Research On Characteristics Of Pipeline’s Singularity Under Water Hammer Excitation

With the development of modern industry and life,pipelines have been widely used in water conservancy,electric power,oil and natural gas industries.In daily life and industrial production,the safeness of the pipeline has become an important characteristic that the workers must take into account when laying the pipeline.In this paper,the non-penetrating damage of pipeline,the decrease of local wall thickness of pipeline,and the change of property of local pipe material are defined as the appearance of singularities of pipeline which have a lot of characteristics such as depth,axial length.For example,when the local wall thickness of the pipe decreases,the singularity corresponds to the decrease of the wall thickness,and the depth of the singularity is the percentage of the wall thickness decrease.To study the origin,development and evolution of this kind of singularity,the location and characteristics of the singularity on the pipeline will be obtained before the rupture of the singularity,which is convenient for the fixed-point excavation and maintenance cost evaluation.When the pipeline is running stably,if the pump is suddenly stopped or the valve is shut off,the water hammer will easily occur.The highest pressure caused by the periodic fluid fluctuation can reach dozens of times of the normal operating pressure of the pipeline,which is one of the main problems of pipeline operation safety.Scholars at home and abroad have carried out a great deal of numerical analysis and experimental research on the generation of water hammer,the calculation of the speed of water hammer wave,etc.A lot of achievements have been obtained about the devices of preventing water hammer,pipeline topology,auxiliary facilities and so on.The steady operation of the pipeline is maintained,but the cost of the pipeline project increases correspondingly.The water hammer wave is transmitted in the pipeline which is the transmission channel of the water hammer wave.During the transmission process,it will carry a number of characteristic parameter values associated with the flow pipeline.To obtain and evaluate the physical properties of pipeline singularities from these parameters is a self-detection method.It has obvious advantages in the aspects of flow loss control,detection cost,pipeline monitoring cost and so on.In this paper,the relationship between the parameters of water hammer wave and the multi parameter set of pipeline singularity is studied by using the water hammer wave as the excitation.A three-dimensional model of a fluid-free pipe and a fluid-filled pipe are constructed,and COMSOL is used to simulate the sudden water hammer phenomenon at the end of the fluid pipeline.What’s more,the detection points are set to detect the singularities of the pipeline with different characteristics,and the effects of these singularities on the parameters such as stress,pressure and displacement of the pipeline are studied.It is found that when the inner fluid is ignored,with the increase of the depth of the singularity,the stress waves between the detection points appear ripple and amplitude increases.Considering the fluid in the pipe,when the water hammer excites,the stress wave amplitude increases with the depth of the singularity when the singularity exists in the pipeline.The effect of the axial length of the singularity under water hammer excitation is not as obvious as that of the depth of the singularity.The damping design of the pipeline can be realized by changing the local material of the pipeline.The simulation is verified by experiment,and the experimental system including valve,booster pump,water pipe,water tank,high precision accelerometer,flowmeter and data acquisition system is set up.Compared with the simulation data,the experimental data shows a similar trend: the depth of the singularity increases and the amplitude of the pipeline vibration increases,but the effect of the axial length of the singularity on the pipeline vibration is not obvious,the vibration parameters of pipeline change with the change of singularity material.The results of this paper show that there is a corresponding relationship between the singularity characteristics and pipe vibration parameters under the excitation of water hammer.The research based on the characteristics of pipeline singularity under water hammer excitation provides the mechanism feasibility to realize the pipeline leak detection before the pipeline singularity becomes the leak point.