Jungsoo Ryue

Ground vibration from trains: experimental parameter characterization and validation of a numerical model

Trains running on railway tracks on the surface of the ground or in tunnels induce vibrations in the ground which propagate away from the track. These may be experienced as feelable vibration or as audible rumbling noise in the buildings nearby, both of which are difficult to control. As the properties of the ground differ widely between locations they must be characterized for a particular site in order to make reliable predictions. This article describes field measurements of the vibration at two sites with soft clay soil in Southern England. The properties of the ground material, including its layered structure, have been identified from comparisons between results of a layered ground model and measurements obtained using impact excitation. Presentation in the wavenumber-frequency domain is particularly helpful for this purpose. Measurements of vibrations from passing trains are then compared with predictions using a semianalytical model for ground vibration from trains and good agreement is found.

Study on the Rolling Noise Model Using an Analysis of Wheel and Rail Vibration Characteristics

Rolling noise is an important source of noise from railways; it is caused by wheel and rail vibrations induced by acoustic roughness at the wheel/rail contact. To reduce rolling noise, it is necessary to have a reliable prediction model that can be used to investigate the effects of various parameters related to the rolling noise. This paper deals with modeling rolling noise from wheel and rail vibrations. In this study, the track is modeled as a discretely supported beam by regarding concrete slab tracks, and the wheel vibration is simulated by using the finite element method. The vertical and lateral wheel/rail contact forces are modeled using the linearized Hertzian contact theory, and then the vibration responses of the wheel and rail are calculated to predict the radiated noise. To validate the proposed model, a field measurement was carried out for a test vehicle. It was found that the predicted result agrees well with the measured one, showing similar behavior in the frequency range between 200 and 4000 Hz where the rolling noise is prominent.

Track-Based Control Measures for Ground Vibration – The Influence of Quasi-Static Loads and Dynamic Excitation

Ground vibration from surface trains is induced by two main excitation mechanisms, due to the moving quasi-static loads and dynamic loads due to track roughness. The relative importance of these two mechanisms has been investigated using a semi-analytical model of the coupled vehicle, track and ground system. The track is represented as an infinite, layered beam resting on one or more elastic soil layers, overlying a three-dimensional half-space of ground material. The train is modelled as a multi-body system with both primary and secondary suspensions and its motion is included. The quasi-static and dynamic loads have been investigated over a wide range of conditions for locations close to the track and further away. Results are shown in terms of insertion gains for both dynamic and quasi-static components for a wide variety of conditions. It is confirmed that an assessment of the effect of a change in support stiffness should not be based on measurements too close to the track – in the case considered the distance should be at least 10 m to give representative results.

Characteristics of Vibration and Sound Radiated from Rails of Concrete Slab Tracks for Domestic High Speed Trains

An important source of noise from railways is rolling noise caused by wheel and rail vibrations induced by acoustic roughness at the wheel-rail contact. In the present paper, characteristics of rail vibration and radiated sound power from concrete slab tracks for domestic high speed train(KTX) is investigated by means of a numerical method. The waveguide finite element and boundary element are combined and applied for this analysis. The concrete slab track is modelled simply with a rail and rail pad regarding the concrete slab as a rigid ground. The wave types which contribute significantly to the rail vibration and radiated noise are identified in terms of the mobility and decay rates. In addition, the effect of the rail pad stiffness on the radiated power is examined for two different rail pad stiffnesses.

Wave propagation in railway tracks at high frequencies

In terms of the long range rail inspection, rail vibration which can propagate over long distances along rails may be a useful tool to detect rail defects. In order to understand long range wave propagation in railway tracks, it is required to identify how far vibration can travel along a rail. To answer this question, the attenuation characteristics of all propagating waves should be determined. In this work decay rates of propagating waves are investigated for frequencies up to 80 kHz. The Wavenumber Finite Element (WFE) method is used to represent a track which has a rail on a continuous foundation. Different damping loss factors are introduced in this model for the damping in the rail and in the foundation. By this simulation, the efficient wave types and their decay rates are predicted. These are presented in terms of what is measurable on various regions of the rail cross-section. In order to validate the simulation results, an experiment was performed on an operational railway track. The measured results are presented for comparison with the simulated ones and good agreement between them is found.

