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

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

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

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

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

Treating clinical mastitis in dairy cows with essential oils

Clinical mastitis is the main concern in dairy farming today, but there are very few drugs that are compatible with organic specifications. Our study was conducted in order to evaluate the therapeutic efficiency of the intramammary infusion of three essential oils, Thymus vulgaris, Rosmarinus verbenone and Laurus nobilis. Fifty-five cases of mastitis were treated with 10 ml of a mixture of the three oils (1.5% each in sunflower oil). Forty-five others were treated with 10 ml of a mixture of Thymus vulgaris and Rosmarinus verbenone (6% of each in sunflower oil or in water). The recovery rate was only 40%, which is deemed unsatisfactory

Computing the broadband vibroacoustic response of arbitrarily thick layered panels by a wave finite element approach

A robust procedure for the prediction of the dynamic response of layered panels within a SEA wave-context approach is proposed hereby. The dispersion characteristics of two dimensional composite orthotropic structures are predicted using a Wave Finite Element method. By manipulating the mass and stiffness matrices of the modelled structural segment a polynomial eigenvalue problem is formed, the solutions of which correspond to the propagation constants of the waves travelling within the structure. The wavenumbers and group velocities for waves comprising out of plane structural displacements can then be calculated. Using the numerically extracted wave propagation data the most important SEA quantities of the structure, namely the modal density and the radiation efficiency of each wave type are calculated. The vibroacoustic response of the structure under a broadband diffused excitation is then computed within a SEA approach. The impact of the symmetric and the antisymmetric vibrational motion of the panel on its sound transmission loss is exhibited and the approach proves robust enough for thin as well as for thick layered structures