# Influence of Posture Change on Train Running Safety under Crosswind
## 3 Validation
### Experimental Validation  
The current numerical method was verified using a full-scale test carried out in a CRH3 train, such as that used in the numerical simulations. As presented in Figure 6a, the PP7-E1 system was used in the test. PP7-E1 is an integrated navigation device developed by NovAtel. The G320 inertial module was added based on the PwrPak7 satellite navigation receiver, using a 7 series SPAN combination algorithm, and were incorporated into the current PP7-E1 (PwrPak7-E1) integrated navigation device. The PP7-E1 device can output real-time positioning and attitude measurement data, as well as more primitive satellite navigation data and inertial data (satellite observations, ephemeris, acceleration, angular rate, etc.). As shown in Figure 6a,b, the entail data acquisition system in the full-scale test included the PP7-E1 receiver, I/O cable, GNSS antenna, antenna cable, PP7 power cable, power supply, and a laptop. During the test, the GNSS antenna-based PP7-E1 test system ensured a time accuracy of 20 ns RMS under the maximum speed limit of 499 m/s and a speed error of less than 0.015 m/s, while an attitude angle error of 0.038\({}^{\circ}\) could be obtained after post-processing. In the experiment, a data output frequency of 100 Hz was adopted to ensure that the transient change of the train attitude was well captured. This system was employed to measure the attitude change of the second car of a CRH3 train, as shown in Figure 6c.  
Note that this experiment aimed to verify the accuracy of the dynamic response output by the dynamic model results, whose input was obtained from the numerical simulation methods in Sections 2.2-2.4. That is, the CFD results (the aerodynamic forces and moments) and the dynamic system were not verified individually; instead, the whole process was validated directly using the dynamic response from the experiment, which was not only a challenge to the CFD method but also to the dynamic model. The test was conducted in an environment with almost no wind, so a similar environment between 4 and 5.5 s in the simulation was used for verification. Figure 6d shows a comparison of the test and simulation results of the overturning angle, and Figure 6e shows the difference of the  
Figure 6: The validation of the numerical method: (**a**) the entire PP7-E1 system; (**b**) the schematic diagram of PP7-E1 system; (**c**) the measuring setup in the car; (**d**) the rolling rotation obtained by numerical simulation and test; (**e**) the maximum value of the rotation acceleration obtained by numerical simulation and test.  
maximum acceleration of \(R_{x}\), \(R_{y}\), and \(R_{z}\). Note that the full-scale test results were shown after a filtered processing. It can be seen that the numerical simulation results obtained by using the present methodology in this study were generally in good agreement with the full-scale test. However, there were some obvious differences in the beginning, which could be attributed to the influence of the trailing car suffering the crosswind flow in the numerical simulation, which in turn changed the surrounding flow of the middle car. In addition, the ambient wind speed in the full-scale test could not be kept at 0 as in the numerical simulation, which was also a source of some differences. Nevertheless, the error between the current numerical simulation results and the experimental results is sufficient to guide engineering problems.