Object Drop Detection on Railway Track Through Rayleigh Wave Sensing Using Laser Vibrometer
TL;DR: It was established that the waves propagating along the railway track are indeed Rayleigh waves and can pave way to a technology on real-time railway track monitoring for obstacle detection.
Abstract: The feasibility of obstacle detection along a railway track through Rayleigh wave sensing was empirically studied using a laser vibrometer mounted along railway tracks at specific test sites. The impact of obstacles like rock and timber of varying weights dropped on rail head, rail ballast, and sleeper was recorded using the laser vibrometer. It could detect the vibrations generated by the impact of rock and timber drop from a distance of 2 km. The results were cross-verified using finite-element simulation and it was established that the waves propagating along the railway track are indeed Rayleigh waves. Sensing of Rayleigh wave generation under object drop along railway track can pave way to a technology on real-time railway track monitoring for obstacle detection.
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TL;DR: This paper proposes a methodology to model the OCL with local dropper defect using a nonlinear finite element approach and shows that the defect on the first or last dropper within a span is the most detrimental to the current collection quality.
Abstract: The local dropper defect is the most common fault in the early service stage of the overhead contact line (OCL) system. The plastic deformation and loose of a dropper may cause the variation of the contact line height, which has a direct effect on the contact performance of the pantograph-OCL system. This paper proposes a methodology to model the OCL with local dropper defect using a nonlinear finite element approach. Employing a developed TCUD (Target Configuration under Dead Load) method, which takes the vertical defective dropper position in the contact line as additional constraints, the local dropper defect is exactly added in the initial configuration of the OCL model. Several simulations of pantograph-OCL interaction are run with different positions of the defective dropper. The effect of local dropper defect on the pantograph-OCL contact forces is analysed. The results show that the increase of the defect degree causes the increment of the contact force peak around the defective dropper point. The defect on the first or last dropper within a span is the most detrimental to the current collection quality, as it directly causes the increase of maximum contact force, which challenges the safe operation of the pantograph-OCL system, and should be strictly restricted. The PSD (Power Spectral Density) analysis of contact force indicates that the dropper defect distorts the frequency characteristics of the contact force. The energy of contact forces decreases at the dropper-interval related frequencies due to the presence of dropper defect. Similarly, a significant `break' of the dropper-interval frequency component can be observed in the time-frequency representation of the contact force. This phenomenon has the potential to be used to identify and locate the defective dropper from the measured contact force.
39 citations
Cites background from "Object Drop Detection on Railway Tr..."
...Normally, the pantograph-OCL system is the most vulnerable part in the electrified railway, as it suffers multiple impacts from the vehicle-track vibration [2], the temperature variation [3], the irregularities on the contact line [4], the unsteady wind load [5] and some other complicated disturbance [6]....
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TL;DR: First, the phase-based motion extraction method is improved by directly transforming the phase variations into the displacement without the computation of phase gradient, which is then converted into acceleration information to describe the vibration.
Abstract: Video cameras are capable to collect high-density spatial data as each pixel is a sensor. An issue is that the video data is difficult to convert into the motion information, such as displacement. This paper presents a novel camera-based vibration measurement methodology for the lightweight structure. First, the phase-based motion extraction method is improved by directly transforming the phase variations into the displacement without the computation of phase gradient. The displacement is then converted into acceleration information to describe the vibration. Moreover, the proposed vibration measurement is investigated for a lightweight structure without attached sensors to change the physical properties. The measurements of the acceleration signals from camera and accelerometer are compared for verification. The experimental results for the effect of mass-loading, different camera parameters and down-sampling on the measurement validate the effectiveness of the proposed method.
17 citations
Cites background from "Object Drop Detection on Railway Tr..."
...vibration measurement do not need sensors to install on the structure, thus avoiding the mass-loading effects [5]–[7]....
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TL;DR: In this paper , a fast and accurate object detector termed improved R-CNN is proposed by introducing new up-sampling parallel structure and context extraction module (CEM) into the architecture of CNN.
8 citations
TL;DR: In this paper , a novel architecture called FarNet is proposed for long-range railway track point cloud segmentation, which is mainly divided into three parts, i.e., spherical projection, attention-aggregation network and results refinement.
