Track Displacement Research Articles

Railway Track Irregularity Estimation Using Car Body Vibration: A Data-Driven Approach for Regional Railway

Track and preventive maintenance are necessary for the safe and comfortable operation of railways. Track displacement measured by track inspection vehicles or trolleys has been primarily used for track management. Thus, vibration data measured in in-service vehicles have not been extensively used for track management. In this study, we propose a new technique for estimating track irregularities from measured car body vibration for track management. The correlation between track irregularity and car body vibration was analysed using a multibody dynamics simulation of travelling rail vehicles. Gaussian process regression (GPR) was applied to the track irregularity and car body vibration data obtained from the simulation, and a method was proposed to estimate the track irregularities from the constructed regression model. The longitudinal-level, alignment, and cross-level irregularities were estimated from the measured car body vibrations and travelling speeds on a regional railway, and the results were compared with the actual track irregularity data. The results showed that the proposed method is applicable for track irregularity management in regional railways.

Non-linear critical speed in high-speed ballasted railways with ground reinforcement

When constructing or upgrading high-speed railway lines on soft soils, reinforcing the soil foundation becomes crucial. This not only involves small track displacements but also increases the critical speed, thereby ensuring safe and efficient regular operations. Nevertheless, existing studies on the critical speed phenomenon in high-speed railway tracks with ground reinforcement are limited, and they all assume a linear elastic behavior for both the soils and reinforcement materials. The main novelty of this research is that it presents the first study on the effect of non-linear soil behavior on the critical speed of high-speed railway ballasted tracks with soil reinforcement and introduces a novel simplified approach based on an equivalent homogeneous soil layer by replacing the soil layer containing inclusions/columns. To accomplish this, a full 3D non-linear numerical model was developed and experimentally validated. The findings from a detailed and comprehensive parametric analysis demonstrate a significant influence of non-linear behavior on the critical speed, resulting in reductions of up to 30% compared to the linear elastic scenario. Furthermore, it is found that the soil-reinforcement stiffness contrast, the area replacement ratio, and the plasticity index of the soil foundation play a crucial role in the critical speed. Other aspects such as the installation pattern and the thickness of soft soil have a relatively lower impact on the critical speed.

Viscoelastic Rheological Modelling of the Lateral Dynamic Response of Ballasted Railway Tracks

This article presents a novel methodology for evaluating the response of ballasted railway tracks under train-induced loading along lateral directions. The main focus of this study is the development of a computational technique that can capture the lateral response of ballasted railway tracks, which has been ignored in past studies. The proposed approach employs a viscoelastic rheological track model in which three substructure layers are simulated using discrete masses, Hooke’s (springs) and Newtonian elements (dampers). The methodology is successfully validated against the data from experimental and analytical investigations published in the literature. Subsequently, parametric investigations are conducted to study the influence of axle load, train speed, and granular layer thickness on the track response. The results indicate that as the axle load (20 to 40 t) and train speed (70 to 200 km/h) are increased, there is a corresponding increase in track displacements (both lateral and vertical) by 100% and 26.2%, respectively. However, an increase in the granular layer thickness (0.1 to 0.75 m) reduces ballast top displacement (lateral and vertical) by 20–30%. The results demonstrate the capability of the proposed computational approach to capture the transient response of railway tracks and the influence of neighbouring layer properties on the track response. The proposed methodology can be helpful to practising railway engineers for assessing the performance of ballasted railway tracks along lateral directions.

Modelling and analysis of train-track-subgrade-soil dynamic interaction subjected to the interfacial damage of slab induced by uneven settlement

