PRELIMINARY THEORETICAL INVESTIGATION OF INFLUENCE OF TRACK GEOMETRICAL DEFECTS ON WHEEL-RAIL FORCES

Rail and track defects are one of the most important sources of dynamic loads generated by a moving train. The oscillations and vibrations decrease the ride comfort, increasing the track deterioration and noise emission. In the spectrum of the vibrations of railway vehicles, the track geometrical irregularities generate excitations at low frequencies, usually below 30Hz, that are responsible for the dynamic behavior of the vehicle. A comprehensive multi-body simulation model of a four-axle passenger rail vehicle is implemented in the multi-body simulation software (MBS) and it is used for analyzing the potentially dangerous running condition. On basis of these multi-body model simulations, the influence of the track irregularities on the vehicle-track dynamic interaction, mainly in terms of lateral (Y) and vertical (Q) wheel-rail forces, their ratio (Y/Q) and contact angle (delta), is investigated. Four kinds of the track related irregularities, according to the ORE B176 standard, are statistically determined: lateral, vertical, roll and gauge. Each one of these, is examined in two different levels of severity (low, high) by means of excitation signals in distance domain on the basis of a Power Spectral Density (PSD) function. In order to individuate the worst run condition varying the train speed within of this range: 70 - 200 km/h, the two different combinations of irregularity levels are implemented. Finally, the relations between the main dynamic parameters (Y, Q, Y/Q, d) and the track irregularities severity level are analyzed, under certain geometrical conditions. These studies are to be considered in preparation to future investigations aimed to obtain the best simplified model to describe the railway alignment defects occurrence and their evolution