Track Unevenness Research Articles

Measuring Track-Related Pointing Errors on the Nanshan Radio Telescope with an Optical Pointing Telescope

The need for precise radio telescope pointing has driven great attention to investigating the effect of antenna local deformation or irregularity, such as unevenness in the azimuth track. Although the track-alidade interaction model is commonly used to investigate the pointing effect of track unevenness (such as the works on DSN 34 m antennas and the Green Bank Telescope), few experiments have been done to test the effectiveness of this model independently from the overall pointing model. To address this issue, a method utilizing an optical pointing telescope (OPT) for determining the impact of track unevenness on pointing is proposed. This method uses a group of reference pointing data collected by an OPT mounted at the bottom of the antenna alidade to extract the twist effect of the alidade from the radio telescope pointing data, thus compared with the predicted twist by the track-alidade model. This method was applied to the 26 meter Nanshan Radio Telescope (NSRT 26 m), achieving good agreement with the model-predicted values.

Track Unevenness Prediction Based on Static Track Inspection Data Matching

A track static misalignment prediction model based on track median deviation is created using an IGA-BP neural network in order to precisely predict the trend of ballastless track static misalignment. The historical static track median deviation detection data are matched using actual compensation edit distance (ERP) to finish the correspondence processing of the original data. The precisely matched data are used to train the model, forecast irregularities in the track median, and compare results with other traditional prediction techniques. The outcomes demonstrate that the IGA-BP neural network can more accurately predict the nonlinear time series data development trend. In comparison to other prediction models, the IGA-BP neural network model’s average relative error and root mean square error are 0.091 and 0.110, respectively. The prediction accuracy is raised by between 43% and 60%, demonstrating the IGA-BP neural network model’s efficacy in predicting static upsets on ballastless tracks and presenting a workable strategy for track predictive maintenance.

Measurement and Correction of Pointing Error Caused by Radio Telescope Alidade Deformation based on Biaxial Inclination Sensor.

One of the key reasons for the deterioration of antenna pointing accuracy for radio telescopes is the deformation and tilt of antenna alidades, which primarily result from track unevenness and thermal gradients. A high-precision inclinometer measurement system is installed to investigate the tilt of the antenna alidade and the pointing errors caused thermally. An environment control box with a leveling base was designed to reduce the interference of the external environment, which proved to be effective in guaranteeing the zero-point stability and repeat accuracy of the inclinometer. The tilt of the alidade caused by the track unevenness was measured by a test of slowly rotating the antenna along the azimuth at windless nighttime. A 5-day antenna stationary test and a 48 h astronomical pointing error measurement were performed, which proved the inclinometer measurement system is capable of measuring the thermally induced inclinations with acceptable accuracy. Through a preliminary compensation experiment, the pointing error is compensated from 37″ to 12″, which shows that the application of the system has a good effect on improving the pointing accuracy of the antenna. The system with high measurement accuracy, good system stability, and low computational complexity, proves an effective tool for the radio telescope to solve the problem of real-time measurement and compensation for antenna pointing errors.

Dynamic Analysis of CRTS II Ballastless Track-Vehicle System Based on Moving Unit Method

On account of the influence of the discontinuity of CRTS II ballastless track slabs and the discrete support of track pads on the high-speed rail vehicle-ballastless track system, a vibration analysis calculation model of the ballastless track-vehicle coupling system was established on the basis of the moving unit method. The dynamic response of the system at different travel speeds and with and without consideration of the track plate discontinuities was investigated. The effect of the random process discontinuity on the dynamic response of the steel rails was analyzed by Fourier inverse transform on the high and low discontinuity spectra of ballastless rails on China’s high-speed rail. We also generated time domain samples of the track discontinuity corresponding to the three percentile spectra. The results show that the dynamic response of the track structure increases with the speed of the train under the condition of track unevenness, with the dynamic response of the steel rail being the most significant, while the dynamic response of the track slab and concrete foundation decreases step by step compared with that of the steel rail; the discontinuity of the track slab has a low impact on the vertical acceleration of the vehicle and does not affect the smoothness of the train; the magnitude of the dynamic response of the rail increases as the amplitude of the irregularities increases or the wavelength decreases. In the wavelength of 2~30 m, the maximum and as the wavelength of the discontinuity sample increases, the oscillation of the power response time curve decreases significantly and tends to be smooth.

