Onboard measured nonstationary stress diagnostics for FPSO operational damage assessment by a novel log-integral extrapolation scheme

Abstract This case study benchmarks a novel design approach for assessing the survival function of nonlinear nonstationary dynamic systems subjected to combined stochastic, nonstationary environmental loadings, with a particular focus on offshore engineering and naval architecture. The proposed design methodology benchmarks a novel log-integral (4-parameter generalized Weibull) extrapolation scheme of the Integrated Cumulative Distribution Function (ICDF) for accurate modeling of failure or damage probabilities aboard an operational Floating Production Storage and Offloading (FPSO) unit. The proposed design approach provides a robust tool for reliability and safety assessment of operational vessels and offshore structures in adverse deep-water conditions, particularly in ocean-wave environments. Predicted design values have been cross-validated against a 4-parameter Weibull distribution parametric fit. The combination of ICDF and onboard sensor measurements may provide offshore engineers with a robust framework for enhancing the reliability analysis of marine structures under dynamic, rapidly changing loading conditions. The primary novelty of this study lies in combining full-scale hot-spot stresses, measured by onboard-installed sensors using a novel integral ICDF extrapolation scheme, which is particularly suitable for design purposes when the underlying dataset is representative yet limited in size. A novel formulation of the fundamental design concept, such as Most Probable Maximum (MPM), for a non-Gaussian process with clustering (narrow-band) effects is presented, expressed as a memory-modified mean up-crossing rate in a practical engineering context.