Analysis and Improvement of Secondary Suspension Effects on Ride Comfort of Passanger Railcar (Case of Addis Ababa Light Rail Transit Service)

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Speed and track irregularities are the main causes of vibrations in rail vehicles. They bring a discomfort, fatigue and motion sickness to passengers depending on its frequency content. In this thesis the analysis and improvement of the secondary suspension effects on a passenger ride comfort of rail vehicle by considering the current random track irregularities are evaluated via the Sperling ride index. The current track irregularities data were collected from Addis Ababa Light Rail Transit Service (AALRTS) then converted to time domain and curve fitted using sine functions. The half car model of a vehicle with two bogies, two suspension levels, and a flexible carbody for one car is considered for mathematical modeling of the vehicle vibrations. The response due to pitch and bounce were numerically analyzed using MATLAB / Simulink and Universal Mechanism multibody dynamic simulation software (UM-MBS). The results obtained from two numerical simulations matched between each other. The results show that bounce vibrations affect more the ride comfort than pitch vibrations and as the speed increases the ride comfort worsens according to Sperling ride index evaluations. In addition to these analyzes, if the secondary suspension damping ratio falls between 0.1 and 0.3 the ride comfort is improved. Finally, optimizations of suspension parameters were done for worst track irregularities scenario by using MATLAB/Simulink/ Response optimization tool which led to reducing the ride discomfort significantly than the current suspension parameters. The evaluations concluded that the AALRTS vehicle vertical response is at good conditions with current track irregularities. The ride comfort is improved by 9.87%, 14.62%, and 15.17% at the center of the carbody, above bogie front and above rear bogie respectively.



AALRTS, passenger rail vehicle, random track irregularities, secondary suspension, ride comfort