The effect of rolling stock characteristics on differential railway track settlement: An engineering-economic model

Railway track geometry deteriorates under repeated train loading. When linespeed is increased or new rolling-stock is introduced this can alter the future rate of change of differential settlement and track geometry. Therefore this paper presents a novel combined engineering-economic approach to investigate the effect of increasing train speeds, adding additional passenger movements, and adding additional freight movements to an existing line. Firstly a numerical algorithm is presented to compute differential track settlement. An important novelty of the model is its use of the wavenumber finite element method coupled with settlement relationships in a manner that allows for track irregularities to evolve after every load passage (i.e. taking into account the evolution of the track unevenness profile before applying each subsequent train passage). Unlike traditional approaches this allows the model to faithfully simulate mixed traffic conditions, including the coupled interactions between different rolling stock types and track geometry. The engineering model is used to predict tamping intervals, and then coupled with an economic model capable of calculating deterioration elasticities and marginal costs. It is shown that higher speeds result in higher dynamic forces and cause a faster rate of deterioration of track geometry, thus increasing marginal cost. The model is then used to investigate the effect of adding additional train movements to a passenger line. It is shown that additional movements increase the rate of track degradation and marginal costs, particularly if the additional traffic is freight. This is because freight vehicles typically have one only layer of (stiff) suspension, thus generating elevated dynamic forces compared to passenger vehicles.

A Probabilistic Model for the Amplification of the Vibration Response of Railway Bridges Due to Random Track Unevenness in High-Speed Traffic

In combination with the moving train, track irregularities have a significant influence on the structural response of railway bridges. Compared to the ideal case of perfect track geometry without any irregularities, an amplification of the response is observed. This paper proposes a probabilistic model to predict this dynamic response amplification of railway bridges due to random track irregularities when subjected to high-speed trains. The developed regression model, based on a parametric numerical study, provides the mean and standard deviation of the dynamic response amplification separately for bridge deflection and acceleration, since large differences are found for these vibration variables. Depending on the span, mass, fundamental frequency, and damping coefficient of simply supported bridges, dynamic response amplification statistics are approximated for a range of train speeds and different track qualities. The proposed model estimates the dynamic response amplification due to random track irregularities at predefined exceedance probabilities, and a customized amplification factor is determined that is consistent with the semi-probabilistic safety concept used in structural design. An application example shows the superiority of this model compared to the commonly used code-based approach.

Detection of mechanical stress in the steel structure of a bridge crane

A significant negative aspect in the operation of bridge-type cranes are the technical problems associated with wear of the wheels and the crane track, which causes crane skewing. The main causes of crane skewing include unevenness of the crane track, unequal loading of the traction drives depending on the position of the crane trolley, slips and different sizes of travel wheels and combinations of these causes. Firstly, this paper presents a design solution that can be used to detect the magnitude of mechanical stress and deformation of the steel structure of the crane, caused by the effects of skewing. The mechanical stress generated by the transverse forces of the deformed geometric shape of the crane bridge structure is recorded by mechanical stress detectors installed in the inner corners of the crane bridge. The resulting electrical signal from element mechanical voltage detectors, loaded by axial forces, can be used for feedback control of separate crane travel drives controlled by frequency converters. Secondly, this paper presents the calculation of the lateral transverse forces according to CSN 27 0103 and the determination of the values of mechanical stresses of the deformed steel structure of the crane bridge of a two-girder bridge crane using the finite element method in the program MSC.MARC 2019. Finally, this paper presents the structural and strength design of mechanical stress detectors and the conclusions of laboratory tests of axial force loading of mechanical stress detectors on the test equipment. At the same time, it presents records of the measured axial forces acting in the mechanical stress detectors, arising from the deformation and warping of the crane bridge by the known magnitude of the axial force acting on the crossbeam and from the deformation of the crane bridge caused by the crane operating modes.

