Study on Effect of Cycle Counting Correction Factors in Spectral Based Fatigue Computation

This paper investigates the effect of various cycle counting correction factors in spectral fatigue damage calculations. Spectral fatigue calculations are based on complex stress transfer functions established through direct wave load analysis combined with stress response analysis. Cycle counting correction factors are introduced in the computation process to cater swell’s effect and to reduce the conservatism in the results due to narrow band approximation for a wide band random process. In this study, fatigue life of a ship structural detail is predicted by spectral method utilizing ANSYS software along with 3D liner sea-keeping code AQWA. Cumulative fatigue damage is calculated by a MATLAB program based on direct calculation procedure of spectral fatigue using cycle counting correction factors proposed by Wirsching, Rice and Dirlik. The results show an overall decrease in the computed fatigue damage and a corresponding increase in the expected fatigue life of the structure.