Running Safety Research Articles

Influence of rail weld irregularity on dynamic stress of bogie frame based on vehicle-track rigid-flexible coupled model

To examine the effects of rail weld irregularity on the dynamic stress of the bogie frame, a numerical model which considers the bogie frame flexibility is established. Field measurements were conducted to validate the reliability of the proposed model and the bogie frame’s modal vibration including the bending deformation of cross beams at 50 Hz can be observed. A comparison between the flexible bogie frame model and the traditional multi-body dynamics model is conducted to investigate the influences of the bogie frame’s flexibility on wheel-rail interactions. Then the numerical model of the rail weld joint is proposed to study the P2 resonance performance and the dynamic stress patterns of the bogie frame. A comparison of influences with different rail weld irregularities and parameter studies are conducted. Then the effects of fastener stiffness on P2 resonance frequencies are discussed. The results show that it is necessary to consider the bogie frame’s flexibility in simulations which will aggravate the wheel-rail vibrations. The short wavelengths in combination with a certain speed could induce the bogie frame’s modal vibration and large track supporting stiffness will threaten the running safety of the vehicle which may also contribute to the formation of wheel out-of-roundness. Besides, the limit values of the rail weld irregularities are discussed to provide a reference for rail surface grinding from different aspects.

The Wheel Flat Identification Based on Variational Modal Decomposition—Envelope Spectrum Method of the Axlebox Acceleration

The wheel flat can cause train and rail system infrastructure damage and endanger the running safety. To monitor the early wheel flat, it is urgent to carry out the theoretical basic research on the relationship between the vibration signal and the wheel flat. Moreover, to extract the characteristics of the wheel flat, an advanced and effective signal processing method need to be studied. A three-dimensional vehicle-track coupled dynamics model verified by field test is established based on the multi-body dynamics at first. The acceleration of the axlebox excited by the different wheel flat length is obtained by the dynamic simulation. The simulation considers the influence of various speeds and the short-wavelength track irregularities. Then, a combined method based on the variational modal decomposition (VMD) and the envelope spectrum (ES) is employed to detect the wheel flat signal. The feasibility of the method is further validated by comparing the co-existence of the wheel flat and the wheel eccentricity. Finally, field test is carried out to detect the wheel flat by using this method. The results indicate that the VMD-ES method accurately extracts the impact characteristics of the wheel flat and can quantitatively identify the wheel flat faults of small sizes.

POSSIBILITIES OF IMPROVING A RAIL VEHICLE RUNNING SAFETY WITH INDEPENDENTLY ROTATING WHEELS

This work is focused on the possible ways of improving the running safety of a railway vehicle, which uses IRWs (independently rotating wheels) in a bogie. It discusses the main positive and negative properties of an application of IRWs for a railway vehicle while it is running in a curve. There are evaluated running properties of a railway vehicle in terms of safety for IRWs and a standard wheelset (SW). It is assumed that a wheelset design with IRWs will reduce the risk of derailment of a railway vehicle in a curve with a smaller radius because it will be reached a more favourable distribution of decisive forces in the wheel/rail contact. A designed wheelset with IRWs differs from other IRWs designs; in this case, only a flange can rotate independently from a wheel treat surface about the axis of rotation. Further, this research presents an analysis of a friction forces distribution of the friction forces in a contact of a flange and a rail head and a comparison with an SW. The obtained results allow concluding that it is advisable to use the wheels with the perspective wheel design (including independently rotating) to reduce the resistance to movement and improve the running properties of a railway vehicle for safety.

