Fatigue damage model comparison with formulated tri-modal spectrum loadings under stationary Gaussian random processes

A riser system experiences a tri-modal process. It is excited by combined loads composed of low frequency response due to riser tension, mid-range excitation frequency from waves and high frequency excitation due to vortex induced-vibration. This study proposes ideal tri-modal spectrum formulations for parametric study. The formulated spectrum is used to compare various fatigue damage models developed to predict fatigue damage for wide band spectrum through theoretical or empirical approaches. The most reasonable fatigue damage is calculated as a reference by inverse Fourier transform, rain-flow counting method and Palmgren–Miner rule. The results conclude that the Benasciutti–Tovo and JB models currently represent the most appropriate fatigue damage for tri-modal spectrum.