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The paper describes a model to calculate the transmission loss of both curved laminate and sandwich composite panels within statistical energy analysis (SEA) context. The vibro-acoustic problem is developed following a wave approach based on a discrete lamina description. Each lamina is considered to consist of membrane, bending, transverse shearing and rotational inertia behaviors. Moreover, the orthotropic ply angle of each lamina is considered. Using such a discrete lamina description, the dispersion behaviors of the panel are correctly represented. Using the dispersion curves, the radiation efficiency, the modal density, as well as, the nonresonant and the resonant transmission are computed. Moreover, expression for the evaluation of the ring frequency and the critical frequencies of such panels is given. The described model is shown to handle accurately, both laminate and sandwich composite shells. Additionally, a transmission loss test is presented to confirm the validity of the presented model.

Porous materials are widely used for improving sound absorption and sound transmission loss of vibrating structures. However, their efficiency is limited to medium and high frequencies of sound. A solution for improving their low frequency behavior while keeping an acceptable thickness is to embed resonant structures such as Helmholtz resonators (HRs). This work investigates the absorption and transmission acoustic performances of a cellular porous material with a two-dimensional periodic arrangement of HR inclusions. A low frequency model of a resonant periodic unit cell based on the parallel transfer matrix method is presented. The model is validated by comparison with impedance tube measurements and simulations based on both the finite element method and a homogenization based model. At the HR resonance frequency (i) the transmission loss is greatly improved and (ii) the sound absorption of the foam can be either decreased or improved depending on the HR tuning frequency and on the thickness and properties of the host foam. Finally, the diffuse field sound absorption and diffuse field sound transmission loss performance of a 2.6 m 2 resonant cellular material are measured. It is shown that the improvements observed at the Helmholtz resonant frequency on a single cell are confirmed at a larger scale.

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The principal aim of this work is to present a model for the transmission loss of sandwich composite cylindrical shells. The effects of membrane, bending, and transverse shearing as well as rotational inertia are considered in all of the layers composing the structure. The elastic constants of any layer are related to the orthotropic angle-ply defined as the angle of the principal directions of the layers material to the global axis of the shell. Fundamental relations are expressed using the dynamic equilibrium relations of the unit forces in the structure. The structural impedance, critical frequencies and ring frequency are computed numerically in the general case of symmetrical laminated composite shell. Their expressions are developed in a wave approach context. A general eigenvalue approach to compute the dispersion curves of such structures is presented. Using these curves, the radiation efficiency, the modal density, the group velocity an the resonant and nonresonant transmission loss are computed and used within SEA framework to predict the sound transmission loss of these structures. Comparisons with existing models and experimental data are also discussed.