Abstract: Rail track segmentation is key to environmental perception of autonomous train. However, due to the complexity of railway track environment, critical issues such as the detection of rail tracks with different curvatures remain to be overcome. In this study, a novel architecture called FarNet is proposed for long-range railway track point cloud segmentation. The proposed FarNet is mainly divided into three parts, i.e., spherical projection, attention-aggregation network and results refinement. Specifically, spherical projection converts the LiDAR point cloud into a pseudo range image, and attention-aggregation network enables railway track detection using the pseudo range image. Furthermore, in the attention-aggregation network two components, i.e., spatial attention module and information aggregation module, are proposed to enhance the capability of rail track segmentation. Last, the results refinement helps further filter out the noise points after segmentation. Experimental results show that the proposed FarNet achieved 98.0% mean intersection-over-union (MIoU) and 98.9% mean pixel accuracy (MPA) for rail track segmentation.
1 citations
13 May 2022
TL;DR: A railway foreign body intrusion detection method that optimizes the YOLOv4 model that has good results and performance in detection accuracy and detection speed, effectively solving the problems of missed detection, misdetection, and low detection accuracy of foreign objects in the current road foreign object intrusion scene.
Abstract: To solve the problem of low accuracy of detection and positioning of invading foreign body targets of the scene of railway foreign body intrusion, this paper proposes a railway foreign body intrusion detection method that optimizes the YOLOv4 model. First, the self-built railway foreign body intrusion limit dataset was expanded to solve the model over-fitting problem and improve the generalization ability of the model. Second, replace the backbone feature extraction network in the YOLOv4 model with a lightweight feature extraction structure, which effectively reduces the total number of parameters and deepens the number of network layers. Experiments show that the algorithm has good results and performance in detection accuracy and detection speed, effectively solving the problems of missed detection, misdetection, and low detection accuracy of foreign objects in the current road foreign object intrusion scene.
References
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Book•
01 Jan 1995
TL;DR: In this paper, the authors present a single-degree-of-freedom (SDF) system, which is composed of a mass-spring-damper system and a non-viscous Damping Free Vibration (NFV) system.
Abstract: I. SINGLE-DEGREE-OF-FREEDOM SYSTEMS. 1. Equations of Motion, Problem Statement, and Solution Methods. Simple Structures. Single-Degree-of-Freedom System. Force-Displacement Relation. Damping Force. Equation of Motion: External Force. Mass-Spring-Damper System. Equation of Motion: Earthquake Excitation. Problem Statement and Element Forces. Combining Static and Dynamic Responses. Methods of Solution of the Differential Equation. Study of SDF Systems: Organization. Appendix 1: Stiffness Coefficients for a Flexural Element. 2. Free Vibration. Undamped Free Vibration. Viscously Damped Free Vibration. Energy in Free Vibration. Coulomb-Damped Free Vibration. 3. Response to Harmonic and Periodic Excitations. Viscously Damped Systems: Basic Results. Harmonic Vibration of Undamped Systems. Harmonic Vibration with Viscous Damping. Viscously Damped Systems: Applications. Response to Vibration Generator. Natural Frequency and Damping from Harmonic Tests. Force Transmission and Vibration Isolation. Response to Ground Motion and Vibration Isolation. Vibration-Measuring Instruments. Energy Dissipated in Viscous Damping. Equivalent Viscous Damping. Systems with Nonviscous Damping. Harmonic Vibration with Rate-Independent Damping. Harmonic Vibration with Coulomb Friction. Response to Periodic Excitation. Fourier Series Representation. Response to Periodic Force. Appendix 3: Four-Way Logarithmic Graph Paper. 4. Response to Arbitrary, Step, and Pulse Excitations.Response to Arbitrarily Time-Varying Forces. Response to Unit Impulse. Response to Arbitrary Force. Response to Step and Ramp Forces. Step Force. Ramp or Linearly Increasing Force. Step Force with Finite Rise Time. Response to Pulse Excitations. Solution Methods. Rectangular Pulse Force. Half-Cycle Sine Pulse Force. Symmetrical Triangular Pulse Force. Effects of Pulse Shape and Approximate Analysis for Short Pulses. Effects of Viscous Damping. Response to Ground Motion. 