A model for railway induced ground vibrations in the frame of preliminary assessment studies

This thesis focuses on the development of an analytical model for the generation and propagation parts of a global model of ground induced vibrations to be used in preliminary assessment studies for the case of at-grade railway infrastructures. The model is designed prioritising its speed, simplicity and usability ahead its accuracy modelling the real railway system. This model takes into account the subgrade as a viscoelastic and homogeneous half-space, the superstructure as a 2-layer supporting model and the vehicle as 1DOF system. With the aim of simplify the model, the superstructure/subgrade interaction is studied in terms of the wheel/rail contact dynamics, bounding in what cases this interaction can be neglected. The adaptation of this model when a far eld semi-analytical model is desired to be used as the propagation model is fully developed, by means of the dimensioning of the near eld and far eld regions

An energy flow study of a double-deck tunnel under quasi-static and harmonic excitations

© 2016. This version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/This paper presents a comparison between the vibration energy flow radiated by a double-deck tunnel and the one radiated by a simple tunnel when both are excited by constant or by harmonic moving loads. For both cases, the radiated energy is computed using a three-dimensional semi-analytical model of the system. The total energy radiated upwards is presented for a wide range of load speeds, when a constant moving load is considered, and for a wide range of excitation frequencies, when the excitation is a harmonic moving load. Significant differences have been obtained, first, for constant loads moving at very high speeds and, second, for harmonic loads moving at typical speeds for underground trains.Peer ReviewedPostprint (author's final draft

A 2.5D automatic FEM-SBM method for the evaluation of free-field vibrations induced by underground railway infrastructures

This paper presents an efficient method to predict underground railway-induced vibrations. The method uses the finite element method (FEM) to model the railway tunnel structure and the singular boundary method (SBM) to model the wave propagation in the surrounding soil. The FEM mesh and the distribution of SBM collocation points at the tunnel/soil interface are generated using an automatic meshing strategy. The presented method is one of the main components of VIBWAY, a user-friendly prediction tool to address railway-induced vibration problems. This paper presents three calculation examples in which the soil response due to forces applied on the tunnel structure are computed in terms of transfer functions. The results obtained for each one of the calculation examples are compared with those computed using a model based on a 2.5D FEM-BEM approach. The presented comparisons show that the proposed approach is a suitable strategy for predicting underground railway-induced vibrations, both in terms of accuracy and computational efficiency. Moreover, the use of an automatic meshing strategy and the SBM formulation not only eases the implementation of the approach but it also makes it easier to use, which is one of the key features of the VIBWAY tool.Peer ReviewedPostprint (published version

The effect of onboard passengers’ seating arrangement on the vertical ride comfort of a high-speed railway vehicle

This research is concerned with the impact of onboard passengers’ seating arrangement on the carbody flexural vibrations of a high-speed railway vehicle. In this regard, the previously developed passenger body-seat models are used to consider the dynamic influence of the passengers. The carbody is modeled using the Euler–Bernoulli beam model to evaluate its flexural deformation. The frequency-domain analysis demonstrates that the carbody behaves almost like a rigid body when the vehicle is full of passengers. It is established that the passengers' presence causes a 31% enhancement of the ride quality determined based on EN 12299 standard for a fully occupied vehicle compared with an empty car. A scaled model of a ratio of 1:24.5 of the Shinkansen vehicle is constructed for validation purposes. The experimental results exhibit a similar trend as found by the simulations in terms of the impact of the passengers’ distribution on the carbody flexural vibrationsPostprint (author's final draft

Dynamic response of a double-deck circular tunnel embedded in a full-space

© 2016. This version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/A three-dimensional dynamic model for calculating the ground-borne vibrations generated by harmonic loads applied on the interior floor of a double-deck circular tunnel is developed. The response of the system is obtained coupling the interior floor subsystem and the tunnel-soil subsystem in the wavenumber-frequency domain. The interior floor is modeled as a thin plate of infinite length in the train circulation direction and the tunnel-soil system is described using the Pipe in Pipe model. Some numerical instabilities of the resulting expressions are overcome by using analytic approximations. The results show that the dynamic behavior of the interior floor clearly influences the magnitude of the coupling loads acting on the tunnel structure. The soil response to a harmonic load acting on the double-deck tunnel is compared to the one obtained for the case of a simple tunnel finding significant differences between them for the whole range of frequencies studied. The proposed model extends the prediction of train-induced vibrations using computationally efficient models to this type of tunnel structure.Peer ReviewedPostprint (author's final draft

A methodology for the calculation of the noise radiated by the rails and the tunnel structure in railway tunnels

