A review of recent research on structural monitoring in railway industry is proposed in this paper, with a special focus on stress-based solutions. After a brief analysis of the mechanical behaviour of ballasted railway tracks, an overview of the most common monitoring techniques is presented. A special attention is paid on strain gages and accelerometers for which the accurate mounting position on the track is requisite. These types of solution are then compared to another modern approach based on the use of optical fibres. Besides, an in-depth discussion is made on the evolution of numerical models that investigate the interaction between railway vehicles and tracks. These models are used to validate experimental devices and to predict the best location(s) of the sensors. It is hoped that this review article will stimulate further research activities in this continuously expanding field.
Railway local irregularities are a growing source of ground-borne vibration and can cause negative environmental impacts, particularly in urban areas. Therefore, this paper analyses the effect of railway track singular defects (discontinuities) on ground vibration generation and propagation. A vehicle/track/soil numerical railway model is presented, capable of accurately predicting vibration levels. The prediction model is composed of a multibody vehicle model, a flexible track model and a finite/infinite element soil model. Firstly, analysis is undertaken to assess the ability of wheel/rail contact models to accurately simulate the force generation at the wheel/rail contact, in the presence of a singular defect. It is found that, although linear contact models are sufficient for modelling ground vibration on smooth tracks, when singular defects are present higher accuracy wheel/rail models are required. Furthermore, it is found that the variation in wheel/rail force during the singular defect contact depends on the track flexibility, and thus requires a fully coupled vehicle/track/foundation model. Next, a parametric study of ground vibrations generated by singular rail and wheel defects is undertaken. Six shapes of discontinuity are modelled, representing various defect types such as transition zones, switches, crossings, rail joints and wheel flats. The vehicle is modelled as an AM96 train set and it is found that ground vibration levels are highly sensitive to defect height, length and shape.
With the development of new lines and the increase of traffic on existing lines, the problem caused by railway-induced ground vibrations is becoming bigger and bigger. The present paper focuses on wheel flat modelling in prediction schemes which determine railway-induced ground vibrations and which have applications to urban tramways. A comprehensive flat spot model is developed and included in an existing vehicle/track model taking into account Hertz's contact law. The associated non-linear stiffness is calculated in a pre-processing step by solving the three-dimensional wheel/rail contact problem. A two-step approach for predicting ground vibrations, developed by the authors, is then applied, including the track/soil interaction through a foundation model and the ground wave propagation by means of a fully three-dimensional finite element model. Predicted results are presented, based on the T2006 tram and on the railway site of Haren (Belgium). A specific analysis is proposed for studying the vehicle dynamics on flexible tracks, and for calculating the effect provided by the wheel flat impact on the rail heads. Results related to the contact force between the wheel with a flat spot and the rail are presented. A series of periodic impacts are generated when the flat spot comes into contact with the rail head with magnitude depending on the track flexibility at the contact point. The key conclusions are discussed, based on the sensitivity analysis of the flat spot size and the train speed. Both parameters affect the critical speed of the vehicle/track system, defined as the speed where loss of contact occurs. The ground vibration levels were found to increase with speed and decrease with distance.
This is a repository copy of The effect of railway local irregularities on ground vibration.
Isothermal amplification is an emerging approach for non-invasive, rapid and cost-effective real-time monitoring of cancer specific mutations through circulating tumour DNA (ctDNA). This study demonstrates a compact allele specific (AS) loop mediated isothermal amplification (LAMP) strategy, termed ‘AS-Mini-LAMP’, modelled using wild type (WT) and mutation specific reactions targeting the estrogen receptor ESR1 c.1138G>C (p.E380Q) missense mutation. Allele selectivity, encoded at the 5’-end of the forward and backward inner primers (FIP and BIP) promotes enhanced selectivity upon self-hybridisation, loop formation and self-primed exponential amplification. Inclusion of unmodified self-stabilising (USS) primers aimed to reduce the likelihood of non-specific allele amplification through competitive inhibition and to enhance reaction velocity through an assisted strand displacement ‘swarm’ priming effect. The two assays were optimised using short synthetic WT and E380Q mutant DNA templates, and subsequently validated to a limit of detection of 500 mutant copies in under 25 minutes in ddPCR-confirmed positive (20.7% variant allele frequency) and negative patient plasma cfDNA samples. These results demonstrate the ability of AS-Mini-LAMP to achieve sensitive and selective amplification of actionable mutations present within plasma ctDNA.
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