Track Structure Model Research Articles

Damage characteristics and mechanical properties of CRTS III track structure in curved sections under longitudinal uneven subgrade settlement

This paper first presents a CRTS III track structure (TS) model specifically designed for curved sections, highlighting its adjustable superelevations feature that enhances adaptability to various high-speed railway curve profiles. The model considers the distribution of steel bars within the TS, concrete damaged plasticity, as well as contact nonlinearity. Afterward, the intricate impacts of longitudinal uneven subgrade settlement (LUSS) position (7 positions), amplitude (5–30 mm), wavelength (5–30 m), and TS superelevation (15–175 mm) on structural damage, stress, deformation, and interlayer gap are studied. The findings reveal that: 1) Under different LUSS positions, the concrete base (CB) experiences the most severe damage, particularly on its thick side. For the TS with 175 mm superelevation, in the wavelength range of 10–20 m, the maximum damage value of CB exceeds 0.9 when LUSS amplitude reaches 20 mm. With the movement of LUSS position, the main damage position of CB changes obviously. When the concrete stress reaches the tensile strength, the steel bars located in adjacent positions progressively assume the primary role in load-bearing. 2) The influence of LUSS on TS deformation and interlayer gap is inevitably associated with the distance between settlement center and expansion joints. Interlayer gaps vary among structural components, which are primarily distributed near settlement center, expansion joints, and settlement edges. 3) As the amplitude increases, both CB and self-compacting concrete layer (SCCL) damage are aggravated. Increasing wavelength initially causes damage to increase, then decrease, and 10–20 m is the most unfavorable wavelength range for most cases. 4) The effect of superelevation on TS damage is complex, varying with structural components and settlement characteristics. In most cases, as superelevation increases, the damage to CB increases, whereas the deformation decreases.

Spectral composition of secondary electrons based on the Kiefer-Straaten ion track structure model.

The major part of energy deposition of ionizing radiation is caused by secondary electrons, independent of the primary radiation type. However, their spatial concentration and their spectral properties strongly depend on the primary radiation type and finally determine the pattern of molecular damage e.g. to biological targets as the DNA, and thus the final effect of the radiation exposure. To describe the physical and to predict the biological consequences of charged ion irradiation, amorphous track structure approaches have proven to be pragmatic and helpful. There, the local dose deposition in the ion track is equated by considering the emission and slowing down of the secondary electrons from the primary particle track. In the present work we exploit the model of Kiefer and Straaten and derive the spectral composition of secondary electrons as function of the distance to the track center. The spectral composition indicates differences to spectra of low linear energy transfer (LET) photon radiation, which we confirm by a comparison with Monte Carlo studies. We demonstrate that the amorphous track structure approach provides a simple tool for evaluating the spectral electron properties within the track structure. Predictions of the LET of electrons across the track structure as well as the electronic dose build-up effect are derived. Implications for biological effects and corresponding predicting models based on amorphous track structure are discussed.

Overview of PHITS Ver.3.34 with particular focus on track-structure calculation

This paper presents the latest updates on PHITS, a versatile radiation transport code, focusing specifically on track-structure models. Track structure calculations are methods used to simulate the movement of charged particles while explicitly considering each atomic reaction. Initially developed for radiation biology, these calculation methods aimed to analyze the radiation-induced damage to DNA and chromosomes. Several track-structure calculation models, including PHITS-ETS, PHITS-ETS for Si, PHITS-KURBUC, ETSART, and ITSART, have been developed and implemented for PHITS. These models allow users to study the behavior of various particles at the nano-scale across a wide range of materials. Furthermore, potential applications of track-structure calculations have also been proposed so far. This collection of track-structure calculation models, which encompasses diverse conditions, opens up new avenues for research in the field of radiation effects.

