Quantification of uncertainty in the prediction of railway induced ground vibration due to the use of statistical track unevenness data

Versión PostprintEnvironmental vibrations due to railway traffic are predominantly due to dynamic axle loads caused by wheel and track unevenness and impact excitation by rail joints and wheel flats. Because of its irregular character, track unevenness is commonly processed statistically and represented by its power spectral density function or its root mean square (RMS) value in one-third octave bands. This statistical description does not uniquely define the track unevenness at a given site, however, and different track unevenness profiles matching the statistical description will lead to different predictions of dynamic axle loads and resulting ground vibration. This paper presents a methodology that allows quantifying the corresponding variability in ground vibration predictions. The procedure is derived assuming the geometry of the track and soil to be homogeneous along the track. The procedure is verified by means of Monte Carlo simulations and its usefulness for assessing the mismatch between predicted and measured ground vibrations is demonstrated in a case study. The results show that the response in time domain and its narrow band spectrum exhibit significant variability which is reduced when the running RMS value or the one-third octave band spectrum of the response is considered.Ministerio de Economía y Competitividad BIA2010-1484

Wind-structure interaction simulations for the prediction of ovalling vibrations in silo groups

Wind-induced ovalling vibrations were observed during a storm in October 2002 on several empty silos of a closely spaced group consisting of 8 by 5 thin-walled silos in the port of Antwerp (Belgium). The purpose of the present research is to investigate if such ovalling vibrations can be predicted by means of numerical simulations. More specifically, the necessity of performing computationally demanding wind-structure interaction (WSI) simulations is assessed. For this purpose, both one-way and two-way coupled simulations are performed. Before considering the entire silo group, a single silo in crosswind is simulated. The simulation results are in reasonably good agreement with observations and WSI simulations seem to be required for a correct prediction of the observed ovalling vibrations

A 2.5D coupled FE-BE model for the prediction of railway induced vibrations

Ground vibrations induced by railway traffic at grade and in tunnels are often studied by means of two-and-half dimensional (2.5D) models that are based on a Fourier transform of the coordinate in the longitudinal direction of the track. In this paper, the need for 2.5D coupled finite element-boundary element models is demonstrated in two cases where the prediction of railway induced vibrations is considered. A recently proposed novel 2.5D methodology is used where the finite element method is combined with a boundary element method, based on a regularized boundary integral equation. In the formulation of the boundary integral equation, Green's functions of a layered elastic halfspace are used, so that no discretization of the free surface or the layer interfaces is required. In the first case, two alternative models for a ballasted track on an embankment are compared. In the first model, the ballast and the embankment are modelled as a continuum using 2.5D solid elements, whereas a simplified beam representation is adopted in the second model. The free field vibrations predicted by both models are compared to those measured during a passage of the TGVA at a site in Reugny (France). A very large difference is found for the free field response of both models that is due to the fact that the deformation of the cross section of the embankment is disregarded in the simplified representation. In the second case, the track and free field response due to a harmonic load in a tunnel embedded in a layered halfspace are considered. A simplified methodology based on the use of the full space Green's function in the tunnel–soil interaction problem is investigated. It is shown that the rigorous finite element-boundary element method is required when the distance between the tunnel and the free surface and the layer interfaces of the halfspace is small compared to the wavelength in the soil.Junta de Andalucía IAC08-II-3343Ministerio de Educación y Ciencia JC2008-0013

Probing top-Higgs non-standard interactions at the LHC

Effective interactions involving both the top quark and the Higgs field are among the least constrained of all possible (gauge invariant) dimension-six operators in the Standard Model. Such a handful of operators, in particular the top quark chromomagnetic dipole moment, might encapsulate signs of the new physics responsible for electroweak symmetry breaking. In this work, we compute the contributions of these operators to inclusive Higgs and t tbar h production. We argue that: i) rather strong constraints on the overall size of these operators can already be obtained from the current limits/evidence on Higgs production at the LHC; ii) t tbar h production will provide further key information that is complementary to t tbar measurements, and the possibility of discriminating among different contributions by performing accurate measurements of total and differential rates.Comment: 8 pages, 9 figures. v2: Logarithmic contribution of the top quark chromomagnetic operator to Higgs production by gluon fusion correcte

