Global Analysis Of Steel Catenary Riser And Floating Body Considering Riser-Soil Interaction

Steel Catenary Riser(SCR)is the key equipment of offshore oil and gas exploitation.It provides a pressure bearing connection between the riser and the platform through the flexible joint,and fixes the bottom of the riser at the seabed wellhead by anchoring.In addition,the vibration of the platform causes the reciprocating movement between the riser and the seabed soil,which makes the riser touchdown zone become a high incidence area of fatigue damage.Therefore,the global analysis of SCR and floating body is key under the coupling of riser and soil as the main research object for numerical simulation.Firstly,based on the analysis model of SCR and floating platform,supplemented by fatigue analysis theory,and on the basis of non-linear low-strength seabed soil,this paper studies the influence of the motion mode,three-dimensional motion period and amplitude of the platform on the dynamic behavior of the riser touchdown zone,including the stress distribution,penetration displacement and fatigue damage distribution at the touchdown point and so on.The results show that the heave motion of the platform has the greatest influence on the dynamic response of the touchdown point and the top of the riser.Due to the lateral resistance of the seabed in the touchdown zone,the impact of the sway motion on the dynamic response of the touchdown point is small,and the coupling of three-dimensional motion will reduce the fatigue damage of SCR touchdown zone to a certain extent.Therefore,only considering the heave motion of the platform to predict the fatigue damage of the riser is not accurate.Secondly,the three-dimensional riser soil interaction is taken as the main research content,and the floating body three-dimensional motion excitation is taken as the boundary condition of the top of the riser.The influence degree of undrained shear strength,shear strength gradient,suction factor,suction decay parameter and re-penetration migration parameter on the dynamic response of the riser touchdown zone is studied,and the influence of linear seabed and nonlinear seabed on the dynamic response of SCR touchdown zone is also further studied.The results show that the larger the values of undrained shear strength and suction factor,the greater the fatigue damage in the riser touchdown zone,and the obvious influence degree.The values of suction decay parameters and re-penetration migration parameters are inversely proportional to the fatigue damage in the riser touchdown zone,and the shear strength gradient has the least influence on the dynamic response in the riser touchdown zone.All the results of this paper verify the rationality of three-dimensional movement of the platform to predict the fatigue damage of riser touchdown zone,and study the sensitivity of nonlinear seabed soil parameters,providing reference for the subsequent riser design work.