Volume 103, Issue 3, March 1998
Index of content:
- GENERAL LINEAR ACOUSTICS 
103(1998); http://dx.doi.org/10.1121/1.421267View Description Hide Description
The scattering by a pair of spatially disjoint local regions of complex (multiscale) stiffness heterogeneity in an unbounded thin linearly elastic plate is investigated. Issues of the mutual interaction of the spatially disjoint scatterers and its manifestation within a homogenized, or effective, formulation governing large scale response fields are the focus. It is shown analytically and numerically that while one must incorporate scatterer/scatterer coupling for estimating the large scale response field, one can neglect this coupling in estimating the effective measures for describing the scatterers.
103(1998); http://dx.doi.org/10.1121/1.421268View Description Hide Description
The conventional formulation of geometric acoustics in the presence of inhomogeneous (spatially varying) absorption is examined. This formulation is found to fail under conditions of multipath propagation, because interference between ray paths is not taken into account when the absorptive losses are calculated. The example of high-frequency attenuation due to a surface bubble layer is studied, and Weston’s correction term is discussed.
Application of the integral equation method to acoustic wave diffraction from elastic bodies in a fluid layer103(1998); http://dx.doi.org/10.1121/1.421269View Description Hide Description
A method is proposed for solving the wavediffraction problem by employing a system of space-localized inhomogeneities in a longitudinally homogeneous waveguide. The method combines integral equations and eigenfunction methods. As an illustration of this method, acoustic diffraction is calculated from a system of different, parallel cylinders arbitrarily placed in a liquid layer. The problem is reduced to a system of integral-functional equations relative to fields excited in elastic bodies and sources of scatteredwaves on the surface of the cylinders. Standard methods may be used for solving the systems of equations. Numerical solutions are found for various versions of the system of elastic cylinders in a liquid layer with perfectly “soft” and “hard” walls. The method allows: (1) the calculation of the scattering matrix for reflected and transmitted waves with any given accuracy; (2) the construction of the amplitude-frequency and the phase-frequency characteristics for the matrix elements; and (3) the calculation of the distribution of field sources on the surface of each cylinder and the scatteredwave field both in the near and far zones.
103(1998); http://dx.doi.org/10.1121/1.421270View Description Hide Description
The acoustic resonances of a submerged fluid-filled cylindrical shell are analyzed as the shell cross section is deformed from circular to elliptical geometry. A schlieren visualization system is used to image standing wave fields within insonified water-filled shells of different eccentricities, and to locate the resonance frequencies of the fluid column. The acoustic behavior of elliptical cavities with infinite and finite surface impedances are modeled and the theory used to predict the resonance frequencies of the fluid column and calculate the pressure distribution in the acoustic field. As the symmetry of the circular shell is broken by deforming it to the more general ellipse the resonance spectrum changes; mode splittings and level crossings are observed as the eccentricity increases. The experimental observations of resonancepatterns and frequency variation are in good agreement with the theoretical predictions.