## 5 Results and Discussion
### Analysis of the Ride Comfort Indices  
Figure 12 features the ride comfort indices in the carbody reference points, calculated for the reference parameters of the model vehicle (see Table 4), depending on velocity. Generally, the ride comfort indices increase along with the velocity in all the carbody reference points. This rise is not continuous, due to the geometric filtering effect. According to both methods of ride comfort assessment, the values of the ride comfort indices in all three carbody reference points are very close, up to 80 km/h. As velocity is going up, the  
Figure 11: Effect of the frequency weighting upon the carbody dynamic response in the reference point \(B_{2}\): (**a**) at the bounce resonance frequency (1.17 Hz); (**b**) at the pitch resonance frequency (1.53 Hz). Figure 10: Effect of the frequency weighting upon the carbody dynamic response in the reference point \(B_{1}\): (**a**) at the bounce resonance frequency (1.17 Hz); (**b**) at the pitch resonance frequency (1.53 Hz). highest values of the ride comfort indices are recorded in the reference points above the two bogies. The ride comfort index \(N_{MVZ}\) shows that the comfort index at the carbody center increases, at high velocities, reaching almost the same values with the indices in the points above the bogies. For instance, at 240 km/h, the ride comfort indices are 1.68 at the carbody center, 1.72 above bogie 1 and 1.86 above bogie 2. These readings can be correlated with the results in Figure 6, diagrams (a) and (b), based on which the ride comfort index \(N_{MVZ}\) at the carbody center was anticipated to be affected by the bending vibration at high velocities, which is the dominant vibration mode. The diagrams in Figure 12 highlight another important aspect--under the same running conditions for the vehicle, the two ride comfort assessment methods lead to significantly different results. The values for the ride comfort indices \(W_{z}\) prove a weaker ride comfort than the one indicated by the ride comfort indices \(N_{MVZ}\), which was estimated based on the analysis of the Figures 9-11. For instance, the ride comfort index \(N_{MVZ}\) implies a very good comfort and good comfort, while \(Wz\) shows that the ride comfort is just noticeable at a low velocity, yet becomes strong irregular or very irregular at velocities higher than 160 km/h. Moreover, at the same velocity, there are also large differences in terms of ride comfort of the carbody reference points. At 240 km/h, for example, the ride comfort index indicates good comfort in all three points, whereas \(Wz\) marks that the ride comfort is very irregular above bogie 1, strong irregular, but still tolerable above bogie 2 and cleary noticeable at the carbody center. The explanation lies in the frequency weighting that is different for the two ride comfort assessment methods; in all the carbody reference points, the weighting function corresponding to [PERSON]'s method reduces the influence of the dominant vibration modes--bounce and pitch--less than the corresponding function for the mean comfort method. Based on the Figures 13 and 14, the influence of the carbody bending frequency upon the ride comfort indices is analyzed. Practically, the change in the bending frequency within the 6-12 Hz interval leads to a reduction in the carbody flexibility by an increase of the bending modulus (\(EI\)) from 2.42 \(\times\) 10\({}^{9}\)Nm\({}^{2}\) to 7.11 \(\times\) 10\({}^{9}\)Nm\({}^{2}\). The ride comfort index \(N_{MVZ}\) is more affected by the value of the carbody bending frequency, which is visible irrespective of velocity, in all the carbody reference points. Sensitive changes in the ride comfort index \(N_{MVZ}\) occur at the carbody center, at high velocities, where the weighting of the carbody bending vibrations is important (see Figure 6, diagram (b)). Unlike the ride comfort index \(N_{MVZ}\), the changes of the ride comfort \(W_{z}\) only take place at the carbody center at velocities higher than 160 km/h, which is consistent with the observations in Figure 7c.