169 results on '"David Thompson"'
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2. Plug-in cross-dispersing module for the Large Binocular Telescope’s infrared spectrograph LUCI
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Hyukmo Kang, David Thompson, Al Conrad, James Wiese, Heejoo Choi, Vishnu Reddy, and Daewook Kim
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Space and Planetary Science ,Control and Systems Engineering ,Mechanical Engineering ,Astronomy and Astrophysics ,Instrumentation ,Electronic, Optical and Magnetic Materials - Published
- 2022
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Catalog
3. Receptance of a semi-infinite periodic railway track and an equivalent multi-rigid body system for use in truncated track models
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Xiaozhen Sheng, Yuanpeng He, Songtao Yue, and David Thompson
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Acoustics and Ultrasonics ,Mechanics of Materials ,Mechanical Engineering ,Condensed Matter Physics - Published
- 2023
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4. Sources of variability in metro train-induced vibration
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Xiangyu Qu, David Thompson, Meng Ma, Minghang Li, and Evangelos Ntotsios
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Mechanical Engineering - Abstract
In previous in-situ measurements of metro trains it has been found that the velocity level on the track or tunnel wall may vary significantly between different train passages, even though the measuring section, the type of trains and the track and tunnel conditions are identical. An investigation is carried out into the sources of this variability, using a 3D train-track numerical model. This is built using the software SIMPACK and ABAQUS, and is connected through one-way coupling to a finite element model of the tunnel and soil. These models are used to study the influence of various train parameters, including the wheel and rail unevenness, train speed and degree of train loading. For comparison, in-situ measurements were made of the dynamic response of the rail and tunnel wall. The rail roughness at the site as well as the wheel unevenness of all 48 wheels for one train were measured. The results from the model indicate that the wheel unevenness affects the rail velocity level in the frequency region between 25 and 250 Hz and tunnel wall vibration above 5 Hz. The rail velocity level can vary by up to 20 dB due to wheel unevenness, with the largest variations occurring in the frequency bands 50–63 Hz. Variations in passenger loading affect the train-induced vibration by up to 4.5 dB, mainly in the low frequency region. When the train speed varies within a range of ±20% relative to the nominal speed 60 km/h, the frequencies of the peaks are shifted and the level in some frequency bands can change by as much as 10 dB. However, the largest influence is that of the wheel unevenness. It is concluded that the variation in these parameters, especially the wheel and rail unevenness, should be considered to achieve reliable predictions of train-induced vibration. more...
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- 2022
5. A model of a rotating railway wheel for the prediction of sound radiation
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David Thompson, Jose Martínez-Casas, Víctor Tomás Andrés, and Francisco D. Denia
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Acoustics and Ultrasonics ,Mechanics of Materials ,Mechanical Engineering ,Condensed Matter Physics - Abstract
The axial symmetry of a railway wheel is taken into account to expand its vibrational response around the circumferential direction using Fourier series. This allows the vibroacoustic problem of the wheel to be formulated in a two-dimensional frame, solving for the dynamic and acoustic variables analytically in the circumferential direction. By adopting an Eulerian approach, the inertial effects associated with the rotation of the wheelset are included in the model, assuming a constant angular speed of rotation. To represent a railway wheelset, the wheel is constrained at the inner edge of the hub and the contribution of the rigid body motion of the wheelset is superimposed on its response. The latter is evaluated analytically under the assumption of small rigid body displacements. The computational efficiency of the proposed methodology is found to be three orders of magnitude greater than a full three-dimensional methodology, without compromising the accuracy. The results are compared in terms of acoustic radiation with the commercial package Ansys, showing similar sound power levels in almost all the frequency range apart from some differences at low frequencies due to the use of an acoustic model based on radiation ratios. more...
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- 2023
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6. A transferable method for estimating the economic impacts of track interventions: Application to ground-borne noise reduction measures for whole sections of route
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Marcus Young, Simon Blainey, Evangelos Ntotsios, John Preston, Georgios Rempelos, and David Thompson
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050210 logistics & transportation ,Computer science ,Mechanical Engineering ,Noise reduction ,05 social sciences ,010501 environmental sciences ,Track (rail transport) ,01 natural sciences ,Automotive engineering ,Vibration ,Noise ,0502 economics and business ,Life cycle costing ,Economic impact analysis ,0105 earth and related environmental sciences - Abstract
The environmental impacts of noise and vibration are becoming increasingly important in the assessment of new and upgraded railway routes. Vibration from railways propagates through the ground to nearby buildings where it may cause annoyance as feelable vibration or as re-radiated noise. To tackle the adverse effects of ground-borne noise a range of possible interventions are available, including softer rail pads, under-sleeper pads and under-ballast mats. The installation costs of such interventions are generally higher for the higher-performing track types. Additionally, there are potential effects on track maintenance costs which may be positive or negative, for example by reducing sleeper damage or increasing the need for ballast tamping. This study presents a socio-economic analysis of the effects of several interventions to reduce ground-borne noise. By selecting a whole route, the installation and whole-life costs are assessed using Network Rail’s Vehicle-Track Interaction Strategic Model (VTISM) and these are offset against benefits in terms of reduced social costs. Ground-borne noise is predicted at various distances from the alignment using the Modelling of Train Induced Vibration (MOTIV) model and the effect of track interventions is determined as insertion loss spectra. The re-radiated noise within a typical domestic building is then estimated using generic building transfer functions. Geographic Information System tools are used to estimate the population affected by ground-borne noise and their expected level of exposure. The methodology is illustrated using a case study route between Brighton and Portsmouth in the South of England. more...
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- 2020
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7. Fatigue analysis of coil springs in the primary suspension of a railway vehicle based on synthetic spectrum for time-varying vibration load
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Tengfei Wang, Jinsong Zhou, Wenjing Sun, David Thompson, Zhanfei Zhang, and Qiushi Wang
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Mechanical Engineering - Abstract
The fatigue life of coil springs is usually predicted with a stationary Gaussian vibration load and deterministic structural parameters. However, the obtained fatigue life is inconsistent with the observed fatigue life of fractured springs which varies within a wide range. The work aims to propose a method to predict the fatigue life of the coil spring by considering the time-varying vibration load, i.e., root mean square (rms) varies with time and the uncertainties of geometric parameters. First, a synthetic method for time-varying vibration loads is proposed. The time-varying load is decomposed into multiple stationary Gaussian short samples represented by their power spectral density (PSD). These PSDs are synthesized according to the distribution characteristics of spectral values, in which data that are non-Gaussian are processed with the Johnson system. Second, the influence of parameter uncertainties in the coil spring is studied by a Monte Carlo analysis of the stress frequency response function. Finally, the fatigue life is calculated and compared with the results predicted by using the measured stress. The results show that the synthetic spectrum has almost the same damage potential as the measured time-varying load. In comparison with results predicted from the measured stress, the synthetic spectrum gives much better estimates of the fatigue life of the coil spring than the average spectrum. Parameter uncertainties of coil springs significantly affect fatigue life and should be taken into account. more...
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- 2023
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8. Effect of train speed and track geometry on the ride comfort in high-speed railways based on ISO 2631-1
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Mani Entezami, David Thompson, Michael J. Griffin, and Chi Liu
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Vibration ,Vehicle dynamics ,020303 mechanical engineering & transports ,0203 mechanical engineering ,Computer science ,Mechanical Engineering ,Whole body vibration ,020302 automobile design & engineering ,Train ,Track geometry ,02 engineering and technology ,Operating speed ,Automotive engineering - Abstract
The operational speeds of passenger trains have been increasing and now often exceed 300 km/h. Higher speeds can lead to increased vibration and reduced ride comfort for railway passengers. This study investigates the combined effect of speed and track geometry on vibration discomfort in high-speed trains. Railway vehicle dynamic models with various levels of complexity are used, with the measured geometry of a section of a high-speed track as an input. The models have been calibrated with vibration measurements carried out in a train running over this section of the track and then applied to predict the vibration discomfort at increased speeds. To evaluate the vibration discomfort at speeds up to 400 km/h, information on track geometry should include wavelengths up to at least 150 m. Vertical irregularities have the greatest effect at all speeds but lateral irregularities are also important. Both the vertical and lateral irregularities of a high-speed track should be controlled at wavelengths of 50–100 m that excite rigid modes of the car body, corresponding to frequencies of typically 1–2 Hz. Additionally, vertical irregularities with wavelengths of 5–12 m that excite the fundamental flexible mode of the car body, typically around 10–15 Hz, should also be controlled. The effects of cant, the rates of change of cant, and the radius of vertical curves are also evaluated although they only have a small effect on vibration discomfort. more...
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- 2019
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9. The influence of vehicle–track dynamic coupling on the fatigue failure of coil springs within the primary suspension of metro vehicles
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David Thompson, Jinsong Zhou, and Wenjing Sun
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Engineering ,business.industry ,Mechanical Engineering ,Fatigue testing ,020302 automobile design & engineering ,02 engineering and technology ,Dynamic stiffness ,Structural engineering ,Track (rail transport) ,Coil spring ,Dynamic coupling ,020303 mechanical engineering & transports ,0203 mechanical engineering ,Automotive Engineering ,Fracture (geology) ,Safety, Risk, Reliability and Quality ,business ,Suspension (vehicle) - Abstract
Steel coil springs are commonly used in the primary suspension of rail vehicles, usually in the form of two concentric springs. They exhibit strong internal resonances, which can lead to high vibration amplitudes within the spring itself. In some metro vehicles, large numbers of spring failures have occurred due to fatigue fracture in working conditions. The cause of these failures is investigated by studying the vehicle/track interaction, the modal response of the coil springs and the stresses occurring within them in working conditions. A finite element model is used to determine the modal parameters of the primary suspension. The resulting dynamic stiffness matrix is then included in a multi-body vehicle model and coupled to a model of the track. This coupled model is used to investigate the effect of the dynamic properties of both the springs and the track on the stresses in the springs. The springs exhibit strong internal resonances at around 50-60 Hz, at which very large stresses occur in both springs. This frequency range coincides with the P2 resonance frequency (wheelset mass bouncing on the track stiffness) for the standard slab track system used on this metro system. For other track systems, the P2 resonance occurs at a different frequency and the stresses are lower. These results are confirmed with field test data. From the stresses the weakest position in the inner spring is identified, which is found to correspond to the position of common breakages found in field observations. Some guidelines are proposed for reducing the vibration and stress, so that the fatigue fracture incidents can be reduced. more...
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- 2019
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10. Modelling, simulation and evaluation of ground vibration caused by rail vehicles
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David Thompson, Georges Kouroussis, and Evangelos Ntotsios
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Engineering ,business.industry ,Mechanical Engineering ,020302 automobile design & engineering ,02 engineering and technology ,Automotive engineering ,Vibration ,Noise ,020303 mechanical engineering & transports ,Sustainable transport ,0203 mechanical engineering ,Automotive Engineering ,Structural vibration ,Safety, Risk, Reliability and Quality ,business - Abstract
There is a great need to develop rail networks over long distances and within cities as more sustainable transport options. However, noise and vibration are seen as a negative environmental consequ... more...
