A revision on the railway safety criteria evolution has shown that the fundamentals of wheel/rail contact phenomena have not been completely addressed. Limitations encountered on the available criteria for safety against derailment have motivated a deeper analysis on the wheel rolling mechanism. The contact mechanics were completely modelled with two tangential components, lateral and longitudinal forces, including spinning effects. An extended three-dimensional formula for the railway wheel flange climb derailment process is derived. Results show that calculated values agree with the classical formulation, and extend its application. This formulation allows the identification of L/V limit values for a three-dimensional rolling-contact mechanism. It can help to identify more reliable limits, relocating the safety margin for the dynamic operation of a railway vehicle.

The goal of the present study is the development of a spectral method to obtain the frequency response of the half-vehicle subjected to a measured pavement roughness in the frequency domain. For this purpose, a half-vehicle dynamic model with a two-point delayed base excitation was developed to correlate with the spectral density function of the pavement roughness, to obtain the system spectral transfer function, in the frequency domain. The vertical pavement profile was measured along two roads sections. The surface roughness was here expressed in terms of the spectral density function of the measured vertical pavement profile with respect to the evenness wave number of the pavement roughness. A frequency response analysis was applied to obtain the vertical and angular modal vehicle dynamic response with the excitation of the power spectral density (PSD) of the pavement roughness. The results show that at low speed, the vehicle suspension mode is magnified due to the unpaved track signature. At 120 km/h in an undulated asphalted road, the first vehicle vibration mode has a significant motion amplification, which may cause passenger discomfort.

This work analyses the effect of friction in suspension components on a race car vertical dynamics. It is a matter of fact that race cars aim at maximising their performance, focusing the attention mostly on aerodynamics and suspension tuning: suspension vertical and rolling stiffness and damping are parameters to be taken into account for an optimal setup. Furthermore, friction in suspension components must not be ignored. After a test session carried out with a F4 on a Four Poster rig, friction was detected on the front suspension. The real data gathered allow the validation of an analytical model with friction, confirming that its influence is relevant for low frequency values closed to the car pitch natural frequency. Finally, some setup proposals are presented to describe what should be done on actual race cars in order to correct vehicle behaviour when friction occurs.

Dynamic vehicle behavior is used to identify safe traffic speed limits. The proposed methodology is based on the vehicle vertical wheel contact force response excited by measured pavement irregularities on the frequency domain. A quarter-car model is used to identify vehicle dynamic behavior. The vertical elevation of an unpaved road surface has been measured. The roughness spectral density is quantified as ISO Level C. Calculations for the vehicle inertance function were derived by using the vertical contact force transfer function weighed by the pavement spectral density roughness function in the frequency domain. The statistical contact load variation is obtained from the vehicle inertance density function integration. The vehicle safety behavior concept is based on its handling ability properties. The ability to generate tangential forces on the wheel/road contact interface is the key to vehicle handling. This ability is related to tire/pavement contact forces. A contribution to establish a traffic sa...

The motivation for this research is to make a comparison between dynamic results of a free railway wheelset derailment and safety limits. For this purpose, a numerical simulation of a wheelset derailment submitted to increasing lateral force is used to compare with the safety limit, using different criteria. A simplified wheelset model is used to simulate derailments with different adhesion conditions. The contact force components, including the longitudinal and spin effects, are identified in a steady-state condition on the verge of a derailment. The contact force ratios are used in a three-dimensional (3D) analytical formula to calculate the safety limits. Simulation results obtained with two contact methods were compared with the published results and the safety limit was identified with the two criteria. Results confirm Nadal`s conservative aspect and show that safety 3D analytical formula presents slightly higher safety limits for lower friction coefficients and smaller limits for high friction, in comparison with the simulation results with Fastsim.Mechanical Department of the Escola Politecnica da Universidade de Sao Paulo (EP-USP) in Sao Paulo, BrasiCompanhia Vale do Rio Doce - VAL

Analytical models to evaluate vehicle dynamic handling properties are extremely interesting to the project engineer, as these can provide a deeper understanding of the underlying physical phenomena being studied. It brings more simplicity to the overall solution at the same time, making them very good choices for tasks involving large amounts of calculation iterations, like numerical optimization processes. This paper studies in detail the roll gradient, understeer gradient and steering sensitivity vehicle dynamics metrics, starting with analytical solutions available in the literature for these metrics and evaluating how the results from these simplified models compare against real vehicle measurements and more detailed multibody simulation models. Enhancements for these available analytical formulations are being proposed for the cases where the initial results do not present satisfactory correlation with measured values, obtaining improved analytical solutions capable of reproducing real vehicle results with good accuracy