# Influence of Posture Change on Train Running Safety under Crosswind
## 5 Conclusions  
The WRANS turbulence model was employed to calculate the time-varying aerodynamic forces and moments of the train with and without a preset posture as it passes through a crosswind region. Based on the different characteristics of the train derailment coefficient and wheel load reduction rate, the effect of each car's preset posture on running safety was also investigated. The transient changes of the running posture of each car of the train with and without the designed posture were also compared and analyzed in five degrees of freedom. The main conclusions can be drawn as follows:  
Figure 17: Running safety domain in terms of the relationship between the speed of crosswind and train.  
The original posture provided significant changes to the train's aerodynamic coefficients. Various effects and laws of the aerodynamic coefficients were found at different separated cars. These discrepancies can be attributed to the different flow patterns such as the pressure distribution and vortex structure around the trains with and without present posture. Obvious fluctuations exist in the aerodynamic coefficients when the train enters and exits the wind barrier.
2. A slightly larger maximum derailment coefficient was found on the first bogie of the leading car with a preset posture. This difference in the trailing car was not as obvious as that of the leading car. The development law as well as the maximum and minimum values of wheel load reduction rate hardly changed with the preset attitude. The maximum values of these two indicators of the leading car were higher than those of the trailing car, indicating that the leading vehicle has greater running safety risks.
3. There were obvious differences in the displacement characteristics of the three cars in the lateral direction and the rolling rotation, and the magnitude of the posture changes decreased from the leading car to the trailing car. The pitching rotation changes of the three cars were the most active, and the difference caused by the preset posture was not limited to the crosswind region. The influence of a given posture on the yawing angle is clear and simple, which made the positive yawing rotation of the leading and trailing cars larger and increased the negative yawing rotation of the middle car in reverse.
4. A train's critical speed is higher when there is a weaker crosswind, and it is lower when there is a stronger crosswind. The train's ability to overcome crosswind decreases as it speeds up. The train with the consideration of posture is proven to withstand weaker crosswind.
5. Further work may lie in the reproduction of the time-varying posture modifications based on the Dynamic Fluid Body Interaction (DFBI) technique.  
Conceptualization, J.Y. and T.C.; methodology, E.D.; software, E.D.; validation, S.C.; formal analysis, S.C.; investigation, S.C.; resources, W.Y.; data curation, J.Y.; writing--original draft preparation, J.Y.; writing--review and editing, S.G. and Z.G.; visualization, J.Y.; supervision, T.C.; project administration, T.C.; funding acquisition, W.Y. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Natural Science Foundation of China (Grant No. 51978670).  
Not applicable.  
The authors acknowledge the computing resources provided by the High-Performance Computing Center of Central South University.  
The authors declare no conflict of interest.