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- 2019
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11. Efficient LiDAR-Based Object Segmentation and Mapping for Maritime Environments
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Jeremy Brown, David Thompson, and Eric Coyle
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Occupancy grid mapping ,Horizon (archaeology) ,business.industry ,Computer science ,Mechanical Engineering ,Visibility (geometry) ,Ocean Engineering ,Object (computer science) ,Lidar ,Polygon ,Computer vision ,Segmentation ,Motion planning ,Artificial intelligence ,Electrical and Electronic Engineering ,business - Abstract
This paper proposes a method that utilizes a 3-D occupancy grid to efficiently map a large area while retaining simple representations of objects for path planning and provide spatial characteristics of objects, which may be used for object classification. To enable large-scale mapping of objects, a region around the unmanned surface vehicle (USV) is defined where a high density of LiDAR returns is expected, termed the visibility horizon. The polygon intersection between the visibility horizon and the newly detected objects is computed, as well as the polygon subtraction of the visibility horizon from the mapped list of polygons. The two polygon lists are then combined using a polygon union operation, with the objects retaining class designations. The result is a 2-D map that contains polygon representations of objects, where the object is described with a tunable number of vertices and may have an associated object class. Thus, providing necessary information for path planning and tasking. The resultant polygons are shown here to be accurate to 20 cm using a 10-cm occupancy grid and 16-ft-long unmanned surface vehicles with four multibeam LiDAR sensors. more...
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- 2019
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12. Effect of rail dynamics on curve squeal under constant friction conditions
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Bo Ding, David Thompson, and Giacomo Squicciarini
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Physics ,Acoustics and Ultrasonics ,Mechanical Engineering ,Mode (statistics) ,Stiffness ,02 engineering and technology ,Mechanics ,Condensed Matter Physics ,Track (rail transport) ,01 natural sciences ,Instability ,Finite element method ,Damper ,Noise ,020303 mechanical engineering & transports ,0203 mechanical engineering ,Mechanics of Materials ,0103 physical sciences ,Mode coupling ,medicine ,medicine.symptom ,010301 acoustics - Abstract
Curve squeal noise is a severe railway noise problem that can occur when a railway vehicle negotiates a sharp curve. It is usually characterised by a very loud tonal noise and can be very annoying for people in the vicinity. It is generally attributed to friction-induced instability, either due to a falling friction characteristic with increasing sliding velocity or to a mode coupling mechanism which can lead to instability even for a constant friction coefficient. The squeal frequency is usually associated with one or more wheel modes. However, the wheel is coupled dynamically to the track and insufficient attention has been paid in previous research to the role played by the rail dynamic behaviour. In this paper, the effect of the rail dynamics on curve squeal under constant friction conditions is investigated by means of different modelling approaches. The rail is firstly modelled using a waveguide finite element (WFE) model and it is found that the inclusion of the rail dynamics in the model can lead to squeal in some situations where it would otherwise not occur. Various effects are then considered that may introduce additional resonant behaviour into the rail dynamics. These include the effect of the rail cross mobility, rail cross-section deformation, the influence of the periodic support of the rail and reflections between multiple wheels on the rail. The effect of the rail pad stiffness is also explored. However, the results show that all these factors have little influence on the predicted curve squeal instabilities. By means of a reduced model, the main characteristics of the rail dynamics that can result in squeal are then assessed. It is shown that the mass and damping-like behaviour of the infinite rail are at the origin of the instabilities rather than any modal behaviour of the track. Curve squeal may occur for a single wheel mode even if the rail is represented by a damper, which is a close approximation to the vertical mobility of the track at high frequencies. This forms a third possible mechanism for curve squeal in addition to falling friction and wheel mode coupling. more...
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- 2019
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13. On the target frequency for harvesting energy from track vibrations due to passing trains
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V.G. Cleante, David Thompson, Gianluca Gatti, Michael J. Brennan, Universidade Estadual Paulista (Unesp), Univeristy of Calabria, and University of Southampton
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Ballast ,0209 industrial biotechnology ,Computer science ,Acoustics ,Aerospace Engineering ,Train-induced vibration ,02 engineering and technology ,01 natural sciences ,020901 industrial engineering & automation ,Band-pass filter ,Deflection (engineering) ,0103 physical sciences ,Track vibration ,010301 acoustics ,Trainload frequency ,Civil and Structural Engineering ,Energy harvesting ,Mechanical Engineering ,Subgrade ,Computer Science Applications ,Vibration ,Amplitude ,Control and Systems Engineering ,Signal Processing ,Train - Abstract
Made available in DSpace on 2019-10-06T15:18:13Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-01-01 There is an increasing desire to monitor the structural integrity of railway tracks and the supporting ballast and subgrade. Track vibration has been proposed as a potential energy source to power wireless sensors for this purpose. Vibration-based energy harvesting devices generally exploit resonance, and hence need to be tuned to a particular target frequency. Thus, to harvest energy from the vibrations of a passing train, the spectral content of the track vibration needs to be known. This paper describes a fundamental investigation into the factors that govern this spectral content. A simple model of the train and the track, together with data from five trains passing at four different sites are used in this investigation. It is shown that the deflection under an individual wheel effectively acts as a bandpass filter, restricting the acceleration spectrum of sleeper vibration to low frequencies. The train geometry has an important effect on which specific trainload frequency has the largest response amplitude. For the trains studied, it was found that the 7th trainload frequency had the highest amplitude in four out of the five cases. The physical reasons as to why this trainload frequency is the largest are discussed. Departamento de Engenharia Mecânica Universidade Estadual Paulista (UNESP) Department of Mechanical Energy and Management Engineering Univeristy of Calabria Institute of Sound and Vibration Research University of Southampton Departamento de Engenharia Mecânica Universidade Estadual Paulista (UNESP) more...
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- 2019
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14. Vibration reduction of a high-speed train floor using multiple dynamic vibration absorbers
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David Thompson, You Taiwen, Sun Yu, Dao Gong, Jinsong Zhou, and Chen Jiangxue
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Vibration ,Reduction (complexity) ,Engineering ,Dynamic Vibration Absorber ,business.industry ,Mechanical Engineering ,Acoustics ,education ,Automotive Engineering ,Safety, Risk, Reliability and Quality ,business ,human activities - Abstract
Due to local resonances, high vibration levels of the floor occur frequently in high-speed trains, which have a great negative impact on the ride comfort. A method is presented to control excessive local vibration of the internal floor of a high-speed electric multiple unit train by using multiple dynamic vibration absorbers (DVAs). The possible causes of the high vibration levels of the internal floor are investigated using operational and modal tests. To reduce the vibration, a model of the vehicle body with multiple DVAs is established based on the modal superposition method. The contribution of different modes at the dominant vibration peaks is assessed and targeted. It is found that a strong peak at around 12 Hz is dominated by a single mode, which can be attenuated by using a single DVA, which can be applied outside the car body, such as under-frame equipment. In the frequency region between 30 and 35 Hz several local modes contribute, and can be controlled by using multiple DVAs. Methods are studied to determine the optimal parameters for these DVAs, including location, natural frequency and mass. For a single DVA conventional fixed-point theory is used, whereas for multiple absorbers an optimization method is proposed. Finally, the effect of applying DVA solution is verified in the full vehicle model using frequency responses analysis. The results indicate that the proposed method can effectively reduce the vibration of targeted modes and improve the ride quality considerably in terms of the vertical motion. more...
- Published
- 2021
15. Combining the 2.5D FE-BE method and the TMM method to study the vibro-acoustics of acoustically treated rib-stiffened panels
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Xiaozhen Sheng, David Thompson, Tiesong Deng, Muxiao Li, and Shumin Zhang
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Materials science ,Acoustics and Ultrasonics ,Sound transmission class ,Mechanical Engineering ,Acoustics ,Transfer-matrix method (optics) ,Baffle ,02 engineering and technology ,Condensed Matter Physics ,01 natural sciences ,Finite element method ,symbols.namesake ,020303 mechanical engineering & transports ,Fourier transform ,0203 mechanical engineering ,Mechanics of Materials ,0103 physical sciences ,symbols ,Wavenumber ,Porous medium ,010301 acoustics ,Boundary element method - Abstract
This paper is concerned with the prediction of the vibro-acoustic behavior of rib-stiffened panels treated with multiple layers of porous materials. The acoustically treated rib-stiffened panels are assumed to be uniform and infinitely long in one direction (the longitudinal direction) but the cross-section can have an arbitrary and often complicated shape. Although the two-and-half dimensional structural finite element method (2.5D FEM) and the two-and-half dimensional acoustic boundary element method (2.5D BEM) may be combined to perform the vibro-acoustic prediction, the presence of the multiple layers of acoustic treatment often makes the prediction too time-consuming. More efficient methods are required for such structures and the aim of this paper is to propose such a method. The rib-stiffened panel and the fluid domain containing the incident and reflected sound waves are modelled using 2.5D FEM-BEM while the acoustic treatment layer and the fluid domain containing the transmitted sound waves are dealt with, approximately, using the transfer matrix method (TMM). The coupling of TMM and 2.5D FEM-BEM is formulated in detail. Since the acoustically treated panel is assumed to be flat and baffled, the 2.5D BEM is based on the Rayleigh integral in the wavenumber domain. Meanwhile, the TMM is based on a two-dimensional Fourier transform which implies that the porous layers also extend to cover the baffle; the validity of this assumption is explored. The accuracy and efficiency of the method is compared with a full 2.5D FE-BE method for a homogeneous plate with attached layers of absorbent material. It is shown that the method proposed in this paper can reduce calculation time by about a factor of three compared with the full 2.5D FE-BE method. The proposed method is then applied to study the sound transmission loss (STL) of a typical rib-stiffened panel from a train carriage which is acoustically treated with different porous material layers, demonstrating that the design of the acoustic treatment can have a significant effect on the STL of the panel. more...
- Published
- 2021
16. Investigation of acoustic transmission beneath a railway vehicle by using statistical energy analysis and an equivalent source model
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David Thompson, Giacomo Squicciarini, Juan Giner-Navarro, Martin Rissmann, Francisco D. Denia, Xiaowan Liu, and Hui Li
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0209 industrial biotechnology ,Acoustics ,INGENIERIA MECANICA ,09.- Desarrollar infraestructuras resilientes, promover la industrialización inclusiva y sostenible, y fomentar la innovación ,Aerospace Engineering ,02 engineering and technology ,01 natural sciences ,Under-floor noise ,020901 industrial engineering & automation ,0103 physical sciences ,Sound pressure ,010301 acoustics ,Sound (geography) ,Civil and Structural Engineering ,Statistical energy analysis ,geography ,geography.geographical_feature_category ,SEA ,Mechanical Engineering ,Equivalent source model ,Sound power ,Computer Science Applications ,Power (physics) ,Vibration ,Train noise ,Dipole ,Noise ,Control and Systems Engineering ,Signal Processing ,Geology - Abstract
[EN] An approach is presented for modelling the noise propagation beneath the train floor and this is applied to rolling noise sources. It is assumed that the sound incident on the train floor is made up of a direct and a reverberant component. A combination of two numerical modelling approaches is considered to deal with these: an equivalent source model, to represent the direct component, and statistical energy analysis (SEA) for the reverberant part. In the equivalent source model, the wheel is replaced by monopole and dipole sources, which represent its radial and axial radiation. The rail vertical vibration and the sleepers are replaced by arrays of monopole sources while the rail lateral vibration is replaced by an array of lateral dipoles. The sound power of the rolling noise is obtained by using the TWINS model. In the SEA model, the region beneath the train floor is divided into several volumes and the power input to these subsystems is assumed to be due to the first reflections from the train floor and the ground. The reverberant and direct sound have very similar contributions to the total sound power incident on the train floor although this depends on how the equipment is arranged beneath the train. The modelling approach is verified by comparing the predicted sound pressure levels with laboratory measurements and with field tests., This work has been funded by the China Scholarship Council and the RUN2Rail H2020/Shift2Rail project (Grant agreement No: 777564). The contents of this publication only reflect the authors' views and the Shift2Rail Joint Undertaking is not responsible for any use that may be made of the information contained in the paper. The authors would also like to thank Dr. Hongseok Jeong for his assistance in the laboratory measurements and Metro de Madrid for assistance in the field tests. All data published in this paper are openly available from the University of Southampton repository at 10.5258/SOTON/D1552. more...
