Dynamic behaviors of conventional SCR and lazy-wave SCR for FPSOs in deepwater

摘要

The general and detailed structural/dynamic performances of steel catenary risers (SCRs) and lazy-wave steel catenary risers (LWSCRs) are directly compared under the same storm and floater (deepwater turret-moored FPSO) conditions. Their global performances are simulated by using the hull/mooring/riser fully-coupled dynamic analysis program developed by authors. This study proves that conventional SCRs connected to the FPSO hull exhibit significant dynamic responses and negative tensions, which may induce large structural stress amplification, local dynamic buckling, and serious fatigue damage at the members nearby TD (touch-down) region. The generation, propagation, and decay of the elastic waves generated by the temporal dynamic buckling are investigated in detail. On the other hand, LWSCRs can eliminate the local dynamic buckling for the same floater/storm condition and significantly reduce the stress level and fatigue damage near TDZ (touch-down zone) due to the motion isolation effect. It is because the modified shape with intermediate sag and arch portions can effectively isolate and absorb the downward riser motion. Therefore, LWSCRs can effectively be used for FPSO under very harsh environmental conditions. Despite the big advantage in dynamic characteristics, LWSCR is generally more expensive, more difficult to design, and may have slugging problem for internal flows. (C) 2015 Elsevier Ltd. All rights reserved.