Investigation of Sea Wave and Structure Modelling for Fatigue Assessment of Offshore Structures

Based on the statistical classification of wave scatter diagram,and nonlinear dynamic approach for calculating the fatigue presented by the author,and by efficiently improving the wave energy input,an efficient procedure for calculating the fatigue damage of offshore structures due to wave loading is presented.By applying this procedure into the fatigue calculation of a typical jacket structure,the directional effects and the peak enhancement of waves on the fatigue damage of the jacket structure were first identified.Furthermore,the parameters such as the number of sample points of the adopted wave spectrum,and,the length of time steps in the HHT-α time integration algorithm were also investigated.From the statistical study of the response,it indicates that the extent of nonGaussian structural response is not directly related to the adverseness of sea states,even though the variance of the response is clearly related to the sea state adverseness.The nonlinear dynamic analysis approach presented in this paper has the merit of reducing uncertainties without degrading a required safety level,this may lead to a positive economic impact with regard to construction and maintenance costs.It was successfully applied in several industry projects for the life time extension of offshore installations subject to dynamic wave and wind loads.