| With the continuous increase of the speed of high-speed trains,the kinetic energy of the train increases in square terms.Therefore,the braking distance of the train increases approximately as a square term,it will unable to meet transportation organization and signal command of higher speed trains on existing lines.A drag increasing scheme of installing wind resistance plates in the streamlined parts of the head and the tail cars is proposed in this dissertation,the drag increasing ratio of trains under different angles,numbers,heights and spaces of wind resistance plates are investigated.The parameter scheme of the wind resistance plate with optimal drag increasing effect is obtained,it can effectively increase the braking resistance of the train and shorten the braking distance.The present study has important application value for improving the driving safety of high-speed trains,the main contents of this dissertation are as follows:(1)A new braking method is proposed by installing wind resistance braking plates in the streamlined parts of the head and the tail cars,the influence of wind resistance braking plate placed in the head and the tail cars on aerodynamic drag of the high-speed trains is revealed.The effects of key parameters such as the angle,the number,the height and the space of wind resistance braking plates,on the flow field and the aerodynamic drag around high-speed trains are systematically studied.Under the influence of different key parameters,the increasing ratio of aerodynamic drag between the head and the tail cars is studied.The contribution rate of wind resistance braking plate to the total aerodynamic drag,the variation law of differential pressure and friction drag between the head and the tail cars are investigated.The results show that the maximum drag increasing ratios of the wind resistance braking plate of the head and the tail cars are 466.05% and 342.09%,respectively.The contribution rate of the wind resistance braking plate of the head and the tail cars is the highest,reaching 86.62% and 61.95%,respectively.The drag increasing mechanism of the wind resistance braking plate in the streamlined parts of the head and the tail cars is revealed,it is found that the braking force of wind drag mainly comes from pressure drag,the mathematical equations between the main influencing parameters of wind resistance braking plate and train aerodynamic drag is established.(2)The response surface model between the key parameters of the wind resistance braking plate in the streamlined parts of the head and tail car and the aerodynamic drag of the train is established.The single factor analysis method is used to analyze the influence of the key parameters of the wind resistance braking plate placed on the head and tail cars,on the wind resistance braking force of the head tail car and the whole train.At the same time,the influence of the interaction between the key parameters of the wind resistance braking plate on the wind resistance braking force the train is analyzed by multivariable analysis methods.Finally,the moment independent sensitivity analysis method based on response surface models is used to explore the sensitivity distribution law of key parameters of the wind resistance braking plate placed on the head and the tail cars.The sensitivity of the key parameters of the wind resistance braking plate placed on the head and the tail cars to the wind drag braking force from large to small is: the height of the wind resistance braking plate,the number of wind resistance braking plates,the distance between the wind resistance braking plates and the angle of the wind resistance braking plate.(3)A multi-objective optimization mathematical model for the key parameters of the wind resistance braking plate in the streamlined part of the head and the tail cars is established.The multi-objective optimization scheme and optimization process of the wind resistance braking plate in the streamlined area of the head and the tail cars are proposed.The Kriging model is used to construct the approximate model between the key parameters of the wind resistance brake plating and the aerodynamic drag of the train.The multi-objective optimization of the key parameters of the wind resistance braking plate of the head and the tail cars is carried out by using the NSGA-â…¡genetic algorithm.The Pareto front optimal solution set with the largest total aerodynamic drag coefficient of the head tail car and the total drag coefficient of the whole train is obtained.The optimal matching scheme for key parameters of the wind resistance braking plate in the streamlined part of the head and the tail cars is establish.The optimization results show that the optimal matching parameters of wind resistance braking plate are as follows: the the head and tail car angle of wind resistance braking plate is 86,the number of wind resistance brake plates is 12,the height of wind resistance braking plate is 0.7869 m,and the spacing of wind resistance braking plates is2.9574 m.Under this condition,compared with the original wind resistance train scheme,the aerodynamic drag of the train is increased by27.74%.There are totally 185 Figures,21 Tables,and 237 References. |
