  The probabilistic design of offshore wind turbines aims to ensure structural
safety in a cost-effective way. This involves conducting structural reliability
assessments for different design options and considering different structural
responses. There are several structural reliability methods, and this paper
will apply and compare different approaches in some simplified case studies. In
particular, the well known environmental contour method will be compared to a
more novel approach based on sequential sampling and Gaussian processes
regression for an ultimate limit state case study. For one of the case studies,
results will also be compared to results from a brute force simulation
approach. Interestingly, the comparison is very different from the two case
studies. In one of the cases the environmental contours method agrees well with
the sequential sampling method but in the other, results vary considerably.
Probably, this can be explained by the violation of some of the assumptions
associated with the environmental contour approach, i.e. that the short-term
variability of the response is large compared to the long-term variability of
the environmental conditions. Results from this simple comparison study
suggests that the sequential sampling method can be a robust and
computationally effective approach for structural reliability assessment.