- Published
- 2021
17. An investigation into the effects of modelling assumptions on sound power radiated from a high-speed train wheelset
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Gong Cheng, Xiaozhen Sheng, David Thompson, Jian Han, and Yuanpeng He
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Physics ,Acoustics and Ultrasonics ,Mechanical Engineering ,Moving load ,02 engineering and technology ,Mechanics ,Condensed Matter Physics ,Rotation ,Sound power ,01 natural sciences ,Finite element method ,Suspension (motorcycle) ,Axle ,Noise ,020303 mechanical engineering & transports ,0203 mechanical engineering ,Mechanics of Materials ,0103 physical sciences ,010301 acoustics ,Boundary element method - Abstract
In predicting rolling noise from a railway wheelset, some assumptions are usually required to make the calculations less complicated and more efficient. In this study, the effects of some modelling assumptions on the prediction of sound power radiated from a high-speed train wheelset are investigated by using the finite element and boundary element methods. Use is made of the axi-symmetry of the wheelset to allow the solution to be obtained in terms of a Fourier series in the circumferential direction. Compared with a moving-wheel formulation, the moving-roughness approach is shown to be sufficient provided that the wheelset receptance takes into account the effects of rotation and the rail receptance accounts for the effect of the moving load. Wheel/rail coupling should take account of lateral as well as vertical forces; neglect of the lateral interaction may result in significant overestimates of the contribution of the axial modes of the wheelset, and thus the overall wheelset radiated noise. If the rotation of the wheelset is not considered, its radiated noise may be underestimated by up to 3 dB at frequencies above 2000 Hz. If the wheelset suspension is not included, the overall sound power would be overestimated at frequencies below 2000 Hz. Compared with symmetric excitation of the wheelset, assuming incoherent excitations for the left and right wheel/rail contacts will significantly affect the radiated noise in the frequency range below 2000 Hz but has negligible effect on the important region above 2000 Hz. Finally, the contribution from the axle is shown to be significant below 1000 Hz. In terms of overall A-weighted level, the effect of the lateral wheel/rail interaction, the rotation of the wheelset and the inclusion of bearings and axleboxes should not be neglected. more...
- Published
- 2020
18. Using a 2.5D boundary element model to predict the sound distribution on train external surfaces due to rolling noise
- Author
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Francisco D. Denia, David Thompson, Hui Li, Martin Rissmann, Xiaowan Liu, Giacomo Squicciarini, and Juan Giner-Navarro
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Acoustics and Ultrasonics ,Point source ,Acoustics ,INGENIERIA MECANICA ,09.- Desarrollar infraestructuras resilientes, promover la industrialización inclusiva y sostenible, y fomentar la innovación ,Boundary (topology) ,02 engineering and technology ,01 natural sciences ,0203 mechanical engineering ,0103 physical sciences ,2.5D method ,Sound pressure ,010301 acoustics ,Boundary element method ,Train external surfaces ,Mechanical Engineering ,Boundary element model ,Condensed Matter Physics ,Finite element method ,Rolling noise ,Noise ,020303 mechanical engineering & transports ,Mechanics of Materials ,Loudspeaker ,Scale model ,Geology - Abstract
[EN] In order to be able to predict train interior noise, it is first important to calculate the external sound pressure distribution on the floor, sidewalls and roof. This can then be combined with the transmission loss of the train panels to determine the interior noise. Traditional techniques such as the finite element and boundary element (FE/BE) methods in three dimensions (3D) can achieve this result but are computationally very expensive. In this paper, a wavenumber-domain boundary element (2.5D BE) approach is instead adopted to predict the propagation of rolling noise from the wheels, rails and sleepers to the train external surfaces. In the 2.5D models, only the cross-section of the vehicle is represented by using boundary elements, while the third direction is considered in terms of a spectrum of wavenumbers. The rail is treated directly in the wavenumber domain but, to include the wheel, a method of representing point sources in a 2.5D approach is developed. An inverse Fourier transform is applied to obtain the spatial distribution of the sound pressure on the train surfaces. The validity of this approach has been verified by comparison with experimental data. The 2.5D BE method was first used to predict the sound distribution on a 1:5 scale train surfaces due to a point source below the vehicle, and later it was used to predict the sound pressure on a full-scale metro vehicle due to a loudspeaker. Comparisons of predictions with measurements on the scale model and on the metro vehicle showed good agreements. For a point source below the vehicle, the sound pressure levels on the train floor were found to be around 20 dB higher than on the sides, and the sound pressure on the train roof was negligible. The 2.5D BE method was also used to predict the sound pressure on the metro vehicle surfaces in running operation, in which the predicted sound pressure levels on the train external surfaces agreed with measurements to within 3 dB and similar trends were found in terms of spectra and longitudinal distribution of pressure., The work presented in this paper has received funding from China Scholarship Council and the Shift2Rail Joint Undertaking under the European Union's Horizon 2020 research and innovation programme (grant agreement no. 777564). The contents of this publication only reflect the authors' view and the Joint Undertaking is not responsible for any use that may be made of the information contained in the paper. The authors would also like to thank Dr. Hongseok Jeong for his assistance in the laboratory measurements and Metro de Madrid for assistance in the field tests. The authors are grateful to Dr. Xianying Zhang for providing the measured vibration of the 1:5 scale rail. All data published in this paper are openly available from the University of Southampton repository at 10.5258/SOTON/D1483 more...
- Published
- 2020
19. Design, analysis and experimental validation of high static and low dynamic stiffness mounts based on target force curves
- Author
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Sun Yu, Dao Gong, David Thompson, Tian-Chen Yuan, Jinsong Zhou, and You Taiwen
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Damping ratio ,Mechanical equilibrium ,Materials science ,Design analysis ,business.industry ,Applied Mathematics ,Mechanical Engineering ,Stiffness ,Structural engineering ,Dynamic stiffness ,Force curves ,law.invention ,Computer Science::Robotics ,Vibration isolation ,Mechanics of Materials ,Deflection (engineering) ,law ,medicine ,medicine.symptom ,business - Abstract
In order to improve vibration isolation, soft components can be used in engineering applications, but this can lead to excessive static deflection. An ideal vibration isolator should have a high static stiffness to ensure that it has sufficient load carrying capacity; at the same time, it should have a low dynamic stiffness to maximize the vibration isolation frequency range. Recently, high static and low dynamic stiffness (HSLDS) mounts have been increasingly shown to have significant benefits for various engineering applications. This paper proposes a method for designing HSLDS mounts based on target force curves. In the design method, the HSLDS mount is obtained by placing a negative stiffness structure in parallel with a positive stiffness linear spring. The negative stiffness structure is achieved by using a roller-slider curve which can be designed according to the requirements to achieve the target force curve. HSLDS mounts are proposed with nth-order stiffness behavior which are designed using the method presented here. The results show that, compared with lower order HSLDS mounts based on the same static stiffness, higher order HSLDS mounts have lower dynamic stiffness near the equilibrium position. The Average Method is used to analyze the dynamics of a system based on the nth-order HSLDS mounts, and the displacement transmissibility under harmonic excitation is obtained. The effects of different parameters on the transmissibility are studied. The results show that appropriately increasing the damping ratio is beneficial for the isolation performance of the HSLDS mount. Finally, an experimental prototype is designed and manufactured. The proposed design method and the vibration isolation performance of the HSLDS mount are verified by constant-frequency excitation experiments. more...
- Published
- 2020
20. Effect of different typical high speed train pantograph recess configurations on aerodynamic noise
- Author
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Zhiwei Hu, David Thompson, and Hogun Kim
- Subjects
Computer science ,Mechanical Engineering ,Acoustics ,High speed train ,02 engineering and technology ,Aerodynamics ,01 natural sciences ,Physics::Fluid Dynamics ,Cavity flow ,Noise ,020303 mechanical engineering & transports ,0203 mechanical engineering ,0103 physical sciences ,Aeroacoustics ,Physics::Accelerator Physics ,Pantograph ,Train ,010301 acoustics - Abstract
For high-speed trains, the aerodynamic noise becomes an essential consideration in the train design. The pantograph and pantograph recess are recognised as important sources of aerodynamic noise. This paper studies the flow characteristics and noise contributions of three typical high-speed train roof configurations, namely a cavity, a ramped cavity and a flat roof with side insulation plates. The Improved Delayed Detached-Eddy Simulation approach is used for the flow calculations and the Ffowcs Williams & Hawkings aeroacoustic analogy is used for far-field acoustic predictions. Simulations are presented for a simplified train body at 1/10 scale and 300 km/h with these three roof configurations. In each case, two simplified pantographs (one retracted and one raised) are located on the roof. Analysis of the flow fields obtained from numerical simulations clearly shows the influence of the train roof configuration on the flow behaviour, including flow separations, reattachment and vortex shedding, which are potential noise sources. A highly unsteady flow occurs downstream when the train roof has a cavity or ramped cavity due to flow separation at the cavity trailing edge, while vortical flow is generated by the side insulation plates. For the ramped cavity configuration, moderately large pressure fluctuations appear on the cavity outside walls in the upstream region due to unsteady flow from the upstream edge of the plate. The raised pantograph, roof cavity, and ramped cavity are identified as the dominant noise sources. When the retracted pantograph is located in the ramped roof cavity, its noise contribution is less important. Furthermore, the insulation plates also generate tonal components in the noise spectra. Of the three configurations considered, the roof cavity configuration radiates the least noise at the side receiver in terms of A-weighted level. more...
