Wave characteristics of a cylinder with periodic ribs

This paper deals with wave characteristics of a cylinder with periodic ribs. The equation of motion of the stiffened cylinder is first derived using a receptance coupling method. The dispersion diagrams of the stiffened cylinder are then obtained in order to figure out the effects of the ribs on the wave propagation. Due to the effect of the ribs, the dispersion curves are found to be repeated along the axis of the wavenumber with the repetition period of 2π/d, where d is the rib distance. Also, dispersion curves are found to show a pass and stop band of the waves. The stop bands appeared at the wavenumber of half of the wavenumber periodicity. The stop band becomes wider as the increase of the circumferential order. The waves in the pass bands are propagating well through the ribs without decay. In contrast, the waves in the stop bands are not propagating, but decaying the magnitudes. The decay of the responses in the stop band increases as the circumferential order increase. The change of the rib stiffness causes the cut-on frequency to change and the modal order to jumble. The change of the rib stiffness also leads to generate a wave whose phase velocity is positive, while group velocity is negative.