Stress and permanent deformation amplification factors in subgrade induced by dynamic mechanisms in track structures

ABSTRACT In this paper, the performance of different railway structures – ballasted and two types of slab tracks (Rheda system and a ballastless track only constituted by the concrete slab) – is evaluated in terms of stresses and permanent deformations through the selection of some important parameters: wavelength of the unevenness profile, train’s speed, subgrade’s characteristics and spatial variability of the track unevenness profile. The elastodynamic response of 60 case studies is computed through a 2.5D model FEM-PML and the long-term behaviour is assessed by the implementation of a permanent deformation model. The obtained results are analysed through innovative stress and permanent deformation amplification factors in the subgrade layer. This study concludes that the train’s speed and the mechanical properties of the subgrade are the factors that most affect the long-term performance of the subgrade of railway structures, which must be considered for further optimization of the rail track structures.

Determination of dynamic loading of bearing structures of freight wagons with actual dimensions

The determination of the dynamic loading of the bearing structures of the main types of freight wagons with the actual dimensions under the main operating conditions is carried out. The inertial coefficients of the bearing structures of the wagons are determined by constructing their spatial models in the SolidWorks software package. Two cases of loading of the bearing structures of the wagons – in the vertical and longitudinal planes – have been taken into account. The studies were carried out in a flat coordinate system. When modeling the vertical loading of the bearing structures of wagons, it was taken into account that they move in the empty state with butt unevenness of the elastic-viscous track. The bearing structures of the wagons are supported by bogies of models 18-100. The solution of differential equations of motion was carried out by the Runge-Kutta method in the MathCad software package. When determining the longitudinal loading of the bearing structures of wagons, the calculation was made for the case of a shunting collision of wagons or a "jerk" (tank wagon). The accelerations acting on the bearing structures of the wagons are determined. The research results will help to determine the possibility of extending the operation of the bearing structures of freight wagons that have exhausted their standard service life. It has been established that the indicators of the dynamics of the load-carrying structures of freight wagons with the actual dimensions of the structural elements are within the permissible limits. So, for a gondola wagon, the vertical acceleration of the bearing structure is 4.87 m/s2, for a covered wagon – 5.5 m/s2, for a flat wagon – 5.8 m/s2, for a tank wagon – 4.25 m/s2, for a hopper wagon – 4.5 m/s2. The longitudinal acceleration acting on the bearing structure of a gondola wagon is 38.25 m/s2, for a covered wagon – 38.6 m/s2, for a flat wagon – 38.9 m/s2, for a tank wagon – 27.4 m/s2, for a hopper wagon – 38.5 m/s2. This makes it possible to develop a conceptual framework for restoring the effective functioning of outdated freight wagons. The conducted research will be useful developments for clarifying the existing methods for extending the service life of the bearing structures of freight wagons that have exhausted their standard resource

A Conceptual Investigation of a Large Radio Telescope Support Point Number Effect on Its Pointing Accuracy

The purpose of this paper is to investigate a large radio telescope support point number effect on its pointing accuracy and provide a useful guideline for the large radio telescope design engineer. In a large radio telescope system, the azimuth track is used to support the whole telescope structure and the mounting error as well as the telescope wheel-track contact in a long term can cause unevenness on the azimuth track, which can further deteriorate the telescope pointing accuracy. Even though various compensation methods have been proposed to compensate for this pointing error, it remains as one of the challenges for the telescope pointing error reduction. In this paper, a general telescope pointing error estimation formula has been proposed to investigate different telescope support-point number designs on its pointing accuracy. In this approach, the azimuth track unevenness has been modelled as the Fourier function using the least square method after the raw track profile has been measured. Next, the elevation position matrix, azimuth position matrix, and the azimuth profile matrix can be constructed for different telescope support point numbers, and the telescope pointing error can then be obtained based on the proposed general formula. The telescope pointing error root mean square (RMS) value is used to quantify the effect of the telescope support point number on the pointing accuracy. Two interesting results can be observed in the numerical example. The first one is that the telescope pointing error curves have different dominant peaks during one azimuth track rotation, which is corresponding to the support point number. Another interesting finding is that the RMS value experienced a complex trend with the support point number change, and they are not a simple monotonous increasing or decreasing relationship with the support number. All the results in this paper can provide a useful guideline for reducing the telescope pointing error in the initial design stage.

