Features of mathematical modeling of dynamic processes of car passing railroad turnouts

Dimensions and tolerances in the “wheelset — railway track” system are interconnected, since the normative values of geometric parameters and shape of the elements of the wheelsets and the track's upper structure are directly dependent. In 2018 –2019 in order to establish the minimum permissible thickness of wheel flanges for freight cars in operation and to determine the influence of the thickness and shape of wheel flanges on the safe passage of turnout elements, JSC “VNIIZhT” conducted comprehensive studies, including the development of a methodology and mathematical modeling of the interaction of wheelsets and turnout elements. Features of modeling the dynamic processes of the entry of the first bogie of a freight car into the railway turnout when running to the side track are presented. The process of moving a freight car along the turnout is described depending on the geometric parameters of the wheelset and track elements of the turnout, the position in the gauge of its first bogie before running into the switch point. Results of calculations of the lateral forces of the interaction of the wheelset and the turnout show that when running on, the maximum forces occurred during wheel impacts in the turnout elements, which depend on the conditions of the bogie entering the turnout. The initial position of the bogie and the peculiarities of its motion in the gauge determine the position of the meeting point and the value of the angle of incidence, their combination determines the maximum value of the force when moving to the lateral track, which, depending on the entry conditions, can differ by more than twice. Calculations showed that a change in the angle of inclination of the flange from 60 to 70° leads to a decrease in the safety factor of rolling stock on the turnout by 1.5 times. Required minimum value of the inclination of the wheel flange, ensuring safety (qR parameter), is determined by the creation of conditions that do not allow the wheel to run onto the tip of the switch point. Under existing norms of wear of turnout elements and the relative position of their rail elements, as well as taking into account the results of the calculations, the permissible value of qR should be in the range of 6.0 ... 6.5 mm.

Features of the bridge span performance when shifting the axis of the rail-sleeper grid

Engineering structures form an integral part of the railways, both already operated and yet designed. The joint work of the upper structure of the railway track and the supporting structures of the bridge crossing is an important condition for the normal operation of the railway section without various restrictions and additional work on the current maintenance and diagnostics of structural elements. Presented study is devoted to the investigation of the stress-strain state of a small railway bridge with a beam design, when the axis of the rail-sleeper grid relative to the axis of the bridge is shifted by an amount exceeding the limit value determined by regulatory documents. In the analytical calculation of the behavior parameters and the state of the span under the action of the load, a differential equation is used that describes the vertical vibrations of the beam and allows considering them as a combination of forced and free vibrations. In numerical modeling, the finite element method is used as the solution method, the determining equations of which contain linear and angular displacements of nodes of the calculation scheme as unknowns. As a result of the calculations, graphical dependences for normal and horizontal displacements, internal forces, principal and equivalent stresses at various points of the span are obtained. Presented values show an increase in bending and torsional forces, as well as principal stresses when the axis of the railway track is displaced relative to the axis of the bridge. It is noted that although the increase in stresses (by about 6 %) can generally be considered insignificant, the presence of defects in the span beams (concrete chips, cracks in the stretched zone, exposure and corrosion of working reinforcement, decrease in the calculated cross section, leaching of cement stone from concrete, decrease in concrete strength over time) can make it a significant enough factor limiting the operational capabilities of bridge crossings.

Choosing the type of equivalent circuit of traction substation when calculating shortcircuit currents in 25 kV power supply system

When calculating short circuit currents in the traction network, it is necessary to take into account the input resistance of the traction substation, including the resistance of the transformers of the substation and the resistance of the power supply system. The input resistance during short circuit is determined based on the equivalent circuit of the external power supply system, of which this traction substation is an integral part. Traditionally equivalent circuit of a threephase system has the form of a star, in which the resulting resistances in each phase are connected in series with a source of phase electromotive force, and these sources have a common point. Another equivalent circuit in the form of a triangle is possible, in which on each side the resulting resistances are connected in series with the source of linear electromotive force. It is important to note that neither one nor the other type of equivalent circuit is determined by the connection scheme of the transformer windings of the traction substation. It is only necessary to take into account the absence of a circuit for zero sequence currents. All elements of the equivalent circuit, as is known, should be brought to uniform basic conditions. If the parameters of these elements are expressed in named units, then the basic values are the effective voltage values of the main stage and the rated power of the power transformer of the traction substation. If the components of one and the other equivalent circuits are reduced to one stage of the operating voltage, for example 27.5 kV, then for the same elements of the power supply system, the resistance values in the equivalent circuit in the form of a triangle are three times larger than in the equivalent circuit in the form of a star. In this case, the input resistances of the traction substation for the one and the other equivalent circuits are absolutely identical. Therefore, in the calculation of short circuit currents of the traction network, you can use any of these equivalent circuits of the power supply system and traction substation. Formulas for calculating the resistances of the elements of the power supply system and electrical installations, given in the standards, manuals and reference books, relate to the equivalent circuit of the short circuit in the form of a star. When using an equivalent circuit in the form of a triangle, these resistances must first be tripled, and then divided by three when calculating the short-circuit currents. The meaninglessness of such an operation is obvious. The equivalent circuit of the traction substation and the external power supply system in the form of a triangle when calculating short circuits in the traction network has no advantages compared to the traditional equivalent circuit in the form of a star. The information on the linear currents on the primary and secondary windings of the traction substation transformer during a short circuit in the traction network is given, which is necessary to select the settings of its relay protection kit.

