Energy pass bands in a ribbed cylindrical shell with periodic asymmetries

Abstract

The addition of periodically spaced structures to a cylindrical shell causes energy to propagate at additional wave numbers via a phenomenon known as Brillouin folding. As a result, a load representing one axial mode on a cylindrical shell with circumferentially spaced discontinuities, for example stringers, has distinct energy pass bands and stop bands. Similarly, an excitation representing one circumferential mode on a cylindrical shell with axially spaced discontinuities, for example ribs, also has distinct energy pass bands and stop bands. Discontinuities in both directions lead to energy pass bands when a point force is applied. In this paper, periodically spaced point masses in the axial and circumferential directions are added to a submerged, ribbed, finite cylindrical shell and analyzed via the finite element method. It is seen that Brillouin folding occurs and, in certain circumstances, the energy is split into pass bands and stop bands. For the frequency and circumferential modes where the subsonic energy is most narrowly focused in the axisymmetric shell, a distinct peak in radiated power occurs for the shell with point masses. The energy in this peak is about the same for several examples of different amounts of nonaxisymmetric mass.