Pipe-Soil Interaction And Cut-Off Model Test Of Deep Water Steel Catenary Riser

The riser system is used to the connection between the floating platform and the subsea facility.Steel catenary riser,as a type of riser system,is mainly used for the transportation of oil and gas.The key issues of its research include the interaction with the seabed,the fatigue life of the touchdown point,the coupling response with floating body and Vortex Induced Vibration(VIV).In this paper,the dynamic response and fatigue life of SCR are analyzed by numerical simulation and experimental research considering the coupling of the floating body,combining with nonlinear normal seabed model and lateral Coulomb friction model.The works are as follows:Firstly,taking a SCR on a semi-submersible platform with a working water depth of1000 m as the research object,the platform-riser-seabed global analysis model was obtained based on the nonlinear pipe-soil interaction model including normal nonlinear and lateral resistance models.The sensitivity of the dynamic response and fatigue life to the key parameters of the seabed model in the TDZ of SCR and the global analysis of SCR and the floating body is studied.The influence of different key parameters on the dynamic response and fatigue life in TDZ of riser is obtained by changing the undrained shear strength,strength gradient,suction factor,suction attenuation parameter and re-penetration coefficient of the nonlinear seabed model.Secondly,focusing on the pipe-soil interaction,a prototype riser with nonlinear pipesoil interaction was established based on the P-y curve,and the prototype riser touchdown zone was intercepted to carry out the experimental research of SCR truncation model.Buckingham ? dimensional analysis method and the principle of geometry,motion and dynamic similarity were used to scale the truncated riser.A small-scale test device for the SCR truncation model was built to study the effects of the excitation motion amplitude,soil strength,and excitation motion period on the dynamic response,fatigue damage rate and the depth of the riser in the touchdown zone of the riser of the truncated model.The test device is mainly divided into four parts,the upper three-dimensional sliding table,the truncated riser model,the silty clay soil and the data acquisition system.The validity and accuracy of the test results are verified by using Orca Flex finite element software to establish a 1:1 model.Finally,the fatigue damage rate of riser contact area under small-scale model is evaluated by experimental study of measured stress value.The results show the importance of sensitivity of soil parameters in dynamic response and fatigue analysis of SCR.Numerical simulation and model test are used to verify each other,which provides theoretical basis and reference experience for SCR in offshore oil and gas development and application in China.