Papers by Evangelos Ntotsios
This dataset supports the publication: Wenjing Sun, David Thompson, Martin Toward, Marcus Wiseman... more This dataset supports the publication: Wenjing Sun, David Thompson, Martin Toward, Marcus Wiseman, Evangelos Ntotsios, Stephen Byrne. "The influence of track design on the rolling noise from trams" in Applied Acoustics.
Dataset for paper "Modelling, simulation and evaluation of ground vibration caused by rail v... more Dataset for paper "Modelling, simulation and evaluation of ground vibration caused by rail vehicles" Authors: D.J. Thompson, G. Kouroussis, E. Ntotsios Journal: Vehicle System Dynamics Volume:57 Issue: 7 Pages: 936-983 Accepted: 4 March 2019 DOI: 10.1080/00423114.2019.1602274
Within the context of railway ground-borne vibration, the dynamic pile-soil-pile interaction rema... more Within the context of railway ground-borne vibration, the dynamic pile-soil-pile interaction remains an area that has not been sufficiently investigated. Whilest a number of researchers have scrutinised the vibration response of piled-foundations, their approaches exhibit a compromise between computation time and solution accuracy. In this paper, two models of piled-foundations in a multi-layered half-space are presented; one is an efficient semi-analytical model and another is a fully-coupled boundary element model. The pile is simulated, in both models, by an elastic bar for axial loading and an Euler-Bernoulli beam for transverse loading. A set of comparisons has been performed, including the driving point response of a single pile, the interaction between two piles and the 'far-field' response due to axial and transverse loading on the pile's head. The comparisons reveal that the semianalytical model predicts at most frequencies the driving point response and the dyn...
Notes on Numerical Fluid Mechanics and Multidisciplinary Design, 2021
Railway crossings are an important source of localized ground vibration. Models are required for ... more Railway crossings are an important source of localized ground vibration. Models are required for identifying ways to tackle unacceptable levels of vibration from existing as well as future railway lines. Yet, the use of a prediction model that directly allows for the non-Hertzian wheel-rail contact dynamics and also includes three dimensional calculations of the ground response would be computationally expensive. In order to reduce the computational cost without affecting the accuracy of the predictions, a hybrid approach is proposed for the prediction of ground-borne vibration due to impacts at railway crossings. The approach combines the simulation of the vertical wheel-rail contact force in the time domain and the prediction of ground vibration levels in the far field using a linear wavenumber-frequency-domain approach. The proposed hybrid approach is used to investigate the influence of different vehicle speeds, crossing designs and wheel profiles on predicted ground vibration levels in the free field.
Notes on Numerical Fluid Mechanics and Multidisciplinary Design, 2021
Dataset for paper "The effect of track load correlation on ground-borne vibration from railw... more Dataset for paper "The effect of track load correlation on ground-borne vibration from railways" Authors: Evangelos Ntotsios, David Thompson, Mohammed Hussein Journal of Sound and Vibration Accepted: 02 May 2017Licenses or restrictions placed on the data: Creative Commons Attribution 4.0 File "FigureData.xlsx" contains all data contained in the graphs of the paper. One page is added per figure. Format: Microsoft Excel
This paper focuses on quantifying the level of correlation of the track loading at the wheel/rail... more This paper focuses on quantifying the level of correlation of the track loading at the wheel/rail interface due to rail unevenness and its influence on predictions of ground vibration. The extent to which the unevenness of the two rails is correlated has been estimated from measurements of track geometry obtained with track recording vehicles for six different tracks. It was found that for wavelengths longer than about 3 m the unevenness of the two rails can be considered to be strongly correlated and in phase. To investigate the effect of this on ground vibration, a railway model that works in the wavenumber-frequency domain and includes separate inputs on the two rails has been used. In this model, the track is assumed as an infinite invariant linear structure resting on an elastic stratified half-space. This is excited by the gravitational loading of a passing train and the irregularity of the contact surfaces between the wheels and the rails. The railway model can account or dis...
Dataset for paper: Ntotsios, E., Thompson, D., & Hussein, M. F. M. (2019). A comparison of ground... more Dataset for paper: Ntotsios, E., Thompson, D., & Hussein, M. F. M. (2019). A comparison of ground vibration due to ballasted and slab tracks. Transportation Geotechnics.
