Non-linear frequency-domain analysis of jack-up platforms

The autocorrelation function and higher-order cumulants of the non-Gaussian wave modal force, with a cubic approximation of the Morison drag force and a quartic approximation of the inundation force, are presented. The method utilized is based on Price's theorem for evaluating the associated joint moments of the non-linear wave forces. One- and multi-dimensional fast Fourier transform techniques are employed to obtain the power and higher-order spectra of the wave modal force and structural response. The non-linear frequency-domain analyses of two typical jack-up platforms are carried out using the correlation function based approach, which is numerically much more efficient than either the method based on Volterra-series or time-domain simulation.