Fatigue crack propagation based fatigue assessment in a weld of longitudinal stiffener is conducted. Load history generation method based on storm model has been developed. JWA hind-cast data of North Pacific Ocean are chosen to assembly wave scatter data. Load history is generated based on third generation (3G) storm model. It is found that 3G-storm satisfies all requirements in following characteristics:

  • long-term joint probability of HW and Tw,

  • probability distribution of storm duration,

  • occurrence probability of storm classes and

  • rate of HW change in storm.

The difference of crack propagation life, which is calculated from various storm models, is not too large under the condition chosen. The fatigue damage ratio is almost equal with that of ratio calculated crack propagation life. These show the preciseness of load history generation based on 3G-storm model for fatigue assessment of ship structure members.


In order to clarify fatigue damage, which is occurred in the early ship's design life, fatigue crack propagation (FCP) analysis has been proposed as a rational approach for fatigue assessment of ship structure member. Recently, the research progress of FCP analysis of ship structure members has been increased substantially. Crack propagation analysis depends on preciseness of wave-induced load history used in simulations. The capability of FCP analysis hinges on the emulation accuracy of short-sea history (significant wave height HW, mean period Tw) in actual sea. The short-sea history arises from random sequences in real sea by combining HW, Tw and states condition. Prediction method of HW, Tw and states in a single simulation process, so that can simulate the effect of load sequence in actual sea, is required. Tomita (1995) proposed ‘storm model’, which can simulate the effect of load sequence based on the rough sea (storm).

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