When modelling the railway induced vibration in a building, three main aspects of the problem hav... more When modelling the railway induced vibration in a building, three main aspects of the problem have to be considered: the vibration generation at the moving vehicle-track interaction points, the vibration propagation in the underlying infinite soil, and the vibration reception inside the building. This study proposes a computational modelling approach for predicting the full vibration propagation path from the train vehicles up to the building structure. The method includes a moving train model that is directly coupled to a stationary building structure, with interaction between them through the underlying soil using a single step solution procedure. A semi-analytical model is utilized to model the soil to which rigid objects and structures modelled by finite elements (FE) are coupled. The system is excited by a multi-body vehicle model passing over an irregular track. The proposed modelling approach uses the frequency-domain solution with some parts, such as the railway track, formu...
This paper presents the influence of rail unevenness correlation on the predicted track and groun... more This paper presents the influence of rail unevenness correlation on the predicted track and ground vibration. The study is based on an integrated railway model in the wavenumber-frequency domain with varying complexity describing the dynamic system of a ballasted track on layered elastic half-space. In order to investigate how ground vibration levels are influenced by taking into account different correlation levels between the two rails, the traction variation across the track-ground interface is included and the track model is discretised laterally including both rails separately and allowing for the pitching motion of the sleepers. The paper presents the effect of the different modelling approaches on the response predictions and compares the dynamic response calculated for a range of model/excitation parameters
Dataset supports: Jin, Q., et al. (2017). A 2.5D finite element and boundary element model for th... more Dataset supports: Jin, Q., et al. (2017). A 2.5D finite element and boundary element model for the ground vibration from trains in tunnels and validation using measurement data. Journal of Sound and Vibration.
Applied Acoustics, 2020
Abstract Tramway noise can be significant even though the speeds are relatively low. The influenc... more Abstract Tramway noise can be significant even though the speeds are relatively low. The influence of track design on the rolling noise is studied through a systematic comparison of different tracks on a single network. These include a slab track with embedded sleeper blocks, a ballasted track and a track with embedded rails. Measurements have been taken of rail vibration and noise during tram passages at approximately 55 km/h; the rail and wheel roughness have also been measured. Comparisons are made in terms of track decay rate, rail vibration and pass-by noise. After normalising to the same roughness, the slab track is found to be the noisiest and the ballasted track the quietest. Theoretical models of the various track forms are also presented to give insight into the differences in acoustic performance. The models allow the relative contributions of the track and wheels to the pass-by noise to be identified. In addition the effect of rail dampers added to the slab track is assessed. These attenuate the noise at higher frequencies due to the increase in decay rate, but an increase in radiation is noted at 500 Hz and below, possibly linked to differences in effective roughness.
Transportation Geotechnics, 2018
When a train runs on soft ground it can approach or even exceed the speed of surface waves in the... more When a train runs on soft ground it can approach or even exceed the speed of surface waves in the ground. Under such conditions the amplitudes of the track response increase considerably. Moreover, a resonance-like phenomenon can occur in which a clear oscillation trail can be observed behind the moving axle loads. An investigation is presented of this resonance frequency and the critical speed effect for a track on a layered half-space subject to a moving load. Three different methods are used to investigate this resonance frequency: (i) the spectrum of the response to a moving load, (ii) analysis of the dispersion curves of the ground, and (iii) frequency analysis of the response to a stationary load. A parameter study is presented of a layered half-space ground with different P-wave speeds, S-wave speeds, and depth of the upper layer. The critical speeds are found in each case; in such a layered ground, the critical speed is greater than the Rayleigh wave speed of the soft upper layer due to the influence of the underlying half-space. The oscillating frequencies are shown to vary with the speed of the moving load, tending to reduce when the load speed increases. The P-wave speeds of both the upper layer and the underlying half-space are found to have negligible influence on the critical velocity and on the oscillating frequency; the S-wave speed of the half-space has only a small influence. Larger differences are found when the depth of the layer is varied. Finally, a formula for calculating this resonance frequency is proposed.
