Volume 123, Issue 3, March 2008
Index of content:
- ULTRASONICS, QUANTUM ACOUSTICS, AND PHYSICAL EFFECTS OF SOUND 
Efficient absorbing boundary conditions for Biot’s equations in time-harmonic finite element applications123(2008); http://dx.doi.org/10.1121/1.2832325View Description Hide Description
Absorbing boundary conditions for two phase media previously presented by Zerfa and Loret [Earthquake Eng. Struct. Dyn.33, 89–110 (Year: 2004)] have been improved by considering additionally absorbing waves with auxiliary angles of incidence. These angles are defined at each point on the boundaries, so one can easily implement tensor impedances as analogous to those defined by Krenk and Kirkegaard for isotropic, nonporous media [J. Sound Vib.247, 875–896 (Year: 2001)]. The boundary conditions have been tested and validated in two-dimensional frequency domain simulations.
123(2008); http://dx.doi.org/10.1121/1.2835437View Description Hide Description
An approximate analytical formula has been derived for the prediction of sound fields in a semi-infinite rigid-porous ground due to an airborne source. The method starts by expressing the sound fields in an integral form, which can subsequently be evaluated by the method of steepest descents. The concept of effective impedance has been introduced by using a physically plausible assumption. The integral can then be simplified and evaluated analytically. The analytical solution can be expressed in a closed form analogous to the classical Weyl–Van der Pol formula that has been used for predicting sound fields above a rigid-porous ground. Extensive comparisons with the wave-based numerical solutions according to the fast field formulation and the direct evaluation of the integral have been conducted. It has been demonstrated that the analytical formula is sufficiently accurate to predict the penetration of sound into a wide range of outdoor ground surfaces.