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D.j. Thompson - One of the best experts on this subject based on the ideXlab platform.
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analysis of resonance effect for a railway track on a Layered Ground
Transportation geotechnics, 2018Co-Authors: Jouyi Shih, D.j. Thompson, Evangelos NtotsiosAbstract:Abstract When a train runs on soft Ground it can approach or even exceed the speed of surface waves in the Ground. Under such conditions the amplitudes of the track response increase considerably. Moreover, a resonance-like phenomenon can occur in which a clear oscillation trail can be observed behind the moving axle loads. An investigation is presented of this resonance frequency and the critical speed effect for a track on a Layered half-space subject to a moving load. Three different methods are used to investigate this resonance frequency: (i) the spectrum of the response to a moving load, (ii) analysis of the dispersion curves of the Ground, and (iii) frequency analysis of the response to a stationary load. A parameter study is presented of a Layered half-space Ground with different P-wave speeds, S-wave speeds, and depth of the upper layer. The critical speeds are found in each case; in such a Layered Ground, the critical speed is greater than the Rayleigh wave speed of the soft upper layer due to the influence of the underlying half-space. The oscillating frequencies are shown to vary with the speed of the moving load, tending to reduce when the load speed increases. The P-wave speeds of both the upper layer and the underlying half-space are found to have negligible influence on the critical velocity and on the oscillating frequency; the S-wave speed of the half-space has only a small influence. Larger differences are found when the depth of the layer is varied. Finally, a formula for calculating this resonance frequency is proposed.
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the effect of boundary conditions model size and damping models in the finite element modelling of a moving load on a track Ground system
Soil Dynamics and Earthquake Engineering, 2016Co-Authors: Jouyi Shih, D.j. Thompson, Antonios ZervosAbstract:An investigation is presented of the use of finite element models in the time domain to represent a load moving on a railway track on a flexible Ground. A systematic study is carried out to compare different sizes and shapes of finite element mesh, different boundary conditions intended for suppressing reflections from the truncated model boundaries, and different models of soil damping. The purpose is to develop guidance to assist in selecting appropriate finite element models for moving load problems. To prevent reflections from the boundaries of the finite domain two approaches are compared. A 40 m radius hemispherical finite element mesh has been used first with infinite elements around the perimeter. This approach gives good results for a point harmonic load at the centre of the domain but some problems are highlighted when it is used for moving load calculations. An alternative approach has therefore been investigated based on a cuboid mesh. The base was fixed to prevent rigid-body motions of the model and, rather than use infinite elements at the sides, these were also fixed. It is shown that, provided that a suitable damping model is used, the spurious reflections from the sides of the model can be suppressed if the model is wide enough. On the other hand, if infinite elements are used, the calculations are found to be considerably more costly with little added benefit. Different models of soil damping are also compared. It is shown that a mass-proportional damping model gives a decay with distance that is independent of frequency, making it particularly suitable for this application. The length of model required to achieve steady state has been investigated. For a homogeneous half-space it is found that the required length increases considerably in the vicinity of the critical speed, up to 130 m in the present example, whereas for the Layered Ground a more modest length is sufficient for all speeds.
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a numerical investigation of railway Ground vibration mitigation using a trench in a Layered soil
2012Co-Authors: A Garciabennett, C.j.c. Jones, D.j. ThompsonAbstract:Ground vibration from railway lines at grade often has its highest amplitudes at frequencies around or even below 10 Hz. A Ground vibration ‘barrier’ (i.e. an open or in-filled trench) would be an attractive means of mitigation of vibration since it would not interfere with the engineering or operation of the track. However, before detailed research, a preliminary theoretical study was conducted to test the idea since simple considerations suggest that barriers might have to be unfeasibly deep to be effective. However, the Layered Ground structure is known to be important in determining the spectrum of transmitted vibration and recent practical investigations suggest that trenches of reasonable depth may be effective. As a prelude to more detailed investigations, an investigation has been carried out using a two-dimensional coupled finite element (FE) and boundary element (BE) model. The results indicate that, in the peak frequency range of vibration transmission, for a typical alluvial valley site, reductions of 4 dB at 10 Hz and 8 dB at 14 Hz might be achieved with a 5 m deep trench.
