**5.1 Transmissibility curves**

Transmissibility peaks were identified for all individuals within the two seats. **Figure 4** shows the transmissibility curves for the comfort and touristic seats for individuals M1 to M4. Three transmissibility peaks were identified, T1 (yellow zone), T2 (gray area), and T3 (green zone).

The comfort seat shows T1 transmissibility equal to 0.2 Hz, the T2 transmissibility presents two main peaks, at 1.4 Hz and 2.5 Hz resulting from the same type of movement but with different amplitudes. T3 appears at frequencies equal to 4.9 Hz for M2 and M3, 4.7 Hz for M4, and 4.1 Hz for M1.

The touristic seat presented a peak of 0.2 Hz concerning T1. On this seat, T2 presented two prominent peaks, a common peak of 1.8 Hz for all individuals and a second peak between 2.3 and 3.3 Hz, depending on the subject. The T3 transmissibility area starts at 4.3 Hz for M3, and increases for M1 (4.5 Hz), M2 (4.7 Hz), and M4 (4.9 Hz).

Comparing comfort and touristic transmissibility results, T1 characterizes both seat types at lower frequencies with values of 0.2 Hz. Increased frequencies define the T2 area. The frequency ranges for the comfort and touristic seats are observed to be between 1.4–2.5 Hz and 1.8–3.3 Hz, respectively. Concerning the last transmissibility zone, T3, this presents frequencies between 4.1 and 4.9 Hz for the comfort seat and a range of 4.3–4.9 Hz for the touristic one.

The frequencies reported in this experiment are lower than those reported in the study performed by Ribeiro (4.3 Hz). Introducing new foams and covers with limited

**Figure 4.** *Transmissibility curves: (a) comfort seat, (b) touristic seat.* seams significantly modifies vibration transmission. These factors restrict the foam cellular morphology movements, and the vibration absorption varies compared to the free foam of the pre-renovation seats. Moreover, the new foams may present different mechanical properties from the previous ones, affecting their vibration-transmission capability. Transmissibility values reported by Ribeiro [62] are similar to those of T3.

The frequency values presented in this study are also lower than those presented by several authors [57–60], who found vertical transmissibility around 4.3 Hz, similar to Ribeiro's findings. However, these tests were conducted in a laboratory environment instead of a real rail environment. Moreover, a single seat was considered, and the seat frame was replaced by a simplified rigid metallic structure (approximately 1000 kg) with free foam on top of the surface without covering or other types of movement restrictions.

Matching the present results with the carbody and bogie modal identification conducted by Ribeiro, T1 zone can be associated with foam movements induced by carbody vibrations. T2 and T3 present frequencies within the bogie rigid body movements. Therefore, these transmissibility zones can be associated with this range, which may lead to seat structural movements such as rigid body, torsion, or bending [62].

In agreement with the research of Patelli and Griffin [57] and Zhang et al. [61], transmissibility peaks decreased for higher foam thicknesses; that is, T1 and T2 transmissibility frequencies were higher for the touristic seat than those for the comfort seat. Moreover, the Pendolino seat foam thickness is higher than those of the previous studies; therefore, following the reported trend of those experiments, lower transmissibility frequencies were expected in the present results.
