Research On The Internal Two-Phase Flow Induced Vibrations In Subsea Pipelines Based On The Fluid Structure Interaction Methods

It's usually multiphase flow mixed with oil,gas and water in subsea oil pipeline.When gas and fluid flow through the pipe and it will form various flow patterns gradually which will induce pipe vibration.The vibration of the pipe will cause the damage of the pipeline,thus reducing the efficiency of production.Most of worse,it will bring unpredictable pollution to the environment.In consideration of these,it's highly important to do some research about the vibration induced by multiphase flow of subsea pipeline.This paper embarks from the transmission of single-phase flow in vertical tube.Based on the energy conservation of Hamilton's principle,equation of fluid-structure coupling for vibration of the single-phase flow pipeline is established.After integral solution,expressions for natural frequency of the pipe and internal flow critical velocity are obtained.Compare the results from expressions to results from DNV guideline,there are few differences between these two.Then the relationship between internal flow velocity,internal pressure and pipeline natural frequency was calculated by using Maple software.It is found that the natural frequency of pipeline decreases with the increase of the internal flow velocity and pressure in the pipe.On the foundation of free vibration for single-phase flow pipeline,using the concept of two sliding speed ratio,in the simply supported end and another clamped end,deduces equation for vibration of multi-phase flow.Besides,the function of outer flow field is simplified as added mass.Then analyze the difference of natural frequency between considering the additional mass or not.It is found that natural vibration frequency of pipe becomes smaller when the outer flow field is considered.After that,the influence of parameters on the frequency is discussed respectively.In addition,the modal analysis of the pipeline is carried out,and the rationality of the derived formula is verified by comparing the calculated results with the formula.Finally,ANSYS/CFX module is used to analyze the vibration of pipeline under complex flow pattern.And by setting the different gas and liquid ratio,the changes of stress and displacement of key point are accessible to be monitored.Besides,the law of vibration for pipeline is also available.