Effect of lateral misalignment defects of rail joints on dynamic derailment behaviour in railway turnouts

This study aims to investigate the mechanism of wheel jumping derailment in the railway switch panel after a freight wagon passes over a rail joint defect (RJD) situated before the switch. For this purpose, a 3D vehicle-track (turnout) coupled dynamic model that considers the elastic deformation of the rails and wheelsets has been established. Several extreme running conditions, including sharp curves, low-speed railway turnouts, lateral misalignment defects of RJs, and empty wagons are all considered in the simulation model. The vertical wheel rise limit for the railway switch panel is presented for the evaluation of a quasi-static derailment risk. The wheel-rail impact behaviour and the evolution of the derailment processes in the switch panel are revealed, and the effects of wagon load and misalignment width of RJ sections on the vehicle’s dynamic response and running safety are investigated. The results show that the root cause of the high derailment risk in the railway switch is a lower wheel rise limit at the front region of the switch rail when compared with the mainline. This dynamic derailment limit is sensitive to the car-body load and the misalignment width. Severe lateral defects of the RJ before the switch toe should therefore be avoided.

Improving vehicle’s seismic safety by equipping railway bridges with FPB and misalignment control device

Running safety of the railway vehicles on the bridge during earthquakes is a major concern for railway engineering. To reduce the derailment risk of railway vehicles on bridges, friction pendulum bearings (FPB) are proposed to be equipped on simply supported bridges in this study. The full nonlinear behavior of the FPB is introduced into the vehicle-bridge interaction model. The effect of FPB’s manufacturing variations, including the shear pin’s strength and friction coefficient, on the misalignment was investigated. The manufacturing variations of the FPB were found to produce large lateral misalignment, which further contributes to large wheel-rail forces when the vehicle passes over the girder ends. It diminishes the improvement in the vehicle’s seismic safety provided by FPBs. Thus, a misalignment control device is proposed to limit the misalignment of the railway bridges equipped with FPBs. The vehicle-bridge interaction analysis results show that no wheel uplift occurred on the bridge equipped with FPBs and misalignment control devices during an earthquake. It indicates that the FPB significantly reduces the vehicle’s derailment risk on bridges compared with the non-isolated bearings.

Calculation of Basic Indicators of Running Safety on the Example of a Freight Wagon with the y25 Bogie

Freight wagons are among the most widely used means of transporting goods by land. Such a number of wagons and transported material and amount of material need to meet requirements in terms of safety and reliability. A wagon bogie is a key element in the wagon running safety point of view. The Y25 bogie is a most used bogie for freight wagons in the region of the central and west Europe. As this bogie was developed several decades ago, it is interesting to evaluate its running properties according to current standards. The presented research brings results of calculation of chosen basic indicators in terms of running safety. The calculations of the freight wagon with the Y25 bogie was performed by means of a multibody model. Simulation computations were carried out for an empty and loaded wagon, which has been running in curves with various radii and at several running speeds.

Measurement and evaluation of wheel profiles of a rail vehicle on an underfloor wheelset lathe

Wheel profile form directly affects the dynamic behaviour of rail vehicles. Moreover, it is an important factor to ensure the safe running of a high-speed vehicle. As off-line measurements do not provide high-efficiency and high-accuracy wheel profile measurements, we focused on on-machine measurement and evaluation for obtaining the wheel profiles of a rail vehicle in this study. By combining the wheel machining with the wheel measurement, the measurement and evaluation of radial and axial wheel profiles on the underfloor wheelset lathe were proposed. The measurement of radial wheel profile based on two laser sensors was introduced, and the corresponding error models of on-machine measurement were established. The error models were used to separate the measurement errors from the measurement data. This can improve the accuracy of measuring the radial wheel profile effectively. For measuring the axial wheel profile, an adaptive correction method of profile error was proposed to suppress the measurement error, which was the basis for obtaining an accurate equivalent conicity. By measuring radial and axial wheel profiles, polygonisation evaluation and equivalent conicity were obtained to evaluate the radial and axial dynamic behaviours of a wheelset, respectively. Finally, the measurements were applied to an underfloor wheelset lathe to verify the effectiveness of measuring wheel profiles. In this study, we not only improved working efficiency for the machine tools, but also provided a high-accuracy measurement method for the wheel profiles of rail vehicle.

