Jordi Vinolas

Modelling of suspension components in a rail vehicle dynamics context

Suspension components play key roles in the running behaviour of rail vehicles, and therefore, mathematical models of suspension components are essential ingredients of railway vehicle multi-body models. The aims of this paper are to review existing models for railway vehicle suspension components and their use for railway vehicle dynamics multi-body simulations, to describe how model parameters can be defined and to discuss the required level of detail of component models in view of the accuracy expected from the overall simulation model. This paper also addresses track models in use for railway vehicle dynamics simulations, recognising their relevance as an indispensable component of the system simulation model. Finally, this paper reviews methods presently in use for the checking and validation of the simulation model.

Rail vehicle passing through a turnout: analysis of different turnout designs and wheel profiles

In recent years, different systems have been developed in order to improve the dynamic behaviour of railway vehicles when passing through turnouts. Some of these improvements consist in varying the geometry of the switch itself and including moveable crossing vees. It is worth mentioning that they are designed by taking a certain wheel profile into consideration, i.e. it is assumed that the wheel profile does not change. The objective of the current study is to determine the influence that the turnout design has on vehicle dynamics, as well as the influence that the variability in wheel profiles can have on the effectiveness of the different systems. In order to do this, the MBS software Simpack was used to model one vehicle with two different turnouts and four different profiles. The results show that the geometrical design of the turnout has a critical influence on the vehicle/turnout. We also concluded that the wheel profile does not have a significant influence when the vehicle passes through turnouts.

Using the stationary tests of the acceptance process of a rail vehicle to identify the vehicle model parameters

The accuracy of multi-body simulation results relies on the model building process and the accuracy of the model parameters. A more widespread use of vehicle dynamic calculations in the acceptance process would be possible if the validation of the model was secured. This paper proposes a methodology for an objective and direct identification of the values of the parameters of a rail vehicle model, using the results of the stationary tests defined in the acceptance process of railway vehicles (EN14363). The methodology also takes into account the variability of the measuring process by providing a probabilistic estimation of the identified parameters. The methodology is validated using an example of a virtual wheel unloading test (simulation). Four significant model parameters can be accurately calculated: vertical primary and secondary suspension stiffness, stiffness of the anti-roll bar, and height of the null moment point (the lateral/roll coupling effect of the air spring). Finally, a reduction method is shown which decreases the uncertainties of the identified parameters by up to 50%.

A new parameter identification methodology for a modal analysis test of a rail vehicle

The validation of vehicle mathematical models is a key part of the virtual acceptance process since it is essential to ensure a precise representation of the reality. The model validation procedure should include validation of stationary but also dynamic tests. However, parameter identification from on-track tests is a challenging task due to the non-controlled excitation and the great variability of the test results. Thus, an alternative solution by means of a vehicle modal analysis is proposed, developing a parameter identification methodology for dynamic vehicle model parameters. This methodology calculates estimated values of the vehicle model parameters that have an influence on the excited vehicle vibration modes. Moreover, a new criterion for taking into account the effect of the measurement uncertainties on the selection process of the vehicle parameters is developed. Finally, experimental results show that not only estimations of the suspension stiffness parameters can be obtained, but damping values and structural frequencies from the vehicle bodies can also be estimated.

A two-dimensional computational parametric analysis of the sheltering effect of fences on a railway vehicle standing on a bridge and experiencing crosswinds

