Antonio Carrarini

Reliability based analysis of the crosswind stability of railway vehicles

The computational models used to assess the crosswind stability of railway vehicles by multibody simulation (MBS) are affected by large uncertainties. Especially, the aerodynamic loads acting on the vehicle are difficult to model and the respective parameters cannot be easily acquired. Such uncertainties are usually neglected in the safety norms even though their effects on the risk assessment can be very large. In this paper the problem is tackled by modelling the most influential but uncertain parameters as stochastic variables. The resulting task can be efficiently managed by reliability techniques, mainly inherited from structural mechanics. This finally leads to the substitution of the conventional characteristic wind curve (CWC) by the probabilistic characteristic wind curve (PCWC). The proposed approach is referred to the most recent European norms for crosswind stability and exemplified on the test case of a German high speed train (ICE2).

Efficient models and techniques for the computational analysis of railway vehicles in crosswinds

Nowadays, crosswind stability is a key topic for the homologation of railway vehicles and thus it is a pivotal boundary condition in their design process. In most countries, the safety proof is based on the numerical multibody simulation of the driving behaviour of the vehicle assuming a worst case wind scenario. The conservativeness of this approach is aggravated by the uncertainties in the parameters of the simulation models. In this work, some possible improvement of the safety proof are discussed mainly concerning the computational model of the vehicle. An alternative approach based on reliability techniques is then presented and discussed, leading to a more efficient assessment of the risk, and thus to a reduction of the safety factors.

Bridging the Gap from Multibody Simulations to Acoustic Analysis

Multibody simulation plays an essential role in the initial design phase of railway vehicles in which conceptual issues are investigated. It is as well the state-of-the-art method in order to study and optimize the running dynamics and comfort of railway vehicles in details. However, acoustic issues could not be ad ressed so far by multibody analysis. This is due to the fact that the validity of the used multibody models is restricted to the very low frequency range. In addition, multibody methodology is not prepared to evaluate acoustic measures in order to assess a railway vehicle under consideration.

Influences on Nonlinear Judder Vibrations of Railway Brakes

The paper reports on a joined research project of Knorr-Bremse, Siemens Mobility and the Institute of Robotics and Mechatronics. The goal of the project was to analyse the dynamical behaviour of friction brakes for high-speed trains. It was intended to gain insight into possible vibration mechanisms and to assess the potential for lay-out and operation improvements for future light-weight designs. In particular, the frequency range up to 250 Hz has been addressed, since the corresponding excitation is unavoidable at least to some extent and has to be considered when the brake system is designed. The study includes a comprehensive multibody simulation study and its comparison to experimental results at the test rig of Knorr-Bremse in Munich. The simulation model is adapted step by step in order to clearly identify and separate the influences on the dynamical properties of the complete brake system including its mounting. Additionally a minimal model is introduced that demonstrates some characteristics of the brake system. It turned out that the underlying knowledge is essential for the mechanical lay-out, which could be demonstrated by solving a particular vibration problem in an actual high-speed project.