Modal Identification of Train Passenger Seats Based on Dynamic Tests and Output-Only Techniques

Abstract

Railways are one of the most efficient and widely used mass transportation systems for mid-range distances, also being pointed out as the best strategy to reach European Union decarbonisation goals. However, to increase railways attractiveness, it is necessary to improve the quality of the ride, namely its comfort, by decreasing the vibration at the passenger level. This article describes the experimental vibration modal identification of train seats based on a dedicated set of dynamic tests performed on Alfa Pendular and Intercity trains. This work uses two output-only modal identification techniques: the transmissibility functions and the Enhanced Frequency Domain Decomposition (EFDD) method. The last method allows us to clearly distinguish the seat structural movements, particularly the ones related to torsion and bending of the seat frame, from the local vertical foam vibrations. The natural frequencies and mode shapes are validated by matching the results derived from the transmissibility functions and EFDD method. The identified modal parameters are particularly relevant to characterise the vibration transmissibility provided by the foams (local transmissibility) and the vibration transmissibility derived from the metallic seat frame (global transmissibility).

Railways Passengers Comfort Evaluation through Motion Parameters: A Systematic Review

“…This study evidences the importance of carbody natural frequencies on seat transmissibility [25]. Following the same approach as Ribeiro et al [53], Silva et al [55] expanded the experimental setup on 1st and 2nd class seats of Alfa Pendular trains to investigate its transmissibility and modal identification in real-world conditions. Authors found that seat movements depend on foam's inability to absorb vibration and the carbodyʹs natural frequencies.…”

“…Therefore, the influence of the seat structural frame and foam leather cover on transmissibility was proved. This was the first experiment that contemplated all aspects of seat dynamics on seat transmissibility, namely the effect of the seat cushionʹs flexibility and carbody components on seat transmissibility [55]. Figure 4 presents the simplified experimental setup used by Ribeiro et al [53] and the expanded experimental setup developed by Silva et al [55].…”

“…This was the first experiment that contemplated all aspects of seat dynamics on seat transmissibility, namely the effect of the seat cushionʹs flexibility and carbody components on seat transmissibility [55]. Figure 4 presents the simplified experimental setup used by Ribeiro et al [53] and the expanded experimental setup developed by Silva et al [55]. Based on a simplified experimental setup, Ribeiro et al [53] instrumented a 2nd class Alfa Pendular seat to experimentally and numerically, investigate its transmissibility in a rail environment.…”

“…Ebe and Griffin [9] related multiple static physical foam characteristics to subjects' impressions of sitting comfort. Based on four foams with equal hardness but different densities (45,52,55, and 65 kg/m 3 ), the influence of density, hysteresis loss, and the SAG factor on sitting comfort was investigated. The low-density foam (45 kg/m 3 ) was judged as the least comfortable foam, whereas high-durability foam (55 kg/m 3 ) was ranked as the most comfortable seat.…”

Indirect Assessment of Railway Infrastructure Anomalies Based on Passenger Comfort Criteria

“…As mentioned, the standard determines acceleration measurements at interface surfaces where vibrations are transmitted to the user. However, it is well known that the seat modifies vibration transmission [50][51][52][53]. Additionally, the floor represents the closer location between the users and the carbody.…”