In this paper, a dynamic model is established to investigate the dynamic behavior of train-track-subgrade-soil (TTSS) interaction. The effects of interfacial damage of the track slab induced by soil settlement on the dynamic interaction system are considered. The model framework is established by the finite element method. The soil settlement-induced track deformation is calculated by a practical iteration algorithm, where the nonlinear interfacial damage is simulated by the cohesive zone model. The simulation model is verified by comparison with other models. In regards to the excitations of the dynamic TTSS interaction system, two types of track irregularities are considered, namely the conventional track irregularities generated by known spectrums, and the additional irregularities caused by soil settlement. In the numerical study, the dynamic performances of the TTSS interaction subjected to interfacial damage, and soil settlement are compared. Next, the short wavelength irregularity is discussed as well. From the results, the vibration enhancement can be observed in the time and frequency domain. The interfacial damage of the track enhances the vibration both in low- and high-frequency domains, while the impacts of settlement are only observed in the frequency band of 0∼3 Hz. The frequency band of vibrations triggered by short wavelength irregularities is correlated with its wavelength range. Moreover, the settlement with different wavelengths and amplitudes is studied. It is shown that the increase of settlement amplitude and decrease of settlement wavelength lead to higher damage degree in amplitude and wider spatial distribution. In regards to the dynamic responses, the vehicle accelerations, wheel-rail contact forces, track displacement, and soil displacement are more sensitive to the settlement amplitudes varying from 10 to 80 mm, while the sensitive settlement wavelength is concentrated in 20 to 40 m.

Comparative evaluation of meteorological inputs for improved storm surge modeling: A case study of tropical Cyclone Vayu

The selection of meteorological inputs in storm surge is crucial, with wind and pressure fields playing a significant role in energy transfer and the study area's bathymetry. While using observed track information for wind and pressure drop has been the standard approach for the past decade, recent studies have highlighted the need for atmospheric inputs from models like the Weather Research and Forecast model (WRF) for storm surge forecast. This study aims to compare the performance of a DELFT-3D FM storm surge model forced with inputs from IMD (India Meteorological Department) observed the best track and pressure drop (EXP-1) and wind and pressure fields from WRF (EXP-2) for Tropical Cyclone Vayu, which occurred in the southern Arabian Sea basin in June 2019. The study compares the simulated storm water levels and highlights the benefits of using time and space-varying wind and pressure input for improved surge representation. Results show that the WRF-DELFT setup outperforms the IMD-DELFT setup, particularly for tide gauge locations close to the storm eye. The simulated storm surge captures the intensified stage of Vayu and provides a more realistic representation than the model forced with IMD track data. However, biases and limitations, such as inadequate representation of land surface parameterization, are identified. The study suggests further exploring wave-induced effects on total water level and multiple cyclone scenarios to enhance wind speed and track displacement prediction accuracy and improved land-sea parameterization can help address these limitations.

An innovative approach to continuously monitor rail track surface displacement during freezing-thawing seasons

Large differential displacement as a result of freeze–thaw cycles (FTC) is a major issue affecting the safety and performance of railway tracks constructed in cold regions. Current track monitoring methods in winter are mainly based on visual inspection and manual measurements. The frequency of FTC is expected to increase under future climate and thus it is essential for railway operators to employ new methods of inspection that allow continuous and remote monitoring of railway tracks during the freeze–thaw period. While sensors are commonly used to measure localized track displacement, the advantages and limitations of using instruments that are capable of collecting data over a segment of track is not well understood. This paper investigates the use of a micro electro-mechanical sensor (MEMS) based instrument for monitoring surface displacement of railway tracks during FTC. The ShapeArray™ instrument, in this case the SAAX inclinometer, is a MEMS based sensor that was selected due to its ability to collect data over a segment of track (up to 150 m). Two sets of SAAX inclinometers were installed on a 50-metre section of track to measure data during two freezing-thawing periods. Analysis of the field data suggests that the main limitation of using MEMS-based sensors is their sensitivity to fluctuations of ambient temperature which may be confused with their responses to actual track displacement. A data analysis technique has been developed to remove the unwanted variations so that the instrument can be effectively used for monitoring track displacement during FTC. The comparison of the processed measurements with data collected from a digital level suggested that it provides a reasonably accurate measure of track surface displacement. Overall, the limited investigations in this project suggests that using MEMS-based sensor along with proper data processing techniques can provide useful information about the differential displacement over a segment of track, a key parameter for the safety of railway operation. The measurements can also be transferred through the cloud, enabling track engineers to remotely monitor track condition in near-real-time without the need to access the track and interrupt trains operations.

