Mooring line fatigue in an offshore guyed tower

A probabilistic method is presented for the fatigue analysis of the mooring lines of a guyed tower. The wave loading is idealized as the first component of a two-dimensional Markov process. Using Ito's rule of stochastic differentials, differential equations for moments up to the fourth order are obtained, and these are solved using numerical techniques for both Gaussian and non-Gaussian methods. The displacement response is modelled as a mixture distribution. The probability distribution of guyline tension is then estimated. The probability density for peak guyline tensions is estimated by mapping a Gaussian process into the non-Gaussian process of guyline tensions using the double inversion technique and estimating level crossings. The tension fatigue is estimated using Palmgren-Miner's rule. It is shown that the fatigue damage estimated using non-Gaussian closure is greater than that estimated using Gaussian closure.