Analysis on statistical uncertainties of wave loads and structural fatigue reliability for a semi-submersible platform.

The statistical uncertainties of wave loads have large proportions in the structural fatigue strength analysis of offshore platforms. To investigate the uncertainties of wave loads during predicting fatigue loads, the assessing methods and formulas are proposed involving the wave spectrum, sea wave height, wave loading transfer function, zero-crossing period, possibility of sea state occurrence and wave direction; meanwhile, the model test of the wave loads is carried out in a see-keeping basin for studying the uncertainty of the wave loading transfer function. The corrected formulas of the significant wave height and mean zero-crossing period are statistically regressed by calculating the sea states in the Northwest Pacific and South China Sea. Furthermore, the influence factors of the sea states of difference seasons are analysed, and the distribution law of the wave direction of the wave loads and fatigue life of a semi-submersible platform are investigated. Finally, the fatigue reliability index of typical structures for a semi-submersible platform is assessed on the basis of uncertainties of wave loads and the other uncertainties of structural factors. • The uncertainties of wave load are investigated during predicting fatigue loads, such as wave spectrum, sea wave height. • A model test of wave load is carried out in a basin to study the uncertainties of wave loading transfer functions. • The fatigue reliability index of typical structures for a semi-submersible platform is assessed. [ABSTRACT FROM AUTHOR]