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The wheel wear of heavy-duty locomotives is more complicated than that of other vehicles when it affects tractive force and adhesion control. The purpose of this article is to calculate wheel wear on a curved track using a co-simulation dynamic model of a heavy-duty locomotive with adhesion control. Additionally, the effect of creep threshold, decline slope, curve radius, and passing speed on wheel wear is further investigated. The findings demonstrate that wheel wear can be successfully decreased by adjusting the creep threshold and decline slope of adhesion control parameters. The wheel-rail stick-slip vibration behavior on the curve track can be eliminated by increasing the curve's radius and passing speed, but the vertical wear at the left wheel's flange will rise sharply with the increase of passing speed on right hand curve. [ABSTRACT FROM AUTHOR]

Maglev vehicles apply the entire vehicle load uniformly onto bridges through levitation forces. In assessing the dynamic characteristics of the maglev train–bridge coupling system, it is reasonable to simplify the distributed levitation force as a concentrated force. This article theoretically derives the analytical response of bridge dynamics under the action of a single constant force and conducts numerical simulations for a moving single constant force and a series of equally spaced constant forces passing over simply supported beams and two-span continuous beams, respectively. The topic of discussion is the response of bridge dynamics when different degrees of force concentration are involved. High-precision displacement and acceleration sensors were utilized to conduct tests on the Shanghai maglev line to verify the accuracy of the simulation results. The results indicate that when simplifying the distributed levitation force into a concentrated force model, a frequency ratio can be used to analyze the conditions for resonance between the train and the bridge and to calculate the critical speed of the train; the levitation distribution force of a high-speed maglev vehicle can be simplified into four groups of concentrated forces based on the number of levitation frames to achieve sufficient accuracy, with the dynamic response of the bridge being close to that under distributed loads. [ABSTRACT FROM AUTHOR]

In order to explain the wheel-rail stick-slip vibration phenomenon of alocomotive in a curve, a co-simulation dynamic model taking into account adhesion control was established to reproduce the locomotive wheel-rail curve stick-slip vibration behavior, and the effect of parameters such as creep threshold, descent slope, rail surface condition and track curve radius on the stick-slip vibration behavior was measured by the traction force and the overall dispersion of adhesion coefficient. The results illustrate that the wheel-rail curve stick-slip vibration is caused by the dynamic traction force fluctuation under the adhesion control, and the increase of creep threshold will lead to the decrease of tractive force fluctuation amplitude and the decrease of stick-slip vibration intensity, which will increase the adhesion utilization rate, However, the increase of descent slope, the decrease of track curve radius and wheel-rail friction coefficient have the opposite effect on stick-slip vibration behavior. This phenomenon can be eliminated by improving the rail surface condition, expanding the track curve radius and lowering the locomotive traction force. [ABSTRACT FROM AUTHOR]

A friction draft gear model was developed to assess the degraded dynamic characteristics of worn draft gears in the vehicle impact condition. It presents an approach to simulate multiple typical wear profiles of wedge shoes and reflect their effects on the draft gear performance. Based on the rated design indexes and existing overhaul regulations of MT-2 type friction draft gears in China, the safety wear limits for wedge shoes with different wear profiles were classified and assessed. The results indicate that wedge shoes with uniform or concave wear can significantly worsen draft gear performance, and the existing maintenance limit of 1 mm only applies to wedge shoes with uniform wear but not to the most common wedge shoes with concave wear. Also, for wedge shoes with concave wear, when the wear area covers 50%, 75%, and 100% of the total main friction surface, the corresponding safety wear limits are 0.5 mm, 0.8 mm, and 1.3 mm, respectively. Therefore, it is proposed to design multiple graded and dynamic maintenance limits to ensure the service safety of MT-2 type friction draft gears. [ABSTRACT FROM AUTHOR]

