## 2 Field Test and Dynamic Model of Low-Floor Train Passing Switch
### Coupling Dynamic Model of Low-Floor Trains and Turnout Switch  
In the test, a 70% low-floor train was adopted. The vehicle-track coupling dynamics model was constructed with the help of multi-body dynamics software, UM9.1.1.0. The rail profiles were measured in the test and imported into UM. A basic module of the train consists of two motor vehicles and one trailer vehicle (Figure 3). A motor vehicle in Figure 4a includes one carbody, one bogie, four axle boxes, two integrated wheels, and suspension devices. A trailer vehicle in Figure 4b has the same parts as motor vehicle except for the two independently rotating wheelsets. In Figure 4, the red, green and blue lines show longitudinal, horizontal and vertical orientations, respectively. The low-floor vehicle used in the field test contains two modules (i.e., six vehicles in total), and a corresponding model was established in UM, as shown in Figure 5. There are a total of 24 wheels of the two modules, of which the treads were measured by the WS2016-3W-LFT wheel tread measuring instrument. The motor and trailing bogies have the same wheel profiles. The main parameters of the dynamic model are listed in Table 1. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameters** & **Motor Vehicle** & **Trailer Vehicle** \\ \hline Wheelset mass/kg & 1500 & 560 (Single wheel) \\ Bogie mass/kg & 2970 & 1971 \\ Carbody mass/kg & 18 & 6.6 \\ Wheel radius/m & 0.33 & 0.33 \\ Wheel base/m & 1.492 & 1.492 \\ Primary longitudinal stiffness/(N\(\cdot\)m\({}^{-1}\)) & \(4\times 10^{6}\) & \(4.5\times 10^{6}\) \\ Primary lateral stiffness/(N\(\cdot\)m\({}^{-1}\)) & \(4\times 10^{6}\) & \(4.5\times 10^{6}\) \\ Primary vertical stiffness/(N\(\cdot\)m\({}^{-1}\)) & \(8.9\times 10^{5}\) & \(7.46\times 10^{5}\) \\ Primary longitudinal damping/(N\(\cdot\)s/m) & 5000 & 5000 \\ Primary lateral damping/(N\(\cdot\)s/m) & 5000 & 5000 \\ Primary vertical damping/(N\(\cdot\)s/m) & 10,000 & 10,000 \\ Secondary longitudinal stiffness/(N\(\cdot\)m\({}^{-1}\)) & \(1.2\times 10^{6}\) & \(1.2\times 10^{6}\) \\ Secondary lateral stiffness/(N\(\cdot\)m\({}^{-1}\)) & \(1.2\times 10^{6}\) & \(1.2\times 10^{6}\) \\ Secondary vertical stiffness/(N\(\cdot\)m\({}^{-1}\)) & \(4.5\times 10^{5}\) & \(6.1\times 10^{5}\) \\ Secondary longitudinal damping/(N\(\cdot\)s/m) & 1000 & 1000 \\ Secondary lateral damping/(N\(\cdot\)s/m) & 1000 & 1000 \\ Secondary vertical damping/(N\(\cdot\)s/m) & 2000 & 2000 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Main parameters of dynamics model. Figure 2: Field test of low-floor trains passing n. 6 turnout: (**a**) The general test configuration; (**b**) the strain gauges applied on the rail waist. To investigate the dynamic performance of low-floor trains passing the turnout switch in facing direction based on the vehicle-track coupled dynamics theory [20], the left (outer) rails in the switch of the no. 6 turnout (stock rail and blade rail) were treated as variable profile rails in the MBS dynamic software, while the right (inner) rail and the closure rails were treated as a constant profile rail (50 kg/m rail). For the stock rail and blade rail, 15 profiles were measured, as shown in Figure 6. The FASTSIM method was employed to solve the wheel-rail contact relationship. The plane and vertical sections of the line were mapped by a total station, as shown in Figure 7a. It should be noticed that there is a reverse curve in the line before the turnout, of which the radius is 50 m. After the reverse curve, there is a 1.2 m long tangent, which connects the reverse and the turnout. In addition, by amplifying the measured data at the tangent, it can be observed that it is not an ideal straight line, but a fold line bent towards the inside of the line (Figure 7b), in which the maximum internal shift distance is 10 mm and geometrical difference between the measured and ideal irregularity along the x-coordinate were shown in Figure 7c.