Vibration and Acoustic Responses of an Orthotropic Composite Conical Shell in a Hygroscopic Environment

Abstract

The vibration and acoustic radiation for an orthotropic composite conical shell in a hygroscopic environment are explored through the wave propagation approach and Galerkin method. Theoretical results of the natural vibration and far field sound pressure are presented with incremental moisture content. The effects of incremental stiffness and different semi-vertex angle on the acoustic radiation characteristics are studied too. It is found that the natural frequencies decrease with incremental moisture content. The wavenumbers associated with the lowest frequency mode reaches the modal indices corresponding to the lowest buckling mode near the critical buckling moisture content. With the increasing moisture content, a shifting of natural frequencies toward lower frequency band could be observed in lower frequency band of the modal density in constant frequency band. The overall sound pressure level (SPL) decreases generally with the moisture content, but shows a marginal increase near the critical buckling moisture content. The modal density and overall SPL decrease with the incremental stiffness generally, which increases with the decrease of the semi-vertex angle.