Abstract
The dynamic response analysis of fixed offshore cylindrical shell structures subjected to wind-induced random ocean waves is studied by using the free vibration data in water, which was already obtained by three different approaches; Rayleigh-Ritz method, finite element method and matrix progression method. The incident random waves can be simulated from Pierson-Moskowitz wave height spectrum through the superposition of a number of simple harmonic waves of different wave heights, periods and phases. The hydrodynamic pressures on a vibrating shell subjected to ocean waves are computed by taking the sum of the pressure components of incident waves, diffracted waves assuming a restrained structure and radiation waves generated by the motion of a shell by a linear potential flow theory. The effects of dynamic interaction between a shell and water can be estimated as the added mass in phase with the acceleration of a shell and the radiation damping in phase with the velocity of a shell in the uncoupled modal equation of motion which can be derived by making marking use of the orthogonality of mode shapes in water. The response quantities such as displacements and stress resultants are obtained in the frequency domain and in the time domain. In order to show the application of the theory and the procedure, some numerical calculations are carried out. Based on the numerical results, the effects of shell configuration and water depth on the dynamic behaviours and the effects of radiation damping on the response quantities are discussed.