5. Numerical Evaluation of Dynamic Response. Time-Stepping Methods. Methods Based on Interpolation of Excitation. Central Difference Method. Newmark's Method. Stability and Computational Error. Analysis of Nonlinear Response: Central Difference Method. Analysis of Nonlinear Response: Newmark's Method. 6. Earthquake Response of Linear Systems. Earthquake Excitation. Equation of Motion. Response Quantities. Response History. Response Spectrum Concept. Deformation, Pseudo-Velocity, and Pseudo-Acceleration Response Spectra. Peak Structural Response from the Response Spectrum. Response Spectrum Characteristics. Elastic Design Spectrum. Comparison of Design ad Response Spectra. Distinction between Design and Response Spectra. Velocity and Acceleration Response Spectra. Appendix 6: El Centro, 1940 Ground Motion. 7. Earthquake Response of Inelastic Systems. Force-Deformation Relations. Normalized Yield Strength, Yield Strength Reduction Factor, and Ductility Factor. Equation of Motion and Controlling Parameters. Effects of Yielding. Response Spectrum for Yield Deformation and Yield Strength. Yield Strength and Deformation from the Response Spectrum. Yield Strength-Ductility Relation. Relative Effects of Yielding and Damping. Dissipated Energy. Energy Dissipation Devices. Inelastic Design Spectrum. Applications of the Design Spectrum. Comparison of Design and Response Spectra. 8. Generalized Single-Degree-of-Freedom Systems. Generalized SDF Systems. Rigid-Body Assemblages. Systems with Distributed Mass and Elasticity. Lumped-Mass System: Shear Building. Natural Vibration Frequency by Rayleigh's Method. Selection of Shape Function. Appendix 8: Inertia Forces for Rigid Bodies. II. MULTI-DEGREE-OF-FREEDOM SYSTEMS. 9. Equations of Motion, Problem Statement, and Solution Methods. Simple System: Two-Story Shear Building. General Approach for Linear Systems. Static Condensation. Planar or Symmetric-Plan Systems: Ground Motion. Unsymmetric-Plan Building: Ground Motion. Symmetric-Plan Buildings: Torsional Excitation. Multiple Support Excitation. Inelastic Systems. Problem Statement. Element Forces. Methods for Solving the Equations of Motion: Overview. 10. Free Vibration. Natural Vibration Frequencies and Modes. Systems without Damping. Natural Vibration Frequencies and Modes. Modal and Spectral Matrices. Orthogonality of Modes. Interpretation of Modal Orthogonality. Normalization of Modes. Modal Expansion of Displacements. Free Vibration Response. Solution of Free Vibration Equations: Undamped Systems. Free Vibration of Systems with Damping. Solution of Free Vibration Equations: Classically Damped Systems. Computation of Vibration Properties. Solution Methods for the Eigenvalue Problem. Rayleigh's Quotient. Inverse Vector Iteration Method. Vector Iteration with Shifts: Preferred Procedure. Transformation of kA A = ...w2mA A to the Standard Form. 11. Damping in Structures.Experimental Data and Recommended Modal Damping Ratios. Vibration Properties of Millikan Library Building. Estimating Modal Damping Ratios. Construction of Damping Matrix. Damping Matrix. Classical Damping Matrix. Nonclassical Damping Matrix. 12. Dynamic Analysis and Response of Linear Systems.Two-Degree-of-Freedom Systems. Analysis of Two-DOF Systems without Damping. Vibration Absorber or Tuned Mass Damper. Modal Analysis. Modal Equations for Undamped Systems. Modal Equations for Damped Systems. Displacement Response. Element Forces. Modal Analysis: Summary. Modal Response Contributions. Modal Expansion of Excitation Vector p (t) = s p(T). Modal Analysis for p (t) = s p(T). Modal Contribution Factors. Modal Responses and Required Number of Modes. Special Analysis Procedures. Static Correction Method. Mode Acceleration Superposition Method. Analysis of Nonclassically Damped Systems. 13. Earthquake Analysis of Linear Systems.Response History Analysis. Modal Analysis. Multistory Buildings with Symmetric Plan. Multistory Buildings with Unsymmetric Plan. Torsional Response of Symmetric-Plan Buildings. Response Analysis for Multiple Support Excitation. Structural Idealization and Earthquake Response. Response Spectrum Analysis. Peak Response from Earthquake Response Spectrum. Multistory Buildings with Symmetric Plan. Multistory Buildings with Unsymmetric Plan. 14. Reduction of Degrees of Freedom. Kinematic Constraints. Mass Lumping in Selected DOFs. Rayleigh-Ritz Method. Selection of Ritz Vectors. Dynamic Analysis Using Ritz Vectors. 