Improving the critical speeds of high-speed trains using magnetorheological technology

With the rapid development of high-speed railways, vibration control for maintaining stability, passenger comfort, and safety has become an important area of research. In order to investigate the mechanism of train vibration, the critical speeds of various DOFs with respect to suspension stiffness and damping are first calculated and analyzed based on its dynamic equations. Then, the sensitivity of the critical speed is studied by analyzing the influence of different suspension parameters. On the basis of these analyses, a conclusion is drawn that secondary lateral damping is the most sensitive suspension damper. Subsequently, the secondary lateral dampers are replaced with magnetorheological fluid (MRF) dampers. Finally, a high-speed train model with MRF dampers is simulated by a combined ADAMS and MATLAB simulation and tested in a roller rig test platform to investigate the mechanism of how the MRF damper affects the train\u27s stability and critical speed. The results show that the semi-active suspension installed with MRF dampers substantially improves the stability and critical speed of the train

Development and evaluation of a versatile semi-active suspension system for high-speed railway vehicles

With the increase in speed of high-speed trains, their vibration will become fiercer and fiercer, especially when the lateral resonance of the car body occurs. This paper develops a versatile semi-active suspension system with variable stiffness (VS) magnetorheological elastomer (MRE) isolators and variable damping (VD) magnetorheological (MR) dampers for high-speed trains, aiming to improve ride comfort by avoiding car body resonance and dissipating vibration energy. As the first step, a multifunction VSVD semi-active suspension system for high-speed railway vehicles was designed and prototyped, including four VS-MRE isolators and two VD-MR dampers. After that, a scaled train model, composing of a car body and a secondary lateral suspension system was designed and built to evaluate the performance of the new VSVD suspension system; a control strategy based on short-time Fourier transform (STFT) and sky-hook was proposed to control the new suspension system. Two different excitations, harmonic excitation and random excitation, were applied to evaluate the train\u27s VSVD suspension. As a comparison, four alternative suspension systems, including passive-off suspension, passive-on suspension, pure VS suspension, and pure VD suspension were also evaluated. The evaluation results verified that the VSVD suspension of the train can avoid lateral resonance of car body and dissipate the vibration energy efficiently. The comparison verified that the VSVD suspension system outperforms the passive-off suspension, passive-on suspension, pure VS suspension, and pure VD suspension

Vibration suppression in high-speed trains with negative stiffness dampers

Copyright © 2018 Techno-Press, Ltd. This work proposes and investigates re-centering negative stiffness dampers (NSDs) for vibration suppression in high-speed trains. The merit of the negative stiffness feature is demonstrated by active controllers on a high-speed train. This merit inspires the replacement of active controllers with re-centering NSDs, which are more reliable and robust than active controllers. The proposed damper design consists of a passive magnetic negative stiffness spring and a semi-active positioning shaft for re-centering function. The former produces negative stiffness control forces, and the latter prevents the amplification of quasi-static spring deflection. Numerical investigations verify that the proposed re-centering NSD can improve ride comfort significantly without amplifying spring deflection

Multi - objective sliding mode control of active magnetic bearing system

Active Magnetic Bearing (AMB) system is known to inherit many nonlinearity effects due to its rotor dynamic motion and the electromagnetic actuators which make the system highly nonlinear, coupled and open-loop unstable. The major nonlinearities that are associated with AMB system are gyroscopic effect, rotor mass imbalance and nonlinear electromagnetics in which the gyroscopics and imbalance are dependent to the rotational speed of the rotor. In order to provide satisfactory system performance for a wide range of system condition, active control is thus essential. The main concern of the thesis is the modeling of the nonlinear AMB system and synthesizing a robust control method based on Sliding Mode Control (SMC) technique such that the system can achieve robust performance under various system nonlinearities. The model of the AMB system is developed based on the integration of the rotor and electromagnetic dynamics which forms nonlinear time varying state equations that represent a reasonably close description of the actual system. Based on the known bound of the system parameters and state variables, the model is restructured to become a class of uncertain system by using a deterministic approach. In formulating the control algorithm to control the system, SMC theory is adapted which involves the formulation of the sliding surface and the control law such that the state trajectories are driven to the stable sliding manifold. The surface design involves the transformation of the system into a special canonical representation such that the sliding motion can be characterized by a convex representation of the desired system performances. Optimal Linear Quadratic (LQ) characteristics and regional pole-clustering of the closed-loop poles are designed to be the objectives to be fulfilled in the surface design where the formulation is represented as a set of Linear Matrix Inequality optimization problem. For the control law design, a new continuous SMC controller is proposed in which asymptotic convergence of the system’s state trajectories in finite time is guaranteed. This is achieved by adapting the equivalent control approach with the exponential decaying boundary layer technique. The newly designed sliding surface and control law form the complete Multi-objective SMC (MO-SMC) and the proposed algorithm is applied into the nonlinear AMB in which the results show that robust system performance is achieved for various system conditions. The findings also demonstrate that the MO-SMC gives better system response than the reported ideal SMC (I-SMC) and continuous SMC (C-SMC)

An experimental effort to improve the Nimbus high resolution infrared radiometer Final report, 1 May 1964 - 15 Feb. 1965

Electronics modifications and improved detector cooling for Nimbus high resolution infrared radiomete

Suitability of Tilting Technology to the Tyne and Wear Metro System.