Static and dynamic response characteristics of a ballastless track structure of a high-speed railway bridge with interlayer debonding under temperature loads

The ballastless track structure of a high-speed railway (HSR) undergoes interlayer debonding during its service due to train loads, environmental loads, and construction. A CRTS Ⅱ ballastless track slab structure is a longitudinally-continuous reinforced concrete structure, and the temperature load is a major factor in the occurrence of interlayer debonding. However, the effect of temperature loads on the static and dynamic response of the CRTS Ⅱ ballastless track structure of an HSR bridge following interlayer debonding is unknown. This study established a finite element simulation model of a ballastless track structure over a bridge and a vertically-coupled dynamic vehicle–track–bridge simulation model. The deformation generated by the track structure at temperature loads was inputted as track irregularity to the dynamic simulation model, and the change laws of the deformation and dynamic response of the track structure under different temperature loads was studied. The results showed that under different temperature loads, the ballastless track slab first undergoes longitudinal deformation, followed by transverse deformation. On this basis, the dynamic response of the HSR ballastless track structure over a bridge with interlayer debonding was found to increase with increasing temperature loads, while the frequency band changed from single to complex. This study not only provides insights into the effects of temperature loads on track structure damage, but also lays a theoretical foundation for the development of maintenance and repair plans for railroad departments.

Thermal arching and interfacial damage evolution of CRTS-II slab track under solar radiation in alpine and plateau regions

Arch deformation and interface failure of CRTS-II slab track have become crucial issues for the operation safety of high-speed railways. However, few researchers investigated the mechanics and deformation behaviour on CRTS-II slab track exposed to high-altitude plateau climatic environments. This study proposes an analysis approach for thermal arching and interface damage evolution of the slab track structure under solar radiation in alpine and plateau environments. The time-dependent solar temperature distribution is loaded on the refined finite element model (FEM) of the slab track structure’s thermal deformation in high-altitude plateau climatic environments. The analysis approach is validated by comparing the calculated and experimental data. The track slab's maximum and minimum vertical temperature gradient (VTG) are 94.49 °C/m and −45.02 °C/m, respectively. The narrow joint damage is an incentive for the inverted V-shaped thermal arching and interface separation of the slab track structure under solar radiation. The interfacial gap of slab track structure in alpine and plateau regions reaches more than 14 mm during summer. The proposed analysis approach is a valuable reference to the construction temperature, maintenance, and damage monitoring of slab track structure in alpine and plateau regions.

Implementation of the electron track-structure mode for silicon into PHITS for investigating the radiation effects in semiconductor devices

In order to elucidate the mechanism of radiation effects in silicon (Si) devices, such as pulse-height defects and semiconductor soft errors, we developed an electron track-structure model dedicated to Si and implemented it into particle and heavy ion transport code system (PHITS). Then, we verified the accuracy of our developed model by comparing the ranges and depth-dose distributions of electrons in Si obtained from this study with corresponding experimental values and other simulated results. As an application of the model, we calculated the mean energies required to create an electron–hole pair in crystalline Si. Our calculated result agreed with the experimental data when the threshold energy for generating secondary electrons was set to 2.75 eV, consistent with the corresponding data deduced from past studies. This result suggested that the improved PHITS can contribute to the precise understanding of the mechanisms of radiation effects in Si devices.

Flying without a Net: Space Radiation Cancer Risk Predictions without a Gamma-ray Basis.

The biological effects of high linear energy transfer (LET) radiation show both a qualitative and quantitative difference when compared to low-LET radiation. However, models used to estimate risks ignore qualitative differences and involve extensive use of gamma-ray data, including low-LET radiation epidemiology, quality factors (QF), and dose and dose-rate effectiveness factors (DDREF). We consider a risk prediction that avoids gamma-ray data by formulating a track structure model of excess relative risk (ERR) with parameters estimated from animal studies using high-LET radiation. The ERR model is applied with U.S. population cancer data to predict lifetime risks to astronauts. Results for male liver and female breast cancer risk show that the ERR model agrees fairly well with estimates of a QF model on non-targeted effects (NTE) and is about 2-fold higher than the QF model that ignores NTE. For male or female lung cancer risk, the ERR model predicts about a 3-fold and more than 7-fold lower risk compared to the QF models with or without NTE, respectively. We suggest a relative risk approach coupled with improved models of tissue-specific cancers should be pursued to reduce uncertainties in space radiation risk projections. This approach would avoid low-LET uncertainties, while including qualitive effects specific to high-LET radiation.