- Published
- 2020
21. Numerical investigation of the effect of cavity flow on high speed train pantograph aerodynamic noise
- Author
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David Thompson, Zhiwei Hu, and Hogun Kim
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Physics ,Leading edge ,010504 meteorology & atmospheric sciences ,Renewable Energy, Sustainability and the Environment ,Turbulence ,Mechanical Engineering ,Acoustics ,Flow (psychology) ,Aeroacoustic analogy ,Aerodynamics ,01 natural sciences ,010305 fluids & plasmas ,Noise ,0103 physical sciences ,Pantograph ,Roof ,0105 earth and related environmental sciences ,Civil and Structural Engineering - Abstract
Reducing train pantograph noise is particularly important. In this paper, the flow behaviour and noise contribution of simplified geometries representing high-speed train pantographs and the roof cavity at 1/10th scale are investigated. The Improved Delayed detached-Eddy Simulation (IDDES) turbulent model is used for the flow field simulation and the Ffowcs Williams & Hawkings aeroacoustic analogy is used for far-field noise prediction. The pantograph recess geometry is simplified to a rectangular cavity and two simplified DSA350 pantographs are included. The effect of the pantograph cavity is studied by comparing the flow behaviour and radiated noise from cases with and without the cavity, and also for different train running directions. When the pantographs are installed in a cavity, the shear layer, separated from the cavity leading edge, interacts with the pantographs, and generates large pressure fluctuations on the pantograph surfaces. In comparison with pantographs installed on a flat train roof, the flow around the pantographs with the cavity has different characteristics in terms of the velocity profile upstream of the pantographs. The study shows that the main noise source is from the panhead of the raised pantograph which produces strong tonal noise and this noise source is affected by the cavity flow. more...
- Published
- 2020
22. Investigation of train-induced vibration and noise from a steel-concrete composite railway bridge using a hybrid finite element-statistical energy analysis method
- Author
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Xiaozhen Li, Quanmin Liu, Peipei Xu, Qingsong Feng, and David Thompson
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Timoshenko beam theory ,Ballast ,Acoustics and Ultrasonics ,business.industry ,Mechanical Engineering ,02 engineering and technology ,Structural engineering ,Condensed Matter Physics ,Span (engineering) ,Track (rail transport) ,01 natural sciences ,Finite element method ,Vibration ,Noise ,020303 mechanical engineering & transports ,0203 mechanical engineering ,Mechanics of Materials ,0103 physical sciences ,business ,010301 acoustics ,Geology ,Statistical energy analysis - Abstract
In this study a hybrid finite element-statistical energy analysis (FE-SEA) method is used to investigate the structure-borne noise of a steel-concrete composite railway bridge. The rail is represented by an infinite Timoshenko beam connected to the sleepers which are regarded as finite Timoshenko beams supported in ballast. The fasteners and ballast are simplified as a series of springs with complex stiffness. This model allows the receptance of the track to be determined. The wheel-rail forces are computed in the frequency domain from the contact-filtered roughness and the receptances of the wheel, track, and contact. The forces transmitted to the bridge are determined by substituting the wheel-rail forces into the equation of motion for the track. This model could also be applied to a slab track mounted on a bridge. A hybrid FE-SEA method is introduced in which FE is used to model the concrete deck and SEA is used to model the steel girders. This enables the computation of the vibration and noise of the composite railway bridge. The proposed method is verified by comparing its predictions with field measurements. The structure-borne noise level of the bridge is found to increase with train speed v by approximately 20lg(v). It is shown that the adjacent spans in a multi-span bridge can be ignored in deriving the bridge-borne noise at receiver points in the middle of the main span, provided that the distance to the track centreline is less than 0.3 times the length of the main span. more...
- Published
- 2020
23. Effect of cavity flow control on high speed train pantograph and roof aerodynamic noise
- Author
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David Thompson, Zhiwei Hu, and Hogun Kim
- Subjects
Acoustics ,Noise reduction ,Computational Mechanics ,Transportation ,02 engineering and technology ,01 natural sciences ,High-speed train ,0203 mechanical engineering ,0103 physical sciences ,Aeroacoustics ,Noise control ,Electrical and Electronic Engineering ,lcsh:TF1-1620 ,010301 acoustics ,Noise barrier ,Physics ,020301 aerospace & aeronautics ,Pantograph ,Cavity flow ,Turbulence ,Mechanical Engineering ,Pantograph recess ,Aeroacoustic analogy ,Aerodynamics ,Computer Science Applications ,Flow velocity ,lcsh:Railroad engineering and operation ,Noise (radio) - Abstract
The pantograph and its recess on the train roof are major aerodynamic noise sources on high-speed trains. Reducing this noise is particularly important because conventional noise barriers usually do not shield the pantograph. However, less attention has been paid to the pantograph recess compared with the pantograph. In this paper, the flow features and noise contribution of two types of noise reduction treatments rounded and chamfered edges are studied for a simplified high-speed train pantograph recess, which is represented as a rectangular cavity and numerically investigated at 1/10 scale. Improved delayed detached-eddy simulations are performed for the near-field turbulent flow simulation, and the Ffowcs Williams and Hawkings aeroacoustic analogy is used for far-field noise prediction. The highly unsteady flow over the cavity is significantly reduced by the cavity edge modifications, and consequently, the noise radiated from the cavity is reduced. Furthermore, effects of the rounded cavity edges on the flow and noise of the pantographs (one raised and one folded) are investigated by comparing the flow features and noise contributions from the cases with and without rounding of the cavity edges. Different train running directions are also considered. Flow analysis shows that the highly unsteady flow within the cavity is reduced by rounding the cavity edges and a slightly lower flow speed occurs around the upper parts of the raised pantograph, whereas the flow velocity in the cavity is slightly increased by the rounding. Higher pressure fluctuations occur on the folded pantograph and the lower parts of the raised pantograph, whereas weaker fluctuations are found on the panhead of the raised pantograph. This study shows that by rounding the cavity edges, a reduction in radiated noise at the side and the top receiver positions can be achieved. Noise reductions in the other directions can also be found. more...
- Published
- 2020
24. Wave interference in railway track due to multiple wheels
- Author
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Qi Li, Simian Lei, Yaojun Ge, and David Thompson
- Subjects
Timoshenko beam theory ,Physics ,Total internal reflection ,Acoustics and Ultrasonics ,Mechanical Engineering ,Residue theorem ,Mathematical analysis ,Phase (waves) ,Resonance ,Condensed Matter Physics ,Track (rail transport) ,Noise (electronics) ,Power (physics) ,Mechanics of Materials - Abstract
A resonance pattern at frequencies from around 400 Hz to 1000 Hz has often been observed from measured rail accelerations. Such resonances are important for rail noise and corrugation. Although this pattern has been reported and discussed in several papers in terms of wave reflections between multiple wheels, the aim of this study is to investigate the generation mechanism of this resonance phenomenon in detail, and to give both mathematical and physical insight. An infinite Timoshenko beam with continuous supports is adopted for modeling the track system, and the point and transfer receptances of the rail for a stationary harmonic excitation are explicitly obtained by the residue theorem. A frequency-domain method is then presented to calculate the power spectral densities of the wheel-track coupled system responses to stochastic irregularities with the moving irregularity model. It is found that the multiple peaks can be explained by using the phase closure principle. Moreover, total reflection between the two wheels may occur at around 700 Hz, which results in the highest peak in the response. more...
- Published
- 2022
- Full Text
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25. Reduction of aerodynamic noise from square bars by introducing spanwise waviness
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David Thompson, Zhiwei Hu, Vincent Jurdic, and Xiaowan Liu
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Physics ,Acoustics and Ultrasonics ,Waviness ,Bar (music) ,Mechanical Engineering ,Noise reduction ,Mechanics ,Wake ,Condensed Matter Physics ,Vortex shedding ,01 natural sciences ,010305 fluids & plasmas ,Vortex ,Physics::Fluid Dynamics ,Amplitude ,Mechanics of Materials ,0103 physical sciences ,010301 acoustics ,Noise (radio) - Abstract
This paper presents an investigation, using both numerical and experimental methods, of the application of spanwise waviness to reduce aerodynamic noise from square bars. The numerical simulations are performed using the Delayed Detached-Eddy Simulation approach to obtain the near-field unsteady flow properties, which are then used to calculate the equivalent source terms in the Ffowcs Williams-Hawkings equation for far-field noise prediction. For a straight square bar in cross-flow, which produces strong tonal noise associated with the vortex shedding, a benchmark study shows good agreement between numerical simulations and measurements in terms of far-field noise spectra. Waviness is then introduced along the bar span and the influence of the amplitude and wavelength of the waviness is studied. When the wave amplitude is nearly half the bar width, a large noise reduction of as much as 30 dB is found from both numerical simulations and measurements, including a 10 dB reduction in the broadband level. The influence of the wavelength is much smaller. Analysis of the flow features show that, with increased wave amplitudes, the spanwise flow becomes significant and strong crossflow vortices develop in the near wake which effectively suppress the primary vortex shedding. This reduces the noise level significantly, especially the tonal noise associated with the vortex shedding. more...
- Published
- 2018
- Full Text
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26. Numerical assessment of CaOx renal calculi development in space using PBE coupled to urinary flow and species transport
- Author
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Mohammad Kassemi, David Thompson, and Elise Griffin
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Fluid Flow and Transfer Processes ,business.industry ,Mechanical Engineering ,030232 urology & nephrology ,Calcium oxalate ,Population balance equation ,Numerical assessment ,Nephron ,Mechanics ,030204 cardiovascular system & hematology ,Computational fluid dynamics ,Condensed Matter Physics ,Oxalate ,03 medical and health sciences ,chemistry.chemical_compound ,0302 clinical medicine ,medicine.anatomical_structure ,chemistry ,Volume fraction ,medicine ,business ,Urinary flow - Abstract
Recently collected astronaut data indicate that space travel has a profound impact on the nephron biochemistry with increasing risk of renal stone development during long duration missions. In this paper, a Population Balance Equation (PBE) model is developed to compute the size distribution of nucleating, growing and agglomerating calcium oxalate (CaOx) renal calculi as they are transported through the different nephron sections. The PBE model is coupled to a Computational Fluid Dynamics (CFD) model that solves for the steady state flow of urine, the concentrations of ionic species, calcium and oxalate, and the transport of the crystals along the nephron using a two-phase interpenetrating Eulerian framework. Simulation are performed based on measured averaged post-flight astronaut 24 h. urine biochemistry to assess the size distribution of the CaOx crystals developed under microgravity conditions. The important effects of agglomeration on the aggregate size distributions and the impact of wall friction on the CaOx volume fraction distributions are carefully examined. Simulations are also presented to indicate the important mixing effect that the cascading nephron configuration may induce during the passage of the particles through the various nephron subsections. Parametric numerical predictions for the microgravity astronaut biochemistry are compared to those for normal and stone-former subjects on Earth. It is concluded that under nominal conditions the largest calcium oxalate aggregate sizes developed in space will be still below the critical range for problematic stone development. However, computations also indicate that in microgravity the highest CaOx volume fractions occur next to the tubule and duct walls. This suggests that there may be an increased potential for wall adhesion and possibility of evolution towards critical stone sizes. more...