Investigating the Mitoprotective Effects of S1P Receptor Modulators Ex Vivo Using a Novel Semi-Automated Live Imaging Set-Up.

In multiple sclerosis (MS), mitochondrial alterations appear to contribute to disease progression. The sphingosine-1-phosphate receptor modulator siponimod is approved for treating secondary progressive MS. Its preceding compound fingolimod was shown to prevent oxidative stress-induced alterations in mitochondrial morphology. Here, we assessed the effects of siponimod, compared to fingolimod, on neuronal mitochondria in oxidatively stressed hippocampal slices. We have also advanced the model of chronic organotypic hippocampal slices for live imaging, enabling semi-automated monitoring of mitochondrial alterations. The slices were prepared from B6.Cg-Tg(Thy1-CFP/COX8A)S2Lich/J mice that display fluorescent neuronal mitochondria. They were treated with hydrogen peroxide (oxidative stress paradigm) ± 1 nM siponimod or fingolimod for 24 h. Afterwards, mitochondrial dynamics were investigated. Under oxidative stress, the fraction of motile mitochondria decreased and mitochondria were shorter, smaller, and covered smaller distances. Siponimod partly prevented oxidatively induced alterations in mitochondrial morphology; for fingolimod, a similar trend was observed. Siponimod reduced the decrease in mitochondrial track displacement, while both compounds significantly increased track speed and preserved motility. The novel established imaging and analysis tools are suitable for assessing the dynamics of neuronal mitochondria ex vivo. Using these approaches, we showed that siponimod at 1 nM partially prevented oxidatively induced mitochondrial alterations in chronic brain slices.

Optical and Thermal Image Processing for Monitoring Rainfall Triggered Shallow Landslides: Insights from Analogue Laboratory Experiments

This study explores the innovative use of digital image processing (DIP) techniques, also named PhotoMonitoring, for analysing the triggering conditions of shallow landslides. The approach, based on the combination of optical and infrared thermographic imaging (IRT), was applied to a laboratory-scale slope, reproduced in a flume test apparatus. Three experiments were conducted to replicate rainfall-induced shallow landslides, applying change detection and digital image correlation analysis to both optical and thermal images. The method combines IRT’s ability to measure ground surface temperature changes with DIP’s capacity to track movement and displacement. Results showed the high reliability of the displacement time-series obtained through IRT-DIP with respect to the reference optical-DIP. The IRT-DIP technique also detects anomaly signals two minutes before landslide occurrence that can be regarded as a possible failure precursor. This study testifies to the potential of image analysis as a remote sensing technique, demonstrating the ability of DIP to capture the dynamics of shallow landslides, as well as the advantages of optical–IRT combinations to follow slope deformation processes during night-time. This approach, if properly adapted to real-scale scenarios, may contribute to a better understanding of landslide behaviour, improve landslide monitoring strategies, and promote more effective early warning systems (EWS).

Hydroclimate variability in the central Mediterranean during MIS 17 interglacial (Middle Pleistocene) highlights timing offset with monsoon activity

Mediterranean climates are characterized by warm, dry summers and mild, rainy winters. Previous studies suggest that over the last 1.36 Myr, Mediterranean winter rainfalls were in phase with the African monsoon. Here we present a high-resolution terrestrial and marine dataset for the Marine Isotope Stage 17 interglacial (Middle Pleistocene) from Southern Italy, showing that precipitation rates and regimes in the central Mediterranean varied independently of the monsoon system. Specifically, events of extreme summer precipitation were promoted by increased regional insolation rates and/or extratropical cyclones, and their magnitude was further enhanced by the advection of cool and humid North Atlantic air during stadials. Our findings provide new information on the short- to mid-term natural hydroclimatic variability of the Mediterranean basin, and offer new critical insights on land–ocean interactions at the regional scale by complementing previous analyses on the displacement of storm tracks toward southern Europe.

