1,721,005 research outputs found
Incorporating Rainfall Forecast Data in X-SLIP Platform to Predict the Triggering of Rainfall-Induced Shallow Landslides in Real Time
Full text linkExtreme and prolonged rainfall resulting from global warming determines a growing need for reliable Landslide Early Warning Systems (LEWS) to manage the risk of rainfall-induced shallow landslides (also called soil slips). Regional LEWS are typically based on data-driven methods because of their greater computational effectiveness, which is greater than the ones of physically based models (PBMs); however, the latter reproduces the physical mechanism of the modelled phenomena, and their modelling is more accurate. The purpose of this research is to investigate the prediction quality of the simplified PBM SLIP (implemented in the X-SLIP platform) when applied on a regional scale by analysing the stability of rain forecasts. X-SLIP was updated to handle the GRIB files (format for weather forecast). Four real-time predictions were simulated on some towns of the Emilia Apennines (northern Italy) involved in widespread soil slips on 5 April 2013; specifically, maps of factors of safety related to this event were derived assuming that X-SLIP had run 72 h, 48 h, 24 h and 12 h in advance. The results indicated that the predictions with forecasts (depending on the forecast quality) are as accurate as the ones derived with rainfall recordings only (benchmark). Moreover, the proposed method provides a reduced number of false alarms when no landslide was reported to occur in the whole area. X-SLIP with rain forecasts can, therefore, represent an important tool to predict the occurrence of future soil slips at a regional scale
A methodology for assessing the feasibility of fleet compositions with dynamic demand
No full textIn the last twenty years, European Union has promoted liberalisation and competition within the rail system under EC Directive 91/440 and the Railway Packages concerned, and all Member States now try to pursue the difficult task of considering both public (sustainability, accessibility, employment, etc.) and commercial interests (profit, return on investment, growth). In this context, it is necessary to carry out analyses about rail services so as to gain useful information for increasing efficiency, effectiveness and productivity. In many cases, great importance has been attached to Key Performance Indicators (KPIs) which do not usually consider customer needs. This paper aims to promote a Decision Support System (DSS) for assessing rail services taking both service quality and performance indexes into account. In particular, the procedure is based on a microscopic simulation model combined to an assignment tool for assigning dynamically passengers to services. Thus, demand peaks, temporary capacity variations, temporary over-saturation of supply elements, and formation and dispersion of queues can be considered providing a more precise analysis of rail services. An application on metro Line 1 in Naples (Italy) is presented in order to explain the workings of the model. Numerical results demonstrate that this approach is very useful for planning or managing rail systems in accordance with passenger satisfaction and operational efficiency
Experimental analyses on cellular polymers in different forms for geotechnical applications
No full textCellular polymers represent an important category among the polymeric materials. Nowadays they experience large applications in different areas (packaging, building, sport, road safety). There is already a widespread geotechnical use of these materials, e.g. for settlements reduction or soil strengthening, especially for existing structures. However, a need of a deeper mechanical properties study is required. Oedometric and triaxial laboratory tests have already been carried out on polyurethane samples obtained from ready-to-be-used slabs (RTBU samples). However, because of a will of polyurethane foam injection inside the soil, an ad-hocprepared foam needs to be prepared and its mechanical properties to be investigated. This paper is therefore aimed to analyse the geotechnical behaviour of the ad-hoc-prepared foam (by testing AHP samples), studying the influence of several factors on the applicability, and comparing the results with the failure tests conducted on RTBU samples
WAVE PROPAGATION IN SANDY SOIL – AN EXPERIMENTAL AND NUMERICAL MODEL
No full textExisting seismic retrofitting techniques are mainly structural and invasive. Since earthquakes generates from soil and seismic waves propagate through it, alternative solutions for seismic retrofitting have been thought, concerning the insertion of innovative materials in the soil. Polyurethane materials (such as Styrodur or ElastoPor) have already been widely investigated by laboratory testing. In order to evaluate the benefit of their insertion in the soil in terms of PGA decrease and frequency content modification, a little-scale wave propagation study is now introduced. Controlled impact hammer tests adapted to geotechnical uses are performed in a small test wood caisson filled with sand. A FEM model is therefore presented and calibrated on the basis of the comparison with the experimental results. A good agreement between experimental and numerical results allows to anticipate future numerical application of the model to larger studies finalised to the evaluation of seismic amelioration due to polyurethane insertion
Benefits of a combined micro-macro approach for managing rail systems in case of disruptions
No full textOptimisation and simulation tools are nowadays vital for planning and managing rail systems, providing performance analysis and evaluation of interactions very rapidly and without any kind of disturbance to the service. Recently, thanks to the development of computers and software, complex railway operations can be optimised and simulated realistically. We may distinguish between combinatorial optimisation and simulation models which can be also classified into macroscopic and microscopic models depending on the adopted level of network details. The former models describe the network and the timetable in a simple way by means of a simplified graph. The latter models consist of the specification of all technical characteristics related to infrastructure, rolling stock and signalling system as well as timetable data.
