In order to maintain a uniform distribution of pareto-front solutions, a modified NSGA-II algorithm coupled with a dynamic crowding distance(DCD) method is proposed for the multi-objective optimization of a mixed-flow...In order to maintain a uniform distribution of pareto-front solutions, a modified NSGA-II algorithm coupled with a dynamic crowding distance(DCD) method is proposed for the multi-objective optimization of a mixed-flow pump impeller. With the pump meridional section fixed, ten variables along the shroud and hub are selected to control the blade load by using a three-dimensional inverse design method. Hydraulic efficiency, along with impeller head, is applied as an optimization objective; and a radial basis neural network(RBNN) is adopted to approximate the objective function with 82 training samples. Local sensitivity analysis shows that decision variables have different impacts on the optimization objectives. Instead of randomly selecting one solution to implement, a technique for ordering preferences by similarity to ideal solution(TOPSIS) is introduced to select the best compromise solution(BCS) from pareto-front sets. The proposed method is applied to optimize the baseline model, i.e. a mixed- flow waterjet pump whose specific speed is 508 min?1?m3s?1?m. The performance of the waterjet pump was experimentally tested. Compared with the baseline model, the optimized impeller has a better hydraulic efficiency of 92% as well as a higher impeller head at the design operation point. Furthermore, the off-design performance is improved with a wider highefficiency operation range. After optimization, velocity gradients on the suction surface are smoother and flow separations are eliminated at the blade inlet part. Thus, the authors believe the proposed method is helpful for optimizing the mixed-flow pumps.展开更多
When the subway train operates at a speed higher than 100 km/h,the corresponding aerodynamic issue becomes severe.To meet the future requirement for the speedup of subway trains,a research on the critical diameters of...When the subway train operates at a speed higher than 100 km/h,the corresponding aerodynamic issue becomes severe.To meet the future requirement for the speedup of subway trains,a research on the critical diameters of the subway tunnel for trains operating at 120 and 140 km/h has been performed based on passengers’aural discomfort caused by rail tunnel pressure variation.A three-dimensional computational fluid dynamic approach has been adopted for analysis.Meanwhile,trains with different airtight indices are considered and the pressure variations inside and outside the trains are both under investigation.Based on the corresponding criteria for different airtight indices,critical tunnel diameters for trains running at different speeds have been determined.This study would aid in the tunnel section design for future high-speed subway trains.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.5137610051306018+4 种基金51206087and 51179091)the National Key Technology Research and Development Program(Grant No.2011BAF03B01)State Key Laboratory for Hydroscience and Engineering(Grant Nos.2014-KY-05 and 2015-E-03)Laboratory of Science and Technology on Waterjet Propulsion
文摘In order to maintain a uniform distribution of pareto-front solutions, a modified NSGA-II algorithm coupled with a dynamic crowding distance(DCD) method is proposed for the multi-objective optimization of a mixed-flow pump impeller. With the pump meridional section fixed, ten variables along the shroud and hub are selected to control the blade load by using a three-dimensional inverse design method. Hydraulic efficiency, along with impeller head, is applied as an optimization objective; and a radial basis neural network(RBNN) is adopted to approximate the objective function with 82 training samples. Local sensitivity analysis shows that decision variables have different impacts on the optimization objectives. Instead of randomly selecting one solution to implement, a technique for ordering preferences by similarity to ideal solution(TOPSIS) is introduced to select the best compromise solution(BCS) from pareto-front sets. The proposed method is applied to optimize the baseline model, i.e. a mixed- flow waterjet pump whose specific speed is 508 min?1?m3s?1?m. The performance of the waterjet pump was experimentally tested. Compared with the baseline model, the optimized impeller has a better hydraulic efficiency of 92% as well as a higher impeller head at the design operation point. Furthermore, the off-design performance is improved with a wider highefficiency operation range. After optimization, velocity gradients on the suction surface are smoother and flow separations are eliminated at the blade inlet part. Thus, the authors believe the proposed method is helpful for optimizing the mixed-flow pumps.
基金supported by the National Basic Research Program of China("973"Project)(Grant No.2011CB711100)the National Natural Science Foundation of China(Grant No.11302233)
文摘When the subway train operates at a speed higher than 100 km/h,the corresponding aerodynamic issue becomes severe.To meet the future requirement for the speedup of subway trains,a research on the critical diameters of the subway tunnel for trains operating at 120 and 140 km/h has been performed based on passengers’aural discomfort caused by rail tunnel pressure variation.A three-dimensional computational fluid dynamic approach has been adopted for analysis.Meanwhile,trains with different airtight indices are considered and the pressure variations inside and outside the trains are both under investigation.Based on the corresponding criteria for different airtight indices,critical tunnel diameters for trains running at different speeds have been determined.This study would aid in the tunnel section design for future high-speed subway trains.