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Modelling Ground vibration from railways using wavenumber finite- and boundary-element methods
Proceedings of the Royal Society A: Mathematical Physical and Engineering Sciences, 2005Co-Authors: X. Sheng, C.j.c. Jones, D.j. ThompsonAbstract:A mathematical model is presented for Ground vibration induced by trains, which uses wavenumber finite- and boundary-element methods. The track, tunnel and Ground are assumed homogeneous and infinitely long in the track direction (x-direction). The models are formulated in terms of the wavenumber in the x-direction and discretization in the yz-plane. The effect of load motion in the x-direction is included. Compared with a conventional, three-dimensional finite- or boundary-element model, this is computationally faster and requires far less memory, even though calculations must be performed for a series of discrete wavenumbers. Thus it becomes practicable to carry out investigative study of train-induced Ground vibration. The boundary-element implementation uses a variable transformation to solve the well-known problem of strongly singular integrals in the formulation. A 'boundary truncation element' greatly improves accuracy where the infinite surface of the Ground is truncated in the boundary-element discretization. Predictions of vibration response on the Ground surface due to a unit force applied at the track are performed for two railway tunnels. The results show a substantial difference in the environmental vibration that could be expected from the alternative designs. The effect of a moving load is demonstrated in a surface vibration example in which vibration propagates from an embankment into Layered Ground. © 2005 The Royal Society.
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Ground vibration generated by a harmonic load moving in a circular tunnel in a Layered Ground
Journal of Low Frequency Noise Vibration and Active Control, 2003Co-Authors: X. Sheng, C.j.c. Jones, D.j. ThompsonAbstract:All modes of transport impact on e environment. Although railways are seen as environmentally advantageous in many ways, the issues of noise and vibration are often seen as their weakness. For trains running in tunnels where direct airborne noise is effectively screened, structure-borne or ‘Ground-borne’ noise caused by vibration propagated through the Ground is the most important concern. The vibration of interest in this case has frequency components from about 15 Hz to 200 Hz.To understand the mechanisms of vibration propagation from tunnels, a predictive model has been developed for Ground vibration generated by a stationary or moving harmonic load applied in a circular lined or unlined tunnel in a Layered Ground. This study is the first step towards the use of discrete wavenumber methods to model Ground vibration from underGround trains. Discrete wavenumber methods fall into three categories: the discrete wavenumber fictitious force method, the discrete wavenumber finite element method and the discre...
Alexandra Branzan Albu - One of the best experts on this subject based on the ideXlab platform.
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ICPR - Layered Ground truth: Conveying structural and statistical information for document image analysis and evaluation
2016 23rd International Conference on Pattern Recognition (ICPR), 2016Co-Authors: Melissa Cote, Alexandra Branzan AlbuAbstract:This paper addresses the problem of semantic overlap across document objects in the context of Ground truth representation for document layout analysis. Document object categories often share primitives from a low-level perspective (e.g. regions inside bars in a bar chart resemble backGround), making it difficult to evaluate document layout segmentation methods based on pixel classification, as most datasets and Ground truth models focus on document objects. We propose a novel Ground truth model that utilizes structural and statistical pattern recognition concepts. Statistical pixel-based data derived from low-level elemental patterns are Layered onto high-level structural object-based data. We also present evaluation metrics that take advantage of the Layered Ground truth model, allowing a contextual evaluation of pixel classification algorithms. We apply the proposed model to two recent pixel classification approaches, evaluated on business document images that exhibit a challenging mixture of textual, graphical, and pictorial elements through varied layouts. The proposed model allows to obtain very detailed, comprehensive, and intuitive information on the strengths and limitations of the evaluated approaches that would be impossible to obtain through other models.
