Methodology for simulation of the post-failure behavior of flexible catenary risers

Abstract

New discoveries have been constantly pushing the use of marine risers to harsher environments, moving to ultra-deep waters. However, even with recent advances in the analysis and design of risers, these structures still fail. The rupture of a riser often implies high environmental and economic costs and can compromise the lifespan of neighboring structures, such as other risers, anchoring systems, and submarine equipment. This work aims at performing post-failure analysis of flexible catenary risers to understand their behavior after the rupture occurs. The dynamic buckling phenomenon is discussed and the influence of important parameters such as element length, time step, tangential drag coefficient, soil stiffness, and slenderness is assessed and discussed. This paper also shows that the hysteretic nonlinear bending stiffness has a great influence on the falling riser dynamics. Results are shown in terms of the fall time, and the riser accommodation on marine soil. A statistical analysis using random waves is also performed to assist in understanding the problem and in determining a safe region around the riser to avoid impact with other elements of the submarine layout. The proposed methodology provides important results for damage mitigation in case of accidents in future riser designs.