Study On The Vortex Induced Vibration Response Of Span Section Of The Flexible Submarine Pipeline

As the key component of offshore oil field,the submarine pipeline is one of the main equipments in offshore oil and gas exploitation.However,pipeline span occurs frequently due to the complexity of the marine environment,uneven bottom configuration and seabed erosion.The fatigue damage of the span pipeline is most likely to occur under the influence of vortex induced vibration etc,which results in the pipeline fracture,thus causes serious maritime accidents such as oil leakage.Hybrid riser is a combination of rigid riser and flexible jumper,providing a smooth and organized underwater arrangement,the hybrid riser base hooks up to the steel suction anchor which connected to the floating structure through the flexible span jumper,and tension provided by the buoyant tank.This essentially reduces the dynamic response by decoupling the riser movement from the floating structure.Under the function of current,the flexible span jumper inevitably occur with the vortex vibration and the large span ratio jumper will also stimulate the high-order vibration mode,resulting in large deformation,large displacement of the tube and other dynamic response which easily induced fatigue damage.Once the vibration frequency is close to the natural frequency of the jumper,resonance will be induced,leading to the span jumper failure or even fracture in a short time which will cause huge economic losses.At present,most of the vibration tests in vortex-induced vibration experiments around the world rely on intrusive devices such as strain gauges and acceleration sensors which are stick close to the surface of the pipe along with the pipe vibration,it will inevitably change the flow field around the pipeline and the properties of the pipeline itself,such as density,elastic modulus,Poisson's ratio,wall roughness,and other physical parameters that have a critical effect on the vibration of the pipeline,and the complex variability of the flexible tube vibrations increase importance of these physical parameters on results analysis,small changes may greatly affect the accuracy of the experimental results,thus ensuring the stability of the surrounding flow field and fixing the pipe parameters is very important.In this experiment,a non-intrusive vibration trapping mean is adopted to avoid destroying the flow field environment and changing the physical parameters of the pipeline.That is high-speed camera technology which is used to proceed non-intrusive mean of the subject,and finally realize non-intervention,non-interference pipeline vibration test.In this paper,the submarine span pipeline under shear current is used as the study object,the experimental device of flexible span pipe vibration response under the action of shear flow is designed,experimental test method of collecting pipeline vibration feature by high-speed camera and image analysis methods are formulated.Finally,successfully capturing the "beat"phenomenon of the spanning pipe.Through the comprehensive analysis of variation of the vibration mode,vibration frequency and vibration displacement over time,analyzing the effect of the velocity,"beat" phenomenon and gap G on the vortex induced vibration response of flexible span pipe.In addition,the vortex-induced vibration of the flexible span jumper under different flow rate conditions is studied.The variation of the vibration modes,vibration frequency and vibration displacement over time of the flexible span jumper is analyzed synthetically,and comparing with the vibration of the submarine span pipeline.