Modelling of the shape of railway transition curves from the point of view of passenger comfort

In the past, railway transition curves were not used. Instead of it, a simple connection of the straight track and circular arc was applied. Nowadays, such simplicity is not allowed due to the increasing vehicle operating velocities. It is mainly visible in the high-speed train lines, where long curves are used. The article aims to develop a new shape of railway transition curves for which passenger travel comfort will be as high as possible. Considerations in this paper concern the polynomials of 9th- and 11th-degrees, which were adopted to the mathematical model of the mentioned shape of curves. The study's authors applied a 2-axle rail vehicle model combined with mathematically understood optimisation methods. The advanced vehicle model can better assign the dynamical properties of railway transition curves to freight and passenger vehicles. The mentioned model was adopted to simulate rail vehicle movement in both cases of the shape of transition curves and the shape of circular arc (for comparison of the results). Passenger comfort, described by European Standard EN 12299, was used as the assessment criterion. The work showed that the method using the 2-axle railway vehicle model combined with mathematically understood optimisation works correctly, and the optimisation of the transition curve shape is possible. The current study showed that the 3rd-degree parabola (the shape of the curve traditionally used in railway engineering) is not always the optimum shape. In many cases (especially for the long curves), the optimum shape of curves is between the standard transition curves and the linear curvature of the 3rd-degree parabola. The new shapes of the railway transition curves obtained when the passenger comfort is taken into account result in new railway transition curves shapes. In the authors' opinion, the results presented in the current work are a novelty in optimisation and the properties assessment of railway transition curves.

Experimental Study on Flow and Heat Transfer Characteristics in the Circular-Arc-Shaped Flow Channel

Different parameters of the circular-arc, trapezoidal and equal cross-section-shaped flow channels were analyzed, and the core volume goodness factor was used for the comparison of the three different types of flow channels. During the experiment, the Reynolds number (Re) on the air side ranged from 1200 to 5100. The results showed that the overall heat transfer performance of the three channels in this paper are circular-arc, trapezoidal and equal cross-section in order from good to bad. The overall heat transfer enhancement performance of the circular-arc flow channel is the best, which is 9–26.2% and 3.6–11.8% higher than that of the equal and trapezoidal cross-section flow channels, respectively. This showed that although the divergent flow channel structure reduces the fluid velocity in the flow process, it weakens the convective heat transfer performance in the flow channel. However, this gradually decreasing cross-sectional area improves the downstream heat transfer area and reduces the pressure drop in the flow process, thus promoting the overall heat transfer performance. With the increase in the circular radius (R), both the j and f factors increase, and the highest overall heat transfer performance is obtained at R = 300 mm. The convective heat transfer coefficient increases with the decrease in the inlet height.

Stability Analysis of Slope Based on Limit Equilibrium Method and Strength Reduction Method

Drawing on the theories of limit equilibrium and finite-element strength reduction, this paper explores the instability modes and stability change laws of the slope in zones E, W, and S of Jiajika spodumene mine, through rock mechanics tests, field survey, and numerical simulation. The results show that the sliding mode of the slope is circular arc sliding or circular arc + plane sliding. Overall, the final slope of the open-pit mine is generally stable under the current design, and the slope of the current steps is reasonable.

Geometric design and analysis of scroll compressors with a novel circular involute modified wrap

The scroll geometry in the central region of the scroll wrap plays a crucial role in determining the working performance of scroll compressors. In order to improve the comprehensive performance of scroll wraps, in this study, a novel circular involute modified wrap was put forward, in which the central and peripheral wrap profiles were connected by a circular involute in the central regions, so that a pair of fully smooth and correct meshing scroll wraps were generated. A geometric model of the involute modified wrap were proposed, and then equations of the wrap profiles and relations between geometric parameters were derived. Effects of geometric parameters on the shape and performance of the involute modified wrap were discussed in detail. Furthermore, the compression ratio of the involute modified wrap was studied by numerical simulation, and the deformation of the involute modified wrap produced by temperature load and pressure load was calculated, compared with the conventional circular arc modified wrap under the same geometric shape of scroll compressors. Study results demonstrate that the proposed involute modified wrap may simultaneously improve the compression ratio and the strength of wrap head for scroll compressors; in addition, the involute modified wrap is good for design flexibility, and therefore is superior to the circular arc modified wrap.

Theoretical Analysis of Thin Curved Rod Displacements V. P. Lugovoi1)

The paper presents a comparative theoretical analysis of the movements of the curved rods of various curvature forms, which can be applied as tools for ultrasonic treatment of holes in fragile materials. It has been shown that the traditional processing of holes by an ultrasonic method is based on the use of straight rods, in which the amplitudes of displacements on the working – free end corresponds to the value of displacements at the point of its attachment to the ultrasonic oscillation concentrator. Supplementing the configuration of a straight rod with a curvilinear shape in the form of a circular arc or a spiral twisted by one turn will allow obtaining additional displacements caused by the elastic properties of a section with a curved shape. The paper considers several calculated schemes of a curvilinear rod bounded by angles j equal to p/2, p and 2p, fferent direction of the external force action. The obtained results have shown that an increase in the circular arc angle leads to a corresponding increase in the elastic displacement index of the rod free end. In this case, the total displacements of the rod free end will be made from displacements caused by vibrations of the acoustic system and the displacements of a curved thin rod from an external force. Calculations have established that the magnitude of the elastic displacements of curved rods is influenced by the shape and magnitude of the angle, the direction of the external force, the radius of curvature, the rigidity of the cross section. The considered schemes of thin rods with curvilinear sections can find practical application in ultrasonic oscillatory systems for processing small-diameter holes in fragile materials. This increases the intensity of tool oscillations and improves the process performance.