# Dynamic Characteristics of Urban Rail Train in Multivehicle Marshaling under Traction Conditions
## 3 Model Validation  
To verify the accuracy and reliability of the urban rail train dynamic model, the measured tracking data and simulation data of a subway line in Beijing were used for comparative analysis, mainly to compare the vertical acceleration of the axle box and the gearbox box. In the actual test train, the fourth vehicle was selected as the test vehicle, the acceleration sensor was arranged on the axle box and the gearbox box for the tracking test, and the acceleration data of the corresponding components were obtained. The sensor uses a three-axis vibration acceleration sensor and the principle is piezoelectric. The gear box uses a vibration acceleration sensor with a range of 50 g, and the axle box uses a vibration acceleration sensor with a range of 50 g. The location of the sensor is above the axle box and to the left of the gear box case. The direction of the sensor: \(x\) axis is longitudinal, \(y\) axis is transverse and \(z\) axis is vertical. The sampling frequency is 10 K Hz. The scene photo is shown in Figure 2.  
Compared with the actual operating conditions of urban rail trains, the simulated train parameters have certain differences which have a certain impact on the simulation results. The simulation model uses the measured track spectrum of a line in Beijing as the track excitation. The train simulation data and measured data are shown in Figure 3. Because the working conditions of urban rail trains in actual operation are very complex, they will experience continuous acceleration, coasting and braking, and will continue to pass through curves and turnouts, and the measured map will have a larger rail impact.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Specification** & **Value** \\ \hline Tooth number of pinion/gear & 16/107 \\ Modification coefficient of pinion/gear (mm) & 0.31449\(-\)0.07614 \\ Face width of pinion/gear (mm) & 70/70 \\ Module (mm) & 85.367 \\ Pressure angle (\({}^{\circ}\)) & 20 \\ Helix angle (\({}^{\circ}\)) & 17 \\ Poisson ratio & 0.3 \\ Young modulus (GN/m) & 206 \\ Damping coefficient (kN-s/m) & 5 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Main parameters of gear model.  
Figure 2: Sensor layout in the field test. **(a)** Layout of sensors on axle box, and the red circle indicates that the axle box; **(b)** Layout of sensors on gearbox, and the red circle indicates that the gearbox.  
Therefore, the axle box, as the component with the closest contact distance with the wheel and rail, has the most obvious impact on the rail in the measured data. Since this situation is not considered in the simulation model, the overall vibration acceleration of the simulation model is smaller than the measured data. In this paper, the actual acquired vibration signals are low-pass filtered using a digital filter to filter out the high-frequency noise signals in the acquisition process. The comparison between the vertical dynamics simulation data of the urban rail train and the measured data is shown in the figure. Although there is a certain difference between the simulation data and the test data, the overall vibration characteristics are in good agreement with the measured data, so the established simulation model is more reasonable.