Validation of a New Longitudinal Train Dyna Mics Code for Time Domain Simulations and Modal Analyses

Abstract

Large speeds and axle-loads are required for modern freight trains, which can cause a big rise in in-train forces on wagon coupling elements for both tensile and compressive states, thus possibly leading to breaking of the coupling systems and to train derailments, respectively. Therefore, longitudinal train dynamics (LTD) simulations are a key tool for the prediction of the in-train forces and for the design of coupling and braking systems as well as for the optimization of the train composition. LTD simulations are typically carried out in time domain, to account for all the system non-linearities, mainly the hysteretic behaviour of the coupling system mechanical impedance characteristic. Although time domain simulations are a powerful tool to predict in-train forces considering all the system non-linearities, also frequency domain analyses can be useful to quickly compute the system dynamic behaviour. More in detail, modal analysis can provide important information on the system natural frequencies, so that the frequency content of the input forces can be checked to avoid the excitation of the system natural vibration modes.The paper shows the development of a new efficient time domain simulation LTD code implemented in MATLAb, provided with a modal analysis post-processing routine. The code was validated on the four time domain simulation scenarios suggested by the international benchmark of LTD simulators, and a simplified modal analysis was also carried out on the same train configurations. The validation process highlighted that the new code provides stable numerical outputs with a good computational efficiency, while the modal analysis routine showed that the train eigenfrequencies can vary significantly according to the deflection, relative speed and loading state on each coupler.

Dynamic indicators influencing design solution for modernization of the freight rolling stock

“…In trains the longitudinal forces sometimes reach a value exceeding the strength of the frame of some wagon designs. Studies have shown that the large values of impact and tractive forces are due mainly to the sudden starting of the train; the in draught of a partially compressed train, especially with a fully uncompressed tail end having wagons with brakes not released; and braking by a stop-crane in the train tail end at a low speed and a compressed train at the beginning of braking [15][16][17][18].…”

A numerical method for the simulation of freight train emergency braking operations based on the UIC braked weight percentage

“…The authors' research group developed in past activities the in-house MATLAB LTDPoliTo code [6][7][8], which was validated on the simulation scenarios proposed in the context of the international benchmark of LTD simulators [9,10] (''the benchmark'' in the rest of the paper). However, the LTDPoliTo code in its original form does not consider the braking forces due to the air brake system, as the air brake forces were outside the scope of the benchmark and only dynamic braking forces provided by the locomotives were considered.…”

Development of a numerical tool for the computation of rail wheel-brake shoe thermo-mechanical interaction based on a 2D plane finite element model

“…The tool can investigate stop and drag braking operations, 1Bg and 2Bg block configurations as well as different brake shoe materials, however the preliminary results presented in the next section only refer to drag braking operations and traditional P10 cast iron brake shoes. The Matlab routine solves both the longitudinal train dynamics (LTD) equation and the rotational equilibrium equation for the braked wheel, based on an existing LTD code [18][19][20][21] and an existing heuristic wheel-rail adhesion model [22][23][24][25] developed in past activities. Starting from the results computed by the Matlab routine, which for drag braking operations correspond to wheel-shoe pressing force and friction coefficient, the FE contact module calculates the distribution of the normal and tangential pressure at the wheel-shoe interface, thanks to the application of ANSYS 2D surface-to-surface contact elements CONTA172 and TARGE169, solving the problem with the augmented Lagrangian method [26].…”