- Published
- 2018
- Full Text
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27. A 2.5D finite element and boundary element model for the ground vibration from trains in tunnels and validation using measurement data
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Evangelos Ntotsios, Daniel Lurcock, Qiyun Jin, David Thompson, and Martin Toward
- Subjects
Acoustics and Ultrasonics ,business.industry ,Continuous modelling ,Mechanical Engineering ,0211 other engineering and technologies ,02 engineering and technology ,Structural engineering ,Condensed Matter Physics ,01 natural sciences ,Finite element method ,Vibration ,Axle ,Mechanics of Materials ,0103 physical sciences ,Train ,Invariant (mathematics) ,business ,Material properties ,010301 acoustics ,Boundary element method ,Geology ,021101 geological & geomatics engineering - Abstract
A numerical model is presented for the ground-borne vibration produced by trains running in tunnels. The model makes use of the assumption that the geometry and material properties are invariant in the axial direction. It is based on the so-called two-and-a-half dimensional (2.5D) coupled Finite Element and Boundary Element methodology, in which a two-dimensional cross-section is discretised into finite elements and boundary elements and the third dimension is represented by a Fourier transform over wavenumbers. The model is applied to a particular case of a metro line built with a cast-iron tunnel lining. An equivalent continuous model of the tunnel is developed to allow it to be readily implemented in the 2.5D framework. The tunnel structure and the track are modelled using solid and beam finite elements while the ground is modelled using boundary elements. The 2.5D track-tunnel-ground model is coupled with a train consisting of several vehicles, which are represented by multi-body models. The response caused by the passage of a train is calculated as the sum of the dynamic component, excited by the combined rail and wheel roughness, and the quasi-static component, induced by the constant moving axle loads. Field measurements have been carried out to provide experimental validation of the model. These include measurements of the vibration of the rail, the tunnel invert and the tunnel wall. In addition, simultaneous measurements were made on the ground surface above the tunnel. Rail roughness and track characterisation measurements were also made. The prediction results are compared with measured vibration obtained during train passages, with good agreement. more...
- Published
- 2018
- Full Text
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28. Dynamic response of a curved railway track subjected to harmonic loads based on the periodic structure theory
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David Thompson, Linlin Du, Weifeng Liu, and Weining Liu
- Subjects
Physics ,020303 mechanical engineering & transports ,0203 mechanical engineering ,Structural load ,business.industry ,Mechanical Engineering ,Harmonic load ,Harmonic ,020302 automobile design & engineering ,02 engineering and technology ,Structural engineering ,Track (rail transport) ,business - Abstract
In this study, the authors have analysed the dynamic response of a curved railway track that is subjected to moving and non-moving harmonic loads. The track is considered as a curved Timoshenko beam supported by periodically spaced discrete fasteners. The displacement and rotation of the curved rail are expressed as the superposition of track modes in the frequency domain. Periodic structure theory is applied to the equations of motion of the curved track, allowing the dynamic response of the track to be calculated efficiently in a reference cell. The effect of the stiffness and damping of the fasteners, the fastener spacing and the radius of curvature on the mobility and decay rate of the track are analysed for non-moving loads on the rail head. The vibration of the rail due to moving loads is also discussed. It is found that the dynamic response of a curved rail with a large radius has the same characteristics as that of a straight track. However, the dynamic response of the track is significantly affected when the radius of curvature becomes small. The radius affects the mobility; it also has an effect on the track decay rate below 2000 Hz and the velocity of the rail in the vertical direction when the radius is smaller than about 15 m and for the lateral direction when it is less than about 30 m. Moreover, the curvature has a significant influence on the vertical/lateral cross mobility, the magnitude of which increases as the radius is reduced. When the radius is larger than 10 m, the amplitude of the lateral vibration under a moving vertical load and the vertical response to a moving lateral load are inversely proportional to the radius. more...
- Published
- 2018
- Full Text
- View/download PDF
29. A two-and-half dimensional finite element/boundary element model for predicting the vibro-acoustic behaviour of panels with poro-elastic media
- Author
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Xiaozhen Sheng, David Thompson, Hongseok Jeong, and Tiesong Deng
- Subjects
Materials science ,Acoustics and Ultrasonics ,Biot number ,Sound transmission class ,Mechanical Engineering ,Linear system ,02 engineering and technology ,Mechanics ,Condensed Matter Physics ,01 natural sciences ,Finite element method ,Soundproofing ,020303 mechanical engineering & transports ,0203 mechanical engineering ,Mechanics of Materials ,0103 physical sciences ,Elasticity (economics) ,Porous medium ,010301 acoustics ,Boundary element method - Abstract
Solid panels with additional poro-elastic materials are widely used in engineering, mainly for sound insulation. In many cases, the panels are constructed in such a way that they can be idealised to be infinitely long and uniform in one direction, forming a so-called two-and-a-half dimensional (2.5D) structure. Although the 2.5D finite element and boundary element methods (FEM-BEM) are particularly suitable for predicting the vibro-acoustic behaviour of such structures, up to now the presence of poro-elastic media have not been adequately considered. In this paper a 2.5D FE-BE vibro-acoustic model is presented which accounts for solids, fluids and poro-elastic media. The poro-elastic media are modelled using the 2.5D FE approach based on the mixed displacement-pressure formulation of Biot's theory. The solids are also modelled using the 2.5D FE method but based on the linear theory of elasticity. The internal fluids are modelled using the 2.5D FE method as well. For a flat panel, the external fluid on both sides of the panel can be modelled using the 2.5D BE method based on the Rayleigh integral. The coupling between the various sub-models is derived in detail. The accuracy of the model is demonstrated by applying it to simple multi-layered structures for which solutions can be produced using other well-established methods. It is demonstrated that the elasticity of the solid frame of a porous medium has a great influence on the vibro-acoustics of a structure containing the porous material. The method is then applied to investigate the sound transmission loss (STL) of a typical railway vehicle floor structure. Results show that STL can be greatly improved by proper arrangement of porous material layers between the interior wooden floor and the outer extrusion; however, the load bearing supporting beams may significantly reduce the benefit of the porous material layers. more...
- Published
- 2021
- Full Text
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30. Wavenumber–domain separation of rail contribution to pass-by noise
- Author
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Ines Lopez Arteaga, Luca Manzari, David Thompson, Leping Feng, Elias Zea, Giacomo Squicciarini, and Dynamics and Control
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Engineering ,Microphone array ,Acoustics and Ultrasonics ,Railway ,Acoustics ,Separation (aeronautics) ,Strömningsmekanik och akustik ,Wavenumber–domain ,02 engineering and technology ,Noise separation ,01 natural sciences ,Domain (software engineering) ,0203 mechanical engineering ,0103 physical sciences ,Electronic engineering ,Wavenumber ,010301 acoustics ,Railway noise ,Fluid Mechanics and Acoustics ,business.industry ,Mechanical Engineering ,Condensed Matter Physics ,ComputingMilieux_GENERAL ,Noise ,020303 mechanical engineering & transports ,Mechanics of Materials ,Train ,business - Abstract
In order to counteract the problem of railway noise and its environmental impact, passing trains in Europe must be tested in accordance to a noise legislation that demands the quantification of the noise generated by the vehicle alone. However, for frequencies between about 500 Hz and 1600 Hz, it has been found that a significant part of the measured noise is generated by the rail, which behaves like a distributed source and radiates plane waves as a result of the contact with the train's wheels. Thus the need arises for separating the rail contribution to the pass-by noise in that particular frequency range. To this end, the present paper introduces a wavenumber–domain filtering technique, referred to as wave signature extraction, which requires a line microphone array parallel to the rail, and two accelerometers on the rail in the vertical and lateral direction. The novel contributions of this research are: (i) the introduction and application of wavenumber (or plane–wave) filters to pass-by data measured with a microphone array located in the near-field of the rail, and (ii) the design of such filters without prior information of the structural properties of the rail. The latter is achieved by recording the array pressure, as well as the rail vibrations with the accelerometers, before and after the train pass-by. The performance of the proposed method is investigated with a set of pass-by measurements performed in Germany. The results seem to be promising when compared to reference data from TWINS, and the largest discrepancies occur above 1600 Hz and are attributed to plane waves radiated by the rail that so far have not been accounted for in the design of the filters. QC 20170801 Roll2Rail more...
- Published
- 2017
- Full Text
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31. Atomic layer deposition of Y-stabilized ZrO2 for advanced DRAM capacitors
- Author
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Chandreswar Mahata, Bo Eun Park, Wan Joo Maeng, Chang Wan Lee, Han-Bo-Ram Lee, Il Kwon Oh, David Thompson, and Hyungjun Kim
- Subjects
Materials science ,Band gap ,Hardware_PERFORMANCEANDRELIABILITY ,02 engineering and technology ,Dielectric ,01 natural sciences ,Capacitance ,law.invention ,Atomic layer deposition ,Hardware_GENERAL ,law ,0103 physical sciences ,Hardware_INTEGRATEDCIRCUITS ,Materials Chemistry ,Leakage (electronics) ,010302 applied physics ,Dynamic random-access memory ,Hardware_MEMORYSTRUCTURES ,business.industry ,Mechanical Engineering ,Metals and Alloys ,021001 nanoscience & nanotechnology ,Capacitor ,Mechanics of Materials ,Optoelectronics ,0210 nano-technology ,business ,Dram - Abstract
With accelerated shrinking of integrated circuit, the fabrication of metal-insulator-metal (MIM) capacitors having a high capacitance density and low leakage current for dynamic random access memory (DRAM) has become a challenge. In this study, we investigated Y-stabilized ZrO2 as a novel high-k material for DRAM capacitors. We used atomic layer deposition (ALD) to produce Y-stabilized ZrO2; this technique enables easy control of the Y concentration by changing the ratio of ZrO2 to Y2O3 ALD cycles. This technique is suitable for future DRAM capacitors, as it provides superior thickness controllability and conformality. Y doping into ZrO2 increases the oxygen vacancy content in the films and transforms the ZrO2 crystal structure from monoclinic to cubic. As a result, the dielectric constant is significantly increased from 19.1 to 30.2. Moreover, Y doping shifts the defect level into the conduction band rather than the energy bandgap, resulting in about 60 times lower leakage current density for Y-doped ZrO2 compared to undoped ZrO2. It is notable that the dielectric properties and the leakage current density are simultaneously enhanced, indicating that Y-doped ZrO2 is a promising candidate to satisfy the requirements of future DRAM capacitors. more...
- Published
- 2017
- Full Text
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32. Prediction of rail and bridge noise arising from concrete railway viaducts by using a multilayer rail fastener model and a wavenumber domain method
- Author
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Qi Li and David Thompson
- Subjects
Engineering ,Urban rail transit ,business.product_category ,business.industry ,Mechanical Engineering ,02 engineering and technology ,Structural engineering ,Physics::Classical Physics ,01 natural sciences ,Fastener ,Bridge (nautical) ,Domain (software engineering) ,Vibration ,Noise ,020303 mechanical engineering & transports ,0203 mechanical engineering ,0103 physical sciences ,Wavenumber ,business ,010301 acoustics - Abstract
Concrete viaducts are an important part of urban rail transit systems but they produce considerable noise, thereby affecting the communities living nearby. The vibration generated at the wheel–rail interface is transmitted along the rail and also onto the bridge; hence, noise is radiated from both the rail and the bridge. To facilitate noise prediction, it is desirable to develop a model that takes into account the generation and transmission of vibration in the train–track–bridge system. The vibration and the associated noise of the track–bridge system are computed with a unified vibroacoustic model using a wavenumber domain finite element and boundary element method. An important aspect to note is the frequency-dependent stiffness of a typical rail fastener utilized on bridges due to the resonance of the baseplate between the two rubber pads. In this study, to allow for this effect, a multilayer fastener model is proposed. The proposed procedure is applied to a viaduct with a U-shaped section and compared with field measurements during the passage of trains. The elastic modulus and damping of the rubber pads and the equivalent loss factor of the rail are chosen by fitting the calculated track decay rates to those estimated from the measured rail accelerations under train passages. The wheel–rail combined roughness is also derived from the measured rail vibration. A comparison is then made between the simulated and measured bridge vibration to verify the proposed method as well as the parameters used in the track–bridge system. The predicted noise levels are also compared with the measured results. The effects of the fastener model, fastener stiffness, bridge damping, and interference between multiple wheels are then discussed. It has been found that the bridge noise has a non-negligible effect on the total A-weighted noise levels in the region beneath the bridge and up to 30 m away from the track. more...