It is worth noting that macroscopic models are very useful during the planning process when it is necessary to design service frequencies and offered capacities to satisfy the travel demand. The major benefit of this approach is the possibility to consider jointly several features of the rail system obtaining reliable results. By contrast, microscopic models reproduce the network as closely as possible to the "real world"; basically, this kind of modelling allows evaluating the interactions among trains and the performance of the network precisely and generally they are used to design timetables or analyse the robustness of the service.
The aim of this paper is to propose a new approach for planning and managing the rail system combining both approaches macroscopic and microscopic. In particular, an optimisation model, based on a macroscopic approach, represents the kernel of the procedure and it is used as a first step to study any kind of scenario. The microscopic simulation model, by contrast, generates detailed (and precise) data, such as headways or running times, to overcome the approximations of the macroscopic model. Above all, in case of disruptions, the combination of the two models provides reliable results taking advantage of the benefits of the two approaches.
Numerical applications have been applied in a realistic case taken from a real metro network located in the south of Italy; the preliminary results show the effectiveness of the proposed approach
An experimental and numerical model for wave propagation studies in sandy soils
No full textIn recent years, an ever increasing interest in reducing seismic risk is developing. Innovative solutions related to soil interventions are going to be studied. This paper shows the preliminary steps of the construction of an experimental apparatus, whose aim is the study of wave propagation in little scale through a sandy soil, in axisymmetric conditions. Single-Input-Multiple-Output impact hammer tests are performed in order to study the experimental response in both time and frequency domain. Alongside the experimental system, a 3D – FEM model able to reproduce the experimental tests is therefore proposed, for its calibration and in order to determine the problem unknowns with back analysis procedures. Results from the numerical modal and dynamics analyses show a great correspondence with the experimental data, confirming the goodness of the system
A methodological approach for managing rail disruptions with different perspectives
No full textPublic transport systems represent a potentially effective tool for managing mobility in urban and metropolitan areas. In particular, especially in high density contexts, rail systems can be adopted as the backbone of transportation services. However, rail systems are also somewhat vulnerable to system failure since, for instance, a faulty train cannot be easily removed or overtaken. Hence, our proposal is to develop an off-line procedure based on a microsimulation approach for analysing the most frequent breakdown conditions and suggesting the adoption of optimal intervention strategies. Finally, different perspectives (i.e. requirements of passengers and rail operators) are proposed and applied in the case of a real metro line in the south of Italy
A sensitivity analysis of recovery solutions in the case of rail disruption management
No full textIn this paper, we propose a sensitivity analysis for evaluating the effectiveness of recovery solutions in the case of disturbed rail operations. Indeed, when failures or breakdowns occur during daily service, new strategies have to be implemented so as to react appropriately and re-establish ordinary conditions as rapidly as possible. In this context, the use of rail simulation is vital: for each intervention strategy it provides the evaluation of interactions and performance analysis prior to application of corrective action. However, in most cases, simulation tasks are deterministic and fail to allow for the stochastic distribution of train performance and delays. Hence the strategies adopted might not be robust enough to ensure effectiveness of the intervention. We therefore propose an off-line procedure for disruption management based on a microscopic and stochastic rail simulation which considers both service operation and travel demand. An application on a real metro line in Naples (Italy) shows the benefits of the proposed approach in terms of service quality
The influence of dwell times on rail service planning
No full textDue to the constant increase in travel demand, rail systems are more and more dense and service providers have the difficult task of planning a timetable which has to be robust and stable. Moreover, in order to increase customers??? satisfaction, it is necessary to provide sufficient transport capacity avoiding train and platform congestion and guaranteeing a good level of service quality. To reach this target, in this framework we provide an appropriate timetable evaluation which considers the dynamic effect of dwell time at station on the service in the case of metro networks
Experimental Analyses on Cellular Polymers for Geotechnical Applications
No full textCellular polymers represent an important category within the area of the polymeric materials. Although these materials are experiencing a growing importance from both an industrial and an economic point of view, there is not such a big and detailed corresponding scientific literature. Except for the researches directly supported by the manufacturing companies, mainly interested, there are only few scientific and engineering studies about this argument. This article is aimed to the geotechnical characterisation of the rigid polyurethane foam and the extruded polystyrene foam and their physical- mechanical properties. The mechanical behaviour is investigated through oedometric and triaxial tests, performed in either PUR and XPS samples at different densities. As a result, the influence of the density on the relationship stress-strain for the materials is obtained. Practical methods and procedures about how to adapt the geotechnical tests on such materials, different from the soil, are also illustrated. At the end of the analyses, a first attempt of interpretation is given, so that an analytical model for the geotechnical description of cellular polymers can be developed
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