Development and validation of proton track-structure model applicable to arbitrary materials

A novel transport algorithm performing proton track-structure calculations in arbitrary materials was developed. Unlike conventional algorithms, which are based on the dielectric function of the target material, our algorithm uses a total stopping power formula and single-differential cross sections of secondary electron production. The former was used to simulate energy dissipation of incident protons and the latter was used to consider secondary electron production. In this algorithm, the incident proton was transmitted freely in matter until the proton produced a secondary electron. The corresponding ionising energy loss was calculated as the sum of the ionisation energy and the kinetic energy of the secondary electron whereas the non-ionising energy loss was obtained by subtracting the ionising energy loss from the total stopping power. The most remarkable attribute of this model is its applicability to arbitrary materials, i.e. the model utilises the total stopping power and the single-differential cross sections for secondary electron production rather than the material-specific dielectric functions. Benchmarking of the stopping range, radial dose distribution, secondary electron energy spectra in liquid water, and lineal energy in tissue-equivalent gas, against the experimental data taken from literature agreed well. This indicated the accuracy of the present model even for materials other than liquid water. Regarding microscopic energy deposition, this model will be a robust tool for analysing the irradiation effects of cells, semiconductors and detectors.

Temperature features of the asphalt concrete waterproofing layer on high-speed railway in cold regions

The asphalt concrete waterproofing layer (ACWL) has been used as a potential waterproofing structure for the subgrade in Chinese high-speed railway in cold regions. The waterproofing behavior and dynamic response of ACWL have been evaluated in the previously published studies. However, the research on the temperature and thermal stress distribution in ACWL track structure has not yet been studied. This research aims at investigating the strain distribution of ACWL under the temperature influence in winter. The field test was conducted to monitor the strain changes on the ACWL surface under ambient temperature. A 3D numerical model of track structure with ACWL was also developed based on the thermo-mechanical coupled method. The field test results indicated that the longitudinal strain on the ACWL surface changed periodically with the air temperature while the tensile strain increased with the decrease in temperature. The temperature analysis showed that the temperature change inside the track structure caused by the daily temperature change was mainly focused on the depth range from the track slab to the base plate. The maximum negative temperature gradient inside the track slab was reported to occur at 4:00 a.m in winter. The geotextile was further introduced to weaken the bond between the base plate and the ACWL. The calculations proved that the geotextile could effectively reduce the peak tensile strain on the ACWL surface at the joints of the base plates. 1 m − 2 m geotextile was recommended to be placed at both sides of the joint of the base plates.

Hybrid analytical-numerical modelling of ground vibrations from moving loads in a tunnel embedded in the saturated soil

The dynamic response of a floating-slab track and underground railway tunnel embedded in saturated soils under moving loads are investigated by a hybrid analytical-numerical method. The tunnel is modelled as thin cylindrical shell surrounded by saturated soil of infinite radial extent. A two-layered beam structure is used to model the floating-slab track. In the continuous floating-slab track, the slab is an infinitely long Euler–Bernoulli beam while in the discontinuous one, the slabs are modelled as a periodic structure consisting of beams of finite length. The coupled equations of the tunnel-soil system are solved in the frequency-wavenumber domain with the aid of Fourier transform and Fourier decomposition. The track structure and tunnel-soil model are coupled by force and displacement continuity conditions at the tunnel invert. Numerical results for the track, tunnel and soil responses are presented for a moving point and train load. It is found the critical velocity of a track-tunnel-soil system approaches the shear wave speed of the soils. The natural frequencies of the track have significant influence on the soil displacement and pore pressure. Furthermore, an increase of the soil permeability leads to a decrease of the displacement as well as the pore pressure in the free field.

Static Strain Analysis of CRTS I Bi-Block Ballastless Track

In this paper, relying on the National Engineering Laboratory of High-Speed Railway Construction Technology, a full-scale model of the double-block ballastless track structure is established, and the strain analysis of the layered track structure under different static loads is carried out, which has a certain practical significance for the design and maintenance of the high-speed railway ballastless track in our country. Research conclusion: (1) Under the action of static load, the sleeper directly under the rail is under compression; the four corners of the sleeper are tensile strain; (2) The strain at each measuring point on the surface of the track slab around the sleeper is compressive strain; the edge of the top surface of the track slab is compressive strain; The longitudinal strain at the bottom of the side of the track slab is tensile strain; (3) Under static load, the longitudinal strain measurement point on the top surface of the base plate is tensile strain at a distance of two sleepers from the static load position; the longitudinal strain at the bottom of the side of the base plate is tensile strain.

