Dynamic Response And Fatigue Life Of Train Skirt

The continuous improvement of train operation speed makes the complex and changeable operation environment more severe.The train aerodynamic performance is one of the key factors to improve the train operation speed.The structure of bogie skirt(skirt and bracket)not only protects the equipment in the bogie area,but also improves the aerodynamic performance of the train.In addition to the vibration and impact load,The structure of bogie skirt(skirt and bracket)also bears the aerodynamic load which changes violently on the skirt during operation.The increase of train operation speed leads to the change dramatically of various loads,which makes the possibility of fatigue failure of the skirt structure increasing day by day,and the safety of train operation has been threatened.The running time of high-speed trains in our country is relatively short,but it is found that the connecting bracket between the body and the bogie skirt appears fatigue cracking.Therefore,it is of great significance to predict the fatigue life of the structure accurately and efficiently.At present,simulation analysis and experimental verification are two commonly used methods to predict the fatigue life of the structure,but it is impossible to simulate the aerodynamic load on the skirt through the shaking table test.Therefore,the aerodynamic load on the skirt is transformed into the basic acceleration excitation,which provides a method for the bench test to simulate the aerodynamic load on the skirt.In this thesis,according to the simplified model of a high-speed train,the first car-intermediate car-rear car is established as the computational aerodynamics model.And the aerodynamic load of the train body surface and the bogie skirt surface can be obtained through the aerodynamic simulation analysis.Then comparing the characteristics of the aerodynamic load under three kinds of conditions-equal speed open line intersection,tunnel intersection and tunnel crossing at the speed of 250 km/h,the distribution of aerodynamic loads of the train body and bogie skirt surface with the time and space varying is obtained.Secondly,the frequency-domain characteristics of aerodynamic loads on skirts under three conditions are obtained by Fourier transform.The peak values of power spectral density of aerodynamic loads under three operating conditions are 2 Hz and 6 Hz.Through the modal analysis and the frequency response analysis under the unit acceleration excitation,the contribution of the modes to the displacement response of the structure at 2 Hz and 6 Hz is extracted,and the total contribution of the first and second modes to the displacement of the structure is more than 90%.According to the load conversion theory based on the acceleration response equivalence and the modal analysis theory,the structure of bogie skirt(skirt and bracket)is decoupled into multiple single degree of freedom system,The first-order and second-order modes are regarded as an independent single degree of freedom system to transform the load.The transformed load is linearly superposed according to the ratio of the contribution of each mode to get the final foundation acceleration excitation.Then,the transformed load is accelerated in frequency domain to obtain acceleration spectrum,which can be used as simulation analysis and test load for future shaking table simulation of skirt structure under aerodynamic load.Finally,the acceleration spectrum and the standard spectrum given in IEC 61373 are taken as the load input of simulation analysis,and the fatigue damage of the structure is obtained.Through comparing and analyzing,it is found that the damage caused by the acceleration spectrum to the structure is greater than the standard spectrum,which shows that the fatigue failure of the structure is mainly caused by the aerodynamic load.