Comparative dynamic analysis of SCR and LWR in the coupled platform–mooring–riser system under internal solitary wave conditions

Abstract

As a frequently occurring and widely distributed environmental load, an internal solitary wave (ISW) always appears with a large amplitude and may result in the instability of deepwater structures and offshore accidents. In this study, a self-developed program was established to describe the dynamic behavior of a coupled platform–mooring–riser system. The response of the platform is based on the rigid body dynamics theory, that of the risers/mooring lines is obtained by the lump mass method, and the coupled effect between them is achieved by a semi-coupled analysis. Two types of riser configurations, steel catenary risers (SCRs) and lazy-wave steel catenary risers (LWRs), in the coupled system were compared under only ISWs and combined excitation of ISWs and random waves. The numerical results were proven to be reliable through validation against previous literature. The results show that different riser configurations have little influence on the platform response or mooring top tension. Both riser configurations exhibit a second-order deformation mode along the riser length and a half-wave shape with time. Additionally, a mutation in the horizontal tension, shear force, and bending moment occurs near the ISW interface. Compared with SCRs, LWRs always produce larger motion characteristics and responses with time differences owing to their complex configuration.