Research And Application Of The Transient Control Method To Pump Systems And Tree Gravitational Flow Systems

With the development of the national economy of China,long-distance water transfer projects have increased in number.Therefore,the primary task is to ensure the safe operation of all projects,especially pump systems and tree gravitational transfer systems.The transient process of pump systems can be caused by several factors.One factor is the disturbance arising from artificial adjustments,e.g.,valve regulation in pump systems,adjustments to the vane fitting angles of adjustable vane pumps,and rotation speed regulations in water pumps.Another factor is the system disturbance caused by other accidental factors,e.g.,pump trip due to power outage.The transient process caused by accidental pump trip is usually the major reason for pipe rupture or other engineering accidents.The water of tree gravitational flow systems comes from a single source,but numerous water consuming points are set up.Compared with ordinary water transfer systems,tree gravitational flow transfer systems are more complicated and face more uncertainties in the transient process.If the end valves of branch pipes are closed or opened successively,the transient pressure wave may be superposed and cause extremely high positive pressure or negative pressure.Therefore,this study explores the transient control methods for pump systems and tree gravitational flow systems.These methods could not only improve the transient control effect on pump systems and tree gravitational flow systems but also reduce the capital investment in transient control measures.Hence,these methods are of great significance in cutting construction costs,improving operational safety,and enhancing system reliability and stability.With the combination of theoretical analysis,numerical simulation,and practical application,this study adopts transient flow theory and a numerical computation method,as well as Matlab,to further investigate the transient control methods for pump systems and tree gravitational flow systems on the basis of previous studies.The findings are as follows.1.Air valves are commonly installed in water pipes.At present,air valves are always used in practical projects.A mismatch of air valve type and hole size may prevent air from entering the pipes timely and thus cause vaporization.It may also cause the air within the pipes to release too quickly and result in transient positive pressure,which may give rise to water column separation.To study the transient control mechanism of air valves,the transient control effect,and the influencing factors of the transient control effect,we employ basic transient flow theory and the method of characteristic to set up the boundary conditions for air valves.Matlab is used to perform the numerical simulation computation for the case.The computation results indicate that an air valve with intake and exhaust holes of varying sizes achieves better transient control effect than an air valve with intake and exhaust holes of the same size.The major influencing factors of the transient control effect of air valves are the intake hole area Ain,exhaust hole area Aout,hole area ratio ?,and upward pressure coefficient?.In practical engineering applications,we need to optimize the computation for the influencing factors of air valves on the basis of practical requirements to achieve an optimal transient control effect.2.A bypass pipe is an affordable and easy-to-use water hammer protection measure often used to control the transient extreme pressure caused by pump trip accidents.At present,some limitations arise when traditional bypass pipes are used in practical engineering.This study seeks to improve traditional bypass pipes by eliminating limitations and developing an improved bypass pipe.Compared with that of traditional bypass pipes,the control valve of the improved bypass pipe is a hydraulic control valve that is opened or closed with a UPS controller.The improvement allows the opening and closing of the hydraulic control valve to be controlled precisely.This enhancement is also conducive to transient control.Mathematical models of the complicated systems of bypass pipes,check valves,and water pumps are set up with the method of characteristic to study the transient control effect of the improved bypass pipe.By taking the water supply project of an industrial zone as a research subject,we conduct a numerical simulation of the transient process of a pump water supply system after an accidental pump trip.Additionally,we perform a sensitive analytical research into the key influencing parameters(diameter d and length l of the improved bypass pipe and the opening and closing times of the hydraulic control valve of the pipe,t1,t2,t3,and t4)of the transient control effect of the improved bypass pipe on the basis of six schemes.Ananalytical comparison is also made between the changes in a typical section of a pump water supply system and pipeline pressure envelop under extreme pressure.The improved bypass pipe with appropriate parameters can bring the transient pressure of the water transfer system under rational control.The study presents a technical basis for the improvement and development of transient control methods for pump systems and thus offers significant academic and practical values.3.This study focuses on the changes in transient pressure at eight outlets caused by the closing of the valves at the end of the branches of a tree gravitational flow water transfer system(the valves are closed at 5,30,50,75,and 100s).With such focus,we simulate the changes in transient pressure at eight outlets caused by the closing of a single valve;the changes in transient pressure at eight outlets caused by the simultaneous closing of 11 valves;the changes in transient pressure at Outlet#8 caused by the simultaneous closing and superposition closing of Valve#9,#10,and#11;and the changes in transient pressure at eight outlets caused by the supposition closing of 11 valves of the tree gravitational flow system.The computation results show that the maximum transient pressure at the same section caused by the closing of each valve appears at the same time and that the maximum transient pressure wave interferes constructively.The increase in pressure ?H2 after the constructive interference of the maximum transient pressure caused by the superposition closing of all valves at the end of the branches exceeds the increase in pressure ?H1 caused by the simultaneous closing of all branch end valves.It also exceeds the accumulated increase in pressure ??H caused by the closing of a single valve.The study puts forward a method for identifying the most unfavorable transient pressure levels for tree gravitational flow water transfer systems.It also proves that the transient pressure after constructive interference is the most unfavorable transient pressure.With this finding,this study present some scientific basis for choosing transient pressure control measures for tree gravitational flow water transfer systems.