Simulation stage-based seabed pre-trenching technique for steel catenary riser touchdown fatigue analysis

Abstract

ABSTRACT The development of seabed trench by the steel catenary riser (SCR) touch-down zone (TDZ) in its early life can be caused by installation loads, direct hydrodynamic loads, and vessel first and second-order motions on the SCR. This paper presents a numerical technique by which pre-trench can be initiated for fatigue response calculations during SCR detailed design analysis. Examples are presented to demonstrate the new approach and how the SCR fatigue response can be calculated in the presence of the created pre-trench. The SCR (after the pre-trenching process) is allowed to respond to the vessel first order six degrees of freedom motions about its nominal position in the presence of the created pre-trench. As demonstrated in this paper, the pre-trenching technique makes it possible to conduct a full time-domain, irregular wave simulations of the SCR in the presence of a pre-trench created using the hysteretic non-linear pipe soil interaction mode.