Study On The Axial Vibration Characteristics Of Stress Wave Excited By Water Hammer In Pipelines

Stress wave pipeline detection technology is a method with small excavation area,long detection section,simple method,convenient construction and dynamic detection.Water hammer is a phenomenon that often occurs with the change of pipeline working conditions,and it often causes strong pipeline vibration due to its huge energy,which is difficult to avoid.When there are singularities(abrupt change points of physical characteristics of pipeline,such as stress concentration,corrosion,scaling and leakage),one or more physical parameters of pipeline,fluid and other boundary conditions may change.Therefore,by analyzing the characteristics of pipeline stress and stress wave under different conditions and parameters,pipeline health monitoring and pretreatment are studied by using the pipeline stress wave vibration excited by water hammer.The method of preventing pipeline leakage is of great value in reducing resource waste and preventing potential safety hazards.The propagation characteristics of stress wave in pipeline depend on the excitation characteristics,pipeline material characteristics,structure and fluid characteristics,flow state and other environmental factors.In this paper,the finite element simulation software and experimental detection method are used to simulate the vibration response of pipeline excited by water hammer caused by the sudden closing of valve.The specific research contents are as follows:1.The amplitude and period variation of water hammer pressure wave under different environmental physical conditions and parameter settings(including elastic modulus,inner diameter and wall thickness of pipeline,velocity and density of fluid,etc.)are studied.2.The stress curves of the valve end of pipeline excited by water hammer effect under different environmental physical conditions and parameter settings were studied.3.Short time Fourier transform(STFT)was used to study the time-frequency characteristics of stress wave axial vibration response of pipeline excited by water hammer under different environmental physical conditions and parameter settings.The results show that the pressure variation and period of water hammer under different parameters are consistent with the theoretical value.The young’s modulus,inner diameter and wall thickness of the pipeline have a nonlinear relationship with the pressure variation of the first water hammer,and the flow velocity and density of the fluid have a linear relationship with the pressure variation of the first water hammer.The amplitude of the valve end stress is affected by the impact of water hammer,the physical parameters of fluid and pipeline,so the periodic variation of the valve end stress is different from that of the water hammer pressure wave.Under the impact of water hammer,the pipeline will produce stress wave response with rich amplitude frequency distribution in time domain.The change of fluid parameters has more significant effect on the amplitude,and the change of pipeline parameters has more significant effect on the vibration frequency.The amplitude frequency characteristics of axial vibration of stress wave with the change of physical parameters include:(1)With the increase of fluid velocity and density,the water hammer pressure will increase greatly,so the amplitude of stress wave will increase greatly.While the increase of Young’s modulus,inner diameter and wall thickness of pipeline will make the amplitude of stress wave decrease slightly.(2)The increase of Young’s modulus,inner diameter and fluid density will increase the overall vibration frequency of stress wave,and the increase of pipe wall thickness will decrease the overall vibration frequency of stress wave.(3)The fluid velocity only affects the amplitude of the stress wave,but has no effect on the vibration mode and frequency.(4)Under the same fixed parameters,changing a single variable has different effects on the time-frequency characteristics of stress wave excited by water hammer.