Computation of dispersion relations for axially symmetric guided waves in cylindrical structures by means of a spectral decomposition method

•A method to calculate real and complex wave numbers in cylinders is presented.•The method is based on transforming equations of motion into an eigenvalue problem.•Hollow cylinders are described as transition between cylindrical rods and plates.•The analytic expressions needed to implement the presented method are provided.•The accuracy depends on frequency and the dimension of the eigenvalue problem. In this paper, a method to determine the complex dispersion relations of axially symmetric guided waves in cylindrical structures is presented as an alternative to the currently established numerical procedures. The method is based on a spectral decomposition into eigenfunctions of the Laplace operator on the cross-section of the waveguide. This translates the calculation of real or complex wave numbers at a given frequency into solving an eigenvalue problem. Cylindrical rods and plates are treated as the asymptotic cases of cylindrical structures and used to generalize the method to the case of hollow cylinders. The presented method is superior to direct root-finding algorithms in the sense that no initial guess values are needed to determine the complex wave numbers and that neither starting at low frequencies nor subsequent mode tracking is required. The results obtained with this method are shown to be reasonably close to those calculated by other means and an estimate for the achievable accuracy is given.