and a sandwich panel with rectangular core are studied. An oriented optimization of the elastic bending waves' propagation versus the acoustic wavenumbers is achieved by using shifted core walls and by keeping the mass and stiffness of the system constant. Standard and optimized configurations are 3D-printed and sound transmission measurements are carried out by using a facility with an uncoupled reverberant-anechoic configuration. The experimental evidences of enlarged bending band-gaps and deformation mechanisms are proved using a reverse approach based on the acoustic radiation of the panels

The modelling of the flow-induced vibrations of periodic flat and axial-symmetric structures with a wave-based method

International audienceThe stochastic response of periodic flat and axial-symmetric structures, subjected to random and spatially-correlated loads, is here analysed through an approach based on the combination of a wave finite element and a transfer matrix method. Although giving a lower computational cost, the present approach keeps the same accuracy of classic finite element methods. When dealing with homogeneous structures, the accuracy is also extended to higher frequencies, without increasing the time of calculation. Depending on the complexity of the structure and the frequency range, the computational cost can be reduced more than two orders of magnitude. The presented methodology is validated both for simple and complex structural shapes, under deterministic and random loads

A WFE and Hybrid FE/WFE technique for the Forced Response of Stiffened Cylinders

International audienceThe 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

Simulating the sound transmission loss of complex curved panels with attached noise control materials using periodic cell wavemodes

International audienceThe sound transmission loss of complex curved aircraft panels under diffuse acoustic field excitation is experimentally and numerically studied. Two different aircraft sidewall panels are considered: a thick composite sandwich panel and a thin aluminium panel with stiffening elements (stringers and frames). Both bare configuration and with attached soundproofing material are tested in laboratory conditions in coupled rooms. The numerical approach relies on a wave finite element method including modal order reduction at cell scale and an extension based on the transfer matrix method, for the inclusion of poroelastic treatments. The results obtained show that the proposed numerical scheme is efficient for predicting the sound transmission loss of such complex structures

Small perforations in corrugated sandwich panel significantly enhance low frequency sound absorption and transmission loss

Numerical and experimental investigations are performed to evaluate the low frequency sound absorption coefficient (SAC) and sound transmission loss (STL) of corrugated sandwich panels with different perforation configurations, including perforations in one of the face plates, in the corrugated core, and in both the face plate and the corrugated core. Finite element (FE) models are constructed with considerations of acoustic-structure interactions and viscous and thermal energy dissipations inside the perforations. The validity of FE calculations is checked against experimental measurements with the tested samples provided by additive manufacturing. Compared with the classical corrugated sandwich without perforation, the corrugated sandwich with perforated pores in one of its face plate not only exhibits a higher SAC at low frequencies but also a better STL as a consequence of the enlarged SAC. The influences of perforation diameter and perforation ratio on the vibroacoustic performance of the sandwich are also explored. For a corrugated sandwich with uniform perforations, the acoustical resonance frequencies and bandwidth in its SAC and STL curves decrease with increasing pore diameter and decreasing perforation ratio. Non-uniform perforation diameters and perforation ratios result in larger bandwidth and lower acoustical resonance frequencies relative to the case of uniform perforations. The proposed perforated sandwich panels with corrugated cores are attractive ultralightweight structures for multifunctional applications such as simultaneous load-bearing, energy absorption, sound proofing and sound absorption

DECOUPLING OF ENERGY TRANSMISSION BETWEEN SUBSYSTEMS OF A COMPLEX STRUCTURE

Experimental vibroacoustic measurements are very common for the study of emitted noise reduction and vibration energy isolation of structures. The most important case is when structures are subjected to an aerodynamic excitation as Turbulent Boundary Layer (TBL). In this paper, a preliminary study is performed on the energy transmission between subsystems of a structure subjected to TBL. A numerical test is developed on a three-plates-in-row system at high frequencies, through the application of Statistical Energy Analysis (SEA). Parameters such as surface dimensions, thickness and damping loss factor are evaluated in different configurations for a first design of a testbench used for vibroacoustic measurements in a wind tunnel