Scoping assessment of free-field vibrations due to railway traffic

The number of railway lines both operational and under construction is growing rapidly, leading to an increase in the number of buildings adversely affected by ground-borne vibration (e.g. shaking and indoor noise). Post-construction mitigation measures are expensive, thus driving the need for early stage prediction, during project planning/development phases. To achieve this, scoping models (i.e. desktop studies) are used to assess long stretches of track quickly, in absence of detailed design information. This paper presents a new, highly customisable scoping model, which can analyse the effect of detailed changes to train, track and soil on ground vibration levels. The methodology considers soil stiffness and the combination of both the dynamic and static forces generated due to train passage. It has low computational cost and can predict free-field vibration levels in accordance with the most common international standards. The model uses the direct stiffness method to compute the soil Green's function, and a novel two-and-a-half dimensional (2.5D) finite element strategy for train-track interaction. The soil Green's function is modulated using a neural network (NN) procedure to remove the need for the time consuming computation of track-soil coupling. This modulation factor combined with the new train-track approach results in a large reduction in computational time. The proposed model is validated by comparing track receptance, free-field mobility and soil vibration with both field experiments and a more comprehensive 2.5D combined finite element-boundary element (FEM-BEM) model. A sensitivity analysis is undertaken and it is shown that track type, soil properties and train speed have a dominant effect on ground vibration levels. Finally, the possibility of using average shear wave velocity introduced for seismic site response analysis to predict vibration levels is investigated and shown to be reasonable for certain smooth stratigraphy's.Ministerio de Economía y Competitividad - BIA2016-75042-C2-1-

GoSam: A program for automated one-loop Calculations

The program package GoSam is presented which aims at the automated calculation of one-loop amplitudes for multi-particle processes. The amplitudes are generated in terms of Feynman diagrams and can be reduced using either D-dimensional integrand-level decomposition or tensor reduction, or a combination of both. GoSam can be used to calculate one-loop corrections to both QCD and electroweak theory, and model files for theories Beyond the Standard Model can be linked as well. A standard interface to programs calculating real radiation is also included. The flexibility of the program is demonstrated by various examples.Comment: 10 pages, Talk given at the International Workshop on Advanced Computing and Analysis Techniques in Physics Research (ACAT), Uxbridge, London, September 201

Scoping assessment of free-field vibrations due to railway traffic

The number of railway lines both operational and under construction is growing rapidly, leading to an increase in the number of buildings adversely affected by ground-borne vibration (e.g. shaking and indoor noise). Post-construction mitigation measures are expensive, thus driving the need for early stage prediction, during project planning/development phases. To achieve this, scoping models (i.e. desktop studies) are used to assess long stretches of track quickly, in absence of detailed design information. This paper presents a new, highly customisable scoping model, which can analyse the effect of detailed changes to train, track and soil on ground vibration levels. The methodology considers soil stiffness and the combination of both the dynamic and static forces generated due to train passage. It has low computational cost and can predict free-field vibration levels in accordance with the most common international standards. The model uses the direct stiffness method to compute the soil Green's function, and a novel two-and-a-half dimensional (2.5D) finite element strategy for train-track interaction. The soil Green's function is modulated using a neural network (NN) procedure to remove the need for the time consuming computation of track-soil coupling. This modulation factor combined with the new train-track approach results in a large reduction in computational time. The proposed model is validated by comparing track receptance, free-field mobility and soil vibration with both field experiments and a more comprehensive 2.5D combined finite element-boundary element (FEM-BEM) model. A sensitivity analysis is undertaken and it is shown that track type, soil properties and train speed have a dominant effect on ground vibration levels. Finally, the possibility of using average shear wave velocity introduced for seismic site response analysis to predict vibration levels is investigated and shown to be reasonable for certain smooth stratigraphy's

Virtual Compton Scattering and the Generalized Polarizabilities of the Proton at Q\u3csup\u3e2\u3c/sup\u3e = 0.92 and 1.76 GeV\u3csup\u3e2\u3c/sup\u3e

Virtual Compton scattering (VCS) on the proton has been studied at the Jefferson Laboratory using the exclusive photon electroproduction reaction ep → epγ. This paper gives a detailed account of the analysis which has led to the determination of the structure functions PLL − PTT/ε and PLT and the electric and magnetic generalized polarizabilities (GPs) αE(Q2)and βM(Q2) at values of the four-momentum transfer squared Q2 = 0.92 and 1.76 GeV2. These data, together with the results of VCS experiments at lower momenta, help building a coherent picture of the electric and magnetic GPs of the proton over the full measured Q2 range and point to their nontrivial behavior