An Intelligent Integrated Method for Reliability Estimation of Offshore Structures Wave Loading Applied in Time Domain

Abstract

Uncertainty management of complex dynamic structural systems vibrating in different media is addressed to design safer and more damage-tolerant structures. The dynamic properties (mass, damping, frequencies, etc.) of a structure vibrating in air (onshore) and in water (offshore) are expected to be different. Frequency contents of dynamic loadings (earthquakes and wave) are also expected to be different and unpredictable. The estimation of structural behavior with altered dynamic properties and uncertainty-filled loadings can be challenging. One of the main crucial loadings for offshore structures (OFS) is wave loading. The wave loading model is realistically developed to satisfy the underlying physics. The uncertainty management is carried out by estimating the underlying risk. A novel risk assessment procedure to estimate the underlying risk is proposed considering all major sources of uncertainty and nonlinearity. It is based on the multiple deterministic analyses-based concept to address uncertainty related issues in the formulation, currently a major research trend in the profession. To satisfy the underlying physics, the structures are represented by FEs. For wider acceptance, the dynamic loadings are applied in time domain. A novel risk evaluation concept using a surrogate metamodel Kriging technique is proposed. The implicit performance functions (PFs) are expressed explicitly using the significantly improved Kriging-based surrogate modeling technique. The proposed method consists of the response surface (RS) concept significantly modified for the structural reliability analyses and several advanced factorial schemes producing compounding beneficial effects. The risks corresponding to the serviceability-related global and strength related local PFs are evaluated. The method is clarified with the help of an informative example by estimating risks for serviceability and strength PFs of a large jacket-type OFS. To compare the performance of structure in wave loading and seismic loading, a site-specific seismic safety assessment method for nonlinear structural systems is used to properly generate a suite of ground excitation time histories. The information on risk for both PFs and both loadings was extracted using about a couple of hundreds deterministic evaluations. The results were verified using thousands of Monte Carlo simulations (MCSs). The authors believe that they proposed an alternative to the basic MCS technique and a novel risk evaluation procedure for OFSs. The proposed uncertainty management concept appears to be exciting.