Life cycle assessment of a railway tracks substructures: Comparison of ballast and ballastless rail tracks

The increase of train speed and axle load is an essential goal to make the railway transport more and more competitive for passengers and freights. On this basis, the unevenness of the railway track is crucial for the safety of the railway due to the high speed of the vehicle. Although ballasted tracks represent by far the most used railway track substructure, in recent years the modernization process has led the development of the ballastless track substructures.In deciding between the use of ballasted or ballastless track substructure there are many important technical, economical and environmental factors that have to be addressed. Based on the above, the principal objective of this study was to evaluate the environmental impact of different railway track substructures including ballast, cast-in sleeper and embedded track systems on the short, medium and long term. To accomplish this task, a life cycle assessment (LCA) was carried out throughout the entire life cycle of the railway infrastructure by using the ReCiPe (H) method. Although such approach is commonly included in the environmental assessment of building products and buildings, it was rarely applied in the analysis of the environmental impacts of railway track substructure.Thus, the result of these LCA showed that ballasted tracks cause the lowest environmental impact for service lives of up to 75 years. On the other hand, the embedded track beds cause the highest environmental impacts, regardless of their service life. The highest contributor for the environmental impacts of the track beds was the steel production.The results of this study will provide relevant environmental information for engineers and decision makers to select the most adequate railway track substructures for addressing issues related to the pursuit of sustainable development.

Two-axle test vehicle for damage detection for railway tracks modeled as simply supported beams with elastic foundation

For damage detection of railway tracks, a two-axle test vehicle is better than a single-axle vehicle due to its capability of self standing and stability. This paper presents a new, comprehensive theoretical framework for a two-axle test vehicle moving over railway tracks modeled as a simply supported beam with elastic foundation. Firstly, closed-form solutions for both the vehicle and rail responses of the system were derived, along with those for the two contact points by a back calculation procedure. Secondly, the driving component of the contact-point response was processed by the Hilbert transform to yield the Instantaneous Amplitude Squared (IAS) for damage detection. Then, the efficacy of the proposed technique was numerically validated by the Finite Element Method (FEM). Particularly, the sensitivity of the proposed technique was investigated against various factors, including the damage severity, multi damages, vehicle speed, track unevenness, track damping, and measurement noise. The result shows that the IAS of the driving component of the contact point response of the railway track is a good damage indicator in that it is of low frequencies and narrow band, while its modal amplitude is sensitive to the stiffness loss in rail supports.

Theoretical investigation into the measurability of rail unevenness and corrugation using the dynamic response of axle box and bogie

Monitoring track unevenness is important for noise and vibration control and track maintenance. Rail corrugation and shorter wavelength track unevenness can be measured using the corrugation analysis trolley, but it is not suitable for measurement over long distance. It is of great significance to study the dynamic behavior of the response of the axle box and bogie to the unevenness excitation for a better understanding of the measurement results. In this paper, the dynamic response of the axle box and bogie to the unevenness excitation is analyzed in the frequency domain by taking account of multiple wheel–rail interactions, which is the case in practice. The response of the axle box and bogie is found to be affected by the so-called P2 resonances at low and medium frequencies and the standing waves of rail vibration at higher frequencies due to the multiple wheel–rail interactions. Based on the analysis of the response of the axle box and bogie, the measurability of track unevenness is discussed. Results show that the measurement of rail unevenness using the axle box response is mainly limited by the P2 resonance. The frequency range of measurement for the ballasted track studied is estimated to be 1–35 Hz, corresponding to the measurable unevenness wavelength of 0.6–20 m (or longer) at a vehicle speed of 20 m/s. Above 200 Hz, the standing waves of rail vibration will cause serious uncertainty in the measurement of short wavelength rail irregularity using the axle box response for the resilient track. Short pitch rail corrugation, however, can be evaluated using the axle box response due to its strong correlation with certain modes of the wheel–track system.

