Nonlinear dynamic and bilinear fatigue reliability analyses of marine risers in deep offshore fields

摘要

Depleting oil reserves in shallow water are opening the avenues of new ventures in deep sea conditions. India is no exception; deep sea explorations are highly recommended and exercised. As part of the design process, there are requirements of structural failure criteria, such as rupture by over loading, fatigue failures, buckling or an unstable fracture. Three-dimensional nonlinear dynamic analysis of riser is obtained in time domain using finite-element solver ABAQUS/Aqua. The response histories so obtained are employed for the study of fatigue reliability assessment of risers. Fatigue model is based on a bilinear relationship that gives the crack growth linked failure criterion to describe the interaction between fracture and plastic collapse. Uncertainty modelling, especially fatigue crack growth parameters, is undertaken with the help of recently published data in support of bilinear crack growth relationship. Results pertaining to fatigue reliability and fatigue crack size evolution are presented using Monte Carlo simulation. The bilinear crack growth model is found to lead to higher fatigue life estimation as compared to linear fracture mechanics model. Sensitivity behaviour pertinent to limit state adopted has been thoroughly investigated. These findings implicate inspection schemes for components of the marine structures to ensure minimisation of the surprises due to wide scatter of the fatigue phenomenon in marine environment.