| In recent years,urban waterlogging disasters caused by heavy rainfall in cities have become more frequent.Waterlogging disasters not only cause huge economic losses,but also seriously threaten the personal safety and property safety of residents.An effective means to reduce waterlogging disasters is to improve and optimize the pipe network system.The construction of the pipe network system mainly has two aspects:pipeline layout and pipe selection.Scholars have conducted a lot of research on pipes and found a suitable new pipe:glass fiber reinforced plastic concrete composite pipe.In this paper,a detailed flow-induced vibration analysis of the pipeline is carried out,which makes up for the shortcomings of the pipeline in the vibration control design theory,and provides a reference for the selection and service conditions of the pipeline.The main research contents and results are as follows:（1）According to the dynamic theoretical model established by the pipeline,the simulation analysis of flow-induced vibration is carried out.According to the comparison of the natural frequencies of the first 30 orders of the pipeline in different states,it is necessary to consider the fluid-structure interaction of the pipeline.When considering the fluid-structure interaction of the pipeline,its natural frequency will be reduced compared with the free state,and the lower frequency is easy to cause the pipe resonance,and the possibility of pipeline damage due to resonance is greatly increased.（2）Observing the modes of each order,it can be found that the main low-order modes that affect the vibration,and according to the displacement data of the low-order mode shape analysis,it can be seen that the concrete layer is mainly displaced in the free state of the pipeline,and the FRP layer is mainly displaced in the fluid-structure interaction state.It shows that flow-induced vibration has the greatest influence on the inner layer,and also confirms the superiority of the design of adding an inner lining layer to the concrete pipe.Therefore,when dealing with actual engineering vibration problems,only low-order modes need to be considered.（3）Based on modal analysis,the influence of different fluid influencing factors on pipeline vibration characteristics is considered.In the fluid velocity part,four velocity parameters of 5m/s,10m/s,15m/s and 20m/s were taken for discussion and research.In the fluid pressure part,four pressure parameters of 0MPa,5MPa,10MPa and 15MPa were taken for discussion.The results show that the fluid velocity has little effect on the natural frequency of the pipeline and is negligible.Under non-high-pressure conditions,fluid pressure has little effect on the natural frequency of the pipeline,so it can be determined that the fluid velocity is not the main influencing factor that deforms the pipeline,and the influencing factor of fluid pressure only needs to be considered when necessary.（4）After considering the influencing factors of fluid,the influencing factors of the tube body were then discussed and analyzed.The influence of three parameters of pipe body length,inner diameter and wall thickness on the vibration characteristics of pipeline is mainly discussed.Among them,the length change of pipe body has a significant impact on the fluid-structure interaction vibration analysis of pipeline.The longer the length of the pipe body,the lower the natural frequency of the pipe,and the greater the maximum displacement of the pipeline;The degree of influence of the inner diameter of the pipe is second,the larger the inner diameter,the higher the natural frequency of the pipe,and the smaller the maximum displacement of the pipe;The analysis results of the wall thickness of the tube are almost identical to the inner diameter of the tube.Therefore,in the practical engineering application of glass fiber reinforced plastic concrete composite pipe,we need to select the appropriate pipe length according to the numerical simulation results.In this way,the influence of flow-induced vibration on the pipeline can be effectively avoided,the possibility of pipeline damage can be reduced,and the service life of the pipeline can be extended.（5）Select the midpoint of the pipeline as the observation point and analyze the harmonic response of the pipeline.The results show that with the increase of the excitation frequency,the displacement of the observation point in all directions peaks.The displacement in the X,Y,and Z directions all peaks at a frequency of 4×10-3Hz,while the displacement in the Z direction peaks at two excitation frequencies:4×10-3Hz,2×10-2Hz,of which 4×10-3Hz peaks are the largest.The maximum displacement in all three directions occurs at 4×10-3Hz,indicating that the corresponding order at 4×10-3Hz,that is,the first and second orders,the amplitude of the observation point is the largest.It shows that the pipeline is most prone to resonance at this time,so the natural frequencies of the first and second orders should be avoided in the actual engineering design.（6）On the basis of harmonic response analysis,the support mode that should be selected for the pipeline is discussed.The results show that under the premise of fixed constraints on the entrances and exits,it is feasible to add constraints to the pipeline to control vibration,while adding constraints in the middle of the pipeline has the best effect on controlling vibration,and the effect in other locations is slightly inferior. |
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