Experimental and Theoretical Evaluation of Elastic Waves in Curved Layered Media

摘要

This report describes the progress achieved during the third period of the studyof elastic wave reflection from the curved and planar media subject to water loading. During the previous period, extensive experimental investigations were initiated to study parametrically the behavior of acoustic beams at curved and planar fluid-solid interfaces. Three types of materials, representative of Navy applications, in two geometries and two sizes, and many values of incident angle and angular or linear coordinates were included in the effort of last year. Simultaneously, an aggressive program of theoretical modeling and experimental verification were mounted and essentially all of the data were compared to predictions of the model. We found, in most cases, very good agreement between model calculations and experimental data. For the theoretical modeling of these effects, the complex source point (CSP) method was used to produce Gaussian line sources to account for the wave-solid interaction for acoustic beams. The scattering problem solved in this work is couched in terms of spectral integrals that are approximated by high-frequency uniform asymptotics. The resulting expressions for the reflected field contain interacting specularly reflected beam and leaky wave contributions which establish the physical basis for the observed phenomena. In addition to the two-dimensional modeling for comparison to experiments, work began to formulate a 3-D beam model within the theoretical framework for this more complicated circumstance as well. In continuation of the efforts of last year, we have extended the two-dimensional model to three dimensions.