Volume 117, Issue 3, March 2005
Index of content:
- GENERAL LINEAR ACOUSTICS 
An efficient method for evaluating diffuse field joint acceptance functions for cylindrical and truncated conical geometries117(2005); http://dx.doi.org/10.1121/1.1850368View Description Hide Description
The evaluation of the response of elastic structures subjected to distributed random excitations is usually performed in the modal space. Random excitations (like acoustic diffuse fields) are usually modeled as weakly stationary random processes and are assumed to be homogeneous. Their characterization basically relies on the power spectral density (PSD) function of the pressure at a particular reference position and a suitable spatialcorrelation function. In the modal space, the distributed random excitation is characterized by a modal PSD matrix made from the joint acceptance functions related to the mode pairs. The joint acceptance function is a double surface integral involving the product of the considered mode shapes and the spatialcorrelation function. The paper shows how to evaluate efficiently this quadruple integral for cylindrical and truncated conical structures excited by an acoustic diffuse field. Basically, the procedure relies on the derivation of alternative expressions for the spatialcorrelation function. The related expressions prove to be more convenient for these geometries and are leading to a reduction of the double surface integral to a combination of simple integrals. A very substantial breakdown of the computational cost can be achieved using the resulting expressions.
Radiative transfer theory for high-frequency power flows in fluid-saturated, poro-visco-elastic media117(2005); http://dx.doi.org/10.1121/1.1856271View Description Hide Description
Some recent mathematical results are used to study the propagation features of the high-frequency vibrational energy density in three-dimensional fluid-saturated, isotropic poro-visco-elastic media. The theory of high-frequency asymptotics of the solutions of hyperbolic partial differential equations shows that their energy satisfies Liouville-type transport or radiative transferequations for randomly heterogeneous materials. For long propagation times these equations can be approached by diffusionequations. The corresponding diffusion parameters—mean-free paths and diffusion constants—associated with Biot’s linear model for such media, are derived. The analysis accounts for the thermal and viscous memory effects of the fluid phase, and the viscous memory effect of the solid phase through time convolution operators. In this respect it also extends the existing mathematical results.