- Published
- 2017
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33. A mixed space-time and wavenumber-frequency domain procedure for modelling ground vibration from surface railway tracks
- Author
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Samuel Koroma, Mohammed Hussein, David Thompson, and Evangelos Ntotsios
- Subjects
Engineering ,Acoustics and Ultrasonics ,business.industry ,Mechanical Engineering ,Mathematical analysis ,0211 other engineering and technologies ,02 engineering and technology ,Condensed Matter Physics ,Track (rail transport) ,Finite element method ,Domain (software engineering) ,Vibration ,020303 mechanical engineering & transports ,0203 mechanical engineering ,Mechanics of Materials ,Control theory ,Frequency domain ,Wavenumber ,Time domain ,business ,Boundary element method ,021101 geological & geomatics engineering - Abstract
This paper presents a methodology for studying ground vibration in which the railway track is modelled in the space-time domain using the finite element method (FEM) and, for faster computation, discretisation of the ground using either FEM or the boundary element method (BEM) is avoided by modelling it in the wavenumber-frequency domain. The railway track is coupled to the ground through a series of rectangular strips located at the surface of the ground; their vertical interaction is described by a frequency-dependent dynamic stiffness matrix whose elements are represented by discrete lumped parameter models. The effectiveness of this approach is assessed firstly through frequency domain analysis using as excitation a stationary harmonic load applied on the rail. The interaction forces at the ballast/ground interface are calculated using the FE track model in the space-time domain, transformed to the wavenumber domain, and used as input to the ground model for calculating vibration in the free field. Additionally, time domain simulations are also performed with the inclusion of nonlinear track parameters. Results are presented for the coupled track/ground model in terms of time histories and frequency spectra for the track vibration, interaction forces and free-field ground vibration. For the linear track model, the results from the mixed formulation are in excellent agreement with those from a semi-analytical model formulated in the wavenumber-frequency domain, particularly in the vicinity of the loading point. The accuracy of the mixed formulation away from the excitation point depends strongly on the inclusion of through-ground coupling in the lumped parameter model, which has been found to be necessary for both track dynamics and ground vibration predictions. more...
- Published
- 2017
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34. The effects of ballast on the sound radiation from railway track
- Author
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David Thompson, Giacomo Squicciarini, Xianying Zhang, and Hongseok Jeong
- Subjects
Ballast ,Engineering ,Absorption (acoustics) ,Acoustics and Ultrasonics ,business.industry ,Mechanical Engineering ,Full scale ,02 engineering and technology ,Structural engineering ,Condensed Matter Physics ,Scale factor ,Track (rail transport) ,01 natural sciences ,Vibration ,Noise ,020303 mechanical engineering & transports ,0203 mechanical engineering ,Mechanics of Materials ,0103 physical sciences ,business ,010301 acoustics ,Scale model - Abstract
In a conventional railway track, the rails are laid on sleepers, usually made of concrete, which are supported by a layer of coarse stones known as ballast. This paper focuses on quantifying the influence that the ballast has on the noise produced by the vibration of the track, particularly on the rail and sleeper radiation ratios. A one-fifth scale model of a railway track has been used to conduct acoustic and vibration measurements. This includes reduced-scale ballast that has been produced with stone sizes in the correct proportions. Two different scaling factors (1:√5 and 1:5) have been adopted for the stone sizes in an attempt to reproduce approximately the acoustic properties of full-scale ballast. It is shown that, although a scale factor of 1:√5 gives a better scaling of the acoustic properties, the stones scaled at 1:5 also give acceptable results. The flow resistivity and porosity of this ballast sample have been measured. These have been used in a local reaction model based on the Johnson-Allard formulation to predict the ballast absorption, showing good agreement with measurements of the absorption coefficient. The effects of the presence of the ballast on the noise radiation from a reduced-scale steel rail and concrete sleeper have been investigated experimentally with the ballast located on a rigid foundation. Comparisons are made with the corresponding numerical predictions obtained by using the boundary element method, in which the ballast is represented by a surface impedance. Additionally the finite element method has been used in which the porous medium is considered as an equivalent fluid. From these results it is shown that the extended reaction model gives better agreement with the measurements. Finally, the effects of the ballast vibration on the sleeper radiation have also been investigated for a case of three sleepers embedded in ballast. The ballast vibration is shown to increase the sound radiation by between 1 and 4.5 dB for frequencies between 20 and 300 Hz at full scale whereas at higher frequencies the effect is negligible. more...
- Published
- 2017
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- View/download PDF
35. The flow and flow-induced noise behaviour of a simplified high-speed train bogie in the cavity with and without a fairing
- Author
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J.Y. Zhu, David Thompson, and Z.W. Hu
- Subjects
Engineering ,business.industry ,Mechanical Engineering ,Flow (psychology) ,High speed train ,Context (language use) ,02 engineering and technology ,Structural engineering ,Aerodynamics ,01 natural sciences ,Bogie ,Noise ,020303 mechanical engineering & transports ,0203 mechanical engineering ,0103 physical sciences ,Train ,business ,010301 acoustics - Abstract
Aerodynamic noise is a significant source for high-speed trains but its prediction in an industrial context is difficult to achieve. In this article, the flow and aerodynamic noise behaviour of a simplified high-speed train bogie at scale 1:10 are studied through numerical simulations. The bogie is situated in a cavity beneath the train and the influence of a bogie fairing on the flow and flow-induced noise that developed around the bogie area is investigated. A two-stage hybrid method is used, which combines the computational fluid dynamics and an acoustic analogy. The near-field unsteady flow is obtained by solving the unsteady three-dimensional Navier–Stokes equations numerically using delayed detached-eddy simulation, and the data are utilised to predict the far-field noise based on the Ffowcs Williams–Hawkings acoustic analogy. Results show that when the bogie is located inside the bogie cavity, the shear layer developed from the leading edges of the cavity interacts strongly with the flow separated from the upstream components of the bogie and the cavity walls. Therefore, a highly turbulent flow is generated within the bogie cavity due to the strong flow impingements and flow recirculations occurring there. For the case without the fairing, the surface shape discontinuity in the bogie cavity along the carbody sidewalls generates strong flow unsteadiness around these regions. When the fairing is mounted in front of the bogie cavity, the flow interactions between the bogie cavity and the outer region are reduced and the development of turbulence outside the fairing is greatly weakened. Based on the predictions of the noise radiated to the trackside using a permeable data surface parallel to the carbody sidewall, it has been found that the bogie fairing is effective in reducing the noise generated in most of the frequency range, and a noise reduction of around 5 dB is achieved in the farfield for the current model case. more...
- Published
- 2017
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- View/download PDF
36. An engineering model for the prediction of the sound radiation from a railway track
- Author
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David Thompson, Giacomo Squicciarini, Xianying Zhang, and Erika Quaranta
- Subjects
Ballast ,geography ,Absorption (acoustics) ,geography.geographical_feature_category ,Acoustics and Ultrasonics ,Mechanical Engineering ,Acoustics ,02 engineering and technology ,Radiation ,Condensed Matter Physics ,Sound power ,Track (rail transport) ,01 natural sciences ,Noise ,020303 mechanical engineering & transports ,0203 mechanical engineering ,Mechanics of Materials ,0103 physical sciences ,010301 acoustics ,Boundary element method ,Sound (geography) ,Geology - Abstract
Models for predicting railway rolling noise such as TWINS are well-established and have been validated against field measurements. However, there are still some areas where improvements are required. In particular, the radiation from the rail is based on a model of a rail in free space whereas in reality the rail is located close to the ground; there are also limitations in the existing model for the sound radiation from the sleepers. Besides, the influence of the ballast absorption on the sound power radiated by the track is neglected. This paper draws on recent research into the effects of the proximity of the rail and sleeper to an absorptive ground on their sound radiation, based on the boundary element method. In reality, the rail is located above the ballast over part of its length, and attached periodically to the concrete sleepers elsewhere. The sound radiation of the rail for those two situations can be predicted using the 2D boundary element method. In order to obtain a realistic rail radiation model for engineering applications, a method to combine those two results is proposed and the resulting average rail radiation is verified by using a 3D boundary element model. An improved sleeper radiation model is also proposed and verified using the 3D boundary element model. These new engineering models for the rail and sleeper radiation have been used together with TWINS to predict the sound radiation from operational tracks and the results have been compared with field measurements. Compared with the TWINS model, the rail radiation is found to be increased below 300 Hz, but decreased above 1 kHz; the sound radiation from the sleeper is reduced compared with the TWINS model below 600 Hz. more...
- Published
- 2019
37. Analysis of the consistency of the Sperling index for rail vehicles based on different algorithms
- Author
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Dao Gong, Sun Yu, Jinsong Zhou, David Thompson, Wenjing Sun, and Chenxin Deng
- Subjects
Measure (data warehouse) ,Engineering ,Index (economics) ,business.industry ,Mechanical Engineering ,education ,Vibration ,Mechanical vibration ,Control theory ,Consistency (statistics) ,Frequency domain ,Automotive Engineering ,Safety, Risk, Reliability and Quality ,business ,human activities - Abstract
Ride comfort indices are used to evaluate the vibration of rail vehicles and to measure the discomfort of passengers. Among the various ride comfort indices, the Sperling index is widely used in China and other countries. However, there are several different methods for determining the Sperling index from dynamic simulations and performance measurements of rail vehicles, and the results obtained by different algorithms are inconsistent.It is therefore difficult to make an accurate evaluation with the different calculation results. In this paper, a comparison is made between algorithms based on time domain and frequency domain analysis and using the second and third powers of the acceleration.The different algorithms are then summarized into a unified equation, and the consistency of the results is analyzed by this equation. It is found that only the r.m.s-based algorithm in the time or frequency domain is stable when analysis is carried out over different sample times. The time-frequency consistency of the r.m.s-based algorithms is verified by Parseval’s theorem and using calculation results from time domain simulations. more...
