Natural vibrations of a stiffened pressurized cylinder with an attached mass

An approximate energy method for determining the natural frequencies and mode shapes of pressurized circular cylinders with equally spaced flexible stringers and an attached point mass is presented. Exact normal modes for the linearized orthotropic shell equations are used to obtain results for the stiffened configuration without a mass attachment. A linear combination of these is next employed as a trial function to approximate the shell deflections with an attached mass. Comparisons of predicted results with test data, obtained from a concurrent experimental program, are made. Both the analysis and tests reveal that any weight addition to a thin-walled cylinder, even if it is very light, can evoke a highly localized response in the vicinity of the attachment. This effect can significantly lower the system's fundamental frequency, thus offsetting much of the stiffening afforded through pressurization.