Model Research On The Inter Diameter Variation Characteristic Of Water Supply Pipe Based On Frequency Response Function

Establishing the model of inter diameter variation characteristics in water supply pipe is not only conducive to locate the corrosion or blockage point in pipeline inwall quickly and accurately,but also plays an important role in evaluating the current state of the pipeline.The corrosion of pipeline inwall leads to the decline of pressure ability of water supply pipeline,and the blockage in pipeline inwall results in the decline of water delivery ability.This paper uses pipeline experiment to test and verify the model of inter diameter variation characteristics.Based on transient flow solution equation: motion and continuity equation.Frequency response equation includes base pipeline information,boundary conditions and the information of inter diameter variation characteristics in pipeline.Frequency curve of transient pressure signal is useful for the optimization solution of inverse problems of basic elements in pipeline.The effect of the location and amplitude of the resonant peak is considered by unsteady friction and steady friction.Friction only has influence on the amplitude of the resonant peak,and has no effect on the location of the resonant peak.Based on the above analysis of the influence of friction on the resonant peak,three aspects of researches will be carried out through theoretical modeling and experimental verification:(1)establish the relation between frequency response pressure(h)and peak number(m),and the location of inter diameter variation characteristics can be calculated by the phase divided by?.(2)deduce the relation between the degree of the resonant peak shift(??rf)and the change in length of pipe wall inter diameter,and the research shows that the higher the periodic disturbance frequency of valve is,the more accurate the assessment of the change in length of pipe wall inter diameter will be.(3)resonant peak shift is an increasing function of the changing degree of inter diameter in pipeline.The maximum of the resonant peak shift can be used to evaluate the degree of changes in pipe wall thickness.The relative frequency(?(r))of the closure valve is less than 2/t0r(linear closure time),linear closure valve is approximately equal to the transient closure valve.The frequency response function of valve linear closure in the end of pipeline is set as an objective function,which covers unknownvariables: the change location of the pipe wall inter diameter and the change degree(pipe wall thickness)of inter diameter in the pipelines system.Combining the frequency response function of the periodic disturbance frequency of valve,the continuous change of pipeline inter diameter can be assessed using the two types of valve closing ways.The objective function is optimized by the genitive algoritm(GA).The error of the periodic disturbance is less than that of linear closing of valve,and total estimation erroris less than4%.Taking into the consideration of the influence of periodic disturbance in boundary conditon on the optimization solution of the inter diameter variation characteristics in pipeline,it’s better to avoid the location where the disturbance of upstream boundary conditions leads to the distortion of frequency response function.And then we can still obtain the accurate result of the inter diameter assessment in pipeline.Time-frequency method is established to carry out a dynamic study on the inter diameter variation characteristics in pipeline.Through empirical mode decomposition(EMD),the collected pressure signal can be denoised and decomposed to model signal.The signal then is performed by Hilbert transform to get the time-frequency spectrum of inter diameter variation characteristics in pipeline.Based on the verified pipe wave velocity and distortion time of inter diameter characteristics,the variation of pipeline characteristics can be located.