Structural Performance of Deepwater Lazy-Wave Steel Catenary Risers for FPSOs

In this paper, the structural performance of deepwater lazy-wave steel catenary risers (LWSCRs) connected to a FPSO is investigated by using hull/mooring/riser coupled dynamic analysis program. Conventional deepwater steel catenary risers (SCRs)connected to the same FPSO hull exhibit significant dynamic responses, which induces large structural stress amplification and local dynamic buckling at the members nearby touchdown region. The corresponding short-term fatigue damage is also serious. On the other hand, LWSCRs eliminate the possibility of local dynamic buckling and significantly reduce the maximum stress level near TDZ (touch-down zone). It is because the riser motion can be isolated from the motion of the floater by the intermediate sag and arch members in the lazy-wave configuration. The general performance of SCRs and LWSCRs is directly compared under the same environmental and floater conditions in terms of ultimate limit state and fatigue limit state. It is shown that LWSCRs show excellent structural performance under severe environmental condition because of the motion isolation effect induced by the geometric characteristics. In addition, the effect of the curvature of the sag and arch members on the dynamic response of LWSCR is also studied to seek the optimal shape.