Research On Influence Of Viscoelastic Mixed Pipeline Characteristics On Its Hydraulic Transient Dynamic Behavior

Pressurized pipelines such as urban water supply,heating,and gas supply are the lifeline to ensure people’s normal life,but there are many problems in pipeline transportation,among which the more prominent problem is the transient hydraulic flow problem that can cause tearing of pipes and fittings.Therefore,it is necessary to study the hydraulic transient dynamic behavior in pressure pipelines.In recent years,the hybrid pipeline system in which elastic pipes and viscoelastic pipes coexist is gradually replacing the single material pipeline system.Compared with the traditional elastic pipes,the velocity of the transient flow pressure wave of the hybrid pipe system and the rate of fluctuation attenuation are different.The reason is that the constitutive properties of viscoelastic pipelines are affected by many factors such as temperature,molecular structure of the material,and pipeline constraints.In addition,the pipeline dimensions of the pressure pipelines studied in the laboratory(the ratio of pipe length to pipe diameter and the ratio of pipe length to wave velocity)are smaller,while the pipeline dimensions in the project are larger than those in the laboratory.Therefore,some research results of the laboratory have limitations in the application of actual engineering.The pipe characteristics and scale characteristics of the mixed pipeline have to be applied to the hydrodynamic behavior of transient flow(transient pressure wave propagation velocity(wave velocity)and the propagation process The decay rate of pressure wave of transient flow,etc.)The following researches are carried out from experimental research and theoretical analysis:First,on the basis of designing and building a pipeline transient flow test bench,a transient pipeline flow experiment was conducted to study the transient flow of upstream and downstream valve closing under different initial flow regimes.Subsequently,on the basis of this experimental platform,some of the elastic pipes were replaced with viscoelastic pipes,and the transient flow experiment of the pipes mixed with viscoelastic pipes was carried out.Collect pressure data at each pressure measurement point.Secondly,the transient flow pressure data of different pressure measurement points under the same experimental conditions are collated and qualitatively obtained the influence law of different pipeline lengths and pipeline materials on transient flow pressure waves.Attenuation analysis of pipeline friction resistance and pressure wave is carried out on transient flow under different initial flow conditions.Then through the spectrum analysis of the pressure wave of each group of transient flow experiments,the variation law of the pressure wave velocity of the transient flow under different working conditions can be obtained.The results show that the attenuation rate of the transient flow pressure wave is related to the initial flow state and the pipeline material;the transient flow pressure wave period(wave velocity)is related to the valve closing characteristics,the fluid in the pipe and the upstream and downstream boundary conditions.Finally,combined with the theoretical analysis of the constitutive characteristics and friction of viscoelastic pipes,the influence of different pipe characteristics on the hydrodynamic behavior of the transient flow in the pipe is obtained.Through theoretical analysis from the small pipeline scale in the laboratory to the actual large pipeline scale,it is found that the dissipation of hydraulic transient pressure waves caused by unsteady friction decreases with the increase of pipeline size and length.In large-scale pipeline systems,the non-steady-state frictional resistance has a small contribution rate to the dissipation of hydraulic transient pressure waves,and the viscoelastic effect of hybrid pipelines is more important.For large-scale pipelines and mixed pipelines with relatively high viscoelastic pipe materials,the transient wave pressure wave velocity is small.Therefore,it is necessary to construct a suitable hydraulic transient attenuation model according to the actual pipeline characteristics to effectively improve the calculation efficiency.