Numerical Study Of Dynamic Response Of Internal Flow On Marine Pipelines

Marine pipelines are one of the important components of offshore platforms,and most of them are flexible risers with larger lengths and larger diameters.As a gas transmission channel,high-speed oil or gas is usually passed through the pipeline,which has a great influence on the vibration amplitude and frequency of the pipeline.However,there are few studies on the internal vibration response of the marine riser pipeline.In this paper,the CFD numerical simulation method is used to study the bidirectional fluid-solid coupling of flexible pipe with large slenderness ratio under internal and external flow conditions,and the influence of internal flow on the vortex-induced vibration of the pipeline is analyzed.Firstly,the unidirectional fluid-solid coupling method is used to simulate the vibration response of the pipeline under the in-flow condition.It is found that under the condition that the other end of the pipeline is fixed at the other end,the internal impact velocity will promote the bending elastic tube.The tendency of the body to produce tension is due to the constraint of the support at both ends,and the overall curvature of the elastic tube shows a relatively obvious increasing trend.Then,through the numerical simulation method,the pipeline under the in-flow condition is simulated,and the Fourier spectrum analysis is carried out.It is found that the main vibration frequency domain and amplitude of the two have a large difference,and the vibration frequency and the no-inflow phase relatively low.When the low-frequency vibration of the pipeline dominates and under the influence of additional power,the frequency of the self-oscillation low frequency will also decrease,and the flexible tube will be more susceptible to the lock-up phenomenon near the low-order natural frequency of the structure.Finally,the effect of the internal flow velocity on the vibration response of the pipeline is further studied.It is founded that the vibration mode of the pipeline changes little at low flow rates.As the inflow velocity increases,the mode shape of the pipe changes greatly,and the amplitude increases,but the increase is small.In order to study the influence of pipeline internal flow in more depth,this paper changes the outflow conditions and compares the effectsof changing the inflow under different outflow environments.In the environment with large outflow,the increase of the internal flow of the pipeline will obviously increase the vibration amplitude of the pipeline and reduce the vibration frequency,and there are some differences in the influence of different locations of the pipeline.