In a crosswind scenario, the risk of high-speed trains overturning increases when they run on viaducts since the aerodynamic loads are higher than on the ground. In order to increase safety, vehicles are sheltered by fences that are installed on the viaduct to reduce the loads experienced by the train. Windbreaks can be designed to have different heights, and with or without eaves on the top. In this paper, a parametric study with a total of 12 fence designs was carried out using a two-dimensional model of a train standing on a viaduct. To asses the relative effectiveness of sheltering devices, tests were done in a wind tunnel with a scaled model at a Reynolds number of 1 × 105, and the train’s aerodynamic coefficients were measured. Experimental results were compared with those predicted by Unsteady Reynolds-averaged Navier-Stokes (URANS) simulations of flow, showing that a computational model is able to satisfactorily predict the trend of the aerodynamic coefficients. In a second set of tests, the Reynolds number was increased to 12 × 106 (at a free flow air velocity of 30 m/s) in order to simulate strong wind conditions. The aerodynamic coefficients showed a similar trend for both Reynolds numbers; however, their numerical value changed enough to indicate that simulations at the lower Reynolds number do not provide all required information. Furthermore, the variation of coefficients in the simulations allowed an explanation of how fences modified the flow around the vehicle to be proposed. This made it clear why increasing fence height reduced all the coefficients but adding an eave had an effect mainly on the lift force coefficient. Finally, by analysing the time signals it was possible to clarify the influence of the Reynolds number on the peak-to-peak amplitude, the time period and the Strouhal number.

Gas damper: potential vehicle performance studied on a full-car model

The Gas Damper (GD) uses gas as internal fluid, obtaining an important dependency on operating frequency and stroke amplitude. The potential performance of GD was analysed previously using a quarter-car model, and offered a new approach to the traditional ride/handling trade-off, especially in off-road vehicles. This paper studies the GD influence on a vehicle’s performance using a more complete model (full-car) to confirm its suitability for that kind of vehicle and also to completely understand the GD behaviour. This is evaluated by assessing ride isolation, road-holding, body control and rollover stability, and is compared to the performance of a hydraulic suspension.

Gas dampers: model development and potential ride performance evaluation

The main characteristic of a gas damper (GD) is the use of gas as internal fluid, which offers an alternative to hydraulic shock absorbers. In this paper, a mathematical GD model is presented and validated. The use of a compressible fluid provides GD with a behaviour dependent on velocity, like conventional dampers, but also with a strong dependency on frequency and on stroke amplitude. This dependency allows an improvement in the traditional compromise between comfort and safety. A quarter-car model is used to evaluate the ride performance that can be expected using the GD, focusing on the cited compromise. Results are compared with the ride performance of a hydraulic shock absorber. Finally, a sensitivity study centred on the stiffness of the internal fluid is presented.

The impact of structural flexibilities of wheelsets and rails on the hunting behaviour of a railway vehicle

ABSTRACT The hunting motion of a passenger coach is investigated using a multibody system in which the wheelsets and the rails can be modelled as flexible bodies. By comparing the results for different model variants, in which the structural flexibilities of the wheelsets and of the rails are either taken into account or neglected, the impact of the flexibilities is analysed. It turns out that the flexibilities of both the wheelsets and the rails have a significant impact on the hunting behaviour by increasing the lateral motions of the wheelsets and lowering the critical speed. In order to investigate the impact of the flexibilities under different operating conditions, the calculations are carried out for track geometries using different rail profiles (60E1, 60E2) and different rail cants (1:40, 1:20) and for different values for the friction coefficient (0.25…0.4) at the wheel–rail contact. The results show that the influence of the flexibilities is the strongest for high lateral forces, which occur e.g. for contact geometries leading to high hunting frequencies and for high values of the friction coefficient. The results also show in some cases a strong impact of the flexibilities on the position of the wheel–rail contact on the running surface of the rail, which is of particular interest with respect to wear simulation.

A new parameter identification methodology for the bogie rotational resistance test of a rail vehicle

A more widespread use of the dynamic simulation of rail vehicles would become possible if the validation of the model was secured and the model parameters were known to be accurate. This paper proposes an analytical methodology for the objective identification of parameter values used in modelling rail vehicles, using the results of a bogie rotational resistance test defined in the acceptance process of railway vehicles (EN 14363). This methodology also takes into account the variability of the measuring process by providing a probabilistic estimation of the identified parameters. The methodology is experimentally validated using test results obtained for an Intercity vehicle. Seven model parameters can be accurately estimated: longitudinal and lateral stiffness of the air-spring secondary suspension, damping and force–speed characteristics of the anti-yaw dampers, longitudinal and lateral stiffness of the emergency spring, and lateral/longitudinal friction coefficient of the emergency spring; they all show excellent correlation with the component tests.