Research On Interaction Between Steel Catenary Risers And Seafloor

With steel catenary risers (SCR) widely used in the development of oil and gas indeepwater, the interaction between touchdown zone and seafloor will easily lead tofatigue damage, and this phenomenon becomes more prominent. It makes the contactproblem to be a focus. The floater which is linked to SCR is affected by wave andcurrent. There will be lateral motion and vertical motion. It affects the interactionbetween touchdown zone (TDZ) and seafloor. Then it leads to generation of trench,and bending moments which have negative effects on fatigue life occuring in the partnear touchdown point (TDP) of the riser.First of all, refer to the literatures domestic and abroad. According to theresearches on experimental phenomena and existing research results, a seafloor-riserinteraction model is established. It considers stiffness degradation of seabed soil andsoil suction. In the model, the seabed soil is simulated by nonlinear springs. Thestiffness of nonlinear springs is described by P-y curve. Then, the model is based onfinite element software ABAQUS. By having a secondary development in ABAQUS,the nonlinear springs are defined by subroutine UEL. So the seafloor-riser interactionmodel has been established in ABAQUS. There is a research mainly on the trenchshape, the location of maximum trench depth point and the bending moment variationof the points near TDP by applying vertical cyclic displacement-load to initial TDP. Itwill provide certain basis for fatigue damage problem of risers. The results show thatunder the action of cyclic displacement-load, there is a trench generated on theseafloor. The trench shape and the maximum depth are related to the nonlinearity ofseafloor, soil stiffness, maximum uplift displacement and numbers of cycles.Finally, this paper analysis the bending moment variation of the points near TDPunder every circumstances which include soil stiffness variation, displacement loadvariation and cyclic numbers variation, it will provide references for further researchon interaction between SCR and seafloor.