The Response of the Tropospheric Dynamics to Extreme States of the Stratospheric Polar Vortex during Enso Phases in Idealized Model Experiments

Extreme states of the stratospheric polar vortex (SPV) affect the average position of the main propagation trajectories of synoptic vortices in the Northern Hemisphere over a time period from 2 weeks to 2 months. This time scale is considered to be one of the most difficult periods in forecasting. Based on the analysis of data from idealized numerical experiments on the Isca platform, we studied the processes of formation of anomalous positions of storm tracks in the Atlantic-European region as a response to sudden stratospheric warmings and events of extremely strong SPV during various phases of the El Niño Southern Oscillation. It was shown that in winter it is impossible to say unambiguously about the southward displacement of the Atlantic storm track during El Niño events without taking into account the intensity of SPV. The intensity of SPV, expressed as the zonal component of wind speed, averaged along 60° N at the level of 10 hPa, has its maximum predictive potential during El Niño.

Tracking Racialized Gentrification-Induced Displacement of Indigenous African American Residents

The disproportionate racial impact of gentrification-induced displacement is becoming more of a topic of debate because of the growing evidence and continued outcry of institutional and systemic racism from communities of color. The lack of research in tracking displacement requires new approaches to studying gentrification to address the challenges of investigating the impact on communities of color. In addition to studying the economic, political, and socially motivated reasons for gentrification, the application of a racism-centered framework can shed light on the role of white hegemony in community and urban development policies and practices. Social work researchers can significantly contribute to the body of literature regarding the impact of gentrification-induced displacement of African American residents by applying one of the many social work frameworks in research. Understanding the disproportionate racial impact of displacement on indigenous residents can inform social policies regarding community development strategies and propose interventions to mitigate the impact.

Discovery, Quantitative Recurrence, and Inhibition of Motion-Blur Hysteresis Phenomenon in Visual Tracking Displacement Detection.

Motion blur is common in video tracking and detection, and severe motion blur can lead to failure in tracking and detection. In this work, a motion-blur hysteresis phenomenon (MBHP) was discovered, which has an impact on tracking and detection accuracy as well as image annotation. In order to accurately quantify MBHP, this paper proposes a motion-blur dataset construction method based on a motion-blur operator (MBO) generation method and self-similar object images, and designs APSF, a MBO generation method. The optimized sub-pixel estimation method of the point spread function (SPEPSF) is used to demonstrate the accuracy and robustness of the APSF method, showing the maximum error (ME) of APSF to be smaller than others (reduced by 86%, when motion-blur length > 20, motion-blur angle = 0), and the mean square error (MSE) of APSF to be smaller than others (reduced by 65.67% when motion-blur angle = 0). A fast image matching method based on a fast correlation response coefficient (FAST-PCC) and improved KCF were used with the motion-blur dataset to quantify MBHP. The results show that MBHP exists significantly when the motion blur changes and the error caused by MBHP is close to half of the difference of the motion-blur length between two consecutive frames. A general flow chart of visual tracking displacement detection with error compensation for MBHP was designed, and three methods for calculating compensation values were proposed: compensation values based on inter-frame displacement estimation error, SPEPSF, and no-reference image quality assessment (NR-IQA) indicators. Additionally, the implementation experiments showed that this error can be reduced by more than 96%.

Nonlinear dynamic responses of ballasted railway tracks using concrete sleepers incorporated with reinforced fibres and pre-treated crumb rubber

Abstract Damages on railway sleepers due to heavy impact loads induced by the movement of trains can be reduced by improving their impact resistance. Fibre-reinforced/pre-treated crumb rubber concrete sleepers (RCSs) have the potential to display significant impact resistance to withstand a high-magnitude impact load. The ideal proportions of pre-treated crumb rubber, steel fibres, and polypropylene fibres (PFs) can be identified based on the minimum cost-to-impact energy ratio after conducting a drop weight impact test on prisms. The numerical model developed to assess the behaviour of ballasted tracks has been validated using both simulation results and field measurements. Numerical studies have been conducted on ballasted rail tracks with steel and PF-reinforced/pre-treated RCSs using LS-DYNA software. Dynamic strain rate-dependent material parameters are introduced in the numerical simulations. The nonlinear effect of higher train speeds on dynamic track responses has been highlighted in this article. Although the static load-carrying capacity and modulus of elasticity of rubber concrete are low, their dynamic performance controls the track displacements from exceeding permissible limits. The outcome of this study will provide new insights into the effects of railway concrete sleepers incorporated with reinforced fibres and pre-treated crumb rubber on railway track performance in order to ensure safety and reliability before it is put into services.