Field measurement of wind shielding effect of bridge tower for wind-vehicle-bridge system

Although the wind barrier was set near the bridge tower, more than 10 traffic accidents under crosswinds happen in the bridge tower area within 1 month of the opening operation of a cross-sea bridge. To investigate the wind shielding effect of the bridge tower, a field measurement scheme of wind-vehicle-bridge system, which is a step-by-step test method, was presented and performed on a long span cable-stayed bridge. Firstly, the horizontal profile of wind speed of bridge deck near bridge tower was obtained through the anemometers. Then, the dynamic response of the bridge was measured under the action of normal operating vehicle when the natural wind speed is low. Finally, the response of the moving car was measured when passing through bridge tower, and the wind speed was recorded simultaneously. The results show that the wind-vehicle-bridge system can be tested by step-by-step test method to understand the wind shielding effect of bridge tower. The displacement response of the bridge is still very small when two large trucks meet, and the coupling effect between the vehicle and the bridge is insignificant when a single car passes through the bridge tower. Due to a large porosity of the anti-collision guardrail, the wind speed at the height of 1 m from the bridge deck has changed dramatically when the car leaves the bridge tower on the windward and entering or leaving the bridge tower on the leeward. Among them, the leeward side change is more obvious, and the response of the leeward side vehicle is also greater. The suitable decrease of the anti-collision guardrail porosity in the bridge tower region will improve the running safety of vehicles.

Longitudinal-vertical dynamics of a high-speed train rescued by locomotives during braking on grades

This paper describes the longitudinal-vertical coupling dynamics of a high-speed train rescued by locomotives during the braking process on grades. The coupler jackknifing behaviour under compressive forces will affect the running safety of the coupling train. In this paper, the longitudinal-vertical impacts by field testing for the locomotive to train rescue scenario are firstly introduced. The quasi-static force analyses of the train and couplers are carried out to study the coupler jackknifing mechanism on graded tracks. The three-dimensional dynamic model of the train and coupler system is then developed. In this model, the coupler rotational motions, hysteresis characteristic of draft gears, braking characteristic are taken into account. The typical responses during the braking process for the high-speed train rescued by the diesel locomotive are reproduced and verified. The running safety of the longitudinal-vertical interaction for selected scenarios is further evaluated. The Influences of train speed and track gradient on the longitudinal-vertical dynamics are also studied. Two improvement measures, including the limitation of the coupler pitch angle and coupler force, are discussed to provide possible solutions.

Running safety and seismic optimization of a fault-crossing simply-supported girder bridge for high-speed railways based on a train-track-bridge coupling system

Running safety and seismic optimization of a fault-crossing simply-supported girder bridge for high-speed railways based on a train-track-bridge coupling system

Mechanical Characteristics of Cluster Perforation String under Running Process in Horizontal Wells with Unconventional Oil/Gas Reservoirs

Summary To improve the safety of cluster perforating tubing strings in horizontal wells with unconventional oil/gas reservoirs, a passing capability analysis model for cluster perforation string in a wellbore is established, in which the friction between downhole tools and borehole wall, fluid resistance, wellbore geometric constraint, and tool variable cross section were accounted for. The model is solved via geometric analyses and the beam-column theory. Then, the cable pump thrust test is carried out in three shale gas wells in South Sichuan, and comparing the measured data with the theoretical calculation results, the correctness of the theoretical model is verified. Based on that, the influences of the cluster numbers, the perforating gun types, the well section length, and the well types on the mechanical characteristics of the cluster perforation string are systematically analyzed. The results obtained demonstrate that, first, the number of perforating gun clusters should be as small as possible when the azimuth angle or well inclination angle changes greatly. In case of a small change of azimuth or deviation angle, the number of perforation gun clusters can be appropriately increased to improve the operation efficiency. Second, when the deviation angle and azimuth angle change greatly in field operation, it is recommended to use a small perforating gun to ensure the smooth running of the perforating string. When a large perforating gun is needed in the field, it is necessary to optimize the well trajectory (reduce the location of the big dogleg in wellbore) to ensure the safe running of the tubing string. Third, in the field well trajectory optimization design, the position of well inclination angle change and azimuth angle change should be staggered to improve the trafficability of perforating tubing strings on-site. Moreover, when increasing the well sections, the position of the knee point should be optimized to be smoother, and the change rate of the parameter value of the well trajectory should be reduced. The research results provide a theoretically sound guidance for designing and practically sound approach for effectively improving the service life of perforating tubing strings in horizontal wells with unconventional oil/gas reservoirs.