In order to find out the influence of suspension form on the medium and low-speed maglev system, first, the transfer functions of the heaving and pitching motions of the two kinds of levitation modules equipped with the two suspensions, respectively, were derived and compared. Second, the coupled-vibration equations of the levitation module, cabin and bridge were presented. At last, two kinds of dynamic models were built to analyse the dynamic performance of the two maglev vehicles. Results show that the effect of the suspension form on the levitation module response is significant, but that on the cabin and bridge is insignificant. The maximum air-gap fluctuation in MVES (maglev vehicle with end-mounted suspension) is about twice that in MVMS (maglev vehicle with mid-mounted suspension) at the speed of 160 km/h. Moreover, the maximum current in MVES is 7.4 A larger than that in MVMS, and the mean power consumption of the levitation system in MVES is 1.2 kW larger than that in MVMS. On the whole, according to the dynamic responses of the two maglev vehicles, the mid-mounted suspension is more conducive to reducing the air-gap fluctuation, current and power consumption of the levitation system. [ABSTRACT FROM AUTHOR]

To investigate the feasibility of a radial bogie for 33 t axle-load diesel locomotives, a radial bogie scheme for large-axle load diesel locomotive was designed based on the concept, structure, and principle of the radial bogie. A dynamics model was constructed in multi-body dynamics software, and the adhesion coefficients, creepages and wear power of the leading wheelset were compared for heavy duty locomotive with the radial bogie and the conventional bogie while passing the curves. Through calculation and analysis, it is found that compared with the conventional bogie, the radial bogie may decrease the wheel slip momentum, improve the adhesion availability of locomotive when passing curves, reduce the wheel-rail wear and inconsistent wear of the left and right wheels, and decrease the frequency of wheelset repairs, which provides valuable insights for the development of large axle-load and high adhesion diesel locomotives. [ABSTRACT FROM AUTHOR]

A comparative study was conducted on Levitation Frame with Mid-set Air Spring (LFMAS) and Levitation Frame with End-set Air Spring (LFEAS). First of all, the work done by air spring force and by track excitation on two levitation frames were analysed, respectively, and the mechanism of the low dynamic interaction of LFMAS with guideway was explained theoretically; then, dynamics simulation and coupled vibration test on LFEAS and LFMAS were carried out using coupled vibration test bench of single levitation frame. Theoretical equations show that both the work done by the air spring forces and by track excitation on LFMAS are less than those on LFEAS under the same vibration condition, demonstrating that LFMAS has better levitation stability than LFEAS. Simulation and test results show that the fluctuation of levitation gap as well as the vibration acceleration of track beam platform, levitation frame and car-body of LFMAS are all smaller than those of LFEAS; with the increase of sine excitation frequency or vehicle speed, the superiority of LFMAS in dynamics performance is more obvious. [ABSTRACT FROM AUTHOR]

Mixed freight trains have more diversified vehicle characteristics and train combination modes than unified freight trains, so it is more difficult for mixed freight trains to predict the accident caused by longitudinal impulse. At present, train dynamics theories and numerical simulation methods have been increasingly used to reduce longitudinal train impulse and decrease freight wagon instability. According to these research experiences, this paper focuses on the marshalling modes of mixed freight trains and their effects on the longitudinal in-rain forces. For this purpose, an advanced simulation model for mixed freight trains was developed and several typical mixed marshalling modes were designed and simulated. The results indicate that, for the mixed train including empty and loaded wagons, empty wagons should be arranged at the tail of the train and should avoid being marshalled together. For the mixed train including marshalled wagons with various actual live loads or nominal axle loads, heavier wagons should be centrally arranged in the front part of the train, and meanwhile marshalled wagons should avoid being sorted by weight in the concave and ascending distribution mode. For the mixed train including marshalled wagons with various body types, container flat wagons and oil tank wagons should be arranged as much as possible in the front of the other wagons. [ABSTRACT FROM AUTHOR]

