# The Influence of Track Irregularity in Front of the Turnout on the Dynamic Performance of Vehicles
## 4 Result Analysis
### Influence of Different Irregularities
#### 4.2.2 Time-Frequency Analysis  
To deeper represent the effect of the irregularities in front of the turnout on the dynamic responses of the vehicle, key dynamic indicators are selected, and time-frequency analysis is carried out. The following are the results of calculations under standard parameters, where the speed is 300 km/h, the wheel-rail friction coefficient is 0.4, the axle load is 16 t, and the wheel tread profile is the standard LMA worn profile. 1. Alignment irregularity  
The influence of the AL in front of the turnout on variations in the wheelset lateral force and lateral acceleration of the vehicle body are shown in Figure 12a,b, and the variations along the distance in the wheelset lateral force and wheelset lateral displacement under the AL at 40 m wavelength are shown in Figure 12c. At the position of the irregularities applied in front of the turnout, extremums of the wheelset lateral force exceed 30 kN under short and medium wavelengths, and the maximum value is 49.8 kN at the wavelength of 10 m. When the vehicle drives into the turnout, the influence of the irregularities in the short and medium wavelengths on the wheelset lateral force is small, and the maximum value of the wheelset lateral force in the turnout area is 32.9 kN at the wavelength of 40 m. As can be seen from Figure 12c, the long wavelength of the irregularity in front of the turnout leads to the wheelset moving left and right in a simple harmonic form. When the vehicle  
Figure 11: The effects of different irregularities in front of turnout on the maximum value of dynamic indicators at different wavelengths: (**a**) Wheel-rail vertical force; (**b**) Wheelset lateral force; (**c**) Derailment coefficient; (**d**) Wheel unloading rate; (**e**) Vertical acceleration of the vehicle body; (**f**) Lateral acceleration of the vehicle body. drives into the turnout in this attitude, the wheelset lateral displacement is right at the extreme value, which means that the wheelset travels close to the switch rail side at this time, and the curved stock rail and the straight switch rail are in contact with the wheel read at the same time, which is a two-point contact, resulting in a surge in the wheelset lateral force. For the lateral acceleration of the vehicle body, the different wavelengths of the irregularities in front of the turnout have a significant effect on the entire turnout area. The extremums of the lateral acceleration occur at 20 m away from the switch rail point under the irregularities at short and medium wavelengths (3 m\(\sim\)10 m), while the maximum of the lateral acceleration occurs at the end of the turnout under the irregularities at long wavelengths (20 m-40 m). Figure 12: Variations along the distance in the dynamic indicators under the AL in front of the turnout: (**a**) Wheelset lateral force; (**b**) Lateral acceleration of the vehicle body; (**c**) Comparison of the wheelset lateral force and wheelset lateral displacement. The Short-Time Fourier Transform with a fixed frequency-domain window function (STFT-FD) is applied for the time-frequency analysis [44]. The STFT-FD method fixes the window size in the frequency domain and uses different window sizes for different frequencies. Better frequency resolution can be achieved with the STFT-FD method. Figure 13 shows the time-frequency diagrams of the wheelset lateral force and lateral acceleration of the vehicle body under the AL in front of the turnout at wavelengths of 3 m and 40 m. The frequency range of the effect of the irregularity at 3 m wavelength on the wheelset lateral force is below 100 Hz, and the influence is mainly in the area in front of the turnout, and the influence on the turnout area is small; however, under the irregularity at 40 m wavelength, the wheelset lateral force has a larger response within the 30 m range behind the switch rail point, and the frequency range of the effect is below 20 Hz.