In this paper, the first-order reliability method (FORM) found in connection with structural reliability analysis is first used in an inverse manner to efficiently obtain an approximate solution of the full long-term extreme response of marine structures. A new method is then proposed where the second-order reliability method (SORM) is used to improve the accuracy of the approximation, resulting in an inverse SORM (ISORM) approach. This method is compared with exact results obtained using full numerical integration. The new method is seen to achieve significantly improved accuracy, yet keep the number of required short-term response analyses within acceptable levels.

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