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

ALMA data suggest the presence of a spiral structure in the inner wind of CW Leo

(abbreviated) We aim to study the inner wind of the well-known AGB star CW Leo. Different diagnostics probing different geometrical scales have pointed toward a non-homogeneous mass-loss process: dust clumps are observed at milli-arcsec scale, a bipolar structure is seen at arcsecond-scale and multi-concentric shells are detected beyond 1". We present the first ALMA Cycle 0 band 9 data around 650 GHz. The full-resolution data have a spatial resolution of 0".42x0".24, allowing us to study the morpho-kinematical structure within ~6". Results: We have detected 25 molecular lines. The emission of all but one line is spatially resolved. The dust and molecular lines are centered around the continuum peak position. The dust emission has an asymmetric distribution with a central peak flux density of ~2 Jy. The molecular emission lines trace different regions in the wind acceleration region and suggest that the wind velocity increases rapidly from about 5 R* almost reaching the terminal velocity at ~11 R*. The channel maps for the brighter lines show a complex structure; specifically for the 13CO J=6-5 line different arcs are detected within the first few arcseconds. The curved structure present in the PV map of the 13CO J=6-5 line can be explained by a spiral structure in the inner wind, probably induced by a binary companion. From modeling the ALMA data, we deduce that the potential orbital axis for the binary system lies at a position angle of ~10-20 deg to the North-East and that the spiral structure is seen almost edge-on. We infer an orbital period of 55 yr and a binary separation of 25 au (or ~8.2 R*). We tentatively estimate that the companion is an unevolved low-mass main-sequence star. The ALMA data hence provide us for the first time with the crucial kinematical link between the dust clumps seen at milli-arcsecond scale and the almost concentric arcs seen at arcsecond scale.Comment: 22 pages, 18 Figures, Astronomy & Astrophysic

SASICE: Safety and sustainability in civil engineering

The performance of the built environment and the construction sector are of major importance in Europe’s long term goals of sustainable development in a changing climate. At the same time, the quality of life of all European citizens needs to be improved and the safety of the built environment with respect to man-made and natural hazards, such as flooding and earthquakes, needs to be ensured. Education has a central role to play in the transformation of a construction sector required to meet increasing demands with regard to safety and sustainability. In this work, the SASICE project is presented. The aim of this project is to promote the integration of safety and sustainability in civil engineering education. The project is organised in the context of the Lifelong Learning Programme, funded by the European Community. The coordinator organisation is the University of Bologna. Nine partner universities from different countries are involved in this transnational project. The universities participating to the project constitute a network of high level competences in the civil engineering area, with several opportunities to improve lifelong learning adopting different media: joint curricula, teaching modules and professor and student exchanges. As a response to the challenge regarding new educational methods in sustainable engineering, teaching modules are developed in 4 thematic areas: (1) Safety in construction, (2) Risk induced by Natural Hazards Assessment, (3) Sustainability in construction, and (4) Sustainability at the territorial level. The development of the teaching modules is based on an extensive analysis of the need for highly qualified education on Safety and Sustainability involving all relevant stakeholders (European and national authorities, companies, research institutes, professional organizations, and universities).The main target is enabling students to introduce these advanced topics in their study plans and curricula and reach, at the end of their studies, a specific skill and expertise in safety and sustainability in Civil Engineering. With our natural resources fading away and our infrastructure in dire need of repair, new trends and challenges in civil engineering education in the concept of “Sustainable Development” are needed to be adressed.<br/

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

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-

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

Longitudinal analysis of the preterm cortex using multi-modal spectral matching

Extremely preterm birth (less than 32 weeks completed gestation) overlaps with a period of rapid brain growth and development. Investigating longitudinal brain changes over the preterm period in these infants may allow the development of biomarkers for predicting neurological outcome. In this paper we investigate longitudinal changes in cortical thickness,cortical fractional anisotropy and cortical mean diffusivity in a groupwise space obtained using a novel multi-modal spectral matching technique. The novelty of this method consists in its ability to register surfaces with very little shape complexity,like in the case of the early developmental stages of preterm infants,by also taking into account their underlying biology. A multi-modal method also allows us to investigate interdependencies between the parameters. Such tools have great potential in investigating in depth the regions affected by preterm birth and how they relate to each other

Spherical parameterization for genus zero surfaces using Laplace-Beltrami eigenfunctions

International audienceIn this work, we propose a fast and simple approach to obtain a spherical parameterization of a certain class of closed surfaces without holes. Our approach relies on empirical findings that can be mathematically investigated, to a certain extent, by using Laplace-Beltrami Operator and associated geometrical tools. The mapping proposed here is defined by considering only the three first non-trivial eigenfunctions of the Laplace-Beltrami Operator. Our approach requires a topological condition on those eigenfunctions, whose nodal domains must be 2. We show the efficiency of the approach through numerical experiments performed on cortical surface meshes