# Reducing Railway Track Vibrations by Applying Particle-Damping Systems
## 4 Conclusions and Future Work  
It was observed that the particle damper systems were capable of efficiently reducing the vibration levels for the frequency ranges and excitation amplitudes studied in the present work. When comparing the performance of different particle materials, the lead spheres proved to be the most efficient solution for the conditions analysed. In some cases, the particle dampers were capable of reducing peak vibrations by more than 20 times. Moreover, it was observed that the studied particle-damping systems were more efficient when larger levels of vibrations were present (for example, in the natural frequencies of the railway track), especially for denser particles like lead and magnetite. Additionally, it was detected that the total particle mass has a stronger impact on reducing vibration levels at lower frequencies. Finally, in cases where the reservoir was completely filled with particles (100% fill), it was noticed that the particle-damping efficiency was reduced when compared to partially filled reservoirs (for the present study, 80%). This observation was in good agreement with the literature. Once the reservoir is completely filled, the particles do not have enough space to move and collide with each other. Since the collisions and friction between particles are intrinsic characteristics, they affect the particle dampers' efficiency and are the main components for energy dissipation. This loss in efficiency can be easily explained. As it was observed in the literature, each type of particle might be very effective at a specific frequency and amplitude range. In the present study, it was observed that FIMO and rubber bands (the lightest particles) presented good vibration attenuation for low excitation amplitudes and low frequencies. On the other hand, lead particles proved to be very effective in attenuating vibration levels at higher frequencies. Consequently, the best material must be chosen by taking into account the target frequency range, and even a combination of materials might be used to cover different frequency ranges. Analysing the average amplitude values for the entire set of frequency ranges and amplitudes, lead particles showed to result in the best damping behaviour. Regarding future work, a wide range of different solutions could be addressed, like analysing the reservoir design and materials, which is an essential step for a better understanding of the particle-damping systems and enhancing their performance. Studying the effects of different reservoir materials, like building and testing an acrylic reservoir, would provide interesting information. Additionally, a combination of transparent reservoir materials and high-speed cameras would provide important insights into the vibration behaviour for each material and volume filling. Moreover, studying the distribution of several smaller reservoirs and how they compare with a single one could improve the overall damper's efficiency without the need to increase the system's total mass. Furthermore, an analysis encompassing the particles' granulometry (like average particle size and distribution effect) and the impact of reservoir internal divisions might help intensify the particle-damping system's effectiveness. Lastly, the application of hybrid damping systems, like particle dampers and tuned mass dampers, could be analysed, and their efficiency compared with single-damper solutions. Later, studies regarding the feasibility of applying the present solution in a real-case scenario would be vital, where factors like economic viability and long-term duration of the particles would be addressed. Conceptualization: A.Z.S. and A.P.C. ; Methodology: A.Z.S. and Y.E.A. ; Investigation: F.K.F., C.P. and A.P.C. ; Writing--Original Draft: F.K.F., C.P. and T.A.F. ; Software: F.K.F. ; Formal analysis: F.K.F. and A.M.P.d.J. Writing--Review and Editing: Y.E.A., A.P.C. and A.M.P.d.J. ; Funding Acquisition: A.M.P.d.J. and T.A.F. ; Resources: A.Z.S. and Y.E.A. ; Supervision: C.P., A.M.P.d.J. and T.A.F.