Research progress on train operation safety in Xinjiang railway under wind environment

Abstract Railway lines in the Xinjiang wind area face severe wind disasters year-round, which seriously affects the safety and economy of the railway in China. Therefore, the wind characteristics and statistics of wind-induced accidents along the Xinjiang railway lines are presented and the basic research route for evaluating the train running safety under crosswinds and effective measures to improve the windproof performances of trains are proposed, which are meaningful to deal with wind-induced train accidents. Based on this research route, a series of numerical simulations are conducted to evaluate train safety and the corresponding measures are provided. The results show the following. The running safety of the train under crosswinds mainly depends on the aerodynamic loads acting on the train. The relationships between the safe speed limit and train type, the load weight, the embankment height, the road cutting depth, the railway line curve parameters, the yaw angle and other factors are obtained. The critical wind-vehicle speed relationship, as well as the engineering speed limit value under different running conditions, are determined. Large values of the aerodynamic and dynamic indices mainly appear in special locations, such as near earth-embankment-type windbreak walls, shallow cuttings and the transition sections between various types of windbreak walls. Measures such as increasing the height of the earth-embankment-type windbreak walls, adding wind barriers with reasonable heights in shallow cuttings and optimizing the design of different types of transition sections are proposed to significantly improve the safe speed limits of trains under crosswinds.

The coupled vibration of train and bridge as high-speed trains meet in crosswind

PurposeThis paper aims to study the influence of aerodynamics force of trains passing each other on the dynamic response of vehicle bridge coupling system based on numerical simulation and multi-body dynamics and put forward the speed threshold for safe running of train under different crosswind speeds.Design/methodology/approachThe computational fluid dynamics method is adopted to simulate the aerodynamic force in the whole process of train passing each other by using dynamic grid technology. The dynamic model of vehicle-bridge coupling system is established considering the effects of aerodynamic force of train passing each other under crosswind, the dynamic response of train intersection on the bridge under crosswind is computed and the running safety of the train is evaluated.FindingsThe aerodynamic force of trains' intersection has little effects on the derailment factor, lateral wheel-rail force and vertical acceleration of train, but it increases the offload factor of train and significantly increases the lateral acceleration of train. The crosswind has a significant effect on increasing the derailment factor, lateral wheel-rail force and offload factor of train. The offload factor of train is the key factor to control the threshold of train speed. The impact of the aerodynamic force of trains' intersection on running safety cannot be ignored. When the extreme values of crosswind wind speed are 15 m·s−1, 20 m·s−1 and 25 m·s−1, respectively, the corresponding speed thresholds for safe running of train are 350 km·h−1, 275 km·h−1 and 200 km·h−1, respectively.Originality/valueThe research can provide a more precise numerical method to study the running safety of high-speed trains under the aerodynamic effect of trains passing each other on bridge in crosswind.

The Influence of Aerodynamic Loads on Carbody Low-Frequency Hunting of High-Speed Trains

Low-frequency hunting problems of high-speed railway vehicles frequently occur due to the complex operating environment and degradation of wheel–rail contact conditions, which significantly affect the running safety and ride comfort of high-speed trains (HSTs). This paper presents a numerical investigation of the influence of aerodynamic loads on the carbody low-frequency hunting behaviors of HST. Considering the effect of aerodynamic loads, a multi-body system dynamics model for a HST train is formulated and applied to reproduce the carbody low-frequency hunting behavior. The influence of aerodynamic loads and wheel–rail contact conditions on the nonlinear stability of HST is analyzed. The range of aerodynamic coefficients of different aerodynamic loads which can stimulate the low-frequency hunting behavior of HST is proposed. The results show that the aerodynamic loads have a prominent effect on the nonlinear stability of HSTs. The low-frequency hunting motion of the HST tail car can be motivated by the lift airflow generated during service operation with a high traveling speed. The running stability of HSTs is more easily influenced by the aerodynamic loads when wheels are reprofiled.

