جستجوی مقالات مرتبط با کلیدواژه "railway" در نشریات گروه "مکانیک"

This paper summarized some common grading curves of ballast layers and found that the content of 16-32 mm ballast particles ("middle-size particles" in this paper) had a significant effect on the direct shear performance of the ballast layer. In this paper, the direct shear tests of the ballast layers with different contents of middle-size particles were reproduced using the discrete element method (DEM). Two different compactions of the ballast samples were used, and the reasons for the changes of shear strength of the ballast layers with different size distributions were analyzed from macroscopic and microscopic perspectives. The results showed that the strengthening effect of the ballast due insertion of middle-particles could only be observed for normally compacted ballast, whereas the same insertion with fully compacted ballast would decrease the shear strengths properties. The fully compacted ballast is subjected to the dilation. The reason of the strengthening effect for the normally compacted ballast were the contraction and dilation processes. Insertion of the middle-size particles up to 20-30% at most increase the dilation processes. Thus, the results show that the ballast layers with conventional narrow particle size distribution (narrow PSD) have higher shear strength than wide range particle size distribution (wide range PSD) if the ballast is good fully compacted. Additionally, it should be noted that the number of small particles will increase during the lifecycle of the ballast layer due to corner brakeage and the external contamination. Moreover, the drainage aspects of the wide range PSD should be considered. Therefore, the excessive insertion of middle-size particles is not justified.

There is a class of tasks that requires considering the dynamics not only for rolling stock but also for the response of the railway track. One of the directions of railway transport development, which encourages the transition to fundamentally new dynamic models of the railway track, is undoubtedly an increase in traffic speed. To solve such problems, the authors applied a model of the stressed-strained state of a railway track based on the dynamic problem of elasticity theory. The feature of this model is the calculation of dynamic stresses and deformations induced by the spread of elastic waves through the objects of the railway track. Based on the mathematical modeling of stress propagation in the under-rail basis, authors have shown the influence of various objects of a railway track on the formation of the outline of the front of the elastic wave and determined the main time intervals. Furthermore, the authors propose the following analytical method, which, in addition to the soil's physical and mechanical properties, considers the properties of the ballast as a layer that transmits pressure to the roadbed and takes an active part in the formation of the interaction space.

In order to promote the windbreak effect of the earth embankment type windbreak wall, enhance the operational speed of the single passenger train and improve the quality of the pantograph-catenary current collection for a locomotive, a three-dimensional RANS turbulence model k-epsilon was used to optimize the shape of windbreak walls. The relationships between the overturning moment of trains, the lateral wind speed at the catenary position and the height (depth) in optimization projects were analyzed. Validation was performed against full-scale experimental data. To understand the flow field around the train with different types of windbreak walls, pressure contours and surface pressure coefficient distributions were investigated. The results show that for the original type windbreak wall, the overturning moment of the passenger car is a little larger. However, for the optimization projects, the trains are basically in a minor negative pressure environment and the aerodynamic forces are much less. The optimal heights of the heightening type (depths for the cutting type) do not change obviously as the train speed increases. When the passenger car stands on the track without movement, the optimal height/depth is the smallest. Behind the original type’s windbreak wall, the lateral wind speed at the catenary position on the leeward line is less than that on the windward line. Meanwhile, as the train runs on the windward or leeward lines, the corresponding lateral wind speed rise sharply by 37.5% and 40.5%, respectively. After the adoption of optimized projects, the speeds of the two lines monotonically decrease. The best height of the heightening type is 0.30 m, and the optimal depth of the cutting type is 1.40 m. From the perspective of engineering application, the heightening type is a more suitable project.

Pantograph is a device that collects electrical current from overhead line to power an electrical locomotive. Pantograph must transmit electrical energy to high-speed rail system without arcing and interrupting power. This paper presents a Fractional Order Fuzzy PID (FOFPID) technique for tuning the optimal control gains of FOPID controller. The Fractional Order Fuzzy PID controller (FOFPID) can decrease rapidly the contact force variation between the pantograph and the catenary in order to minimize damage and wear of the contacting elements. The results are verified that system responses with proposed controller have better performance parameters in both transient state and steady state.