| Several kilometers drilling risers supported only at the platform and the wellhead are a key part of the riser systems.Under the effect of ocean current,long flexible risers is easily excited to vortex-induced vibration,which can cause fatigue damage and even riser fracture or oil leakage.In this paper,the vortex-induced vibration test of the riser-wellhead coupling model is performed under uniform flow according to the actual project.In the test,the platform offset is also considered.Compared with a single riser,the response of vortex-induced vibration of riser-wellhead coupling model is analyzed for different offsets and different current velocity.Firstly,it introduces the background of vortex-induced vibration,the summary at home and abroad about four aspects: theoretical research,numerical simulation,rigid cylinder test,and flexible riser test.Then,it introduces the basis of vortex-induced vibration and the important parameters of vortex-induced vibration,and specifically introduces the new phenomenon of traveling waves and time-sharing of flexible risers.Then it introduces the calculation of the full-scale model and four different spring stiffness scale models by using Orca Flex.The displacement,velocity and tension of different models are compared and analyzed.Therefore,the feasibility of the scale cut-off model is verified and an appropriate spring stiffness is determined for the riser vortex-induced vibration test.Later,the riser-wellhead coupling model and the single riser model tests are introduced.The test facility,test machinery,riser model,pipe-soil device and tension device are described in detail.Finally,the data processing method-modal superposition method is explained in this paper.It analyses drag displacement,drag coefficient,dominant frequency and mode,cross-flow and in-line strain,and amplitude of different riser models(single riser and riser with soil-pipe coupling)under different flow velocity and different platform offsets. |
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