Study On Vibration Characteristics And Control Method Of Gas-Liquid Two-Phase Flow In Pipeline

During the exploitation of offshore oil fields,oil,gas,water and other mixtures are transported to FPSO through submarine oil pipelines for further treatment.Gas-liquid two-phase flow often exists in the pipeline.When the flow flows through the elbow and other positions,it is easy to cause severe vibration of the pipeline.Flow induced vibration is one of the main causes of pipeline failure.Focusing on the flow induced vibration characteristics of pipeline,this thesis focuses on the flow induced vibration law of pipeline under different working conditions,so as to provide reference and basis for two-phase flow pipeline vibration response prediction and vibration control.The main work of this thesis is as follows:Based on Hamiltonian principle,the transverse vibration equation of pipeline with internal flow is established.Based on the vibration mode function of the beam model,the expression of the first two natural frequencies of the pipeline is solved,and the relationship between the natural frequencies of the pipeline and the internal flow parameters and pipeline parameters is obtained.Through numerical simulation and comparison with the theoretical model,it is found that the two results are in good agreement.The fluid structure coupling analysis of two-phase flow pipeline is carried out by using numerical simulation method.The modal of gas-liquid two-phase flow pipeline with elbow is analyzed.The modal analysis results of the three calculation methods are not significantly different in vibration mode,and the natural frequency value of adding fluid solid coupling is smaller.Therefore,it is necessary to add fluid solid coupling analysis to the calculation.The transition process of gas-liquid two-phase flow pattern in elbow is studied.The influence of liquid velocity on convection pattern is stronger than that of gas velocity.With the increase of gas velocity,it mainly shows the characteristics of slug flow with large bubbles wrapped by liquid film;With the increase of liquid velocity,the internal fluid flows alternately by massive bubbles and liquid slugs.In the analysis of flow induced vibration characteristics of pipeline,ten working conditions dominated by slug flow are selected for simulation.The vibration trend of each monitoring point of the pipeline is basically the same.The vibration amplitude at the center of the elbow is the highest,mainly in the inflow direction.With the increase of gas phase velocity of two-phase flow,the amplitude of pipeline displacement and acceleration increases,and the distribution of main vibration frequency is more extensive.With the increase of liquid phase velocity,the amplitude of pipeline displacement decreases,but due to the shortening of charging time,the amplitude of acceleration increases,which has the characteristics of multi peak and high energy in frequency domain.Through the research on the flow induced vibration characteristics of two-phase flow pipeline,the proposed pipeline reconstruction scheme has good vibration reduction effect.At the same time,when designing the pipeline in the early stage,the drastic change of internal flow field should be avoided as far as possible in the process,so as to reduce the harm caused by flow induced vibration.