Performance Evaluation of a Combined Transition System in Slab-Ballasted Railway Track Using a Vehicle-Track-Substructure Interaction Model

Abrupt stiffness variations along the railway track may increase the geometrical and mechanical defects of railway lines. The conjunction points of a railway track with concrete and ballast pavements, which are called slab-ballasted track transitions, are one of the main areas where vertical track stiffness changes sharply. Therefore, the potential benefits of a combined transition system along the slab-ballasted transition, made of an approach slab and additional rails, are studied in this paper. For this purpose, a vehicle-track-substructure interaction model, which included three main segments of the railway track (slab track, transition zone, and ballasted track) was programmed based on the finite element method. A test line with the mentioned combined transition system was built to measure the railway track responses through field study. Then, the three-dimensional (3D) numerical model was validated using the results obtained from the experimental tests. Afterwards, a number of parametric studies were performed to analyze the dynamic responses of the combined transition zone. The results indicated that this type of transition system promotes a smoother stiffness transition between the slab track segment and the ballasted track segment by making the transition in three gradual steps. The track displacements in the analyzed case-study gradually increased by about 22%, 28%, and 34% along the combined transition zone in the junction points of the slab and ballasted tracks.

Linking upwelling intensity and orbital-scale climate variability in South Africa's winter rainfall zone: Insights from a ∼70,000-year hyrax midden record

The climate of Africa's southwestern Cape is characterised by a strongly seasonal winter precipitation regime, with late Quaternary climate variability generally considered to have been driven by the position of the southern westerlies. This paper presents a unique ∼70,000 year-long palaeoclimatic record from a rock hyrax midden from South Africa's winter rainfall zone, enabling the analysis of regional climate systems since the beginning of marine isotope stage 4. The data suggest that the last glacial period was relatively humid compared to the Holocene, likely due to cooler temperatures, more extensive Antarctic sea-ice extent and an equatorward displacement of the westerly storm track. However, orbital-scale climate variability associated with the 23 kyr precessional cycle primarily correlates with changes in upwelling intensity in the Benguela system, implying an important role for the blocking of tropical easterly flow in driving long-term climatic variability. These factors combined during glacial periods to significantly amplify rainfall seasonality in the southwestern Cape, bringing more winter rainfall via mid-latitude frontal systems, while reducing the proportion of summer rainfall, particularly during the glacial periods of the late Quaternary. The results therefore highlight the need to consider a complex suite of circulation systems and dynamics when inferring drivers of long-term environmental change in the region.

A Three-Stage Prediction Method for Track Displacement During Shield Tunneling

Track displacement is an important factor of track irregularity. Existing researches related with track displacement prediction generally ignore the influence from underground construction engineering such as shield tunneling, resulting in inaccurate estimation of track displacement. To fill this gap, we propose a three-stage framework to predict the track displacement when the shield tunnel under crosses the existing tunnel. Firstly, by considering the curved shield tunneling, a three-dimensional model is constructed to estimate the total ground displacement during the whole tunneling process. Furthermore, the soil-tunnel interaction model is established to estimate the deformation of the existing tunnel. To tackle the issue of unknown node displacements, cubic splines are used to interpolate the unknown values of tunnel displacements. On this basis, the direct stiffness method is used to estimate the track displacement and to calculate the track irregularity. Finally, the effectiveness of the proposed method is verified and the prediction performance on the track irregularity is evaluated using a real engineering case and the finite element simulation. The main contributions of this article lie in the modeling of the curved scenario for the estimation of the ground loss, as well as the combination of cubic splines and direct stiffness method, which improve the accuracy of the track displacement estimation during shield tunneling.

