Short pulse sound-wave scattering from an infinite periodic array of rigid flat strips in a fluid.

Abstract

Many submerged structures of interest contain periodically spaced supports or other periodic structural features. When insonified with waves at various frequencies, such periodicities are known to give rise to dispersive phenomena with well-defined pass and stop bands. However, for short pulse (SP) sound waves with their very wide frequency spectra, the scattered sound field exhibits features that are well resolved in the time domain, therefore not well parametrized by superposition of the infinite harmonic wave trains in the frequency domain. To understand the evolution of the SP induced transient field, it is desirable to operate directly in the time domain (TD). For clarification of relevant issues, a systematic investigation has been undertaken for the simple model of an infinite periodic array of flat rigid strips. A reference solution for SP plane-wave scattering has been constructed by an (integral equation)–(method of moments) algorithm implemented numerically via Floquet modes in the frequency domain. The results furnished by this numerical experiment are then parametrized in terms of the TD observables in the data−well-resolved short pulses, interspersed with trailing oscillations, etc. This TD observable-based parametrization (OBP) permits the monitoring of the buildup of the global dispersive spectra from the initially well-resolved multiple scatterings between adjacent strip elements. Wave-oriented signal processing, in the configuration-wave number phase space, systematizes the OBP implementation and explanation of the results. [Work supported by ONR.]