Fusion of Model-Based and Data Driven Based Fault Diagnostic Methods for Railway Vehicle Suspension

Transportation of freight and passengers by train is one of the oldest types of transport, and has now taken root in most of the developing countries especially in Africa. Recently, with the advent and development of high-speed trains, continuous monitoring of the railway vehicle suspension is of significant importance. For this reason, railway vehicles should be monitored continuously to avoid catastrophic events, ensure comfort, safety, and also improved performance while reducing life cycle costs. The suspension system is a very important part of the railway vehicle which supports the car-body and the bogie, isolates the forces generated by the track unevenness at the wheels and also controls the attitude of the car-body with respect to the track surface for ride comfort. Its reliability is directly related to the vehicle safety. The railway vehicle suspension often develops faults; worn springs and dampers in the primary and secondary suspension. To avoid a complete system failure, early detection of fault in the suspension of trains is of high importance. The main contribution of the research work is the prediction of faulty regimes of a railway vehicle suspension based on a hybrid model. The hybrid model framework is in four folds; first, modeling of vehicle suspension system to generate vertical acceleration of the railway vehicle, parameter estimation or identification was performed to obtain the nominal parameter values of the vehicle suspension system based on the measured data in the second fold, furthermore, a supervised machine learning model was built to predict faulty and healthy state of the suspension system components (damage scenarios) based on support vector machine (SVM) and lastly, the development of a new SVM model with the damage scenarios to predict faults on the test data. The level of degradation at which the spring and damper becomes faulty for both primary and secondary suspension system was determined. The spring and damper becomes faulty when the nominal values degrade by 50% and 40% and 30% and 40% for the secondary and primary suspension system respectively. The proposed model was able to predict faulty components with an accuracy of 0.844 for the primary and secondary suspension system.

Research of the impact of geometric unevenness of the railway track on the dynamic parameters of the railway rolling stock with two-stage spring suspension

The paper studies the possibility of using previously developed by the authors spatial mathematical model of the modern diesel train DPKr-2 for parameters determination, with the help of which the dynamic properties of the mechanical part are evaluated. The dependences of maximum accelerations of the body in the vertical and horizontal planes, the coefficients of vertical and horizontal dynamics both in the primary and in the secondary suspension on the speed of the car movement, the amplitude and the length of geometrical unevenness of the railway track were obtained. It is established at what speeds, depending on the parameters of geometrical unevenness of the railway track, the phenomenon of resonance and danger for the diesel train car movement appears. For a particular length of geometrical unevenness, the maximum permissible value of its amplitude over the entire range of speed movement, where the coefficients of vertical and horizontal dynamics in the primary suspension do not exceed permissible limits, has been studied. The adequacy of the mathematical model is checked by comparing the results obtained during calculations with the experimental ones.

Automatic Rail Track Surface Anomaly Detection with Smartphone Based Monitoring System

Railroad companies spend a significant portion of their revenue on track inspections to maintain safety and maximize operational efficiency. Deviations from the designed track geometry over time could lead to poor ride quality and possible derailments. The existing approaches to track inspections are expensive and laborious. The use of low-cost sensors aboard revenue service trains to screen the infrastructure for track irregularities could improve the cost-efficiency of track inspections by targeting the available resources to high-risk locations. Unevenness of rail track running surfaces cause dynamic forces generated at the wheel/rail contacts which in return results the vibration of the car. This study focuses on detecting track unevenness by associating its influence on vibration with it. A comparative analysis is carried out on unevenness response prediction and the accuracy of detecting such track surface unevenness is analyzed with the ground truth location collected by the railroad track inspectors. The main finding of the study were 1) the unevenness event estimation error are within 15 matters with one run for one phone based system and 2) the three-phone based track surface anomaly detection system can improve its forecasting accuracy to 5 meters and to 3 meters with two traversals.

