Spectral fatigue analysis of ship structures based on a stochastic crack growth state model

Fatigue life estimation in ship structures is a very complex problem, because of the stochasticity in the wave loading experienced by the hull and the inherent variability in the material and geometric parameters. On an effort to quantify such aleatoric uncertainties, this work integrates in a novel setting the spectral approach to loading description into a probabilistic fatigue crack growth model. The proposed framework effectively models both the randomness in the experienced sea states and the corresponding random sequence of the sea states that are encountered by the ship and contribute to the fatigue accumulation. The spectral approach eventually allows for the construction of potential crack growth path instances from a single realization of an effective random stress range that is applied for a corresponding realization of number of cycles. The obtained bundle of stochastic crack paths is further used in order to perform reliability estimations in the entire life cycle. Initially the proposed method is presented formally and algorithmically and its application is demonstrated through a numerical case study of a cracked plate where we are interested in estimating its remaining useful life along with the time distribution of the probability of failure.