## 5 Results and Discussion
### Analysis of the Dynamic Response of the Vehicle Carbody
The frequency weighting does not modify the dominant vibration modes in the reference points above the two bogies, namely bounce and pitch (see Figures 7 and 8), yet lowers their effect upon the dynamic response of the carbody. The diagrams (c) of the Figures 6-8 present the power spectral density of the carbody vertical acceleration weighted with the weighting function \(B\), corresponding to [PERSON]'s method. At the carbody center (Figure 6), the frequency weighting does not change the dominant vibration modes. In this case, the influence of the carbody bending is only visible at high velocities, without dominating the spectrum of the power spectral density of the acceleration. In the reference points located above the two bogies, the dominant vibration modes remain the pitch and bounce (see Figures 7 and 8). Similar to the weighting with the weighting function \(H_{ab}\) (see diagrams (b)), the effect of the dominant vibration modes upon the dynamic response of the carbody is visibly lowered after weighting with the weighting function \(B\). The role of the diagrams in Figures 9-11 is to highlight the changes of the dynamic response in the carbody reference points at the dominant resonance frequencies as a result of weighting with the frequency weighting functions \(H_{ab}\) and \(B\),respectively. They also highlight an important feature of the vertical vibrations behavior of the railway vehicle--the geometric filtering effect, extensively analyzed in many papers [34; 50; 51; 52; 53; 54]. Thanks to this effect, a succession of maximum and minimum values occur in the carbody dynamic response, depending on the vehicle wheelbase, frequency and velocity. The geometric filtering is more pronounced at the carbody center, where the effect comes from both the vehicle wheelbase and the bogie wheelbase. The geometric filtering effect has a character nature conditioned by frequency and velocity, with a more important efficiency at high frequencies and low velocities (see Figure 9, diagram (b)). Figure 9: Effect of the frequency weighting upon the carbody dynamic response in the reference point C: (**a**) at the bounce resonance frequency (1.17 Hz); (**b**) at the bending resonance frequency (8 Hz). The diagram (a) in Figure 9 shows that the influence of the bounce vibrations upon the dynamic response at the carbody center is reduced more after weighting with the weighting function \(H_{ab}\) only after applying function \(B\). Based on this observation, it can be estimated that [PERSON]'s method will indicate a weaker ride comfort than the one derived from the mean comfort method, within the velocity range where bounce is the dominant vibration mode. The diagram (b) of Figure 9 points out at the amplification of the carbody dynamic response at the bending resonance frequency, as a result of the weighting with the weighting function \(H_{ab}\), an aspect already noticed above (see Figure 6, diagram (b)). On the other hand, the weighting function \(B\) is noticed to reduce the influence of this vibration mode. The diagrams in Figures 10 and 11 emphasize the fact that the bounce and pitch vibrations in the carbody reference points located above the two bogies are lowered more due to the weighting with the weighting function \(Hab\) compared to the same action with the weighting function \(B\). Therefore, a weaker ride comfort is expected to occur in these carbody reference points while applying [PERSON]'s method versus the mean comfort method.