Evaluation on mechanical behavior of asphalt concrete trackbed with slab panel using full-scale static and dynamic load test

In this study, a full-scale model of a railway track structure using an asphalt concrete trackbed with concrete slab panel (ACTSP) is developed. Slab panels are very important to develop asphalt concrete (AC) track system for minimizing the roadbed pressure due to the trainload and reducing the plastic deformation of the AC. The purpose of this study is to analyze the performance of the subgrade and the AC trackbed under different AC layer concepts. Static and dynamic loads were applied to the whole track system by using the Railway Loading System (RLS). Based on the data acquisition and instrument systems, the displacement of the rail/sleeper, the strain at the bottom of the asphalt concrete, and the pressure characteristics of each subgrade was measured. The pressure distribution efficiency along the track system was also investigated. Based on the full-scale test results, the application of asphalt concrete trackbed is very promising since this technology will noticeably mitigate the impact of pressure on the track system from the trainload. The effectiveness is more prominent in railway structures having an AC trackbed thickness of around 35 cm. In this condition, the dynamic train load results reveal that plastic deformation and tensile strain of rail and panel can substantially be reduced up to 20 and 50%, respectively, compared to the condition of 20 cm trackbed thickness. The results also indicate that the pressure distribution along the panel is improved by using a thicker AC layer roadbed concept. Overall, the findings in the research suggest that asphalt concrete trackbed with slab panel is a novel technology that will reinforce the durability of track components and prolong the service life of railway track structure.

Causes and development characteristics of corrugation on tangential track of metro

In order to investigate the causes and development characteristics of rail corrugation on the tangential section, based on the finite element model of track structure and the vehicle-track space coupled dynamic model, modal analysis and dynamic analysis were carried out for detailed analysis. The results show that the line condition and passing frequency range of measured corrugation are close to those of roaring rail corrugation caused by Pinned-Pinned resonance of track structure, so it is preliminarily considered that corrugation occurring on this section is roaring rail corrugation. The modal analysis of track structure model shows that the vibration mode at the frequency of 513.7 Hz is the transverse Pinned-Pinned resonance of track structure and the vibration mode at the frequency of 1050.0 Hz is the vertical Pinned-Pinned resonance of track structure. The dynamic analysis of vehicle-track space coupled model shows that the amplitudes of rail vertical vibration acceleration levels are higher at the center frequencies of 500 Hz and 1000 Hz, and the one-third octave band widths corresponding to above center frequencies are in the frequency range of Pinned-Pinned resonance of track structure. Therefore, it can be determined that rail corrugation on the measured line is roaring rail corrugation. The changing trends of rail vertical vibration acceleration levels under different sleeper spacings and operating speeds are basically the same and amplitudes of rail vertical vibration acceleration levels at the center frequencies of 500 Hz and 1000 Hz are higher. With the increase of the sleeper spacing and operating speed, the variation trends of rail vertical vibration acceleration levels at 500 Hz and 1000 Hz are almost unanimous. By changing the sleeper spacing and operating speed, the rail vertical vibration acceleration levels can be changed significantly, which shows that the appropriate sleeper spacing (about 700 mm) and operating speed (about 80 km/h) can effectively control the occurrence and development of rail corrugation.

Rail corrugation characteristics in small radius curve section of Cologne-egg fasteners

The typical passing frequencies of corrugation were obtained by analysing the measured corrugation data in small radius curve track with Cologne-egg fasteners. The three-dimensional solid element model of track structure was established with the software ABAQUS, and modal analysis was carried out to determine the relationship between natural frequencies of track structure and passing frequencies of corrugation. By using the material wear model based on friction work theory, the frequency characteristics of corrugation and the development law of wear under different speeds were studied, and the control measures of corrugation were analysed. The new point of this study is to implement the above dynamic analysis from the perspective of vehicle (with flexible wheelsets) track space coupling, which can consider the coupled relationship in three directions of space. The results show that the generation of corrugation is closely related to the mechanical characteristics of track structure. Passing frequencies do not change with speeds, reflecting the frequency-fixing characteristics of corrugation. The analysis of control measures of corrugation shows that the smaller the friction coefficient is, the less likely the rail is to produce corrugation. The existence of rail vibration absorber can eliminate the generation of some short wavelength corrugation and reduce the rail bending vibration, which has a significant effect on the control of corrugation.

