Study On The Vibration Characteristics Caused By Water Suplly Pipeline Leakage

The urban water supply network system takes on the important task of transporting water to every household.It is an indispensable base for the people’s livelihood and production,and its safety and stability are of vital importance.Due to the influence of a variety of natural and artificial factors,Leakage accidents occur frequently in urban water supply network,If the pipe leakage position cannot be found in time,it will cause a great deal of waste of water resources.At present,there are many methods for leakage detection in water supply network.Vibration acoustic technology,as a dynamic nondestructive testing method,has the advantages of convenience and speed,and has gradually become the focus of research.The characteristic of vibration sonic wave caused by pipeline leakage is related to pipeline condition,fully understanding the characteristics of pipeline vibration and leakage vibration signals is an indispensable basic work to effectively identify the vibration signals of pipeline leakage and to carry out in-depth research.In this paper,the mechanism and time frequency characteristics of vibration caused by leakage of water supply pipe are theoretically analyzed and experimentally studied,Then,the mathematical model of pipe vibration is established by combining fluid structure interaction,and the natural vibration characteristics of pipeline are analyzed.First of all,according to the basic theory of fluid mechanics and computational fluid dynamics,the flow field of the leakage pipe caused by the leakage is analyzed.The results show that the unsteady flow separation,cavitation at the leak hole and fluctuating pressure in a turbulent boundary layer are the excitation sources of leak noise of pipe.Then,the vibration characteristics of the pipe under the excitation source are studied with applying thin shell vibration theory.Based on the acoustic theory,the propagation of vibration acoustic wave in the pipeline is analyzed,the attenuation of acoustic wave is mainly caused by the viscous absorption of medium,the heat conduction of medium and the scattering of sound wave.The higher the frequency,the faster the attenuation.Pipeline leak test device and vibration detection system are set up,the vibration and acoustic wave of leakage under different pipeline conditions,hydraulic conditions and interference conditions were collected and analyzed.It is found that the signal energy collected during the leakage of the pipeline is obviously higher than that without leakage,the main frequency of the steel pipe is 2000 Hz,and the plastic pipe is 1500 Hz,and the leakage signal is stochastic and obeys the Gauss distribution.The internal pressure and shunt sizes,forms and pipe material will affect the time-frequency distribution of the signal,among them,the influence of pressure and pipe material is especially obvious.Considering the fluid structure interaction,the mathematical model of the simply supported beam vibration of the fluid filled pipe is established.It is found that the natural frequency of the pipeline is lower than that without considering the fluid structure interaction.The first two orders of frequency are 61.64 Hz and 247.14 Hz respectively,By using MATLAB software,the influence of pipeline physical parameters and fluid flow parameters on pipeline vibration characteristics is discussed.The pipeline vibration frequency decreases with increasing length and density of the pipe,velocity and density of fluid,and increases with the increase of pipe diameter and pipe elastic modulus,With the increase of pipe length,the critical flow velocity of steady-state stability decreased significantly.Then,the vibration induced by pipe fluid is simulated by using ANSYS Workbench software,and the vibration modes and frequencies of the prestressed pipe structure are analyzed.Through the experiment,the leakage phenomenon of water supply pipe is analyzed in multi angle and multi conditions,the characteristics of acoustic vibration of water supply pipeline leakage are summarized.These experimental data and conclusions provide a theoretical basis for leakage detection and location of water supply pipeline,and have certain reference value.