# Influence of Posture Change on Train Running Safety under Crosswind
## 4 Results
### Running Safety
#### 4.3.3 Running Posture  
Furthermore, the coupled dynamic system provides the posture changes of the train passing through the crosswind region with and without the given posture. The running posture is a part of the safety analysis and was studied by a previous study [26], while only the posture of the leading vehicle was investigated. In the present study, the posture changes of the leading, middle, and trailing cars of the trains with and without the initial posture in five degrees of freedom (lateral and vertical displacement and rotation in three directions) were compared and analyzed.  
Figure 16 shows the changes of different degrees of freedom indexes when the train passed the crosswind region with regard to two different initial postures. In the figure, Dy, Dz, Rx, Ry, Rz are the lateral and vertical displacements (unit: m) and the rotation of the x, y, and z axes (unit: rad). The diagram of the running posture of the train is also given in each figure, where the transparent one represents the original position, and another is the posture caused by the crosswind. The same range of the y axis was kept constant for a single degree of freedom to understand the different performances of separated cars.  
Figure 15: Time-varying WLRR values of two wheelsets: (**a**) the first wheelset of the leading car without posture; (**b**) the first wheelset of the leading car with posture; (**c**) the last wheelset of the trailing car without posture; (**d**) the last wheelset of the trailing car with posture.  
According to Figure 16a-c, there were obvious differences in the displacement characteristics of the three cars in the lateral direction, and the magnitude of the displacement decreased from the leading car to the trailing car, which could be attributed to the differences in their lateral forces, as described in Figure 7a-c. In addition, the influence of the given posture on the lateral displacement of the train is consistent with the law of lateral force: the preset posture tended to push the leading car and the middle car further in the direction of the crosswind; while the lateral displacement of the trailing car that did not consider the posture in the crosswind area fluctuated slightly around 0, and that of the trailing car with posture increased, whether same or opposite to the direction of the crosswind. From Figure 16d-f, all three cars had downward vertical displacements, and the corresponding  
they all showed two humps with similar peak values within the crosswind region. Only a slight difference can be found in the leading car, while relatively larger differences were formed in the vertical displacement of the middle and the trailing cars. For the overturning angle shown in Figure 16g,i, due to the similarity of the preset attitude on the lateral and vertical displacements of the leading car (see Figure 16a,d), the overturning angles shown by the two leading cars were almost the same, but the middle car was different: the middle car with posture was found to have a reverse overturning trend much larger than the original car. The overturning rotation of the trailing car was similar to the change in lateral displacement (see Figure 16c). 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 most obvious difference was also found in the middle car: the preset posture reduced the pitching angle not only inside but also beyond the crosswind region to around 0. For the leading and trailing vehicles with a streamlined structure, the preset posture slightly increased their maximum values. As shown in Figure 16m-o, 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.