Analysis And Study Of Fluid Induced Vibration And Its Influencing Factors In LNG Tube

Along with the national energy structure adjustment,liquefied natural gas(LNG)import volume increases,and coastal LNG receiving stations are built constantly.For the cryogenic fluid,the variable exciting force produced by two-phase flow in the LNG tube will cause the pipeline to be subjected to alternating stress for a long time,resulting in breakage.Therefore,the study of induced vibration of two-phase flow has important guiding significance for LNG pipeline transportation safety.In order to solve the problem of pipeline vibration induced by liquefied natural gas,the cryogenic fluid,the coupling effect between fluid and tube structure is studied based on the flow pattern of LNG under different conditions.Firstly,according to the LNG transport process,research object is selected,the physical model,mathematical model and simulation model parameters is established,the flow state of LNG in the pipe under different conditions was carried out by using CFD simulation software.Based on the principle of fluid solid interaction,and coupled calculation of LNG flow and pipeline transient structure is analyzed by finite element software.Than the dynamic response characteristics of the tube structure under the action of fluid are analyzed.Secondly,the simulation value is used as the test value,and the main influencing factors and secondary influencing factors are obtained by orthogonal design method and the multi factor sensitivity analysis for the simulation results.According to the above research methods,the following conclusions are drawn:(1)The bubble polymerization and burst will appear in the process of the two-phase flow flowing the elbow.The increase of ambient temperature,entrance flow velocity,and the decrease of entrance pressure will make pipe cryogenic fluid gasification more obvious.While the entrance velocity increases to a certain extent,the environmental heat transfer effect will also increase.and gasification rate will have a growth trend;in the normal operating range,the pressure changes in the tube gasification boils and the most obvious influence.(2)According to the liquid flow rate getting larger,or the gas content in the inlet section getting lower,the flow pattern in the pipe will change according to the law of stratified flow pattern,plug flow pattern and bubbly flow pattern,and the coupling effect between two phases will increase in sequence.Through the monitoring and comparison of tube wall pressure,the energy level of excited force caused by the plug flow is the highest,and the level of excited force caused by stratified flow is the smallest.(3)The coupling effect between bubbling flow is small,so the vibration of pipeline is mainly caused by liquid phase.After being impacted by fluid,the pipeline will generate larger vibration and then become stable.The increase of inlet velocity,ambient temperature and the decrease of inlet pressure will eventually lead to the increase of vibration intensity,and the alternating stress on both sides of the horizontal direction of the pipeline will also increase.(4)Pipeline vibration strength in numerical simulation is analyzed based on orthogonal design,than use SPSS analyzing significant of simulation results to analyze,according to the size of the significant regression coefficient P value in a table,the impact order of various factors should be ‘inlet velocity> pressure > temperature',and the linear regression equation between pipeline vibration intensity and the influence factors is suitable for the bubble flow.