- Published
- 2019
38. Wheel–rail impact loads and noise generated at railway crossings – Influence of vehicle speed and crossing dip angle
- Author
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David Thompson, Peter Torstensson, Jens C. O. Nielsen, Björn Pålsson, Giacomo Squicciarini, and M. Krüger
- Subjects
Acoustics and Ultrasonics ,business.industry ,Mechanical Engineering ,Magnetic dip ,02 engineering and technology ,Structural engineering ,Condensed Matter Physics ,Track (rail transport) ,Physics::Classical Physics ,01 natural sciences ,Computer Science::Robotics ,Vehicle engineering ,Noise ,020303 mechanical engineering & transports ,0203 mechanical engineering ,Mechanics of Materials ,0103 physical sciences ,Trajectory ,Time domain ,business ,Sound pressure ,010301 acoustics ,Geology ,Beam (structure) - Abstract
Wheel–rail impact loads and noise at railway crossings are calculated by applying a hybrid prediction model. It combines the simulation of non-linear vertical dynamic vehicle‒track interaction in the time domain and the prediction of sound pressure level using a linear frequency-domain model. The two models are coupled based on the concept of an equivalent roughness spectrum. The time-domain model uses moving Green's functions for the linear vehicle and track models, accounting for wheel structural flexibility and a discretely supported rail with spatially-varying beam properties, and a non-Hertzian wheel–rail contact model. Three-dimensional surface geometry of the wheel and crossing is accounted for in the solution of the wheel–rail contact. The hybrid model is compared against field measurements and is demonstrated by investigating the influence of vehicle speed and crossing geometry on the radiated impact noise. Based on simulation results, it is concluded that the impact loads and noise can be mitigated by reducing the effective dip angle at the crossing, which is determined by the vertical trajectory of the wheel when making the transition between wing rail and crossing nose. more...
- Published
- 2019
39. Application of a wavenumber domain numerical method to the prediction of the radiation efficiency and sound transmission of complex extruded panels
- Author
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David Thompson, Jungsoo Ryue, Hyungjun Kim, and Angela D. Müller
- Subjects
Materials science ,Acoustics and Ultrasonics ,Sound transmission class ,Mechanical Engineering ,Acoustics ,Numerical analysis ,Condensed Matter Physics ,Finite element method ,Window function ,Antenna efficiency ,Mechanics of Materials ,Wavenumber ,Waveguide (acoustics) ,Boundary element method - Abstract
Complex-shaped aluminium panels are 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 in predicting their performance at higher frequencies. Where the cross-sectional properties of the panels are constant in one direction, which is the case for extruded panels, wavenumber domain numerical analysis can be applied and this becomes particularly suitable for panels with complex cross-sectional geometries. Because they are based on a two-dimensional model, these methods can reduce the computational cost compared with other numerical methods using full three-dimensional models, while nevertheless including three-dimensional effects. In this paper, a coupled waveguide finite element and boundary element method is applied to predict the radiation efficiency and sound transmission of a double-layered aluminium extruded panel from a train carriage floor. The results are interpreted in the wavenumber domain from which the contributions of different types of waves can be identified. In the calculations, the air cavities between top and bottom panels are considered to examine their contributions to the vibro-acoustic behaviour of the panel. The predicted results are compared with measured ones obtained using a finite length panel. To reflect the finite length of the actual panel used in the measurement, spatial window functions are applied to the sound transmission through the infinitely long panel, giving improved agreement with the measurements. more...
- Published
- 2019
40. Eulerian models of the rotating flexible wheelset for high frequency railway dynamics
- Author
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Juan Monterde, Juan Giner-Navarro, Luis Baeza, and David Thompson
- Subjects
Physics ,Acoustics and Ultrasonics ,Mechanical Engineering ,Mathematical analysis ,Rotational symmetry ,Eulerian path ,Basis function ,02 engineering and technology ,Condensed Matter Physics ,01 natural sciences ,Finite element method ,symbols.namesake ,020303 mechanical engineering & transports ,0203 mechanical engineering ,Mechanics of Materials ,Normal mode ,0103 physical sciences ,symbols ,Solid of revolution ,Constant angular velocity ,010301 acoustics ,Campbell diagram - Abstract
In this paper three formulations based on an Eulerian approach are presented to obtain the dynamic response of an elastic solid of revolution, which rotates around its main axis at constant angular velocity. The formulations are especially suitable for the study of the interaction of a solid with a non-rotating structure, such as occurs in the coupled dynamics of a railway wheelset with the track. With respect to previous publications that may adopt similar hypotheses, this paper proposes more compact formulations and eliminates certain numerical problems associated with the presence of second-order derivatives with respect to the spatial coordinates. Three different models are developed depending the basis function that represents the displacements associated with the deformation; these basis functions are: (1) the shape functions that are used in the three dimensional finite element (FE) method; (2) the undamped mode shapes of the solid; (3) the shape functions that are adopted in the axisymmetric FE approach. Comparisons are shown of calculations carried out using these models. These show the existence of modal veering when analysing the Campbell diagram for a railway wheel. more...
- Published
- 2019
41. A model of a discretely supported railway track based on a 2.5D finite element approach
- Author
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Jungsoo Ryue, Dimitrios Kostovasilis, David Thompson, Qi Li, Martin Toward, Xianying Zhang, and Giacomo Squicciarini
- Subjects
Coupling ,Ballast ,Acoustics and Ultrasonics ,Field (physics) ,business.industry ,Computer science ,Mechanical Engineering ,02 engineering and technology ,Structural engineering ,Condensed Matter Physics ,Track (rail transport) ,Physics::Classical Physics ,01 natural sciences ,Vibration ,Noise ,Transverse plane ,020303 mechanical engineering & transports ,0203 mechanical engineering ,Mechanics of Materials ,0103 physical sciences ,Point (geometry) ,business ,010301 acoustics - Abstract
The dynamic properties of a railway track are important for both the generation of rolling noise and the development of rail corrugation. A conventional track consists of long rails mounted periodically on transverse sleepers and supported in ballast. In order to improve the predictions of the noise and vibration of the track, a model of a discretely supported track is proposed based on the so-called 2.5 dimensional (2.5D) finite element approach, which is used to model an infinite free rail. This is coupled to a finite number of sleepers, by means of an array of springs representing each rail pad, using a receptance coupling method. The sleepers are represented by flexible beams, supported on an elastic foundation. Results are presented in terms of the point mobility and track decay rate and these are compared with the corresponding field measurements for two tracks, one with soft rail pads and one with stiff rail pads. Very good agreement is found between the predictions and the measurement results, especially for the track with soft rail pads. The flexible sleeper model is shown to give improved results compared with a rigid mass model, especially for the track with stiff rail pads. more...
- Published
- 2019
42. Modelling train-induced vibration of structures using a mixed-frame-of-reference approach
- Author
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Lars Vabbersgaard Andersen, Evangelos Ntotsios, David Thompson, and Paulius Bucinskas
- Subjects
Coupling ,Traverse ,Acoustics and Ultrasonics ,Computer science ,Mechanical Engineering ,02 engineering and technology ,Condensed Matter Physics ,01 natural sciences ,Frame of reference ,Finite element method ,Vibration ,020303 mechanical engineering & transports ,0203 mechanical engineering ,Mechanics of Materials ,Control theory ,Simple (abstract algebra) ,Moving frame ,Soil structure interaction ,0103 physical sciences ,010301 acoustics - Abstract
A novel computational modelling approach for prediction of environmental vibration is introduced. The model is formulated in both moving and fixed frames of reference, with a mixed frame of reference formulation introduced to couple the two frames of reference. The resulting system is able to model a vehicle travelling on an infinite railway track, formulated in a moving frame of reference, interacting via the soil with a structure (i.e. building), formulated in a fixed frame of reference. The method utilizes a semi-analytical soil model with the structures modelled using three-dimensional finite elements. Two solution procedures of the full system are proposed: partial coupling, where some secondary effects from reflected waves propagating through soil are disregarded, and full coupling, where the vehicle–track–soil–structure is modelled as a fully coupled system. Both proposed solution procedures offer a one-step approach for solving the whole system in the frequency–spatial domain. The usage of the model is demonstrated in two example cases: one analysing a simple building structure near a railway track, using the partial coupling solution procedure, and another one analysing the behaviour of a vehicle model traversing over a rigid block embedded inside the soil, using the full coupling solution procedure. The introduced modelling approach offers a computationally efficient solution procedure, at the same time being applicable to a wide array of application cases. more...
- Published
- 2021
- Full Text
- View/download PDF
43. Flow behaviour and aeroacoustic characteristics of a simplified high-speed train bogie
- Author
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Zhiwei Hu, Jianyue Zhu, and David Thompson
- Subjects
Engineering ,business.industry ,Mechanical Engineering ,Acoustics ,Context (language use) ,Aerodynamics ,Computational fluid dynamics ,Vortex shedding ,01 natural sciences ,Bogie ,010305 fluids & plasmas ,Vortex ,Physics::Fluid Dynamics ,Noise ,0103 physical sciences ,business ,010301 acoustics ,Wind tunnel - Abstract
Aerodynamic noise can be a significant problem in the operation of high-speed trains; its prediction is difficult to achieve in an industrial context. The aerodynamic and aeroacoustic behaviour of the flow past a simplified high-speed train bogie at scale 1:10 is studied in this paper; the utilized approach is a two-stage hybrid method that consists in computational fluid dynamics and computational acoustics studies. The near-field unsteady flow was obtained by numerically solving the Navier–Stokes equations with the delayed detached-eddy model and the results were used to predict the far-field noise using the Ffowcs-Williams – Hawkings method. The sound radiated from the same scaled bogie model was measured in an anechoic open-jet wind tunnel. The aeroacoustic characteristics of tandem wheelsets were also investigated for comparison purposes. It was found that the unsteady flow past the bogie is characterized by coherently alternating vortex shedding from the axles and more randomly distributed vortices of various scales and orientations from the wheels and frame. The vortices formed behind the upstream geometries move downstream due to convection and impinge on the downstream bodies, generating a highly turbulent wake behind the bogie. The noise predictions correspond fairly well with the experimental measurements for the dominant frequency of tonal noise and the shape of spectra. Vortex shedding from the axles generates tonal noise, with the dominant peak corresponding to the vortex-shedding frequency. The directivity exhibits a dipole shape for the noise radiated from the bogie. Compared with the wheelsets of the bogie, the noise contribution from the bogie frame is relatively weak. more...
- Published
- 2016
- Full Text
- View/download PDF
44. Sound radiation of a railway rail in close proximity to the ground
- Author
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Xianying Zhang, Giacomo Squicciarini, and David Thompson
- Subjects
Ballast ,Engineering ,Acoustics and Ultrasonics ,Wave propagation ,business.industry ,Mechanical Engineering ,Acoustics ,Stiffness ,Allowance (engineering) ,Low frequency ,Physics::Classical Physics ,Condensed Matter Physics ,01 natural sciences ,010305 fluids & plasmas ,Critical frequency ,Mechanics of Materials ,0103 physical sciences ,Electronic engineering ,medicine ,Boundary value problem ,medicine.symptom ,business ,010301 acoustics ,Boundary element method - Abstract
The sound radiation of a railway in close to proximity to a ground (both rigid and absorptive) is predicted by the boundary element method (BEM) in two dimensions (2D). Results are given in terms of the radiation ratio for both vertical and lateral motion of the rail, when the effects of the acoustic boundary conditions due to the sleepers and ballast are taken into account in the numerical models. Allowance is made for the effect of wave propagation along the rail by applying a correction in the 2D modelling. It is shown that the 2D correction is necessary at low frequency, for both vertical and lateral motion of an unsupported rail, especially in the vicinity of the corresponding critical frequency. However, this correction is not applicable for a supported rail; for vertical motion no correction is needed to the 2D result while for lateral motion the corresponding correction would depend on the pad stiffness. Finally, the corresponding numerical predictions of the sound radiation from a rail are verified by comparison with experimental results obtained using a 1/5 scale rail model in different configurations. more...
