## 4 Model Validation
### Derailment Test with a Wagon (DCP Is Installed)  
The next derailment experiment was conducted with one wagon. The DCP of Type 1 was installed and analyzed to evaluate the derailment prevention effects and vehicle behavior when the DCP is installed. The specifications of the wagon are shown Tables 6-8 [23,29]. Additional specifications of bogie are referred in supplementary materials. The primary suspension spring of the welded bogie consists of an inner coil spring and an outer coil spring. The outer spring operates at low loads and the inner spring operates when the load is increased and compressed to a certain displacement. Figure 17 shows the wagon frame. The left is a real shape frame model composed of finite elements and the right is a simplified frame model. The wagon used in derailment tests is shown Figure 18.  
The wagon model consists of two main parts, bogie and body frame. To connect the bogie and frame, three beam elements were used. One beam element was for the center pivot and two elements for side bearer. To verify that the simplified frame model and the real frame model have same behaviors, two models were evaluated under the same testing conditions in simulation. Figure 19: Comparison between the real frame model and the simplified frame model. (**a**) Longitudinal displacement (**b**) Lateral displacement (**c**) Vertical displacement. Figure 17: Different models of the wagon frame. Figure 19 shows a comparison of displacement between the real frame model and the simplified frame model. Displacement was measured at the center of the frame, and X, Y, and Z displacements show similar curves. Since comparison of the two models showed the similar behavior, the reliability of the vehicle models was verified by comparing with the field test and the simplified model given in this study. The speed measured by the speed sensor right before the derailment was 52 (km/h). The first collision after derailment occurred at about 350 ms. The front wheel collided with the seventh sleeper. Figure 20 shows that the collision occurred at the seventh sleeper. After the first collision, the vehicle proceeds and collides with the installed DCP. The lateral displacement is limited by the DCP so that the wheel does not depart from the rail within a certain distance. The configuration at the moment of collision with the DCP is shown in Figure 21, and it is checked that collisions with the DCP occur at the similar location. Comparing damage of the track, Figure 22 shows that there is a difference in the degree of damage between experiment and simulation, but the collision locations of the experiment and simulation were reproduced well because the failure occurred at similar locations. Figure 21: Collision with the DCP. Figure 20: First collision with concrete sleeper. In the field test, only the seventh and eighth sleepers were damaged. In the simulation, damage occurred at the edge of the ninth and tenth sleepers as well as the seventh and eighth sleepers. However, the initial collision occurred at the same location. Figure 23 shows broken sleepers. The lateral displacements of the simulation and field tests are shown in Figure 24. The simulation and derailment experiments showed a maximum difference of 7.97% and 8.07% at the front and center points, respectively, and showed the same trend. Figure 24 also indicates that if the DCP is installed, it guides the wheel of the derailed bogie in the distance shown Figure 25. From the result of the simulation and experiment, it was confirmed that if the DCP is installed, it could prevent a large deviation of the derailed vehicle. Figure 23: Comparison of location of broken sleepers. Figure 22: Comparison of location of broken DCP. The lateral acceleration for the initial 1 s was compared for a period of colliding with the sleepers and DCP, because the DCP is designed based on lateral motion.