Monica Malvezzi

HIL simulation of WSP systems on MI-6 test rig

In this article, a multi-purpose platform for Hardware In the Loop (HIL) testing of safety relevant railway subsystems, such as odometry boards or wheel slide protection systems, is shown. The rig, called MI-6, is a product of the cooperation of Trenitalia with researchers of Dip. Energetica Sergio Stecco (University of Florence). In this work, special attention has been paid to vehicle real-time model optimization according to customer specifications (Trenitalia) and to simulate artificially degraded adhesion between rolling surfaces where conventional adhesion models have poor performances or require unaffordable computational resources for real-time applications. In this article, a heuristic model based on energetic considerations and a wide archive of experimental test (courtesy of Trenitalia Società per Azioni) is presented. Also some simulation results and comparison with the experimental data are shown.

A railway vehicle multibody model for real-time applications

Hardware in the loop (HIL) techniques are widely used for fast prototyping of control systems, electronic and mechatronic devices. In the railway field, several mechatronic on board subsystems are often tested and calibrated following the HIL approach. The accuracy of HIL tests depends on how the simulated virtual environment approximates the physical conditions. As the computational power available on real-time hardware grows, the demand for more complex and realistic models of railway vehicles for real-time application increases. In past research activities, the authors worked on the implementation of simplified real-time models for several applications and in particular for an HIL test rig devoted to the type approval of wheel slide protection systems. The activity has then been focused on the development of a three-dimensional model of the dynamics of a railway vehicle for more complex applications. The paper summarises the features and the results of the study.

Dynamic simulation of railway vehicles: wheel/rail contact analysis

The multibody simulation of railway vehicle dynamics needs a reliable and efficient method to evaluate the contact points between wheel and rail, because their positions have a considerable influence on the direction and intensity of the contact forces. In this work, an innovative semi-analytic procedure for the detection of the wheel/rail contact points (named the DIFF method) is presented. This method considers the wheel and the rail as two surfaces whose analytic expressions are known and is based on the idea that in the contact points the difference between the surfaces has local minima and is equivalent to solving an algebraic two-dimensional system. The original problem can be reduced analytically to a simple scalar equation that can be easily solved numerically (since the problem dimension is one, even elementary non-iterative algorithms can be efficient).

Feasibility of Degraded Adhesion Tests in a Locomotive Roller Rig

Abstract In railway applications, the testing of on-board components is necessary to optimize the efficiency of the systems and to allow high safety levels. In order to reduce the time and the cost of the testing phase, the use of dedicated test rigs is being increased. The current paper summarizes some studies for the realization of a full-scale locomotive roller rig. The main mechanical and control problems that arise in the design of this type of test rig have been highlighted, and in particular, the feasibility of tests with degraded adhesion conditions between the wheel and the rail is simulated.

Train position and speed estimation using wheel velocity measurements

Abstract In order to improve safety and efficiency in the management of modern railways, several systems for monitoring and control of traffic are being developed. Automatic train protection (ATP) systems command an emergency braking procedure if dangerous situations occur, such as insufficient braking distance to one of the next target positions and target velocities. A novel ATP system named SCMT, to be installed on trains running on Italian railways, is currently being designed. One of the components of SCMT is a module for estimating train speed and positions between fixed balises, which communicate to the on-board system the distance to next targets and the velocity requirements at targets. In this paper algorithms are described for distance to target and velocity estimation, capable of compensating for poor wheel-rail adhesion conditions where conventional odometry algorithms may fail. The algorithms were derived using a variety of methods including neural networks, fuzzy logic and crisp logic. The system was designed and trained using a wide set of experimental data, obtained from test runs carried out with different types of vehicles and conditions (in particular, degraded adhesion conditions were investigated).

Probabilistic analysis of braking performance in railways

Abstract To increase safety and efficiency in the management of railway traffic, a new speed control system, named SCMT, is currently being developed by RFI and Trenitalia for the Italian Railways. Other innovative speed supervision systems are being developed in Europe, such as the ETCS/ERTMS, which will also be installed on the new high-speed line Roma-Napoli. All traffic management systems are generally based on a set of supervision curves relating the allowed velocity of the train to the running distance, in order to ensure the respect of speed restrictions on the line by ‘soft’ or ‘hard’ intervention such as an acoustic and visual warning to the driver (soft) and/or service or emergency braking (hard) in the case of train velocity exceeding the permitted one. To elaborate this set of supervision curves, the on-board unit requires train deceleration depending on time and speed as basic information about the braking behaviour of the train. The implementation of a speed supervision system requires a preliminary definition of braking models that allow the conversion of the general parameters affecting the braking performances of trains (such as a braked weight percentage, goods/passenger brake position, brake equipment, train length, etc.) into a basic deceleration profile as a function of time, during the deceleration rise phase, and of speed, during fully developed braking. The deceleration used to evaluate braking curves is obtained by applying a proper safety margin to the nominal deceleration value (which depends on train characteristics). In this paper a probabilistic analysis of train deceleration is carried out, starting from probability distributions of parameters affecting the braking. For the major parameters, the probability distribution was determined on the basis of technical knowledge and experimental results. The aim of this work is to determine the probability that the real deceleration is lower than the nominal value multiplied by a given safety margin.

Control of a full scale locomotive roller rig for the simulation of wheel sliding

In railway applications, the testing activity of on board components is necessary to optimize the efficiency of the systems and to allow a proper safety level. In order to decrease the times and the costs of the testing phases, the use of dedicated test rigs is increasing. This paper summarizes some studies for the realization of a locomotive roller rig. The main control problems that arise in the design of this type of test rigs are focused, in particular the feasibility of tests where degraded adhesion condition between the wheel and the rail are simulated and a control strategy for the roller motors based on the sliding mode technique is presented.