The 10m chord versine is commonly used as the standard to evaluate track irregularity in medium and low speed maglev (MLSM). However, the amplitude frequency of the mid-chord offset method suffers distortion, which is more serious in the short waveform range, and the 10m chord versine will lose a lot of short waveform signals. Therefore, 10m chord versine cannot be used in engineering practice as the true track irregularity. To solve this problem, the method of numerical simulation is used to simulate the process mid-chord offset method. By comparing the errors of 10m chord versine in time domain and frequency domain, the exactness of the "deduced from small to large" algorithm is verified, and two inverse algorithms of "deduced from small to large" are established to obtain the chord versine of small chord length, expand the effective detection range of short waveform irregularity, and the method of "inverse filtering" is used to inverse the short waveform irregularity. The results show that the two inverse algorithms of "deduced from small to large" can well deduce the chord versine of small chord length, and the minimum chord length that can be deduced is twice the step length. Therefore, in order to expand the measurement range of short waveform, the sampling step length should be reduced as much as possible. Compared with model B, model A has a larger error due to the addition of boundary conditions, some outliers appear, step signals appear in the power spectral density, and the absolute error is within 0.025 mm. Model B has high accuracy and good transfer characteristics, and the absolute error can be controlled within 0.001 5 mm. The field measurement of 10m chord versine of F-shaped track of Changsha Maglev Express Line shows that the track irregularities in the wavelength range of 0.5~100 m can be effectively inverted with both models. [ABSTRACT FROM AUTHOR]

A newly-designed maglev vehicle, namely maglev vehicle with mid-mounted suspension (MVMS), with air-springs mounted at the middle of the levitation module, has removed the forced guidance device (FGD). However, there is a paucity of research in the curve negotiation performance of the vehicle without FGD. In order to evaluate the curve negotiation performance of MVMS, comparisons were carried out between two maglev vehicles, namely MVMS and the maglev vehicle with end-mounted suspension (MVES). The guidance modes and mechanisms of the two kinds of vehicles were introduced and their curve negotiation performances were analyzed and compared. First, the guidance mechanism of one levitation module on the curved rail was explicated. Second, the walking mechanisms of the two maglev vehicles were introduced, and the guidance mechanism of each vehicle was illustrated. Third, two dynamic models considering rail irregularities, curved rail, and levitation control were built. Finally, the dynamic performances of the two maglev vehicles on the curved rail with 100 m radius, 6° cross-slope angle, and 0.12°/m gradient of the transition curve and on the straight rail were analyzed. Results show that MVES fails to pass the given curved rail, while MVMS can pass it at the speed of 40 km/h. Moreover, on the curved rail, the electromagnet offset, current, and levitation force in MVES are all larger than those in MVMS. For instance, when the speed is 40 km/h, the maximum vertical and lateral electromagnet offsets of the former are about four and 1.6 times those of the latter, respectively, and the maximum current of the former is about 2 times that of the latter. On the straight rail, the mid-mounted suspension can effectively improve the ride stability of the cabin at each speed. Thus, MVMS has better guiding performance than MVES on curved rail and straight rail. [ABSTRACT FROM AUTHOR]

To evaluate the dynamics of the coupled medium–low-speed maglev train-turnout system, a rigid-flexible dynamics model of the coupled system was developed based on multi-body dynamics theory and finite element method. The modal and dynamic responses results obtained from the model calculations were compared with the field test results, and the dynamic interaction characteristics of the coupled system under different operating conditions were investigated using the validated simulation model. Research results show that both the increase in the support stiffness of the turnout and the rational choice of some key parameters of the coupled system will ensure the levitation stability of the train. Increasing the support stiffness of the turnout by means of adding a trolley to support in the middle of the long-span girder (LSG) facilitates the stable levitation of the train when standing still above the turnout and improves the dynamic performance of the coupled system. By optimising some key parameters, including limiting the flatness of the magnetic pole surface of the turnout track within 1.5 mm, and taking the vertical damping of the air springs for overloaded train within 9000∼11,000 N·s/m, significant improvements in the dynamic performance of the train and the turnout can also be achieved. [ABSTRACT FROM AUTHOR]