A procedure for stochastic fatigue analysis of equipment on floating production / storage / offloading structures (FPSO)

摘要

Floating Production, Storage and Offloading (FPSO) Systems are subjected to sea wave loads which may lead to fatigue failure. In this context, an approach for stochastic fatigue analysis of FPSO topside equipment is developed. Discrete transfer functions at several locations at the topside of the FPSO for various spreading directions are incorporated in the analysis. They are combined with the Ochi-Hubble sea wave elevation spectrum to provide a design spectrum for fatigue analysis at the topside of the FPSO. The response of a generic FPSO topside piece of equipment is simulated by a time series model in a Monte Carlo analysis context. The time series is generated as the output of a Moving Average (MA) filter to a band-limited white noise input. Further, the rainflow cycle counting method is applied to the equipment response time history to identify the significant cycles that induce fatigue damage. By using a S-N fatigue life curve and Miner's linear damage accumulation rule, the fatigue life of the piece of equipment is estimated. The results of the rain-flow cycle counting method are supplemented by results from a power spectrum, exclusively, based approach. It is hoped that further work involving other FPSO systems and wave spectra will refine the developed procedure for this important class of industrial systems.