In this paper, a robust and fast numerical methodology to compute re-radiated noise in underground railway tunnels is proposed. In this study, the noise analysis does not account for the noise radiation from the train wheels, the rest of the rolling stock structure and the aerodynamic noise. The method is based on decoupled approach, where the acoustic and elastodynamic problems are solved separately on the assumption of weak coupling between the two subdomains. Two-and-a-half dimension (2.5D) finite element boundary element (FEM-BEM) is used to analyse the elastodynamic problem. The computation of the re-radiated noise from the vibration of the structure is done with a 2.5D acoustic boundary element method (BEM). The acoustic as well as elastodynamic BEM used in this analysis is based on globally regularized integrals based on singularity subtraction.Peer ReviewedPostprint (published version

RECYTRACK project: elastomeric eco-friendly material based on end-of-life tires blended with organic bind resin for railway applications

Postprint (published version

A high-performance electromagnetic vibration energy harvester based on ring magnets with Halbach configuration

This paper proposes and studies a ring-shaped architecture with Halbach configuration for electromagnetic vibration energy harvesters. The proposed transducer consists of three ring magnets with a linear Halbach array that concentrates its magnetic field in the inner space of the mechanism where a single vertically-centered concentric coil has been located. This particular structure allows to increase the resonant mass within a fixed dimensions of the transducer and reduces the coil resistance for the same number of turns, enhancing its power generation capabilities. The ring-shaped architecture has been compared with several ring magnet arrangements, including single magnets, double-magnet arrays, and an alternative linear Halbach array, using numerical simulations to determine their influence on its performance. Consequently, this work is the first contribution to the applicability of Halbach configurations for electromagnetic vibration energy harvesters within ring-shaped architectures. Also, a geometrical optimization of the proposed transducer has been conducted, mainly as a function of the inner radius, the height, and the wire diameter of the coil, to increase its power generation. The maximum simulated output power for the optimized generator reaches 3.61 mW for an input harmonic vibration of 0.03 g at a frequency of 61.7 Hz, corresponding to a 29.08 mW/cm 3 g 2 normalized power density performance, significantly higher than devices described in the literature for similar applications. Besides, a harvester prototype based on the proposed configuration has been fabricated to validate the modeling strategy used and to certify the reliability of the proposed design regarding power generation capabilities. Several experimental tests have been conducted under harmonic excitation with frequencies ranging between 10 Hz and 100 Hz and a vibration amplitude of 0.03 g. The experimentally measured induced voltage and electrical output power have been found in good agreement with their corresponding simulated values, with a difference of about 2.1% and 5%, respectivelyPostprint (published version

A method based on 3D stiffness matrices in Cartesian coordinates for computation of 2.5D elastodynamic Green's functions of layered half-spaces

This article elaborates on an extension to the classical stiffness matrix method to obtain the Green's functions for two-and-a-half dimensional (2.5D) elastodynamic problems in homogeneous and horizontally layered half-spaces. Exact expressions for the three-dimensional (3D) stiffness matrix method for isotropic layered media in Cartesian coordinates are used to determine the stiffness matrices for a system of horizontal layers underlain by an elastic half–space. In the absence of interfaces, virtual interfaces are considered at the positions of external loads. The analytic continuation is used to find the displacements at any receiver point placed within a layer. The responses of a horizontally layered half-space subjected to a unit harmonic load obtained using the present method are compared with those calculated using a well-established methodology, achieving good agreementPostprint (author's final draft

2.5D singular boundary method for exterior acoustic radiation and scattering problems

In this paper, a numerical methodology based on a two-and-a-half-dimensional (2.5D) singular boundary method (SBM) to deal with acoustic radiation and scattering problems in the context of longitudinally invariant structures is proposed and studied. In the proposed 2.5D SBM, the desingularisation provided by the subtracting and adding-back technique is used to determine the origin intensity factors (OIFs). These OIFs are derived by means of the OIFs of the Laplace equation. The feasibility, validity and accuracy of the proposed method are demonstrated for three acoustic benchmark problems, in which detailed comparisons with analytical solutions, the 2.5D boundary element method (BEM) and the 2.5D method of fundamental solutions (MFS) are performed. As a novelty of the present study, it is found that the 2.5D SBM provides a higher numerical accuracy than the 2.5D linear-element BEM and lower than the 2.5D quadratic-element BEM. Although the results obtained depict that a nodal approximation of the boundary geometry leads to a significant reduction in the accuracy of the 2.5D SBM, the delivered errors are still acceptable. For complex geometries, the 2.5D SBM is found to be simpler and more robust than the 2.5D MFS, since no optimization procedure is required.Peer ReviewedPostprint (published version