Extreme Response and Fatigue Damage of Ship-Shaped FPSO

Abstract

This chapter presents a systematic method to predict extreme response and conduct fatigue assessment in which the site-specific wave conditions and the service history are accounted for. The extreme response is predicted using both short-term and long-term approaches, and the fatigue strength is assessed using a closed-form spectral fatigue method. The proposed approach may be applied to newly built or converted floating production storage offloadings (FPSOs). FPSO design is highly wave condition dependent. Both extreme response and fatigue life can be significantly affected by site-specific wave environments. Collecting accurate wave data is an important part of the design. Wave spectral shapes have significant effects on fatigue life. Choosing the best suitable spectrum based on the associated fetch and duration is required. In predicting extreme responses, the long-term approach is preferred because it has less uncertainty. However, the chapter recommends using the long-term approach together with the short-term approach for obtaining a conservative result. The short-term extreme approach depends on long-term prediction of extreme wave spectra and proper application of the derived wave spectral family. It is not necessarily simpler than the long-term approach.