Wave scattering in cylindrical waveguides: Analyzing flexible shells and liner conditions

Abstract

The scattering of fluid-structure-coupled waves is investigated in a cylindrical waveguide consisting of flexible shells and an expansion chamber connected via annular rigid discs. The scattering performance of the waveguide is studied in the presence of acoustic liners along the walls of the expansion chamber and the geometric variations along interfaces. A mode-matching method is applied to solve the corresponding mathematical problem. The study focuses on fluid- and structure-borne modes propagating in the flexible shells. The eigenfunctions in this case are non-orthogonal and obey generalized orthogonal properties, involving auxiliary parameters related to the ring conditions at the edges of the flexible shells. Although we considered clamped connections, the analysis can be extended to other ring conditions with appropriate changes. Through continuity conditions at the interfaces, orthogonal modes are used to project solutions in liner regions, resulting in linear algebraic systems. The performance of the waveguide is examined in terms of scattering powers and transmission loss as functions of frequency, chamber length, liner length, and porous screen impedance. It is observed that the variations in these parameters have a major influence on acoustic attenuation in the waveguide. These results are relevant for designing acoustic enclosures for different frequency bands.