Computational feasibility of simulating changes in blood flow through whole-organ vascular networks from radiation injury

Vasculature is necessary to the healthy function of most tissues. In radiation therapy, injury of the vasculature can have both beneficial and detrimental effects, such as tumor starvation, cardiac fibrosis, and white-matter necrosis. These effects are caused by changes in blood flow due to the vascular injury. Previously, research has focused on simulating the radiation injury of vasculature in small volumes of tissue, ignoring the systemic effects of local damage on blood flow. Little is known about the computational feasibility of simulating the radiation injury to whole-organ vascular networks. The goal of this study was to test the computational feasibility of simulating the dose deposition to a whole-organ vascular network and the resulting change in blood flow. To do this, we developed an amorphous track-structure model to transport radiation and combined this with existing methods to model the vasculature and blood flow rates. We assessed the algorithm’s computational scalability, execution time, and memory usage. The data demonstrated it is computationally feasible to calculate the radiation dose and resulting changes in blood flow from 2 million protons to a network comprising 8.5 billion blood vessels (approximately the number in the human brain) in 87 hours using a 128-node cluster. Furthermore, the algorithm demonstrated both strong and weak scalability, meaning that additional computational resources can reduce the execution time further. These results demonstrate, for the first time, that it is computationally feasible to calculate radiation dose deposition in whole-organ vascular networks. These findings provide key insights into the computational aspects of modeling whole-organ radiation damage. Modeling the effects radiation has on vasculature could prove useful in the study of radiation effects on tissues, organs, and organisms.

Generation Mechanism and Development Characteristics of Rail Corrugation of Cologne Egg Fastener Track in Metro

By establishing vehicle-track space coupled model and rail corrugation evaluation model, the generation mechanism of rail corrugation was analyzed in frequency domain and time domain, and development characteristics of corrugation were studied by using corrugation growth rate. Analysis based on frequency domain: through modal analysis and frequency response analysis on the finite element model of track structure, it is found that there are natural frequencies of track structure close to measured corrugation passing frequencies. It shows that the vibration modes corresponding to these frequencies can be more easily excited, which can cause the resonance phenomenon of track structure and form the rail corrugation at corresponding frequencies. Analysis based on time domain: the time-history curves of rail vertical vibration acceleration and rail vertical displacement are calculated by using vehicle-track coupled model and the frequency domain transformation of the time-history data is carried out. It is found that there are characteristic frequencies close to the measured corrugation passing frequencies, which indicates that the vibration of track structure at corresponding frequencies is an important reason to promote the formation of corrugation. The change of vehicle speed has no effect on characteristic frequencies of corrugation growth rate curves, which reflects the fixed frequency characteristic of corrugation. With the increase of train operation times, the corrugation corresponding to characteristic frequencies will gradually form and develop, and the increase of vehicle speed will increase the wavelength range and development speed of rail corrugation.

Investigation on Interface Damage between Cement Concrete Base Plate and Asphalt Concrete Waterproofing Layer under Temperature Load in Ballastless Track

The interfacial bond between cement concrete base plate (CCBP) and asphalt concrete waterproofing layer (ACWL) is a weak portion in the newly developed Chinese high-speed railway ballastless track. The interface damage caused due to fluctuating temperature load and dynamic train load is one of the most critical problems in Northern China. This paper aims to investigate the interface damage evolution process under temperature load via experimental and simulation analysis. Full-scale transverse shear tests were performed to explore the interface bond-slip mode of the adjacent ACWL and CCBP. Then, a finite element model of a ballastless track structure was built and a cohesive zone model (CZM) was utilized to model the interface damage initiation, crack propagation, and delamination process under uniform/gradient temperature load. Furthermore, the dynamic response of the ballastless track where CCBP and ACWL were partly/totally debonded was investigated and compared with the perfectly bonded structure. The results demonstrate that bilinear CZM is capable of revealing the interface damage initiation, crack propagation, and delamination process under temperature load. The interface state between the adjacent CCBP and ACWL was greatly affected by temperature changes and the interface bonding state had a great impact on the dynamic response of ballastless track.

