| The safety accidents during operation of water conveyance system of water transfer project are mostly related to the hydraulic transients.Under the background of continuous construction of water transfer projects of different scales in China,it is important to fully consider the inherent characteristics of the hydraulic transients in the feasibility study or preliminary design stage of water transfer project for accurate simulation prediction and effective control of protection.Aiming the lack of complete characteristic curves(CPCs)which is an important parameter for the numerical simulation of the hydraulic transients,and the calculation of the pressure drop after pump failure often relies on numerical calculation programs,the calculation process is cumbersome in the preliminary design stage of water transfer project.Therefore,according to the combination of theoretical deduction and numerical simulation,the regression analysis of theoretical construction method of the CPCs,derivation of the maximum pressure drop formula after pump failure and safety protection are conducted.These research achievements can guide and speed up the design of water transfer project and provide important reference to ensure the operational safety of the project.The main innovations of the thesis include:(1)According to therevised internal character analysis theory,a mathematical model describing the complete characteristics of pump is deduced.Based on multiple measured CPCs,the nonlinear functional relationship between the characteristic parameters of the characteristic operating points and the specific speed is established.Finally,by combining the mathematical model with the nonlinear relationship,a method of theoretically constructing the CPCs with a given specific speed is proposed,which effectively improves the accuracy of the calculation of the hydraulic transient in the preliminary design stage of the water transfer project.(2)Based on the theory of elastic water hammer and the mathematical model of complete characteristics of pump,the IAB unsteady friction model which can better reflect the change of water hammer wave after pump failure is introduced and the formula of maximum pressure after pump failure in long-distance water transfer project is successfully derived.The key parameters in analytical formulas are identified using a modified Morris sensitivity analysis model.The formula is formally simpleand more accurate in theory.Without computer programming,it can calculate the maximum pressure after pump failure,which is convenient for engineering personnel to use in practice.(3)Aiming at the positive and negative water hammer problems caused by the accidental shutdown of the pump in the water delivery system of the long-distance water transfer project with high head and small flow,the protection scheme of the pump-stopping water hammer is proposed,which is controlled by the butterfly valve behind the pump,the air tank and air-valve surge tank.The results show that the combined protection proposed in the thesis can not only better control the positive and negative pressure of the pipeline,the unit parameters meet the design requirements,but also greatly reduce the volume of the air tank.Compared with the behind-pump butterfly valve and air tank protection,the combined protection proposed is more feasible and can provide a reference value for the pump-stopping water hammer protection of similar projects. |
