Probabilistic Fatigue Design for Ocean Structures

Techniques of probabilistic design theory are used to develop a method for fatigue design of structural components in ocean systems. Uncertainties that exist in material behavior, stress analysis, sea state description, as well as in the behavior of the basic theoretical model (namely the Palmgren-Miner rule) are modelled as lognormal random variables. A probability-based algorithm for fatigue design, which does not explicitly require computer analysis is presented in closed form and is, therefore, useful in preliminary design. The analysis can accommodate environments such as the Gulf of Mexico which are characterized by two different wave populations: (1)The operational sea state; and (2)storms. The model can be employed to estimate risks due to fatigue in bottom-founded ocean structures, as well as in a wide variety of other marine and terrestrial systems.