Modeling of chromosome aberration response functions induced by particle beams with different LET.

This study is based on our already published experimental data (Kowalska et al. in Radiat Environ Biophys 58:99-108, 2019) and is devoted to modeling of chromosome aberrations in human lymphocytes induced by 22.1MeV/u 11B ions, 199MeV/u 12C ions, 150MeV and spread-out Bragg peak (SOBP) proton beams as well as by 60Co γ rays. The curvature of the dose-effect curves determined by the linear-quadratic model was considered in the frame of a simple analytical approach taking into account increase in the irradiation dose due to overlapping interaction regions of ion tracks. The model enabled to estimate effective interaction radius which could be compared with the physical expectations. The results were also compared to the Amorphous Track Structure Model of Katz which allows to get some additional information about the ion track structure. The analysis showed that the curvature of the experimental dose-effect curves mainly results from highly efficient repair processes of the DNA damage.

Wayside testing methods for high-frequency vertical wheel-rail impact forces and its applicability

Methods for measuring high-frequency wheel–rail impact forces are indispensable in the study of railway vehicle dynamics. Although there have been many methods proposed for impact force measurement, not all of them are accurate at high-frequencies. Additionally, most of the proposed measurement methods are quasi-static methods that require static calibration. Therefore, the accuracy and applicability of different high-frequency wheel–rail force measurement methods need to be studied and validated dynamically. In this paper, a refined numerical track structure model is constructed to simulate wheel–rail impact behaviors. Under dynamic loading conditions, compare the ‘equivalent value’ and ‘actual value’ of wheel-rail impact forces using different wayside testing methods. The simulation results are then dynamically verified using full-scale indoor test results. The rules dictating effective strain gauge arrangement and the application scope of each measurement method are then obtained, and the relationship between the layout of the strain gauges and the effective measurement length is clarified. The results of this study indicate that the high-frequency wheel–rail impact force measured on site is generally underestimated, and because rail joint splints change the supporting conditions of the rail, the accuracies of all high-frequency wheel–rail impact force measurement methods decrease obviously at such rail joints.

Simulation tests of dynamics of vibroisolated railway lines with vibroisolating system based on elastomer elements

The problem of propagation of vibration waves caused by the movement of rail vehicles in the ground is extremely important from the point of view of environmental protection against negative effects of dynamic impacts caused by rail transport. Therefore, there is a need to develop new methods for analyzing dynamic phenomena related to rail vehicle traffic. One of the methods that can be used to evaluate dynamic interactions is modeling using finite elements. The article presents a dynamic analysis of the track structure model and the impact of the application of its vibroisolation system on the level of ground vibration amplitude associated with the propagation of vibration waves from the track. The application of the finite element meth-od allows for the analysis of the behavior of engineering structures in variable operating conditions dependent primarily on the speed of movement of vehicles on the track. Such analysis includes the use of a number of physical values that can be used to assess the impact of vibration on any engineering object. These values include, above all, acceleration at any measuring point on the measurement cross-section from the track to the engineering construction, e.g. a residential or industrial building as well as displacement or stress, which are dependent on the speed of the rail vehicle. Comparison of these values with generally available criteria and standards allows at the stage of designing the engineering structure for appropriate modifications to the substructure construction to limit the amplitude of the vibrations transmitted to the environment. These modifications consist mainly of the use of an appropriate vibroisolation system in the form of, for example, slabs or mats laid in the rail layer or pads underneath. Correct execution of the simulation requires careful preparation of the numerical model as well as a series of input data. The input data relate mainly to accurate material data concerning both engineering structures (bridges, viaducts, tunnels), rolling stock and soil parameters. Such data allow to prepare a spectrum of forces loading the modelled section of the track. This approach to the design process is particularly important due to the inability to modify the track after built it.