Analysis And Simulation Of Water Hammer In Long-distance Gravity Flow Pipeline In Hilly Area

The problem of uneven distribution of water resources in China is prominent,and the contradiction between supply and demand of water resources is acute.Long distance water transportation projects are an effective way to solve this problem.Long distance pipeline water transportation has been widely used in practical engineering due to its low requirements for geological conditions and external environment,simple construction,low operating costs,and low water quality pollution during the water transportation process.However,during the operation of pipeline water delivery systems,water hammer phenomena often occur due to sudden situations such as valve opening or closing too fast,sudden shutdown of water pumps,etc.,posing a serious threat to the safe operation of the project.Especially in mountainous areas,long-distance gravity flow pipelines are more susceptible to water hammer and damage due to the impact of terrain fluctuations during water delivery operations.Therefore,this article focuses on the characteristics of large drop,long distance,and undulating terrain of gravity flow pipelines in mountainous areas,and conducts water hammer analysis and simulation research on long-distance gravity flow pipelines in hilly areas,in order to accurately predict and prevent water hammer damage to water pipelines,and improve the safety and reliability of pipeline water transportation projects.The main research results are as follows:(1)The basic theory and calculation method of pipeline water hammer are systematically summarized,and the characteristics of water transmission pipeline engineering in hilly areas are analyzed.It is believed that the pressure generated by water hammer waves in curved pipelines is greater than that in straight pipelines.Due to the water hammer phenomenon,serious negative pressure can easily occur at the hump of the pipeline.The traditional water hammer calculation method approximates curved pipelines to straight pipelines,resulting in errors in the calculation results,A water hammer calculation method is proposed for dividing water transmission pipelines into curved sections and straight sections with inclined angles.(2)Using the limit concept,the curved pipe section is vectorized using a tangent based curve method and fitted as multiple equivalent straight short pipes with the same flow cross-section along the pipeline centerline for water hammer calculation.The connection conditions between each fitting short pipe are treated as a simple pipeline in series,and an energy loss correction coefficient is introduced.Considering the local resistance generated by water flow in the bend,the fitting equivalent short pipe and the inclined straight pipe are combined for water hammer calculation,A numerical calculation model for gravity flow pipelines in hilly areas has been established.(3)Taking a gravity flow pipeline water conveyance project in Qianyang County,Shaanxi Province as an example,the traditional method of characteristics and the elbow fitting numerical calculation method established in this paper are used to calculate the water hammer respectively.The calculation results show that the local resistance of the elbow will affect the attenuation process of the water hammer pressure wave,and the positive and negative pressure calculated by the proposed total calculation of the elbow is greater than that calculated by the traditional method of characteristics method,which is consistent with the existing experimental research results,Verified the rationality of the water hammer calculation model established in this article.(4)The water hammer phenomenon occurred without taking protective measures was analyzed.When the control valve at the end of the pipeline was quickly closed,a significant negative pressure was generated at the large undulating position along the pipeline.The positive pressure at the section of the control valve at the end of the pipeline was the largest,with a positive pressure head of 87.58 m.By simulating the changes in water hammer pressure generated under nine different valve closing time conditions,it is concluded that the optimal valve closing time for the example project is 50 s ≤ T ≤ 120 s.(5)Based on the characteristics of water hammer without taking water hammer protection measures,the method of combining intake and exhaust valves and overpressure relief valves to protect water hammer is selected,and the optimal installation location of intake and exhaust valves is determined.The simulation calculation results show that using combined protection measures of intake and exhaust valves and overpressure relief valves can effectively alleviate the occurrence of water hammer in long-distance gravity flow pipelines in hilly areas,ensuring that the pressure in the pipeline is within the allowable range of design pressure.