Service life evaluation of ballastless track construction

The article presents method for calculating service life of ballastless track structure using the track oscillation model as a structure containing three infinitely long beams, the lower of which lies on the modified Winkler base, and the upper and middle are based on elastic layers, mainly having the characteristics of Winkler. The use of this model is due to the need to carry out calculation for bearing concrete slab, the destruction of which is the main reason for the failure of the ballastless track structure. First part of the article presents model for calculating service life of a ballastless structure. When calculating the damage index, which takes the stresses in the bearing concrete slab, to estimate the vertical dynamic forces acting on the track, it is proposed to use a frequency response that determines the dynamic system with input on the track unevenness and output on the dynamic force at the wheel and rail contact in the model oscillations of the track as a three-layer beam. Second part presents estimates of the service life of ballastless structure for various operating conditions and their comparison with the results obtained using the practice method with the single-beam model. Graphs were plotted for the service life of the ballastless track structure on axle loads, the speed of the carriages and the load capacity on the line. Results show the applicability of the single-layer beam model for estimating the service life of the ballastless track structure in the current operating conditions; however, for the promising conditions of high-speed and heavy traffic, it is advisable to use a three-layer model.

Improvement of the pointing precision of the Tianma radio telescope with an inclinometer measurement system

To assure high pointing precision of the Tianma radio telescope (TMRT), new models based on a inclinometer measurement system are added to the classical pointing model. This involves four main tasks. Firstly, the inclinometer measurement system is set up and its precision is evaluated. Secondly, a feedback control strategy for pointing error for the turbulences of uneven azimuth track and thermal deformations of alidade is implemented. Thirdly, after removing the linear effect of uneven track, sine fitting inclinometer data obtains the model of nonlinear effect of azimuth-track-level unevenness. The nonlinear effect is less than ±5 arc-sec. The azimuth angles associated with large pointing error show a good agreement with those corresponding to poor track unevenness. Finally, the TMRT inclinometers monitor the effect of thermal deformations of alidade on the pointing precision of elevation from stow position, to observing almost motionless radio source, to arbitrary postures of radio telescope. The measured data after subtracting other affected factors of inclinometer including intrinsic drift, azimuth-track unevenness, variation of the center of gravity have similar tendency with the simulated results of finite element model (FEM). Applying established real-time modified model to observe the radio source 2334 + 8226, the checking results show that the pointing precision improved 65%.

An efficient approach for prediction of subway train-induced ground vibrations considering random track unevenness

In this paper, an efficient and robust approach is presented for the prediction of subway train-induced ground vibrations considering random track unevenness. The proposed approach is developed by a two-step approach. Firstly, the power spectral density functions of the wheel–rail interaction forces are obtained through the combination of the vehicle–track–tunnel–soil theoretical model and the pseudo-excitation method (PEM). Secondly, by assuming the geometry of the track, tunnel, and soil to be homogeneous along the track, the nonstationary random ground vibrations are solved by combining the PEM and the 2.5D finite element–perfectly matched layers method. To improve computational efficiency, an efficient wavenumber sampling scheme is proposed. In the numerical examples, the proposed approach is validated by comparing the results obtained with the published results. The influence of the train speed on the ground vibrations are also investigated, in which two types of track structure, namely the direct fixation track and floating slab track, are considered.

A new strategy to estimate static loads for the dynamic weighing in motion of railway vehicles

The present paper focuses on the numerical modeling of a weigh-in-motion system developed with the purpose of assessing the static loads imposed by the train onto the track infrastructure. Weigh-in-motion systems would be useful in overcoming the disadvantages typical of the conventional static weighing such as costs and traffic management. However, contrary to the conventional static weighing, weigh-in-motion systems do not allow a direct measurement of the static load since the train–track dynamic interaction gives rise to dynamic loads that are added to the static ones. This study investigates how train speed and track unevenness affect the loads assessed by the weigh-in-motion system. In order to achieve that goal, a comprehensive statistical study was performed based on an extensive amount of calculations. Finally, based on the conclusions and trend identified through the comprehensive parametric study, an approach is proposed to correct the direct result given by the weigh-in-motion system in order to obtain an estimation of the static load.