Index of content:
Volume 135, Issue 1, January 2014
- GENERAL LINEAR ACOUSTICS 
Scattering of ultrasonic waves by heterogeneous interfaces: Formulating the direct scattering problem as a least-squares problem135(2014); http://dx.doi.org/10.1121/1.4845615View Description Hide Description
An analytic-numerical method to simulate the interaction of time-harmonic ultrasonic waves with imperfectly bonded layered structures is presented. In the proposed formulation, elastic layers may be either isotropic or anisotropic and adhesion interfaces are replaced by equivalent continuous distribution of normal and transversal springs. In addition, adhesion imperfections are allowed to be localized in space and are modeled by a corresponding local reduction in spring constants. The resulting direct scattering problem is formulated as a least-squares problem and solved accordingly. The formulation was extended for three different cases: Scattering from imperfectly bonded half-spaces, scattering from imperfectly bonded layered structures and scattering from imperfectly bonded layered plates immersed in acoustic fluid, and numerical simulations corresponding to each one of these cases are presented. The simulations indicate that the method is capable of capturing the scattering resulting from the interaction of ultrasonic waves with defective bonds as well as indicate that ultrasound has the potential of revealing the presence of defective bonds and interfacial heterogeneities.
135(2014); http://dx.doi.org/10.1121/1.4835915View Description Hide Description
The far-field radiation originating from a finite-length pipe is well studied, especially for steady-state conditions. However, because all physical systems do not begin in steady state, these radiation characteristics are only valid after the transient portion of the solution has decayed. Understanding transient radiation characteristics may be important (particularly for systems transmitting very short-duration signals), as they can differ quite significantly. A numerical complication to this problem involves dealing with a sharp corner in the domain of interest. While many numerical studies have attempted to couple solutions from the domains inside and outside a pipe, the analysis presented in this work treats the computational domain as a single region by expressing the entire physical domain as a map from a simple rectangular domain in generalized curvilinear coordinates. This method will be introduced in detail and general results of transient radiation will be presented for an infinitely baffled, finite-length pipe using the finite-difference method expressed in generalized curvilinear coordinates. Comparison will be made to previous results [P. Stepanishen and R. A. Tougas, J. Acoust. Soc. Am. 93, 3074–3084 (1993)] that used a semi-analytic approach with certain assumptions.