## 4 Model Validation
### Derailment Tests with One Bogie  
Derailment tests were performed with only one bogie at first [25]. The speed measured by the speed sensor right before derailment was 27 (km/h). The behavior and accelerations were measured by a high-speed camera and the acceleration sensors. Figure 10 shows the derailment behaviors. They showed that the field test and simulations have a similar derailment behavior. After the bogie was derailed by the derailment device (approx. 420 ms), the front wheel collided with the third sleeper. The rear wheel collided with the fourth sleeper at about 680 (ms) as shown in Figure 10a. Figure 10: Derailment behaviors. (**a**) Derailment behavior (Side view); (**b**) Derailment behavior (Front view). Figure 9: The derailment testing ground. Figure 10b shows the behavior of the bogie after derailment and finally. Although collision between wheel and rail does not occur in the field test while the bogie was running on the sleeper, the wheel collided with the rail in the simulation. This difference in the wheel-rail impact behaviors occurred because the track components were simplified in the simulation, while real track components like tension clamps and screw spikes hindered the wheel-set from moving to the rail in the field test. Figure 11 shows the comparison of damaged sleepers between the field test and the simulation. Although there was a slight difference in damage degree, the damage of sleepers occurred at similar locations. X-displacement and velocity (Longitudinal direction) of the bogie were obtained through the sensors attached to the bogie. Figure 12 shows similar the X-velocity and displacements between the field test and simulations. The Y-displacement (lateral direction) of the bogie was obtained using the trace of wheels. Figure 13a shows the Y-displacement results of the field test and simulations over time. The reason the Y-displacement of the simulation is larger than that of the field test is that the tension clamps and the screw spikes in field tests obstructed the lateral motion of the wheel as mentioned above. As shown in Figure 13b, the distance between the rail and the tension clamp is 155 (mm), which is similar to the lateral difference of 147 (mm). Figure 11: The broken sleepers. Figure 12: The comparison of results between the field test and the simulation. (**a**) X-Velocity (Longitudinal); (**b**) X-Displacement (Longitudinal). The impact accelerations of the bogie were measured by acceleration sensors installed on the bolster. Since the measured acceleration data include unnecessary frequency components such as noise, the data should be filtered by an appropriate filter to analyze the dynamic trend. There are various techniques for data filtering, and there are acceleration-filtering criteria for each field. In case of the vehicle collision test, there is a test standard for handling the vehicle collision data in each country and Butterworth low-pass filtering is generally used. There is no clear standard of impact acceleration filtering for derailment tests of railway vehicles. In Europe, a 40 Hz low-pass filter is usually used to evaluate high-speed train body acceleration [26; 27; 28]. Numerical model validation for car bodies was evaluated using a 40 Hz low-pass filter. But it could lower the peaks of impact accelerations in collision, so a 180 Hz low-pass filter was used according to EN15227 B.2.1, as well. Figures 14 and 15 show the comparison of the measured acceleration data in the field test with the simulation results for each acceleration component using different low-pass filters (40 Hz, 180 Hz). The maximum acceleration occurred at about 420 (ms) after collision with a wheelset and a sleeper. The 180 Hz filtering is shown to vibrate acceleration as it contains high frequency when compared to 40 Hz filtering.