The potential of Fluid Dynamic Absorbers for railway vehicle suspensions

Abstract

The main running objectives concerning the vertical dynamics of passenger rail vehicles are ride comfort and safety. The goal of this thesis is to employ the use of a Fluid Dynamic Absorber to minimize the vertical acceleration of the car body while minimizing the dynamic force fluctuations in the wheel rail contact. The Fluid Dynamic Absorber is a device which employs a tube with a varying cross section containing oscillating fluid. The device is characterized by two effects: The inertia effect of the oscillating fluid in the varying cross section and the damping effect due to the pressure losses during the fluid flow. It is introduced as a potential damping device for automobiles and also for earthquake resistant buildings. The work encompasses the creation of a linearized approximation of the nonlinear model for parameter selection. Then, a non-linear model is built with the help of the Modelica language for use in time simulation of quarter-car models in the Dymola interface. A generalized design methodology for the device is then developed with the help of design procedures used for common tuned mass dampers and liquid column dampers. Finally, the non-linear model built using the Dymola interface is also exported for use in the full-car model in Simpack using Functional Mock-up Interface. A reduction of about 4% to 5% in the magnitude of the root mean square of the carbody acceleration was observed while the wheel-rail dynamic forces remained the same. Further improvement possibilities and the parameters influencing the vertical dynamic behavior of the vehicle are discussed.