Response of composite stiffened shells under stochastic excitation

This paper describes the application of the finite element method to analyse the response of multidegree-linear-elastic structures subjected to stationary random stochastic loading. Normal-mode method is used in this study. For the first time, the random response analysis of composite stiffened shells has been described. Problems relating to concentric and eccentric stiffened composite shells have also been dealt with for the first time which is not available in any existing commercial package. The random distributed loads are assumed as stationary in time but can be nonhomogeneous in space. The formulation of both spatially homogeneous and nonhomogeneous loads have been indicated. The highly popular 9-noded Lagrangian element is used here for the analysis. The formulation of laminated stiffeners are also presented. An improved version of stiffener modelling is presented here in which the stiffener can be place inside the element. This will give more flexibility to the mesh division. As the first order shear deformation theory is incorporated for both the shell and the stiffener, the formulation can accommodate both thin and moderately thick shells. A simple lumped load concept has been used for spatially homogeneous loading. For spatially nonhomogeneous loading, however, the isoparametric shape functions and Gaussian integration technique have been employed to form the generalised nodal cross-spectral density matrix from the excitation. Displacement and stress response spectra for isotropic and composite stiffened plates and shells for different loading (white noise and jet noise) and boundary conditions have been presented here. Results, where available, have been compared to validate the formulation. A large number of new results based on the parametric study has been presented.