Catenary riser sliding and rolling on seabed during induced lateral movement

• Catenary risers contact with seabed is addressed.
• Contact models including friction effects are implemented.
• Rolling effect is included in the model and compared with models with no rolling.
• Results are compared with Orcaflex® models showing good agreement.
• Rolling is captured in cases-studies, but did not affect substantially internal loads.

Catenary risers have an interaction zone with the seabed, usually referenced as flowline. Movements in this region can be induced by sea currents and large offsets in floating unit, leading to touchdown position changes and affecting internal loads along riser length. In this work the contact flowline-seabed is modeled including sliding and rolling friction. Case studies involving large offsets in floating unit and lateral sea currents are solved to better understand the consequences of possible rolling and large sliding. The riser is modeled using a geometrically-exact finite element beam model. The contact is addressed with a new technique to include rotation movements from underlying beam models. This leads to global riser models including complex kinematics, being able to represent scenarios with alternating sliding/rolling and its consequences on internal loads of riser structure. A parametric study is performed to measure the influence of the friction coefficient in tension and torsion along typical flexible pipe and steel pipe catenary risers.