Study Of Out-of-plane Motion Of SCRs With Rigid Swing

With the development of offshore oil and gas industry, exploitation activities indeepwater are increasing greatly. As key equipments connecting platforms and wells,risers hold a significant position in ocean resource development. Steel Catenary Risers(SCRs) are a new type of deepwater risers developed in recent years, they overcomethe limitation of traditional flexible risers and TTRs and become the preffered risersystems in deepwater development now. Vortex induced vibration (VIV) is the coreproblem in the design of SCRs, special configurations and complex flow make theVIV analysis of SCRs much more complicated than TTRs. So the study of dynamicmodel and VIV property of SCRs in this paper has great significance in theory andapplications.SCRs are the flexible structures with large deflection, so the simulation of themby commom beam model is very inaccurate. Based on the theory of flexible cable,SCRs are modeld by small extensible slender rod with bending stiffness in this paper,the large curve of TDP and continuous distribution of tension are considered in themodel, the control equation is established and then the corresponding dynamic code ofSCRs, CABLE3D, is used to solve the static and dynamic problem.Based on VIV experiment of flexible cylinders and the revised lift force model, atwo-way VIV model of SCRs with fluid-structure interaction, beyond lock-in district,is proposed in the paper, both in-line vibration with pulsating drag force andfluid-structure coupling of cross flow are included in the new model. The studiesshow that the model has clear physical interpretation and can describe the VIV ofdeepwater risers pretty well. TDP is the feature point of SCRs, the special analysis ofTDP in the paper shows that the VIV response of the point is the local extremum andthe frequency component is complex, the point decides the fatigue life of SCRs, so theVIV study of TDP is an unavoidable problem in the study of SCRs.Due to the large curvature of sag bends, rigid swing model of SCRs is proposedin the paper, the model takes SCRs as rigid swing systems about the axis from thehanging point to the touch down point (TDP), if the direction of environmental loadhas a angle with SCRs plane, the torque is then produced of the force and the vectorfrom the axis to the riser, which provide the driving force for the swing and the weightof the riser provide the restoring force. The rigid motion is coupled with bendingvibration as inertial force and hydrodynamic damping, then the out-of-plane motion ofSCRs with both bending vibration and rigid motion are simulated. The studies show that the response of rigid motion have a magnitude equal to that of the bendingvibration, rigid motion affects the dynamic response of lower part of SCRs greatlyand can not be ignored in their dynamic analysis.The study of rigid swing model of SCRs and VIV analysis of TDP is still atprimary stage in the paper, the deficiency is unavoidable when the new ideas andmethods for the design and research of SCRs are provided, so the further considerablestudy on the dynamic property of SCRs is very essential in the future.