Model-based sensor fault detection, isolation and tolerant control for a mine hoist

Encoder is essential for speed control and very valuable in condition monitoring for a mine hoist and the failure in sensor measurements can lead to serious accidents. In this paper, a novel encoder fault detection, isolation and tolerant control strategy based on finite time observers and constrained fault-tolerant controller is proposed for a mine hoist. The hybrid nonlinear observers which can converge to the origin in finite time are employed to detect and isolate faulty sensors, a residuals evaluation unit is then used to provide reconstructed signals. The constrained fault tolerant controller is presented to guarantee steady and safe running of the mine hoist when sensor fails. This approach is feasible and practical because it does not require a complicated update process, and the fault tolerance controller also makes the hoist run more reliably. Compared with traditional ways, the proposed method has superior performance and can be more effective, which are verified by experimental results.

Static and dynamic effects of train-track-bridge system subject to environment-induced deformation of long-span railway bridge

Laying ballastless tracks on a long-span railway bridge with a main span greater than 300 m is a challenge in engineering practice and has aroused significant concerns. Influenced by complicated environmental factors, long-span railway bridges in service deform with large amplitudes and complex shapes, which may result in damage to the track structure and threaten the running safety and ride comfort of trains. In this study, we investigate some typical statics and dynamics problems under the actual conditions of a long-span cable-stayed high-speed railway bridge with a main span of 400 m and laying ballastless track. The track-bridge finite element model and dynamic interaction model of the train-track-bridge system are first established. Furthermore, the influences of the complicated environment-induced bridge deformations are comprehensively investigated using the curvature method that reveals the deformation compatibility of the bridge-track system and indicates the dynamic interaction behavior of the train-track-bridge system subject to train running speeds and bridge deformations. Results indicate that excellent dynamic performance of the train-track-bridge system can be achieved by setting an elastic cushion of 0.1 N/mm3 under the track bed. Interface damage between track layers will not occur directly because of the complex deformations of the bridge decks. The bridge deformations induced by the environmental temperature and the concrete creep are qualified. The dynamic responses of the train-track-bridge system are also excellent under the excitations of bridge deformations. Dynamic simulations of the train-track-bridge system are proposed to evaluate long-span bridge deformations subject to complicated service situations in comparison with an oversimplified statics evaluation.

Rail vehicle running safety and steering efficiency evaluation method based on equivalent curvature difference of active steering technology

Active steering technology can effectively solve the contradiction between the running stability and curving performance of traditional bogies. However, the execution deviations between the actual and theoretical steering actions, which expressed in this paper as equivalent curvature differences, would occur when mileage error or other abnormal operating conditions happens. In this study, the influence of equivalent curvature differences on running safety was studied, and a steering efficiency evaluation method was proposed. First, the equivalence between the wheel–rail relationship in the under- and over-steering states and that in the passive state was demonstrated by combining analytical and numerical simulation methods. It was concluded that under- and over-steering states do not worsen the running safety of rail vehicles. Then, the formula for wear number with the equivalent curvature difference as the independent variable was derived based on the linear model of the rail vehicle, and the accuracy of the formula was verified using the nonlinear model. Finally, a steering efficiency evaluation method was established, and a steering efficiency evaluation under different equivalent curvature differences and steering rates was conducted. The results of this study can provide a reference for engineering active steering systems.

