| According to the opinion of the Central Document No.1 of 2020 on the promotion of integrated urban-rural water supply,the urban water transmission network will increase investment and construction.In order to ensure the safe and stable operation of the water transmission network,it should carry out water hammer calculations under multiple working conditions.This article takes the ring water transmission network of an urban-rural integrated water supply project in a county of Jiangsu as an example.It is calculated and analyzed using the water hammer calculation model based on the flow-cutting bridging water hammer model and the MIAB dynamic friction model.1.Based on the basic theory of water hammer and combined with the boundary conditions of the water pipe network,this paper gives the program flow of the water hammer calculation model based on the flow-cutting bridging water hammer model and the MIAB dynamic friction model.It provides a theoretical basis and technical guidance for the calculation of water hammer in the ring water transmission network.The experimental pipeline was built to conduct the flow-cutting bridging water hammer experiment,and the pressure fluctuation law was analyzed and studied.The experimental data was compared with the simulated data to verify the reliability of the water hammer calculation model.2.Take the actual water transmission network as an example to build a water hammer calculation model,and calculate pump-stopping water hammer.The results show that the sudden stop of the pump will cause the pressure fluctuation of the entire water transmission network to be sharp,and its maximum pressure rise exceeds the steady state of 311.89 m.There are many places in the water transmission network that occur the flow-cutting bridging water hammer,seriously endangering its safety.Because pump-stopping water hammer is transmitted from the pump station to the periphery of the transmission network,it is proposed that the focus of water hammer protection should be placed inside the pipeline network(especially the internal supervisor)and other point that occur the flow-cutting bridging water hammer easily.Calculations show that setting a certain number of the box type bidirectional regulating towers can effectively reduce pressure fluctuations caused by pump shutdown.3.Calculate the end valve-closure water hammer caused by the sudden closing of the end of the branch pipe of the ring water transmission network.The results show that the sudden closing of the valve will cause a larger water hammer pressure increase at the valve and the corresponding branch pipe.At the same time,the more valves closed,the more obvious the pressure fluctuation of the pipe network.The worst case is that all valves close rapidly at the same time,resulting in severe pressure boost of the entire water transmission network,with the maximum pressure boost exceeding steady state 168.73 m,seriously endangering the safety of the network.Because the valve closing water hammer has the characteristics of being generated from the valve and transmitted from the periphery of the pipe network to the inside of the pipe network,it is proposed that the protection of the water hammer should be placed at the valve at the end of the branch pipe.Calculations show that the use of orifice flow control valves to extend the end valve closing time can effectively reduce the valve-closure water hammer boost.4.Through the analysis of the data of end valve-closure water hammer,it is found that the longer the branch pipe or the secondary branch pipe,the bigger the pump-stopping water hammer.The greater the flow rate of branch pipe,the greater the fluctuation range of water hammer corresponding to valve closing.When the water hammer boost produced by each valve propagates to the pipe section with a larger diameter,its pressure fluctuation will weaken obviously. |
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