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Layered Ground truth: Conveying structural and statistical information for document image analysis and evaluation
2016 23rd International Conference on Pattern Recognition (ICPR), 2016Co-Authors: Melissa Cote, Alexandra Branzan AlbuAbstract:This paper addresses the problem of semantic overlap across document objects in the context of Ground truth representation for document layout analysis. Document object categories often share primitives from a low-level perspective (e.g. regions inside bars in a bar chart resemble backGround), making it difficult to evaluate document layout segmentation methods based on pixel classification, as most datasets and Ground truth models focus on document objects. We propose a novel Ground truth model that utilizes structural and statistical pattern recognition concepts. Statistical pixel-based data derived from low-level elemental patterns are Layered onto high-level structural object-based data. We also present evaluation metrics that take advantage of the Layered Ground truth model, allowing a contextual evaluation of pixel classification algorithms. We apply the proposed model to two recent pixel classification approaches, evaluated on business document images that exhibit a challenging mixture of textual, graphical, and pictorial elements through varied layouts. The proposed model allows to obtain very detailed, comprehensive, and intuitive information on the strengths and limitations of the evaluated approaches that would be impossible to obtain through other models.
C.j.c. Jones - One of the best experts on this subject based on the ideXlab platform.
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a numerical investigation of railway Ground vibration mitigation using a trench in a Layered soil
2012Co-Authors: A Garciabennett, C.j.c. Jones, D.j. ThompsonAbstract:Ground vibration from railway lines at grade often has its highest amplitudes at frequencies around or even below 10 Hz. A Ground vibration ‘barrier’ (i.e. an open or in-filled trench) would be an attractive means of mitigation of vibration since it would not interfere with the engineering or operation of the track. However, before detailed research, a preliminary theoretical study was conducted to test the idea since simple considerations suggest that barriers might have to be unfeasibly deep to be effective. However, the Layered Ground structure is known to be important in determining the spectrum of transmitted vibration and recent practical investigations suggest that trenches of reasonable depth may be effective. As a prelude to more detailed investigations, an investigation has been carried out using a two-dimensional coupled finite element (FE) and boundary element (BE) model. The results indicate that, in the peak frequency range of vibration transmission, for a typical alluvial valley site, reductions of 4 dB at 10 Hz and 8 dB at 14 Hz might be achieved with a 5 m deep trench.
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Modelling Ground vibration from railways using wavenumber finite- and boundary-element methods
Proceedings of the Royal Society A: Mathematical Physical and Engineering Sciences, 2005Co-Authors: X. Sheng, C.j.c. Jones, D.j. ThompsonAbstract:A mathematical model is presented for Ground vibration induced by trains, which uses wavenumber finite- and boundary-element methods. The track, tunnel and Ground are assumed homogeneous and infinitely long in the track direction (x-direction). The models are formulated in terms of the wavenumber in the x-direction and discretization in the yz-plane. The effect of load motion in the x-direction is included. Compared with a conventional, three-dimensional finite- or boundary-element model, this is computationally faster and requires far less memory, even though calculations must be performed for a series of discrete wavenumbers. Thus it becomes practicable to carry out investigative study of train-induced Ground vibration. The boundary-element implementation uses a variable transformation to solve the well-known problem of strongly singular integrals in the formulation. A 'boundary truncation element' greatly improves accuracy where the infinite surface of the Ground is truncated in the boundary-element discretization. Predictions of vibration response on the Ground surface due to a unit force applied at the track are performed for two railway tunnels. The results show a substantial difference in the environmental vibration that could be expected from the alternative designs. The effect of a moving load is demonstrated in a surface vibration example in which vibration propagates from an embankment into Layered Ground. © 2005 The Royal Society.
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Ground vibration generated by a harmonic load moving in a circular tunnel in a Layered Ground
Journal of Low Frequency Noise Vibration and Active Control, 2003Co-Authors: X. Sheng, C.j.c. Jones, D.j. ThompsonAbstract:All modes of transport impact on e environment. Although railways are seen as environmentally advantageous in many ways, the issues of noise and vibration are often seen as their weakness. For trains running in tunnels where direct airborne noise is effectively screened, structure-borne or ‘Ground-borne’ noise caused by vibration propagated through the Ground is the most important concern. The vibration of interest in this case has frequency components from about 15 Hz to 200 Hz.To understand the mechanisms of vibration propagation from tunnels, a predictive model has been developed for Ground vibration generated by a stationary or moving harmonic load applied in a circular lined or unlined tunnel in a Layered Ground. This study is the first step towards the use of discrete wavenumber methods to model Ground vibration from underGround trains. Discrete wavenumber methods fall into three categories: the discrete wavenumber fictitious force method, the discrete wavenumber finite element method and the discre...