Continuous Rotor Dynamics of Multi-Disc and Multi-Span Rotor: A Theoretical and Numerical Investigation on the Identification of Bearing Coefficients from Unbalance Responses

Identification of bearings’ stiffness and damping coefficients, which strongly affects the dynamic characteristics of rotors, is another inverse problem of Rotor Dynamics. In this paper, aiming at multi-disc and multi-span rotors, two novel algorithms are proposed for identifying each bearing’s coefficients based on the continuous rotor dynamic analysis method. A linear functional relationship between the main complex coefficients and the cross-coupled complex coefficients is obtained, which eliminates the coupling between the coefficients and the rotor unbalance in the forward problem. Then, Algorithm I is proposed. However, it is only suitable for rolling-bearing. To solve the problem, changing the rotating speed slightly is proposed to solve the difficulty that another set of equations cannot be developed because the slope of the proposed linear function is constant when the rotating speed is maintained at a fixed speed. Then, Algorithm II, which can be applied to both rolling-bearing and oil-journal bearing, is provided. Numerical investigations are conducted to study the two methods. It is indicated that there should be a measuring point, called an adjustment point, near each bearing, whose coefficients should be identified, to obtain high identification accuracy. Moreover, the identification accuracy of the two algorithms is strongly related to sensor resolution. When the measuring errors of all the required unbalance responses are zero or the same, the identification errors are almost equal to zero. In conclusion, the proposed algorithms provide a method for monitoring the stiffness and damping coefficients of all bearings in a multi-disc and multi-span rotor under operation conditions to predict rotor dynamic behavior for the safe and steady running of rotating machines.

KONSTRUKSI KARAKTER SISWA VIA PEMBIASAAN SHALAT DHUHA

Research was conducted to provide a description of the character construction of students through the habituation of dhuha prayers at MIS Terpadu Mutiara Hikmah Hessa Perlompongan. The research was conducted using qualitative methods conducted. The collection of information and data was carried out by interviewing techniques with Mr. Suyanto, S.Ag as the Head of Madrasah as the main source, Mrs. Martiya as the guardian of class 6-A, Mrs. Nisa as the 2-A class guardian and also Mrs. Wati as the office staff. Then observation and documentation is taken where the student is the subject. The data analysis technique used goes through three stages: data reduction, data display and drawing conclusions. The validity of the data is tested through engineering triangulation and source triangulation. The results of the research obtained that through the habituation of dhuha prayer at MIS Terpadu Mutiara Hikmah, there are five characters formed in students, namely: (1) Religious; (2) Discipline; (3) On Time; (4) Responsibility; And (5) Honestly. The character of discipline becomes the most prominent character because students are able to manage the time when taking wudhu, preparing prayer equipment to order themselves so that they can perform dhuha prayers immediately and do not interfere with study time later. While on the character of responsibility is shown by the class leader and the imam of prayer. As the leader, the class leader directs his friends not to pray, and as an imam order the shaf and ensure the safe and orderly running of dhuha prayers.

Investigation of ice and snow accumulations on the bogie areas of high-speed trains using ice wind tunnel experiments

Accumulated snow and ice will severely influence the safe operation of high-speed trains in snowy weather, where the snow and ice in the bogie region are the main concerned problems that contribute to such issues. The work presented in this paper initiated experimental studied snow and ice accumulation on the running bogies of the high-speed trains to clarify the snow and ice accumulation process and causes. Two original and two optimized cases with protective schemes combined with electoral heating and an air-flow deflector under the customized train body were adopted to carry out the snow and ice wind tunnel experiments in the Icing-snowing Wind Tunnel (ISWT) of Central South University (CSU). The distributions and mass of the snow and ice were analysed, and the preliminary conclusions were drawn: the leeward side and the depressions of the bogies accumulated a layer of snow, and the melt water sprayed by the rotating brake discs flew everywhere, which contributed to rapidly growing icicles on the bogies and train body during the experiments. Deflectors, protective sleeves and different kinds of heating methods were adopted according to the original cases to optimized where they should be placed, they were capable of reducing the snow and ice mass by 62.9% and 50.4% from the original trailer and motor bogie, respectively. Thus, the optimized schemes were confirmed to be effective to show great application potential to reduce mass and increase running safety for high-speed trains in winter in cold regions.