C. Conti

Finite-Dynamic Model for Infinite Media: Corrected Solution of Viscous Boundary Efficiency

This paper presents the corrected development of viscous boundary efficiency initially proposed by Lysmer and Kuhlemeyer. The expressions of the energy ratio are given, in accordance with the original numerical results, and confirm the authors’ recommendations to minimize the reflected energy of body waves that impinge on the artificial boundary.

Ground propagation of vibrations from railway vehicles using a finite/infinite-element model of the soil

Abstract The purpose of this study is to investigate the generation and propagation of ground vibrations induced by railway traffic, more specifically in the case of urban vehicles. The complete vehicle—track—soil model is developed according to an uncoupled approach: the vehicle—track subsystem is first simulated so as to provide the ground forces which, in turn, are applied to the model of the soil. The vehicle—track model is built with the help of the home-made C++library

Ceramic Foam For Molten metal Filtration

In this study, ceramic foam filters were used for the inductrial filtration of aluminum. Results are compared with laboratory experiments which are in good agreement with trajectory analyses of deep bed filtration for the early stage of filtration. The correlations between structural characteristics of the filter media, filtration parameters and filter efficiency are given. In addition, the most important parameters for the industrial use of filters are discussed.

Using three-dimensional finite element analysis in time domain to model railway-induced ground vibrations

For the prediction of ground vibrations generated by railway traffic, finite element analysis (FEA) appears as a competitive alternative to simulation tools based on the boundary element method: it is largely used in industry and does not suffer any limitation regarding soil geometry or material properties. However, boundary conditions must be properly defined along the domain border so as to mimic the effect of infinity for ground wave propagation. This paper presents a full three-dimensional FEA for the prediction of railway ground-borne vibrations. Non-reflecting boundaries are compared to fixed and free boundary conditions, especially concerning their ability to model the soil wave propagation and reflection. Investigations with commercial FEA software ABAQUS are presented also, with the development of an external meshing tool, so as to automatically define the infinite elements at the model boundary. Considering that ground wave propagation is a transient problem, the problem is formulated in the time domain. The influence of the domain dimension and of the element size is analysed and rules are established to optimise accuracy and computational burden. As an example, the structural response of a building is simulated, considering homogeneous or layered soil, during the passage of a tram at constant speed.

On the interest of integrating vehicle dynamics for the ground propagation of vibrations: the case of urban railway traffic

This paper presents a complete numerical model for studying the vertical dynamics of the vehicle/track interaction and its impact on the surrounding soil, with the emphasis on vehicle modelling. A decoupling between the track and the soil is proposed, due to the difficulty of considering all the subsystem components. The train/track model is based on a multibody model (for the vehicle) and a finite element model (for the track). The soil is modelled using an infinite/finite element approach. Simulations of both models are carried out in the time domain, which is better able to simulate the propagation of the vibration waves and to take into account the possible nonlinearity of a component. The methodology is applied in the case of an urban tram track and validated with the available experimental data. Models for the tram, the track and the soil are described. Results from the complete model of the vehicle and a simple model, based on an axle load, are compared with experimental results and the benefits of a complete model in the simulation of the ground vibration propagation induced by railway vehicles are demonstrated. Moreover, a parametric study of the vehicle wheel type is conducted, which shows the advantage of a resilient wheel, for various rail defects.

A numerical analysis of the influence of tram characteristics and rail profile on railway traffic ground-borne noise and vibration in the Brussels Region

Nowadays, damage potentially caused by passing train in dense cities is of increasing concern and restricts improvement to the interconnection of various public transport offers. Although experimental studies are common to quantify the effects of noise and vibration on buildings and on people, their reach is limited since the causes of vibrations can rarely be deduced from data records. This paper presents the numerical calculations that allow evaluating the main contributions of railway-induced ground vibrations in the vicinity of buildings. The reference case is the Brussels Region and, more particularly, the T2000 tram circulating in Brussels city. Based on a pertinent selection of the vibration assessment indicators and a numerical prediction approach, various results are presented and show that the free-field analysis is often improperly used in this kind of analysis as the interaction of soil and structure is required. Calculated high ground vibrations stem from singular rail surface defects. The use of resilient wheels is recommended in order to reduce the ground-borne noise and vibration to permissible values.

