W.H. Zhang

A Study of Pantograph/Catenary System Dynamics with Influence of Presag and Irregularity of Contact Wire

SUMMARY In order to simulate the dynamic behavior of pantograph/catenary system accurately, a complicated simulation model in vertical is set up, in which not only the pantograph and catenary are included, but also the locomotive and track with irregularity are considered. Based on setting up the model, the dynamic behavior of pantograph/catenary system under condition of China railway system is studied. The parameters of catenary such as length of span, structure height and tension, and structure type of catenary with simple stitched wire or elasticity stitched wire are analyzed. In this paper, the effect of the presag of contact wire on current-feeding is studied, and the reasonable presag is proposeded. The irregularity of contact wire is firstly considered, and its influence on contact force is investigated. In order to improve the dynamic behavior of pantograph/catenary system, the parameters of pantograph such as stiffness, damping and mass are analyzed.

A transient dynamic study of the self-excited vibration of a railway wheel set-track system induced by saturated creep forces

Two dynamic models of a wheel set–track system on a tight curved track and on a straight track are established, in which the friction coupling between the wheel and rail is taken into account. Both the transient dynamic and complex eigenvalue analyses are performed to study the unstable transient dynamics and stability of the wheel set–track system. It is assumed that in the models creep forces between wheels and rails are saturated, that is, approximately equal to the normal forces multiplied by the dynamic coefficients of friction. The simulation results demonstrate that the saturated creep force can induce self-excited vibration of the wheel set–track system. The normal contact force between the wheel and rail fluctuates at the same frequency as the wheel and rail vibrate when the self-excited vibration occurs. And the fluctuation frequency of the normal contact force falls into the range of 60–500 Hz, which corresponds to the frequency range of rail corrugation. This phenomenon indicates that the self-excited vibration of the wheel set–track system may be a main cause of rail corrugation occurrence. Parameter sensitivity analysis shows that the stiffness and damping of the rail fastener have important influences on the oscillation amplitude of the normal contact force. Bringing the friction coefficient below a certain level and increasing the damping of the rail fastener can suppress rail corrugation.

Correlation between the Wear and Vibration of the Contact Strip in a Contact Wire Rubbing against a Contact Strip with Electrical Current

Vibration of the contact strip is an important phenomenon in the process of electrical sliding of a pantograph–catenary system. The correlation between the wear and vibration of a contact strip in a contact strip rubbing against a contact wire was studied. A series of experimental tests was conducted on a high-speed block-on-ring tester under electric current of 200 A, sliding speed of 160 km/h, and normal loads of 40–120 N. Scanning electron microscopy (SEM) and optical microscopy were used to observe the morphology of the worn surfaces. Experimental results indicate that the friction coefficient decreases but the wear rate of the contact strip increases with increasing vibration acceleration. Arc discharge energy increases with increasing vibration acceleration. Suppressing vibration is a practical way to decrease arc erosion wear of the contact strip. The conductivity of the contact strip becomes progressively worse with increasing vibration acceleration.

Determining Damping Characteristics of Railway-Overhead-Wire System for Finite-Element Analysis

ABSTRACT In order to investigate the damping characteristics of railway-overhead-wire systems, we propose herein an approach based on the continuous wavelet transform (CWT) and two existing formulas concerning Rayleigh damping coefficients (RDCs). In the proposed process, the displacement histories of a real catenary are first obtained by using a set of noncontact photogrammetric devices, following which an exclusive catenary damping ratio related to the first dominant modal component in the catenary response is identified through a complex Morlet CWT. Thereafter, iterative finite-element analysis is conducted to find the optimal RDCs, which involves using two related formulas and the similarity between the catenary displacements obtained by simulation and experimentation. The results of our study demonstrate that this combined approach is constructive, especially for structures with closely spaced modes, such as catenaries. For the case studied herein, the catenary modal damping ratio at 1.19 Hz is approximately 1%, and the mass and stiffness proportional Rayleigh damping coefficients are approximately 0.02845 and 0.00274, respectively.

Study on material transfer in the process of contact strips rubbing against a contact wire with electric current

A series of experimental tests on a block-on-ring tester were carried out to obtain a new understanding of severe material transfer in the process of contact strips rubbing against a contact wire with electric current. Three types of contact strip materials including an aluminum-based strip, a copper-based strip, and a pure carbon strip are tested in electric sliding against two contact wire materials including a pure copper contact wire and a copper–silver alloy contact wire. Test results show that there are serious material transfers in these three different friction couples in electric sliding. The aluminum-based strip has the severest material transfer, followed by the copper-based strip. The pure carbon strip has the minimum material transfer. It is found that the material transfer increases with the increase of the sliding speed, the arc discharge intensity, and the contact pressure. In the presence of electric current, contact strip materials are always transferred to the contact wire.

Friction-Induced, Self-Excited Vibration of a Pantograph-Catenary System

the pantograph is coupled with that of the catenary by friction. Stability of the pantograph-catenary system is studied using the finite element complex eigenvalue method. Numerical results show that there is a strong propensity of self-excited vibration of the pantograph-catenary system when the friction coefficient is greater than 0.1. The dynamic transient analysis results show that the self-excited vibration of the pantographcatenary system can affect the contact condition between the pantograph and catenary. If the amplitude of the self-excited vibration is strong enough, the contact may even get lost. Parameter sensitivity analysis shows that the coefficient of friction, static lift force, pan-head suspension spring stiffness, tension of contact wire, and the spatial location of pantograph have important influences on the friction-induced, self-excited vibration of the pantograph-catenary system. Bringing the friction coefficient below a certain level and choosing a suitable static lift force can suppress or eliminate the contact loss between the pantograph and catenary. [DOI: 10.1115/1.4023999]

Experimental and simulation study of wave motion upon railway overhead wire systems

To study the railway overhead wires flexural wave motion that significantly affects the quality of current collection between pantograph and catenary, dynamic responses of a real catenary excited by different excitations are measured and analyzed by using a set of noncontact photogrammetric devices together with the finite-element simulation. Based on the measured and simulated results, the wave motion along the contact wire is investigated and some findings have been obtained. First, it is the first two dominant modal components in the catenary displacement responses that induce a beat phenomenon, and this beat phenomenon is increasingly obvious near the registration arm. Moreover, with the simulated displacement contour, catenary local vibration characteristics affected by the travelling wave can be clearly interpreted. Furthermore, the wave group velocity of contact wire in catenary is determined and verified to be approximately 139.18 m/s; in addition, treating the contact wire in the overhead wire system as an ideal string or a tensioned Euler beam will overestimate the corresponding group velocity with a relative error by about 13.21%.

FULL SCALE ROLLER RIG SIMULATION FOR RAILWAY VEHICLES

SUMMARY The wheel / roller contact interaction has been studied in this paper. Computer simulations of railway vehicle dynamic performance using full scale roller rig have been undertaken. The vehicle stability and dynamic responses have been analysed in time domain for both vehicle running on rollers and on rails. And the error analysis for the roller rig in frequency domain has also been investigated.