The Study On Numerical Simulation Of Water Hammer In Long-distance High-lift Pressure Piping

In the high-lift and long-distance water supply project, as the velocity of pressure piping sudden changes, the water pressure of pipeline was rapidly increase or reduce, this phenomenon was known as water hammer or pump transition hydraulic.Water hammer has a great influence on the operation of water supply projects. The water hammer, especially accident stop pump,was higher 1.5-4 times than normal.The disconnection water hammer was greater than other water hammer. Many water supply projects suffered serious damage because of disconnection water hammer; it caused great losses of the people's production and life.Therefore, calculation of long-distance and high-lift water supply project hydraulic transition has become an important task to ensure the safe of operation of water supply projects.Only did accurate and reasonable numerical simulation of hydraulic transients, and then take the necessary and reliable water hammer protection measures, can ensure the safe operation of water supply project.The primary coverage is as follows:(1)based on the pump border and the valve border has already established, this study established mathematical model of surge tank boundary conditions.(2) Model improvement of hydraulic calculation of the transition process:this study analysis the impact of resistance items to water hammer equation, with the transient flow friction instead of the traditional friction, algorithm optimization of water hammer, simulation of hydraulic transients, thereby enhancing the computational accuracy. (3)Establish theoretical model boundary(pump boundary,valve boundary,surge tank boundary,air valve boundary),theoretical model will be prepared for the VB language module. The results were analyzed by chart display or output. (4)Through a combination of engineering practice, after simulate hydraulic transients and simulated surge tank protective measures, give out a economic and reasonable operating systems of water supply system. (5) Using Visual Basic 6.0 as the development language, combined with SQL Server 2000 database, develop a friendly interface, easy operation, complete functions, reliable performance pump station's hydraulic transition process numerical simulation systems.Several important conclusions can be summarized as follows:(1)The hydraulic transition process of long distance pipe was calculated by the Bruone variable friction model, which had a lot of advantages, such as high accuracy and fast convergence. The method was also the most important innovation in this study. (2) Under the condition of water pumping station design, the close optimum process of butterfly valve was 8s closing 70°and 40s closing 20°and then the minimum speed of the pump was 330r/min. It showed the close optimum process could effectively prevent the reverse phenomenon of the water supply unit. (3)Valve technology solution could protect the unit but it resulted in partial pressure increases the pressure pipe.Under the conditions: the joint protection of butterfly valve and intake valve, the close optimum process of butterfly valve and reasonable choice of air intake valve, water pump station project was safe within the allowable pressure.(4) In this study, some protection measures were proposed to guarantee the safe working of water supply system by one-way surge tank control.The results showed that one-way surge tank could effectively prevent the pipe negative pressure, prevented the occurrence of water hammer of cavities collapsing.