Influence of some vehicle and track parameters on the environmental vibrations induced by railway traffic

A study is performed on the influence of some typical railway vehicle and track parameters on the level of ground vibrations induced in the neighbourhood. The results are obtained from a previously validated simulation framework considering in a first step the vehicle/track subsystem and, in a second step, the response of the soil to the forces resulting from the first analysis. The vehicle is reduced to a simple vertical 3-dof model, corresponding to the superposition of the wheelset, the bogie and the car body. The rail is modelled as a succession of beam elements elastically supported by the sleepers, lying themselves on a flexible foundation representing the ballast and the subgrade. The connection between the wheels and the rails is realised through a non-linear Hertzian contact. The soil motion is obtained from a finite/infinite element model. The investigated vehicle parameters are its type (urban, high speed, freight, etc.) and its speed. For the track, the rail flexural stiffness, the railpad stiffness, the spacing between sleepers and the rail and sleeper masses are considered. In all cases, the parameter value range is defined from a bibliographic browsing. At the end, the paper proposes a table summarising the influence of each studied parameter on three indicators: the vehicle acceleration, the rail velocity and the soil velocity. It namely turns out that the vehicle has a serious influence on the vibration level and should be considered in prediction models.

Investigating the influence of soil properties on railway traffic vibration using a numerical model

This paper presents the influence of dynamic and geometrical soil parameters on the propagation of ground vibrations induced by external loads. The proposed approach is based on a three-dimensional model, focusing on realistic excitation sources like impulse loads and moving railway vehicles. For the latter, a complete vehicle/track model is developed. The simulation is performed in time domain, offering an interesting approach, compared with classic cyclic analyses. The ground is modelled initially as an elastic homogeneous half-space and additionally as a layered half-space. First, the effect of homogeneous soil properties on ground vibration is analysed. Soil stratification is then taken into account, using various configurations. Analysis reveals that as receiver distance increases ground wave reflection in a layered ground plays an important role in the reduction of ground surface motion. This effect is magnified when the phase velocity wavelength becomes large compared with the depth of the surface layer.

Efficiency of resilient wheels on the alleviation of railway ground vibrations

The aim of this paper is to show how resilient wheels, initially used for reducing the noise generated at the wheel/rail contact and stresses on wheels, are also efficient for reducing ground vibrations. Brussels tramway T2000 is considered as an example. A prediction model as complete as possible is used, taking into account the track and the vehicle dynamics. A multibody approach is chosen to describe the vehicle behaviour, over a finite element model for the track. The soil is modelled with the finite/infinite element approach, taking into account the layered configuration of the ground. Three variants of tram are analysed, focusing on the resilient wheel stiffness. The stiffness and damping properties of the wheels are obtained by updating a finite element model. A validation step is presented, based on measurements at the soil surface during the passing of the tram over a rough rail and a local rail defect. A modal decomposition is applied on the vehicle model with emphasis on relevant modal contributions in the wheel/rail forces. A sensitivity analysis of the resilient wheels stiffness is performed, showing a meaningful decrease of ground vibrations using a soft resilient material. This study shows that the vehicle dynamics intervenes in the onset of the vibration waves in the soil and demonstrates the real interest of a compound vehicle/track/soil model in the design of this kind of wheel.

A two-step time simulation of ground vibrations induced by the railway traffic

Recent decades have been fertile in terms of development of vehicle dynamics simulations. But the usual applications dedicated to the train design rarely take into account ground vibrations. In order to assess the influence of vehicle dynamics on track deflection and therefore on ground wave propagation, the vehicle/track system must be studied globally. The track/soil coupling is first investigated, through various track/soil models. From there, a decoupled approach is proposed, which proves valid as far as the soil is sufficiently rigid with respect to the ballast. It works in two stages: the simulation of the vehicle/track subsystem provides in a first step the ground forces, considering the irregularities of the rail as the excitation mechanism. The resulting forces are then applied, in a second step, to the soil subsystem model. Two applications are presented, consisting of the passing of a tram over a local discontinuity and the passing of a high-speed train over a rough track. The results obtained show a good agreement with experimental measurements as well as the importance of the whole vehicle/track/soil dynamics on the level of ground vibration.