Numerical Modeling Approach for Steel Catenary Riser Behavior at Touchdown Zone

Abstract

This paper introduces a new numerical approach in the analysis of the dynamic interaction between the steel catenary riser (SCR) and seabed in the vicinity of the touchdown zone (TDZ). The interaction between the SCR and seabed is modeled by a series of springs distributed along the SCR length. The pipe-soil interaction (the single spring) is simulated by an elastoplastic model in which the penetration resistance is estimated according to the relation to the yield force on the backbone curve. The backbone curve is calculated according to the current soil undrained shear strength (su,av) at the pipe depth. The su,av is evaluated by a recently developed effective stress framework in which the effect of soil remolding during pipe dynamic motion can be well captured by formulating within the framework of critical-state soil mechanics. An example of the whole SCR under cyclic displacements induced by the vessel motion for different wave conditions is analyzed using the proposed numerical approach, and the SCR responses in the TDZ, including the embedment, contact forces, penetration stiffness, and structural responses, are discussed.