Reliability analysis of a tanker subjected to combined sea states

This paper presents a reliability analysis of a tanker subjected to combined sea states using first-order reliability methods. The probabilistic model of the ultimate collapse bending moment of the hull girder is taken to be the result of an advanced collapse analysis of the ship’s cross section. An evaluation of the wave induced load effects that occur during long-term operation of the ship in the seaway is carried out. An improved description of the environmental load effects including both wind-sea and swell partitioning, and different directional spreading for both components, is considered in the evaluation of the long-term distributions of the vertical bending moment, and consequently on the reliability assessment of the tanker. The approach is based on probabilistic models available for the occurrence of double-peaked spectra, the relative occurrence of swell dominated spectra, and average values of the ratios of spectral peaks and of the spectral frequencies for both wind and swell dominated seas.