Tracking Displacement of a Worm-Like Robot With Multiple Sensor Configurations

Tracking Displacement of a Worm-Like Robot With Multiple Sensor Configurations

Deformation mapping between pier settlement and maglev track for high-speed multi-span simply supported maglev bridge

When a bridge pier settles, deformation of the complex coupling between a maglev track and girders may occur because of the disparity between the continuity of the maglev track and discontinuity of the simply supported girder bridge. This introduces additional irregularity to the track, resulting in the combined vibration of the maglev train–bridge system. In this study, a high-speed maglev track–simply supported bridge is considered as the research object. The deformation characteristics of the maglev track caused by the pier settlement are analysed. First, the mapping relationship between the settlement of a single pier and the deformation of the maglev track is theoretically deduced. Then, an analytical model for the deformation of the maglev track is developed. The model is compared with a finite element model and found to have sufficient accuracy. The additional irregularity of the maglev track includes the rigid displacement caused by pier settlement and the elastic displacement influenced by the track and girder. The elastic deformation of the longitudinal beam of the maglev track is the main component of the deformation in the vertical displacement of the maglev track. Based on the established analytical model, the elastic deformation of the longitudinal beam of the maglev track and its main influencing factors are further examined.

A Late Holocene climate reconstruction from the high-altitude Lake Gölcük sedimentary records, Isparta (SW Anatolia)

AbstractA high-resolution multiproxy lake sediment dataset, comprising lithology, radiography, μXRF elemental, magnetic susceptibility (MS), δ13C, and δ18O measurements since ca. AD 400 is presented in this study. Changes in lithology, radiography, magnetic susceptibility (MS), δ13C, and δ18O reflect wet/dry climate periods, whereas variability in log(Ca/K) can reflect warm/cold climate periods. Analyses of the multiproxy results allow the distinction of several climate periods, which may be associated with climatic phenomena such as changes in North Atlantic Oscillation (NAO) and/or solar activity. The influence of NAO−/NAO+ (negative/positive) is suggested to be related with the southward/northward displacement of the storm tracks resulting from the NAO−/NAO+ phases. For solar activity, the influence is explained through a direct increase in solar heating leading to calcite precipitation. The Dark Ages Cold Period (DACP, AD 450–750) reflects cold-dry climate conditions at this site, indicative of a positive North Atlantic Oscillation (NAO+) and low solar activity. The Medieval Climate Anomaly (MCA, AD 950–1250) exhibits wet-dry-wet and warm-cold-warm climate conditions. The wet/dry periods likely are associated with NAO−/NAO+, respectively, and the warm/cold period may reflect relatively high/low solar activity. The Little Ice Age (LIA, AD 1400–1850) is characterized by dry and cold climate conditions, suggesting the influence of NAO+ and low solar activity. Comparison of the results of this study with local and regional results suggests a generally similar climate pattern, which is indicative of similar climate mechanisms. The contradictions can be associated with age-related uncertainties, orographic differences, and/or other regional teleconnections.

A new source finding and tracking analysis approach for the active reflector of five-hundred-meter aperture spherical telescope

The FAST (Five-hundred-meter Aperture Spherical Telescope) is the world’s largest single-aperture radio telescope. During operation, FAST needs to follow the observed celestial body to adjust displacements, which can be divided into two processes: the source finding and tracking. In this paper, a new numerical method based on Vector Form Intrinsic Finite Element (VFIFE) is proposed to simulate the source finding and tracking process for FAST’s active reflector. The basic principle of static equilibrium and calculation flow of the sourcing and tracking analysis is proposed, and the finite element program is compiled to analyze the displacement process of the reflector cable-net structure. Then, six typical test conditions are selected to simulate the sourcing and tracking displacement process. The obtained final form in the equilibrium state adheres to the target configuration, demonstrating the applicability of the suggested approach and the correctness of calculation findings. In addition, the change in the actuator length and the structural force distribution can be simultaneously derived. These values serve as a vital theoretical foundation for FAST’s practical operation and regulation.