This paper attempts to determine the suitability of tilting technology as applied to metro systems, taking the Tyne and Wear Metro as its base case study. This is done through designing and implementing of several tests which show the current metro situation and reveals possible impacts on ride comfort and speed, in case tilting technology has been implemented. The paper provides brief background literature review on tilting technology, its different designs and types, control systems, customer satisfaction and history on the Tyne and Wear metro system. Ride comfort evaluation methods, testing of the Metro fleet comfort levels and simulation modelling through the use of OpenTrack simulator software are also introduced. Results and findings include test accuracy and validations and suggest that although tilting technology could be beneficial with respect to speed (minimal improvements) and comfort, implementing it to the Tyne and Wear metro would be an unwise decision owing to the immense amount of upgrades that would be needed on both the network and the metro car fleet. Therefore, recommendations are subsequently made on alternative systems which could achieve or surpass the levels of comfort achievable by tilting technology without the need for an outright overhaul of lines and trains

Rail roughness and rolling noise in tramways

Companies which manage railway networks have to cope continually with the problem of operating safety and maintenance intervention issues related to rail surface irregularities. A lot of experience has been gained in recent years in railway applications but the case of tramways is quite different; in this field there are no specific criteria to define any intervention on rail surface restoration. This paper shows measurements carried out on some stretches of a tram network with the CAT equipment (Corrugation Analysis Trolley) for the principal purpose of detecting different states of degradation of the rails and identifying a level of deterioration to be associated with the need for maintenance through rail grinding. The measured roughness is used as an input parameter into prediction models for both rolling noise and ground vibration to show the potential effect that high levels of roughness can have in urban environment. Rolling noise predictions are also compared with noise measurements to illustrate the applicability of the modelling approach. Particular attention is given to the way the contact filter needs to be modelled in the specific case of trams that generally operate at low speed. Finally an empirical approach to assess vibration levels in buildings is presented

A study on optical sensors orientation for tomography system development

This paper describes the investigation of optical sensors performance towards the development of optical tomography system. The orientation of the transmitters has been set from 0o until 180o and then the receiver’s responses were analyzed. Hence, sensors capabilities were tested further by placing blockage object in between the transmitter and receiver and the effect of this arrangement were observed. Finally, new designs of sensor jig were introduced based on the results achieved. Copyright © 2012 IFS

Dynamic characteristics of vehicle-wheel/rail nonlinear contact-foundation system

To study the dynamic characteristics of the vehicle-wheel/rail-foundation system of high-speed trains with consideration of nonlinear wheel/rail contact relationship and effects of nonlinear wheel/rail contact behavior on the railway rail, foundation structure and vehicle, a three-dimensional finite element model of vehicle-wheel/rail nonlinear contact-foundation system is established by using ANSYS software in which, the special contact element is used to simulate wheel/rail nonlinear contact and instantaneous separation. The vertical vibration of the whole system and its spread parts due to the track irregularities are calculated. At the same time, the relationships between the vibration of the wheel/rail system and the train speed, foundation stiffness are analyzed. The numerical results show that the appropriate foundation stiffness is conducive to weaken the vertical acceleration of the vehicle and wheel/rail system, and the vertical displacement and wheel/rail contact stress on the rail top increase with the growth of the train speed. The procedure and results from this paper can provide reference for the design of vehicle-wheel/rail system

Vibration Mitigation of Railway Bridge Using Magnetorheological Damper

The purpose of this study is to analyze the railway bridge vibrations and control their negative effects through semi-active magnetorheological (MR) damper. Dynamic analysis of a railway bridge subjected to the moving load is performed. The real structural parameters are used, and the six-axle train is simulated as moving loads. The railway bridge is modeled as Euler-Bernoulli beam theory, and it is discretized through Galerkin method. To mitigate the bridge vibrations, MR damper with a fuzzy logic-based controller (FLC) is positioned at the ends of the bridge. The simulations of the system are performed by MatLab software. Finally, the results are examined both in the time and frequency domains