- Published
- 2016
- Full Text
- View/download PDF
45. Harvesting energy from the vibration of a passing train using a single-degree-of-freedom oscillator
- Author
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David Thompson, Gianluca Gatti, Michael J. Brennan, Maryam Ghandchi Tehrani, University of Calabria, Universidade Estadual Paulista (Unesp), and University of Southampton
- Subjects
Engineering ,Damping ratio ,Acoustics ,Aerospace Engineering ,Train-induced vibration ,02 engineering and technology ,Track (rail transport) ,01 natural sciences ,Square (algebra) ,0103 physical sciences ,010301 acoustics ,Civil and Structural Engineering ,Energy harvesting ,business.industry ,Mechanical Engineering ,Electrical engineering ,Time-limited excitation ,021001 nanoscience & nanotechnology ,Computer Science Applications ,Power (physics) ,Vibration ,Amplitude ,Control and Systems Engineering ,Transient vibration ,Signal Processing ,0210 nano-technology ,business ,Energy (signal processing) - Abstract
Made available in DSpace on 2018-12-11T16:40:46Z (GMT). No. of bitstreams: 0 Previous issue date: 2016-01-01 With the advent of wireless sensors, there has been an increasing amount of research in the area of energy harvesting, particularly from vibration, to power these devices. An interesting application is the possibility of harvesting energy from the track-side vibration due to a passing train, as this energy could be used to power remote sensors mounted on the track for strutural health monitoring, for example. This paper describes a fundamental study to determine how much energy could be harvested from a passing train. Using a time history of vertical vibration measured on a sleeper, the optimum mechanical parameters of a linear energy harvesting device are determined. Numerical and analytical investigations are both carried out. It is found that the optimum amount of energy harvested per unit mass is proportional to the product of the square of the input acceleration amplitude and the square of the input duration. For the specific case studied, it was found that the maximum energy that could be harvested per unit mass of the oscillator is about 0.25 J/kg at a frequency of about 17 Hz. The damping ratio for the optimum harvester was found to be about 0.0045, and the corresponding amplitude of the relative displacement of the mass is approximately 5 mm. Department of Mechanical Energy and Management Engineering University of Calabria Departamento de Engenharia Mecãnica Universidade Estadual Paulista (UNESP) Institute of Sound and Vibration Research University of Southampton Departamento de Engenharia Mecãnica Universidade Estadual Paulista (UNESP) more...
- Published
- 2016
- Full Text
- View/download PDF
46. Reply to 'Discussion on ‘Eulerian models of the rotating flexible wheelset for high frequency railway dynamics’ [J. Sound Vib. 449 (2019) 300-314]'
- Author
-
Juan Giner-Navarro, David Thompson, and Luis Baeza
- Subjects
Physics ,symbols.namesake ,geography ,geography.geographical_feature_category ,Acoustics and Ultrasonics ,Mechanics of Materials ,Mechanical Engineering ,Dynamics (mechanics) ,symbols ,Eulerian path ,Mechanics ,Condensed Matter Physics ,Sound (geography) - Published
- 2020
- Full Text
- View/download PDF
47. Dynamic wheel-rail interaction at high speed based on time-domain moving Green's functions
- Author
-
Songhan Zhang, Gong Cheng, Xiaozhen Sheng, and David Thompson
- Subjects
Flexibility (engineering) ,Frequency response ,Acoustics and Ultrasonics ,Computer science ,Mechanical Engineering ,Modal analysis ,02 engineering and technology ,Condensed Matter Physics ,Rotation ,Track (rail transport) ,01 natural sciences ,020303 mechanical engineering & transports ,0203 mechanical engineering ,Mechanics of Materials ,Control theory ,0103 physical sciences ,Train ,Time domain ,010301 acoustics ,Parametric statistics - Abstract
Many issues of concern in the railway industry are fundamentally caused by dynamic wheel-rail interaction. To deal with these issues, the characteristics of the interaction must be accurately predicted and fully understood; this becomes even more challenging when the train speed is high. Although much research has dealt with wheel-rail interaction, some aspects related to high speed trains still need to be further addressed. In this paper, an approach based on time-domain moving Green's functions developed previously is extended and employed to calculate wheel-rail forces. The extension includes consideration of the flexibility and rotation of the wheelset by incorporating the associated time-domain moving Green's functions in the method. These are derived from the corresponding receptances by applying an experimental modal analysis technique to the calculated frequency response functions. Cases are considered for a single, or multiple, wheelsets rolling over a track represented as an infinitely long periodic structure. Wheel-rail forces are calculated for a set of parameters typical of the Chinese high-speed railway and for a number of typical excitation cases, including purely parametric excitation on a smooth rail, an indentation on the rail, wheel polygonisation and rail corrugation, for the purpose of revealing the frequency content of high-speed wheel-rail interaction. Effects of the wheel rotation on the wheel-rail forces are studied and comparisons are made between a single wheelset and multiple wheelsets. more...
- Published
- 2020
- Full Text
- View/download PDF
48. Modelling of vibration and noise behaviour of embedded tram tracks using a wavenumber domain method
- Author
-
David Thompson, Zhaoran Zeng, Martin Toward, and Wenjing Sun
- Subjects
Physics ,Acoustics and Ultrasonics ,Mechanical Engineering ,Attenuation ,Acoustics ,Physics::Classical Physics ,Condensed Matter Physics ,Track (rail transport) ,Finite element method ,Bogie ,Vibration ,Noise ,Mechanics of Materials ,Wavenumber ,Boundary element method - Abstract
Tracks with rails embedded in a layer of rubber are commonly used for tramways. The vibration and sound radiation behaviour of these tracks differs from that of conventional railway tracks. This is studied here using coupled wavenumber finite element and boundary element models. A detailed analysis is carried out for an embedded rail with a narrow embedding material and comparisons are made with field measurements. The rail, embedding material and surrounding concrete are modelled with finite elements, whereas the support conditions due to the underlying ground are modelled with structural boundary elements coupled to the base of the track model. The sound radiation is calculated using a wavenumber acoustic boundary element model in which it is assumed that there is only one-way coupling with the structure. At low frequencies, vibration of the concrete slab also contributes to the noise radiation. Consequently, the radiated sound is increased compared with that produced by the rail alone at low frequencies but it is reduced above 300 Hz, where the rail and concrete vibrate out of phase with one another; at frequencies above 500 Hz the concrete has negligible effect. The track decay rate has a broad minimum between 500 and 1000 Hz; the noise radiation therefore has a peak in this important frequency region. However, the decay rate increases strongly above 1000 Hz due to the influence of the embedding material. The track considered has a grass in-fill between and outside the rails and allowing for the absorptive effect of the grass leads to a small reduction in the sound radiation. In addition, the attenuation effect of the fairings around the bogie region is estimated taking account of the absorptive effect of the grass surface. The embedded rail models are coupled with a model of a tram wheel and used to predict the rolling noise during the passage of a tram, showing good agreement with field measurements. Finally, various alternative embedded rail designs are compared, including different shapes of the embedding material and different rail profiles. Differences of up to 3 dB are found between the various designs. more...
- Published
- 2020
- Full Text
- View/download PDF
49. Differences between Euler-Bernoulli and Timoshenko beam formulations for calculating the effects of moving loads on a periodically supported beam
- Author
-
David Thompson, Xiaozhen Sheng, and Xianying Zhang
- Subjects
Timoshenko beam theory ,Physics ,Acoustics and Ultrasonics ,Mechanical Engineering ,Stiffness ,Moving load ,Mechanics ,Condensed Matter Physics ,Finite element method ,Bernoulli's principle ,Mechanics of Materials ,Deflection (engineering) ,medicine ,medicine.symptom ,Beam (structure) ,Parametric statistics - Abstract
It is generally considered that a Timoshenko beam is superior to an Euler-Bernoulli beam for determining the dynamic response of beams at higher frequencies but that they are equivalent at low frequencies. Here, the case is considered of the parametric excitation caused by spatial variations in stiffness on a periodically supported beam such as a railway track excited by a moving load. It is shown that large differences exist between the results obtained using Timoshenko and Euler-Bernoulli beams for a railway track with typical parameters; the Euler-Bernoulli beam model underestimates this parametric excitation by around a factor of 3. This difference is shown to be due to shear deformation in the rail, which is significant for span lengths less than about 2 m. A 2.5D finite element model of the rail is used as a reference. This gives a deflection that is closer to the Timoshenko beam model. However, the displacement profile obtained from the Timoshenko beam model has a discontinuity of gradient at the support points, whereas neither the Euler-Bernoulli beam nor the 2.5D finite element model contains the discontinuity of gradient. Finally, the moving load is introduced explicitly in the various periodically supported models. The results for a moving constant load, expressed as an equivalent roughness, are not strongly affected by the load speed until the sleeper passing frequency approaches the vertical track resonance at which the track mass bounces on the support stiffness. Consequently, a quasi-static model gives satisfactory results for moderate load speeds. more...
- Published
- 2020
- Full Text
- View/download PDF
50. A mechanism for overcoming the effects of the internal resonances of coil springs on vibration transmissibility
- Author
-
David Thompson, Wenjing Sun, and Jinsong Zhou
- Subjects
Physics ,Acoustics and Ultrasonics ,business.industry ,Mechanical Engineering ,Natural frequency ,02 engineering and technology ,Structural engineering ,Moment of inertia ,Condensed Matter Physics ,01 natural sciences ,Coil spring ,Dynamic load testing ,Mechanism (engineering) ,020303 mechanical engineering & transports ,0203 mechanical engineering ,Mechanics of Materials ,Spring (device) ,Bushing ,0103 physical sciences ,business ,Suspension (vehicle) ,010301 acoustics - Abstract
Internal resonances in suspension springs can result in significantly increased vibration transmission at the corresponding natural frequencies. Particularly for the case of metal coil springs used in vehicle suspensions, these internal resonances can be as low as 50 Hz and can lead to increased structure-borne noise in certain frequency bands. Although, in practice, this can be mitigated to some extent by using rubber pads in series with the coil springs, high vibration transmission in the vicinity of the internal resonance frequencies remains an important issue. In this paper, a mechanism is identified that can overcome the increased vibration transmission due to the internal resonances. This involves the use of a pivoted arm with a pivot bushing that is relatively stiff for translational motion. The quasi-static load is primarily carried by the suspension spring but the dynamic load at higher frequencies is also transmitted through the pivot bushing. By appropriate selection of parameters, in particular the moment of inertia of the pivoted arm and the stiffness of the pivot bushing, it can be arranged that the dynamic loads acting through the spring and the bushing largely cancel each other out at the spring natural frequency. It is shown that this mechanism is contained within common designs of railway vehicle primary suspension. Nevertheless, their design is largely based on their quasi-static behaviour and this principle of dynamic load cancellation has not previously been explained. The dynamic behaviour of different suspension arrangements is compared and the selection of suitable parameter values that can achieve this dynamic load cancellation is explained. Field measurements are also presented which confirm this behaviour. more...
- Published
- 2020
- Full Text
- View/download PDF
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