01054320

Component

This paper describes how an anisotropic poro-elastic core, plane wave sound transmission model was used to show that the barrier performance of a Nomex-cored honeycomb panel was worse than that of a single homogeneous panel that has the same mass unit area. Therefore, one of the objectives of this paper was to understand the reasons that the sound transmission performance of the particular sandwich panel considered here was relatively poor. In this paper, characteristic dispersion equations were extracted from the sound transmission model by eliminating the contributions of the incident, reflected and transmitted plane waves in order to solve for the propagation characteristics of the freely propagating wave in the sandwich system. Then, the complex wave numbers were found by identifying the conditions under which the coefficient matrix was non-trivial: i.e., when the determinant of the coefficient matrix approached zero. However, it was also necessary to select the physically meaningful roots from amongst the numerous apparent solutions, most of which were spurious in the sense that they did not satisfy the boundary conditions of the problem. To perform that selection, the mode vectors associated with all of the apparent solutions were calculated and were then substituted into the coefficient matrix equation along with the wave number solutions to find the solutions that satisfied the boundary conditions. In order to clarify the wave type associated with each acceptable solution, a decomposition method was used to separate the characteristic equation for the poro-elastic core sandwich panel model into symmetric and antisymmetric components. In order to identify the nature of each of the poro-elastic wave components, an anisotropic elastic-cored sandwich model was also formulated, and its results were compared to those obtained from the poro-elastic sandwich model. Also, by extracting the Rayleigh-Lamb frequency equation5 (the characteristic dispersion equation for a plate with free surfaces) from the anisotropic solid core equation, the numerical approach to finding the free wave characteristics was validated. Then, the complex wave number trajectories were visualized as a function of frequency to illustrate the free wave behavior of the sandwich panels. By performing a parameter study focused on several key factors identified in previous work, practical guidelines for improving the sound barrier performance of the Nomex-cored sandwich panel were identified.

01054353

English

pp 651-662

2004

Noise-Con 04. The 2004 National Conference on Noise Control Engineering

CD-ROM

Figures; Photos; References (7) ; Tables (1)

Core samples; Elasticity (Mechanics); Panels; Sandwich construction; Sound; Sound absorption; Sound barrier; Sound transmission

Poroelasticity; Wave propagation tests

Energy; Environment; Highways; I15: Environment

TRIS, TRB

Jul 25 2007 3:56PM