| In a pressurized water pipeline system,water hammer is an adverse hydraulic phenomenon of rapid pressure and flow vibration in the pipeline,which may cause vibration,pipe burst,negative pressure and other hazards to the pipeline.Therefore,it is necessary to take appropriate measure.Water hammer protection measures of different parameters and sizes directly affect the protection effect and cost,and at the same time influence each other.To ensure the safe operation of the long-distance water supply system while considering the economy,this paper proposes an optimal design method for water hammer protection parameters of the long-distance water supply system to meet the needs of multiple objectives;the main research content is as follows:Based on the basic calculation theory of water hammer,the mathematical model of the hydraulic conversion process of the actual long-distance and high-height difference pressurized water supply system is established using the characteristic line method.By simulating the operating conditions such as unexpected power failure of the pump station,the influence law of water hammer protection device parameters such as double-stage slow closing valve,one-way pressure regulating tower,and pressure regulating well of the pump station on the protection effect is studied to provide qualitative theoretical guidance for design and performance optimization.The results show that the closing law of the pump outlet valve in this paper has an impact on the pump unit reversal situation and pump outlet pressure,and the two-stage closing valve fast closing stage cannot be too quick,while the slow closing time should be as long as possible in the feasible range.Based on the mathematical model of hydraulic transition,a multi-objective optimization model of water hammer protection for water delivery system is developed.This method realizes the rapid optimization of the combined protection measures of different water hammer,improves the design efficiency,and can provide a reference for the protection of water hammer in long-distance water transmission projects.Firstly,a hydraulic transient model was established based on the characteristic line method to calculate the pump shutdown transition process,and the expected sample set was constructed by Latin hypercube sampling.Based on this sample set,the mathematical mapping between the closing law of the pump outlet valve,the size parameters of the regulating well set up in the pipeline and the maximum water hammer pressure value,and the maximum dimensionless reversing speed is established by using the regression prediction algorithm.With the objectives of minimizing the maximum water hammer pressure,minimizing the maximum dimensional reversal speed,and minimizing the cost of water hammer protection,a fast non-dominated genetic algorithm(NSGA-II)is used as the primary model to establish the input interval for the multi-objective optimization problem,construct a multi-objective optimization mathematical model for the optimization of water hammer protection measures,and iteratively search for the optimal parameter set to optimize the water hammer protection scheme and investment.A multi-objective optimization mathematical model is constructed to optimize the water hammer protection measures from the water hammer protection problem.To obtain different biased optimal solutions from the 100 Pareto optimal solutions obtained from the multi-objective optimization mathematical model of the water hammer protection measures optimization problem,the entropy-weighted ideal point method was used,and the simulated values of the different biased optimal solutions obtained were consistent with the predicted values,which verified the accuracy of the way.The analysis of different biased optimal solutions shows that this method can find the better solution in water hammer protection measures engineering requirements and economic investment and provides a solution for other practical engineering multi-objective optimization problems. |
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