Investigation Of Steel Catenary Riser Fatigue In Touchdown Zone

Steel catenary riser has been widely used in exploring oil and gas in deep water due to its low cost and unnecessary tension compensation,etc.However,there is coupled motion between steel catenary risers and floating system under the effect of complicated environment.The fatigue problem caused by cyclic loading is a key issue for the design of the deep-water riser,and the fatigue in touch down zone(TDZ)is especially critical.The touchdown point(TDP)is where the riser first comes into contact with the sea bed,which is the intersection of the hanging section and the streamline section.When riser moves,a new touch down point generates.The variable touchdown point forms a region with a certain length,named TDZ.The frequent riser-soil interaction in the TDZ leads to the decrease of soil stiffness and trench formation.Due to the complicated interaction of riser and soil,it is necessary to study the influence of specific parameters and the formation of trench on the fatigue of the touchdown zone.In response to these issues,the main work of this paper are as follows:1.By establishing a floating system-steel catenary riser-nonlinear soil finite element model,the coupled motion was studied,focusing on the changes in the touchdown zone,such as TDP,depth of penetration,etc.2.By carrying out numerical model of formation of trench under the effect of riser-soil interaction,a method of simulating trench formation is provided.The effect of soil parameters and water depth on trench formation was studied.3.Based on the fitting data of the finite element results,a formula of trench shape was provided,which was compared with he existing cubic polynomial shape formula.4.By comparing the fatigue cyclic stress of the two models between flat seabed and trenched seabed,the effect of trench on fatigue of steel catenary riser in TDZ was studied.