Acoustic scattering from a double periodically bulkheaded and ribbed finite cylindrical shell

Abstract

The sound scattering from a finite vacuumed cylindrical shell simultaneously loaded with the bulkheads and the ribs are studied. The motions of the shell are described by the Donnell equations. Each rib is modeled as a rod of circular curvature where only the normal force is applied. The motions of the bulkheads are decomposed into the out-plate bending motions and the in-plate extensional motions, which are independent of each other. The backscattered sound field is analyzed via the frequency-angle spectra. Compared against the backscattered sound from a ribbed cylindrical shell, the Bloch-Floquet waves disappear at low frequencies but still exist at mid and high frequencies. The Bragg scattering excited by the ribs is unchanged at mid and high frequencies. Besides the ribs' Bloch-Floquet waves and Bragg scattering, there exists the Bragg scattering excited by the bulkheads. The backscattering from a cylindrical shell loaded with just the bulkheads is calculated. When the spacing and the thickness of the bulkheads are equal to those of the ribs, the crests of the Bragg scattering and the Bloch-Floquet waves on the frequency-angle spectra are almost the same as those of the ribbed cylindrical shell. The resonances of the bulkheads are also excited in this case.