MODELLING AND ANALYSIS OF AN INDIAN RAIL VEHICLE WITH SEMI-ACTIVE SUSPENSION SYSTEM

Abstract

There is always demand from passengers for a safe, comfortable and efficient travel. Therefore, several developing countries are focusing to lay new high speed corridors, parallely, they aim to exploit the maximum capacity of their existing huge railway infrastructures with some upgradation in suspension technology to increase the critical speed and ride comfort. The critical speed is an index directly linked with the train stability, while ride comfort refers to the suspension’s ability to maintain oscillations within the range of human comfort. Therefore, this research mainly focuses on upgradation of the suspension system in an existing Indian rail vehicle to enable it to operate at higher speeds with improved ride performance and critical speed. In detail, the thesis dealt with several issues crucial to Indian rail vehicles: (i) lateral train dynamics with passive suspension and evaluation of critical speed; (ii) lateral train dynamics with semi-active suspension and improvement in ride performance and critical speed; (iii) vertical train dynamics and improvement in ride performance; (iv) vertical train dynamics when wheel passes on a fishplate rail joint, using MR damper. The research approach followed mainly modelling and simulation work and validation with available experimental results from the Indian railway’s research organization, i.e Research Design and Standards Organisation (RDSO) as well as lab tests. Primarily, the lateral dynamics of a rail vehicle comprising of a Linke Hofmann Busch (LHB) coach with FIAT bogies is expressed with a seventeen degrees of freedom (DoFs) model, i.e. lateral, yaw and roll DoFs of the car body, front and rear bogies, as well as lateral and yaw motions for each wheelset, is developed and validated with the experimental results reported by RDSO. Then, the model is used to examine the effect of suspension parameters such as damping and stiffness on the critical speed. Moreover, a sensitivity analysis is performed, and it is found that critical speed is the most sensitive to the secondary lateral damping coefficient. Therefore, relevant dampers are replaced with MR fluid dampers. The modified Bouc-Wen model is formulated to characterise the behaviour of the MR damper. Moreover, disturbance rejection and damper force tracking controller are employed to control the MR system. A measured lateral track irregularities are applied as input to simulate the system. A substantial improvement in the critical speed of 19.38 km/h (9.89%) is realised compared to the existing passive suspension, and a significant reduction in the acceleration response of the car body is obtained in a wide frequency spectrum at higher speeds of the train. Hence, the semi-active controlled suspension system improves the critical speed and ride performance as compared to the passive suspension system. In addition, similar studies were carried out on a thirteen DoFs model to realise the vertical train dynamics, comprising vertical, pitch and roll DoFs of the car body, front and rear bogies as well as vertical motions of each wheelset, when subjected to measured track irregularities for a straight track. It was observed that the semi-active suspension with the controllers provides more vibration reduction of the vehicle than the passive one and improves the ride performance for all the considered speeds. Furthermore, the effect of MR damper over conventional passive suspension is studied when a wheel passes over a fishplate rail joint type of track irregularity. In this regard, a finite element (FE) model of the rail joint is created, from which the modal frequencies are computed and validated with experimental results. Subsequently, a model of the wheel moving over the validated rail joint is developed in the FE environment to generate the wheel-track interaction force. This force is input to a 3-DoFs mathematical model of the train and the vertical vibration response is investigated. The modified Bouc-Wen model was used to characterise the MR damper, and the continuous state control approach was used to model the damper controller. The system controller was modelled using two techniques: hybrid-based sliding mode control (SMC) and H∞ control. Results showed that the H∞ control reduced the RMS acceleration of the car body and bogie by 31.28% and 45.27%, respectively. Moreover, the H∞ control provided better rider comfort than the passive suspension and outperformed the hybrid-based SMC.