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Simulations of Ground vibration from a moving harmonic load on a railway track
Journal of Sound and Vibration, 2000Co-Authors: C.j.c. Jones, X. Sheng, Maurice PetytAbstract:Abstract A sequence of results is presented from a model of an oscillating load moving on a track on a Layered Ground. The results allow a visualization of the effect of the relative speeds of the load and the propagation speeds in the Ground structure. This is useful in developing the understanding of the interaction of train speed, track structure and Ground properties for high-speed trains. The simulation shows the excitation of high amplitudes of vibration in the track, the “bow wave” angle of propagation of vibration in the Ground and the transfer of vibrational energy to a higher order mode as the speed of the load exceeds that of the first mode of propagation in the Layered Ground.
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Prediction of Ground Vibration From Railways
Journal of Sound and Vibration, 1996Co-Authors: C.j.c. Jones, J.r. BlockAbstract:Heavy freight trains emit Ground vibration with predominant frequency components in the range 4–30 Hz. If the amplitude is sufficient, this may be felt by lineside residents, giving rise to disturbance and concern over possible damage to their property. In order to establish the influence of parameters of the track and rolling stock and thereby enable the design of a low vibration railway, a theoretical model of both the generation and propagation of vibration is required. The vibration is generated as a combination of the effects of dynamic forces, due to the unevenness of the track, and the effects of the track deformation under successive axle loads. A prediction scheme, which combines these effects, has been produced. A vehicle model is used to predict the dynamic forces at the wheels. This includes the non-linear effects of friction damped suspensions. The loaded track profile is measured by using a track recording coach. The dynamic loading and the effects of the moving axles are combined in a track response model. The predicted track vibration is compared to measurements. The transfer functions from the track to a point in the Ground can be calculated by using a coupled track and a three-dimensional Layered Ground model. The propagation effects of the Ground layers are important but the computation of the transfer function from each sleeper, which would be required for a phase coherent summation of the vibration in the Ground, would be prohibitive. A compromise summation is used and results are compared with measurements
Melissa Cote - One of the best experts on this subject based on the ideXlab platform.
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ICPR - Layered Ground truth: Conveying structural and statistical information for document image analysis and evaluation
2016 23rd International Conference on Pattern Recognition (ICPR), 2016Co-Authors: Melissa Cote, Alexandra Branzan AlbuAbstract:This paper addresses the problem of semantic overlap across document objects in the context of Ground truth representation for document layout analysis. Document object categories often share primitives from a low-level perspective (e.g. regions inside bars in a bar chart resemble backGround), making it difficult to evaluate document layout segmentation methods based on pixel classification, as most datasets and Ground truth models focus on document objects. We propose a novel Ground truth model that utilizes structural and statistical pattern recognition concepts. Statistical pixel-based data derived from low-level elemental patterns are Layered onto high-level structural object-based data. We also present evaluation metrics that take advantage of the Layered Ground truth model, allowing a contextual evaluation of pixel classification algorithms. We apply the proposed model to two recent pixel classification approaches, evaluated on business document images that exhibit a challenging mixture of textual, graphical, and pictorial elements through varied layouts. The proposed model allows to obtain very detailed, comprehensive, and intuitive information on the strengths and limitations of the evaluated approaches that would be impossible to obtain through other models.
