Dynamic Response of a Steel Catenary Riser at Touch Down Zone With Seabed Trenching Development Considered Under Irregular Waves

Abstract The steel catenary riser (SCR) serves as a primary solution for deep-water oil and gas field development, but it encounters complex dynamics due to forced oscillations induced by wave-driven floater motions, especially at the touch-down zone (TDZ). Traditional pipe-soil models often fail to address these challenges, as they do not account for soil remoulding and the impact of irregular motion. This is particularly relevant in real sea states characterized by irregular waves, where the floater’s movements have a significant impact on seabed trenching, thus complicating the dynamic responses of the SCR. To address these issues, this study integrates an innovative effective-stress-based pipe-soil interaction model into a global SCR analysis to explore its dynamic response and fatigue damage under irregular waves. The irregular movements of the floater, derived from response amplitude operator (RAO) data and wave spectra, are applied to the SCR’s top end after a translation to the hang off location. This allows for dynamic simulations that consider the evolution of the seabed and the process of trenching. The study focuses on deriving the dynamic stresses experienced by the SCR at the TDZ and evaluating fatigue damage using the S-N curve method. It also examines the seabed interaction, including the evolution of trenching, changes in seabed stiffness, and soil resistance at various SCR locations. By considering real sea conditions, this study yields insights into trenching and seabed-SCR interactions, promising to enhance design methodologies and bolster offshore infrastructure performance and safety.