15. Numerical Evaluation of Dynamic Response. Time-Stepping Methods. Analysis of Linear Systems with Nonclassical Damping. Analysis of Nonlinear Systems. 16. Systems with Distributed Mass and Elasticity. Equation of Undamped Motion: Applied Forces. Equation of Undamped Motion: Support Excitation. Natural Vibration Frequencies and Modes. Modal Orthogonality. Modal Analysis of Forced Dynamic Response. Earthquake Response History Analysis. Earthquake Response Spectrum Analysis. Difficulty in Analyzing Practical Systems. 17. Introduction to the Finite Element Method.Rayleigh-Ritz Method. Formulation Using Conservation of Energy. Formulation Using Virtual Work. Disadvantages of Rayleigh-Ritz Method. Finite Element Method. Finite Element Approximation. Analysis Procedure. Element Degrees of Freedom and Interpolation Function. Element Stiffness Matrix. Element Mass Matrix. Element (Applied) Force Vector. Comparison of Finite Element and Exact Solutions. Dynamic Analysis of Structural Continua. III. EARTHQUAKE RESPONSE AND DESIGN OF MULTISTORY BUILDINGS. 18. Earthquake Response of Linearly Elastic Buildings. Systems Analyzed, Design Spectrum, and Response Quantities. Influence of T 1 and r on Response. Modal Contribution Factors. Influence of T 1 on Higher-Mode Response. Influence of r on Higher-Mode Response. Heightwise Variation of Higher-Mode Response. How Many Modes to Include. 19. Earthquake Response of Inelastic Buildings. Allowable Ductility and Ductility Demand. Buildings with "Weak" or "Soft" First Story. Buildings Designed for Code Force Distribution. Limited Scope. Appendix 19: Properties of Multistory Buildings. 20. Earthquake Dynamics of Base-Isolated Buildings. Isolation Systems. Base-Isolated One-Story Buildings. Effectiveness of Base Isolation. Base-Isolated Multistory Buildings. Applications of Base Isolation. 21. Structural Dynamics in Building Codes. Building Codes and Structural Dynamics. International Building Code (United States), 2000. National Building Code of Canada, 1995. Mexico Federal District Code, 1993. Eurocode 8. Structural Dynamics in Building Codes. Evaluation of Building Codes. Base Shear. Story Shears and Equivalent Static Forces. Overturning Moments. Concluding Remarks. Appendix A: Frequency Domain Method of Response Analysis.Appendix B: Notation.Appendix C: Answers to Selected Problems.Index.
4,812 citations
"Object Drop Detection on Railway Tr..." refers background or methods in this paper
...prising a damping parameter ξ, expressed in terms of the mass m and the stiffness k which is defined as [32],...
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...To find the values for the Rayleigh damping, we have used the relations between the critical damping ratio and the Rayleigh damping parameters [32]....
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...Knowing the two pairs of corresponding ξi and ωi , results in a system of equations expressed as [32], [ 1 2ω1 ω1 2 1 2ω2 ω2 2 ][ αdM...
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TL;DR: In this paper, finite element incremental formulations for non-linear static and dynamic analysis are reviewed and derived starting from continuum mechanics principles, and a consistent summary, comparison, and evaluation of the formulations which have been implemented in the search for the most effective procedure.
Abstract: SUMMARY Starting from continuum mechanics principles, finite element incremental formulations for non-linear static and dynamic analysis are reviewed and derived. The aim in this paper is a consistent summary, comparison, and evaluation of the formulations which have been implemented in the search for the most effective procedure. The general formulations include large displacements, large strains and material non-linearities. For specific static and dynamic analyses in this paper, elastic, hyperelastic (rubber-like) and hypoelastic elastic-plastic materials are considered. The numerical solution of the continuum mechanics equations is achieved using isoparametric finite element discretization. The specific matrices which need be calculated in the formulations are presented and discussed. To demonstrate the applicability and the important differences in the formulations, the solution of static and dynamic problems involving large displacements and large strains are presented.
