FREQUENCY-DOMAIN ANALYSIS OF OFFSHORE PLATFORM IN NON-GAUSSIAN SEAS

A frequency-domain solution approach for the response of a system whos e inputs are nonlinear transformations of non-Gaussian (nonlinear) wav e kinematic processes is introduced. Particularly, this paper compares the probabilistic response characteristics of jacket-type platforms i n deep water that are subjected to both Gaussian and non-Gaussian rand om wave loadings. Unlike earlier analytical treatments of this class o f system, a statistical description of the wave forces is first develo ped to reflect nonlinearities and associated non-Gaussianity in the wa ve field kinematics. The kinematics are derived from Laplace's equatio n and nonlinear boundary conditions using a second-order Stokes' pertu rbation expansion. The deck response resulting particularly because of the effects of the second-order contribution to the loads on an ideal ized platform is computed. Consideration is given to the importance of the spacing of the legs to the response of the structure. The impact of swell in addition to locally wind-generated waves also is assessed. Ignoring the nonlinearity of the waves results in underestimation of the response level for all scenarios considered.