# Modal Identification of Train Passenger Seats Based on Dynamic Tests and Output-Only Techniques
## 5 Conclusions  
This study performed a dynamic experimental analysis of typical rail seats under a real train in situ environment. This analysis included the modal identification of the seat based on output-only methodologies, namely the transmissibility functions and the EFDD method. The study included the development of dedicated experimental setups that were applied on real train seats, namely the comfort and standard seats of Alfa Pendular and Intercity trains. Being employed in a real train environment, the experiments can realistically consider all aspects of the seat dynamics, particularly the effect of the flexibility of the seat surfaces and carbody components. Based on the results of the dynamic testing, it was possible to draw conclusions about the influence of the seat structural movements and dependence on the foam vibration  
Figure 22: Standard seat experimental modal parameters, where the front and lateral views are presented regarding Intercity trains. absorption capacity. Regarding AP train seats, the inter-subject variability did not affect transmissibility resonances and antiresonances. Moreover, the standard seat presented higher transmissibility peaks than the comfort seat. Compared with laboratory experiments, AP seats presented lower transmissibility resonance peaks, which reveals the influence of the seat structural frame and foam leather cover. These factors significantly modify the vibration transmission; particularly, the cover restricts the foam cellular morphology movements, leading to variations in foam absorption capacity, while the seat frame movements may couple with movements of the carbody components. Modal identification depicted seat bending movements and vertical foam movements. By matching transmissibility and modal identification, it was possible to associate the resonance frequencies with seat and foam natural frequencies and the corresponding amplified movements. In contrast, the antiresonance valleys generated those movement changes on the structural support. The Intercity train's comfort seat is similar to that used in laboratory experiments. The foam is freely placed on top of the seat surface, covered by a non-restricting leather fabric. Its results are close to those of laboratory conditions. The Intercity seats experimental setup allows for concluding about the influence of the seatback local bending movements on the transmissibility response. Seatback transmissibility resonances matched the local bending movement frequencies identified by modal identification. This way, the applied methodology was validated based on the strong correlation between the transmissibility curve and the EFDD method. The present work demonstrated the influence of seat structural frame movements and foam vibration absorption on user-seat vibration transmissibility. Moreover, to the authors' knowledge, this is a pioneer study regarding train seat modal identification, which may be used for further studies concerning seat vibration reduction to increase passengers' comfort. Conceptualization, P.S. and D.R. ; methodology, P.S. and D.R. ; software, P.S. and D.R. ; validation, P.S., D.R., J.M. and E.S. ; formal analysis, P.S. and D.R. ; investigation, P.S. ; resources, P.S. and D.R. ; data curation, P.S. ; writing--original draft preparation, P.S. ; writing--review and editing, D.R., J.M. and E.S. ; visualization, P.S. ; supervision, D.R. and J.M. ; project administration, D.R., J.M. and E.S. ; funding acquisition, P.S., D.R., J.M. and E.S. All authors have read and agreed to the published version of the manuscript. This research was funded by Fundacao para a Ciencia e Tecnologia grant number PD/BD/143161/2019. The authors also acknowledge the financial support from the Base Funding-UIDB/04708/2020 and Programmatic Funding-UIDP/04708/2020 of the CONSTRUCT--Instituto de Estruturas e Construcoes, funded by national funds through the FCT/MCTES (PIDDAC).