A new tri-modal spectral model for evaluating fatigue damage under three or multi-random Gaussian loads

A tri-modal or multi-modal process is one of the main loads in marine and offshore engineering. These resulting fatigue problems should be focused. Some available tri-modal spectral methods for estimating fatigue damage are first reviewed, and then a new tri-modal spectral model is developed based on a generalization of the principle proposed by Han and Ma. In order to validate the accuracy of these methods, a parametric triangular tri-modal spectrum is constructed and time domain solution based on rainflow counting is considered as a reference. The results show that the new developed method provides quite good fatigue damage evaluation compared with RFC solution. Then, the developed tri-modal model is generalized to multi-modal processes and general wideband processes. The generalized principle is to divide a wideband spectrum into several narrowband segments. Different dividing principles are investigated, it is demonstrated that adopting equal-frequency-band principle can give good fatigue damage estimation.