789 citations
Additional excerpts
...time-dependent solution is written as [33], [34],...
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TL;DR: In this article, an updated Lagrangian and a total Lagrangians formulation of a three-dimensional beam element are presented for large displacement and large rotation analysis, and it is shown that the two formulations yield identical element stiffness matrices and nodal point force vectors.
Abstract: An updated Lagrangian and a total Lagrangian formulation of a three-dimensional beam element are presented for large displacement and large rotation analysis. It is shown that the two formulations yield identical element stiffness matrices and nodal point force vectors, and that the updated Lagragian formulation is computationally more effective. This formulation has been implemented and the resulted of some sample analyses are given.
633 citations
Additional excerpts
...time-dependent solution is written as [33], [34],...
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Book•
01 Jan 1993
TL;DR: The drift of Electrons and Ions in Gases can be traced back to the drift chamber of drift-chamber gas as mentioned in this paper, where charged particles and ions drift through the gas.
Abstract: Gas Ionization by Charged Particles and by Laser Rays.- The Drift of Electrons and Ions in Gases.- Electrostatics of Tubes, Wire Grids and Field Cages.- Amplification of Ionization.- Creation of the Signal.- Electronics for Drift Chambers.- Coordinate Measurement and Fundamental Limits of Accuracy.- Geometrical Track Parameters and their Errors.- Ion Gates.- Particle Identification by Measurement of Ionization.- Existing Drift Chambers #x2013 An Overview.- Drift-Chamber Gases.
477 citations
Additional excerpts
...LASER based sensors are widely used in surface scanning and profilometry [1]–[3], particle detection [4], vehicular monitoring [5], navigation [6], [7], security based applications...
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TL;DR: The development of the highly accurate ADER–DG approach for tetrahedral meshes provides a numerical technique to approach 3-D wave propagation problems in complex geometry with unforeseen accuracy.
Abstract: SUMMARY
We present a new numerical method to solve the heterogeneous elastic wave equations formulated as a linear hyperbolic system using first-order derivatives with arbitrary high-order accuracy in space and time on 3-D unstructured tetrahedral meshes. The method combines the Discontinuous Galerkin (DG) Finite Element (FE) method with the ADER approach using Arbitrary high-order DERivatives for flux calculation. In the DG framework, in contrast to classical FE methods, the numerical solution is approximated by piecewise polynomials which allow for discontinuities at element interfaces. Therefore, the well-established theory of numerical fluxes across element interfaces obtained by the solution of Riemann-Problems can be applied as in the finite volume framework. To define a suitable flux over the element surfaces, we solve so-called Generalized Riemann-Problems (GRP) at the element interfaces. The GRP solution provides simultaneously a numerical flux function as well as a time-integration method. The main idea is a Taylor expansion in time in which all time-derivatives are replaced by space derivatives using the so-called Cauchy–Kovalewski or Lax–Wendroff procedure which makes extensive use of the governing PDE. The numerical solution can thus be advanced for one time step without intermediate stages as typical, for example, for classical Runge–Kutta time stepping schemes. Due to the ADER time-integration technique, the same approximation order in space and time is achieved automatically. Furthermore, the projection of the tetrahedral elements in physical space on to a canonical reference tetrahedron allows for an efficient implementation, as many computations of 3-D integrals can be carried out analytically beforehand. Based on a numerical convergence analysis, we demonstrate that the new schemes provide very high order accuracy even on unstructured tetrahedral meshes and computational cost and storage space for a desired accuracy can be reduced by higher-order schemes. Moreover, due to the choice of the basis functions for the piecewise polynomial approximation, the new ADER–DG method shows spectral convergence on tetrahedral meshes. An application of the new method to a well-acknowledged test case and comparisons with analytical and reference solutions, obtained by different well-established methods, confirm the performance of the proposed method. Therefore, the development of the highly accurate ADER–DG approach for tetrahedral meshes provides a numerical technique to approach 3-D wave propagation problems in complex geometry with unforeseen accuracy.
433 citations