G.A.U.S., Mech. Eng. Dept., Univ. de Sherbrooke, Sherbrooke, PQ J1K 2R1, Canada
Actually, the structures used in many industrial areas are of particular type: they generally consist of an assemblage of different materials (multilayer structures) and they exhibit anisotropic properties. Real structures are of finite size and their properties are influenced by boundary conditions. The studies on the sound transmission through structures have been limited to the case of simply supported boundary conditions or clamped ones. The present work is intended to extend these different aspects. A new general model is developed for the characterization of multilayer systems consisting of orthotropic plates with general boundary conditions. This modeling concerns the transmission properties of oblique incident acoustic waves or diffuse field. The aim of the study is the development of tools allowing (1) the understanding of the different mechanisms involved in the transmission process, (2) studies on the influence of different parameters such as boundary conditions, the effect of structures size, and orthotropic properties. This model will allow the simulation of real conditions. A variational approach is used with a Ritz basis for the expansion of the flexural displacement of the structure. The different vibroacoustic parameters are determined from the coefficients in the basis. The transmission coefficient requires the calculation of either the radiation impedances, or the radiated power in the far field. An important discussion will be presented concerning this question. Among the areas applications of this model, one can mention aeronautics involved by structures of composite type, architectural acoustics, shipbuilding, etc.