PSI - Issue 22

B.R. Miao et al. / Procedia Structural Integrity 22 (2019) 102–109 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 3 Aerodynamic pressure under the lateral wind of the vehicle with a speed of 300km/h

4.2. Fatigue life prediction results

The finite element calculation of the carbody structure is carried out to obtain the carbody mass and the first-order natural frequency under the initial design variables. The structure dynamic stresses of the carbody structure are calculated under the combined consideration of wind loads and track excitation. The structure size parameters are used as design variables, and the Von Mises stress and displacement of the carbody structure are used as constraints to the carbody structure. The natural frequency of the first-order vertical bending of carbody is the objective function. According to the multi-disciplinary fatigue optimization design method mentioned above, the dynamic load time histories (including inertial loads and constrained loads, etc.) of the carbody under typical operation load cases are obtained by the vehicle multi-body system dynamics simulation considering the influence of the flexible carbody structure. At the same time, the structural quasi-static stress analysis method is used to calculate the structural dynamic stress. And the quasi-static stress influence factor under the condition of 21 loads are obtained. Finally, the load time histories file are inputted in the software Design life and Isight. Structural fatigue life prediction based on S- N method is performed according to material property parameters. Some fatigue optimization results can be seen in Fig. 4.

(a) Average two-axis ratio cloud image of rear body structure (b) Fatigue life prediction results

Fig. 4 Aerodynamic pressure under the lateral wind of the vehicle with a speed of 300km/h

4.3. Optimization results analysis and discussion Through the execution of the batch file, the maximum equivalent stress and vertical displacement are obtained from the output file as constraints for the optimization calculation. The carbody's mass and first-order bending natural frequency are the optimization objective functions. The NSGA-II optimization algorithm is used to optimize the multi objective optimization of the high-speed carbody. After iterative calculation, the optimal parameter combination of the carbody structure is obtained. The finite element fatigue calculation is carried out on the carbody structure before and after optimization. Some fatigue optimization results can be seen in Table 2 and Table 3.