## 3 Multibody Simulations
### Dynamic Responses of Vehicle When Decelerating through Curved Tracks  
When the train is traveling in strong wind conditions, for example at a wind speed of 25 m/s, according to the above analysis, it can be seen that the maximum critical safety speed of the train is 246 km/h. Therefore, it is necessary to decelerate for safety. To study the influence of the IVS on the dynamic characteristics of the train decelerating curve passing, the initial working conditions of initial velocity \(V_{0}\) = 250 km/h, \(R7000\) m, and \(V_{w}\) = 25 m/s were set. Figure 13 shows the six bogies from the head car to the tail car, the front bogie (FF), the rear bogie (FB) of the head car, the front bogie (MF), the rear bogie (MB) of the middle car, the front bogie (BF) and the rear bogie (BB) of the tail car. The error calculation method in Figure 13 is shown in Equation (11). \(P_{Non}\) is the unloading factor in the case of a fixed connection, and \(P_{With}\) is the unloading factor in the case of considering the IVS. \[\text{Error}=(P_{Non}-P_{With})/P_{Non} \tag{11}\]  
It can be seen that the FF bogie has the highest unloading factor and derailment coefficient of all bogies during train deceleration. Considering the IVS, the unloading factor of the MB and BF bogies is reduced by 2.89% and 3.38%, respectively. The derailment coefficients of the MB, BF, and BB bogies were reduced by 2.25%, 5.66%, and 2.13%, respectively. This is probably because the braking force is uniformly distributed over all wheelsets, and the IVS absorbs the impact loads between the vehicles, thus reducing the unloading factors and derailment coefficients and improving travel safety. In addition, the unloading factors of the vehicle always reach a dangerous value before the derailment coefficient, which is consistent with the study of [PERSON] et al. [30]. Figure 14 shows the lateral acceleration of the head, middle, and tail car bodies during deceleration, and it can be seen that there are four higher peaks in the time domain, and these four peaks correspond to the four transition areas of the curved track section. The lateral acceleration of the head car and tail car are only slightly affected by the IVS. However, considering the IVS reduces the maximum lateral acceleration of the middle car by 49.02%, it shows that the IVS effectively suppresses the lateral vibration of the middle car. Figure 12: The relationship between the unloading factor with Vw and Vc at different radii in the case of fixed connection. (**a**) R4500 m. (**b**) R7000 m. (**c**) R9000 m. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & & **Wind 15 m/s** & **Wind 20 m/s** & **Wind 25 m/s** & **Wind 30 m/s** \\ \hline \multirow{3}{*}{With suspension} & R4500 m & safe & 330 km/h & 234 km/h & 169 km/h \\  & R7000 & safe & safe & 245 km/h & 171 km/h \\  & R9000 & safe & safe & 246 km/h & 175 km/h \\ \hline \multirow{3}{*}{Fixed connection} & R4500 & safe & safe & 252 km/h & 168 km/h \\  & R7000 & safe & safe & 254 km/h & 169 km/h \\ \cline{1-1}  & R9000 & safe & safe & 260 km/h & 173 km/h \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Safe speed in two cases. As shown in Figure 15, the body roll angle is the largest of the body motion angles during train deceleration in crosswind conditions. The IVS had little effect on the maximum roll angle of the head car F and middle car M; however, it reduced the maximum roll angle of the tail car by 5.08%, considering the IVS increases the maximum pitch angle of the middle car M by 8.11%. This is because compared to the fixed connection, the coupler buffer device between the vehicles can absorb the energy of the impact and the existence of backlash between the vehicles allows a certain displacement, so the pitch angle of the middle car increases during deceleration. Similarly, the IVS has little effect on head car F and tail car B but reduces the maximum yaw angle of the middle car by 14%. This is because the dampers between the vehicles work to dampen the yaw motion between the vehicles effectively.