Influence study of parameters of the railway track in plan and profile on the indicators of the railway track and rolling stock interaction

Modern level of development of automated systems opens up great opportunities for designers, making it possible to find optimal solutions for the construction of the railway track using digital modeling methods and automated programs. Moreover, the expansion of technical capabilities should be based on a responsible approach to choosing configuration of the railway track, its parameters in plan and profile. The article is devoted to the study of the influence of the parameters of the railway track in plan and profile on the interaction indicators of the track and rolling stock. Author presented a retrospective analysis of the norms for choosing the largest difference in the slopes of adjacent profile elements and the smallest length of separating pads and transition steepness elements. Also shown is the dependence of the length of separating pads and elements of transition steepness and the dependence of the algebraic difference of the slopes of adjacent elements of the profile of railway lines on the weight of the train with different linear loads. The results of modeling the freight cars running in sections with different combination of the plan and profile of the railway track in the software package “Universal Mechanism” are presented. During the modeling, the dependence of the frame forces on the algebraic difference of the matching slopes was obtained, and a comparative analysis of other indicators of the interaction of the track and rolling stock (lateral forces, vertical forces, longitudinal forces, stability margin) was carried out. The article conclusions summarize the results of the calculations and give recommendations for calculations and modeling the effect of a combination of vertical curves and curves in plan on the indicators of the dynamic interaction of the track and rolling stock.

Experimental study of natural frequencies and forms of the rail oscillations

The article considers the problem of assessing the stability of the continuously welded track at its temperature elongation and proposes a method for this assessment by comparing the actual temperature of fastening the rail strings with the standard one. A method for determining the actual temperature of rail fasteningis presented, which consists in measuring its temperature and natural vibration frequencies, followed by an analysis of the dependence of the change in the natural frequency of the rail head in the transverse direction on the magnitude of the longitudinal force applied to the rail. The methodology of the tests performed at the bench and section of the continuously welded track of the Ozerskaya branch of the Moscow railway is described. The essence of the technique is to determine the values of natural vibrations using various measuring instruments (strain gauges, vibration transducers, sound level meters) at different values of the longitudinal force applied to the rail. Natural vibrations were excited by hitting the rail head in the transverse direction. A comparative analysis of the forms and frequencies of natural vibrations of the rail head is carried out according to the test results in bench and operational area conditions. It was found that the closest convergence of the vibration frequencies of the rail head in the transverse direction corresponds to the first mode of vibration. During bench tests, the dependence of the frequency change of the first form of natural vibrations of the rail head in the transverse direction on the magnitude of the longitudinal force applied to the rail was determined. According to the results of a comparative analysis of the results of measurements of the natural frequencies of rail oscillations, the possibility of using a sound level meter or similar measuring instruments for their registration was established. The calculation of the actual temperature of the rail fastening is also given on the example of the section of the continuously welded track of the Ozerskaya branch of the Moscow railway and its compliance with the normative for this region is established.

Problems of creating a promising biaxial bogie of a shunting diesel locomotive

Recently, in domestic and foreign practice, shunting and industrial diesel locomotives with hydraulic transmission are replaced by diesel locomotives with electric transmission and the number of axles from 2 to 4, which allows reducing the cost of fuel and repair. Accordingly, the problem arises of creating a biaxial bogie of a shunting diesel locomotive with power transmission, as much as possible unified with a triaxial non-pedestal bogie with a wheel diameter of 1050 mm. The analysis of a possible version of a biaxial scientific backlog for a rational choice of design solutions. The need has been established to conduct research on irregularities of access tracks of industrial enterprises to determine the effect of dynamic unloading of diesel locomotive axles on coupling properties and to study its horizontal dynamics by modeling methods with experimental verification of the result on diesel locomotives already produced in order to determine typical options for cross-link nodes between the bogie and the body. For a traction drive with a rigid gear wheel, when assessing the load of nodes under the action of a dynamic moment in the drive, it is impossible to accept the assumption of the shockless nature of the processes in the traction drive and neglect the wheel slippage along the rail, which makes it impossible to correctly model dynamic processes in the drive, and to use previously known empirical regularities for the design of suspension devices for traction electric motors fail according to the layout of the nodes. In order to reduce possible errors in the design of a new individual traction drive for shunting diesel locomotives in conditions of insufficient scientific reserve, it is proposed to choose the option with an elastic gear wheel and suspension with articulated movable links already tested on mainline diesel locomotives that do not have special shock-absorbing elements. Variants of such a suspension are proposed, in which the traction motors are moved relative to the bogie frame with a short length between the axes of the upper and lower hinges, as well as the possibility of its unification with pendulum and spring traverse suspensions. A patent for an invention and two patents for a utility model were obtained for the proposed solutions.

Testing procedure for determining isothermal properties of the freight car body intended for the transport of perishable freights in the absence of specialized climate chamber

According to the Rules for the transport of perishable freights by rail, isothermal vehicles must comply with the provisions of the Agreement on the international transport of perishable foodstuffs and on special vehicles intended for this transport (ATP). The article proposed a technique for determining isothermal properties of the body of freight cars intended for the transportation of perishable freights by testing in the absence of a specialized climate chamber. The requirements of the ATP to the testing conditions are analyzed and the parameters that in the absence of a specialized climate chamber are impossible or difficult to perform are considered in detail. For each such parameter, a sequence of actions has been developed to bring the actual test conditions closer to the requirements of the ATP, and methods that allow adjusting the test results are justified taking into account the reduction of the specified parameters to the requirements of the ATP.

The proposed methodology of heat engineering tests of isothermal cars will allow:

• conduct heat engineering tests of thermos and refrigerated cars with high accuracy of obtaining the final result and the basic requirements of ATP;

• create a mechanism for control and examination of isothermal cars and containers under comparable conditions.