Estimation of rainflow damages in container ships

Paper in proceeding, 2012

The distribution of rainflow cycle ranges for fatigue design of ship structures is often obtained from classification rules as an empirical formula in terms of ship geometry, trade regions, etc. It is well-known that this method includes large uncertainties. In particular, it cannot account for the environmental loads and operational profiles for the fatigue assessment of ship structures. A direct fatigue analysis is supposed to be more realistically describe stresses encountered by ships. Using advanced hydrodynamic and structural analysis, the distribution of the rainflow ranges can be estimated using statistics of the more aggregated quantities, e.g. long-term distributions of encountered significant wave height, ship speeds and heading angles etc., and some mathematical models relating stresses to the quantities. In this paper, a very simple model, based on the narrow band approximation, is presented and then validated using the full-scale measurements of two container ships of different sizes. The application of this model for long-term fatigue analysis is also illustrated in details.