Prediction of radiation ratio and sound transmission of complex extruded panel using wavenumber domain Unite element and boundary element methods

Recently, complex shaped aluminium panels have been adopted in many structures to make them lighter and stronger. The vibro-acoustic behaviour of these complex panels has been of interest for many years but conventional finite element and boundary element methods are not efficient to predict their performance at higher frequencies. Where the cross-sectional properties of the panels are constant in one direction, wavenumber domain numerical analysis can be applied and this becomes more suitable for panels with complex cross-sectional geometries. In this paper, a coupled wavenumber domain finite element and boundary element method is applied to predict the sound radiation from and sound transmission through a double-layered aluminium extruded panel, having a typical shape used in railway carriages. The predicted results are compared with measured ones carried out on a finite length panel and good agreement is found.

Comparison of Track Vibration Characteristics for Domestic Railway Tracks in the Aspect of Rolling Noise

An important source of noise from railways is rolling noise caused by wheel and rail vibrations induced by acoustic roughness at the wheel-rail contact. The main contributors to rolling noise are the sleepers, rail, and wheels. In order to analyze and predict rolling noise, it is necessary to understand the vibrating behaviors of railway tracks, as well as of the wheels. In the present paper, theoretical modeling methods for railway track are reviewed in terms of rolling noise; these methods are applied for the three representative types of domestic railway tracks operated: the conventional ballasted track, KTX ballasted track and KTX concrete track. The characteristics of waves propagating along rails are investigated and compared among the types of tracks. The tracks are modeled as discretely supported Timoshenko beams and are compared in terms of the averaged squared amplitude of velocity, which is directly related to the sound radiation from the rails.

Self Noise Analysis of Towed Array Sonar Induced by Axisymmetric Vibrations Propagating Along Fluid-filled Elastic Hoses

Performance of array sonars towed underwater is limited due to the self-noise induced mainly by the strumming vibration of the towing cable and also turbulent flow around the acoustic sensor module. The vibration of the towing cable generates axisymmetric waves that propagate along the acoustic module of the array sonar and produce self-noise. The present study aims to investigate the characteristics of the self-noise induced by the axisymmetric vibrations of the acoustic module. The waves of interest are the bulge and extensional waves propagating along the fluid-filled elastic hose. Dispersion relations of these waves are predicted by means of the numerical simulation to evaluate the wave speeds. The self-noise induced by the axisymmetric waves are formulated taking into account the damping of the elastic hose and the effect of the damping is investigated.

Wave Propagation in the Strip Plate with Longitudinal Stiffeners

It is important to understand the vibrating behavior of plate structures for many engineering applications. In this study, vibration characteristics of strip plates which have finite width and infinite length are investigated theoretically and numerically. The waveguide finite element approach is used in this study which is known as an effect tool for waveguide structures. WFE method requires only cross-sectional FE model and uses theoretical harmonic solutions for the wave propagation along the longitudinal direction. First of all for a simple strip plate, WFE results are compared with theoretical ones such as the dispersion diagrams, point mobilities, etc. to validate the numerical model. Then in the numerical analysis, the several different types of longitudinal stiffeners are included to the plate model to investigate the effects of the stiffeners in terms of the dispersion curves and mobilities.

Modelling of Railway Tracks for Wave Propagation along Railway Tracks at High Frequencies

It was reported recently that railpads can be included as a continuous elastic support of the rail and the model was justified from experiments. In general, however, railpads are installed discretely on sleepers with a regular span. The effect of the discrete railpad was not clearly examined so far in such a high frequency range. In this paper, the effect of the railpads in track modelling for high frequencies is investigated by means of the finite element analysis. To do that, the railpads are regarded as `a continuous elastic support` and `a discrete elastic support` in this paper. The dispersion relations and decaying features are predicted and compared between the two models up to 80 kHz.