Journal of Sound and Vibration, 2017
Journal of Sound and Vibration, 2017
This paper presents a methodology for studying ground vibration in which the railway track is mod... more 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
Proceedings of the 5th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering (COMPDYN 2015), 2015
In this paper, the dynamic pile-soil-pile interaction (PSPI) in a multi-layered halfspace is inve... more In this paper, the dynamic pile-soil-pile interaction (PSPI) in a multi-layered halfspace is investigated for the prediction of the response of piled foundations due to railway vibrations. Two methods of modelling piled foundations in a multi-layered half-space are presented. The first is an efficient semi-analytical model that calculates the Green's functions of the multi-layered half-space soil using the thin layer and the dynamic stiffness matrix methods. The second is a fully-coupled model that utilises the boundary element (BE) method to simulate the soil, where the Green's functions are calculated using the ElastoDynamics Toolbox (EDT). The paper aims to investigate the accuracy and the efficiency of the semi-analytical model by comparing the predictions of the two methods. A set of comparisons is performed, including the driving point response of a single pile and the interaction between two piles. The comparisons reveal that, at most frequencies, the semi-analytical model can predict the driving point response and the dynamic interaction with acceptable accuracy and computational efficiency. The model is then used for predicting the response of a pile-group due to the vibration field generated by a railway in varying distance from the piles. The vibration field generated by the railway is modelled as the superposition of the response due to harmonic loadings generated at the wheel-rail interface and the vibration response is examined at different points on the free surface away from the piles. The comparisons highlight the efficiency and accuracy of the semi-analytical model and illustrate its practical application.
Journal of Engineering Mechanics, 2016
A new state-space model is formulated for the dynamic analysis of sandwich beams that are made of... more A new state-space model is formulated for the dynamic analysis of sandwich beams that are made of two thin elastic layers continuously joined by a shear-type viscoelastic (VE) core. The model can accommodate different boundary conditions for each outer layer and accounts for the rate-dependent constitutive law of the core through additional state variables. The mathematical derivation is presented with the Standard Linear Solid (SLS) model (i.e., a primary elastic spring in parallel with a single Maxwell element) and then extended to the generalized Maxwell (GM) model. The kinematics equations are developed by means of Galerkin-type approximations for the fields of axial and transverse displacements in the outer layers, and imposing the pertinent compatibility conditions at the interface with the core. Numerical examples demonstrate the accuracy and versatility of the proposed approach, which endeavors to represent the effects of the VE memory on the vibration of composite beams.
Theoretical and computational issues arising in the selection of the optimal sensor configuration... more Theoretical and computational issues arising in the selection of the optimal sensor configuration in structural dynamics are addressed. The information entropy is introduced to measure the performance of a sensor configuration. Asymptotic estimates are used to rigorously justify that selections of optimal sensor configurations can be based solely on nominal structural models, ignoring the time history details of the measured data that are not available in the initial experimental design stage. Heuristic algorithms are proposed for constructing effective sensor configurations that are superior, in terms of computational efficiency and accuracy, to the sensor configurations provided by available algorithms suitable for solving general optimisation problems. The theoretical developments and the effectiveness of the proposed algorithms are illustrated by designing the optimal configuration for an array of acceleration sensors placed on a bridge structure.
Notes on Numerical Fluid Mechanics and Multidisciplinary Design, 2015
To reduce railway induced low frequency vibration, two mitigation measures - open trenches and bu... more To reduce railway induced low frequency vibration, two mitigation measures - open trenches and buried soft wall barriers have been studied in this paper by using coupled finite element-boundary element models. These models were developed at KU Leuven and ISVR, and have been cross-validated within the EU FP7 project RIVAS (Railway Induced Vibration Abatement Solutions). Variations in the width, depth, location of trench and properties of soft barrier material are considered under various soil conditions. Results show that in all ground conditions, the notional rectangular open trench performs better than the other constructions. The width of an open trench has little influence on its performance, whereas increasing the width of a filled trench reduces the stiffness of the barrier, improving the performance of the trench. Likewise, fill materials with lower Young’s modulus give higher insertion losses.
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Papers by Evangelos Ntotsios