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Layered Ground truth: Conveying structural and statistical information for document image analysis and evaluation
2016 23rd International Conference on Pattern Recognition (ICPR), 2016Co-Authors: Melissa Cote, Alexandra Branzan AlbuAbstract:This paper addresses the problem of semantic overlap across document objects in the context of Ground truth representation for document layout analysis. Document object categories often share primitives from a low-level perspective (e.g. regions inside bars in a bar chart resemble backGround), making it difficult to evaluate document layout segmentation methods based on pixel classification, as most datasets and Ground truth models focus on document objects. We propose a novel Ground truth model that utilizes structural and statistical pattern recognition concepts. Statistical pixel-based data derived from low-level elemental patterns are Layered onto high-level structural object-based data. We also present evaluation metrics that take advantage of the Layered Ground truth model, allowing a contextual evaluation of pixel classification algorithms. We apply the proposed model to two recent pixel classification approaches, evaluated on business document images that exhibit a challenging mixture of textual, graphical, and pictorial elements through varied layouts. The proposed model allows to obtain very detailed, comprehensive, and intuitive information on the strengths and limitations of the evaluated approaches that would be impossible to obtain through other models.
X. Sheng - One of the best experts on this subject based on the ideXlab platform.
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Modelling Ground vibration from railways using wavenumber finite- and boundary-element methods
Proceedings of the Royal Society A: Mathematical Physical and Engineering Sciences, 2005Co-Authors: X. Sheng, C.j.c. Jones, D.j. ThompsonAbstract:A mathematical model is presented for Ground vibration induced by trains, which uses wavenumber finite- and boundary-element methods. The track, tunnel and Ground are assumed homogeneous and infinitely long in the track direction (x-direction). The models are formulated in terms of the wavenumber in the x-direction and discretization in the yz-plane. The effect of load motion in the x-direction is included. Compared with a conventional, three-dimensional finite- or boundary-element model, this is computationally faster and requires far less memory, even though calculations must be performed for a series of discrete wavenumbers. Thus it becomes practicable to carry out investigative study of train-induced Ground vibration. The boundary-element implementation uses a variable transformation to solve the well-known problem of strongly singular integrals in the formulation. A 'boundary truncation element' greatly improves accuracy where the infinite surface of the Ground is truncated in the boundary-element discretization. Predictions of vibration response on the Ground surface due to a unit force applied at the track are performed for two railway tunnels. The results show a substantial difference in the environmental vibration that could be expected from the alternative designs. The effect of a moving load is demonstrated in a surface vibration example in which vibration propagates from an embankment into Layered Ground. © 2005 The Royal Society.
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Ground vibration generated by a harmonic load moving in a circular tunnel in a Layered Ground
Journal of Low Frequency Noise Vibration and Active Control, 2003Co-Authors: X. Sheng, C.j.c. Jones, D.j. ThompsonAbstract:All modes of transport impact on e environment. Although railways are seen as environmentally advantageous in many ways, the issues of noise and vibration are often seen as their weakness. For trains running in tunnels where direct airborne noise is effectively screened, structure-borne or ‘Ground-borne’ noise caused by vibration propagated through the Ground is the most important concern. The vibration of interest in this case has frequency components from about 15 Hz to 200 Hz.To understand the mechanisms of vibration propagation from tunnels, a predictive model has been developed for Ground vibration generated by a stationary or moving harmonic load applied in a circular lined or unlined tunnel in a Layered Ground. This study is the first step towards the use of discrete wavenumber methods to model Ground vibration from underGround trains. Discrete wavenumber methods fall into three categories: the discrete wavenumber fictitious force method, the discrete wavenumber finite element method and the discre...
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Simulations of Ground vibration from a moving harmonic load on a railway track
Journal of Sound and Vibration, 2000Co-Authors: C.j.c. Jones, X. Sheng, Maurice PetytAbstract:Abstract A sequence of results is presented from a model of an oscillating load moving on a track on a Layered Ground. The results allow a visualization of the effect of the relative speeds of the load and the propagation speeds in the Ground structure. This is useful in developing the understanding of the interaction of train speed, track structure and Ground properties for high-speed trains. The simulation shows the excitation of high amplitudes of vibration in the track, the “bow wave” angle of propagation of vibration in the Ground and the transfer of vibrational energy to a higher order mode as the speed of the load exceeds that of the first mode of propagation in the Layered Ground.