Study On The Vortex-induced Vibration Of Marine Pipe With Defects Considering Large Deformation

With the development and utilization of marine oil and gas resources,it's the most essential and reliable mode of transportation,marine pipeline,has been drawing people's attention,particularly its safety problems.Marine pipeline fragile can be caused vortex-induced vibration(VIV)under the marine load of current and wave.While opposed to complex marine environment,long term service with defects is common.But this fact is rarely considered in the VIV calculation in previous researches.Thus,the study on the VIV behavior of long span marine pipeline considering the effects of defect is an essencial subject.The main achievements of the dissertation are summarized in the following:(1)Based on the Euler-Bernoulli beam theory,a marine pipeline structure model is established considering the initial axial tension and the tube axial force caused by temperature field.Finite element method considering structural nonlinear large deformation is applied;nonlinear VIV time domain model is used to simulate the vortex-induced force on the pipeline,considering the flow field and pipeline coupling effect in the in-line and cross-flow at the same time;the nonlinear vibration model is solved using the incremental form of time domain integral method;the accuracy of the calculation method is then verified using example calculation;to provide accurate theory method for the study of VIV behavior of pipeline with defect,the proposed model is applied to analyzes the VIV behavior of top tension riser and marine span pipe.(2)Nonlinear fluid-structure coupling vibration calculation method is applied to calculate the VIV behavior of pipe with corrosion defect,the influence of different corrosion depth,position on the behavior is analyzed.A method to forecast the VIV behavior of pipe with corrosion is proposed,which provides theoretical reference to assess fatigue life of pipe with defects.(3)Based on the strain energy release theory and linear fracture mechanics theory,the equations of local flexibility for the straight part-through cracked pipes are proposed.The stiffness matrix of straight part-through cracked pipe is established using the equations of local flexibility,and it have been verified by example calculation.Nonlinear fluid-structure coupling vibration calculation method is used to calculate the VIV behavior of pipe with crack defect.A method is provided to forecast the VIV behavior of pipe with cracks.(4)Based on the theory of elastic mechanics.a 3D multi-layers pipe model considering weak interface between the layers is established using the state space method.the influence of different weaken degree of weak interface between the layers on the natural vibration characteristics of pipe is analyzed.This provides a new way to analyze the VIV behavior of pipe with defect.