Integration of a 1D model with FDS for multiscale analysis of tunnels

Numerical simulations are used to reduce the number of tests required in a lot of scientific fields. It works in that way in the field of Fire science with the usage of CFD (Computational Fire Dynamics). Fire simulations take less time to complete as computer sciences advance. But tunnel simulations with long domains still take long times limiting the opportunities to develop applications in fields that require live time results, like risk assessment, emergency systems, etc. A Multiscale algorithm is presented. This algorithm integrates Whitesmoke, a 1D algorithm developed to simulate fluid flow in networks, into FDS (Fire Dynamics Simulator), a 3D LES program used to simulate fire dynamics. The aim of this integration is optimizing both the calculation time and accuracy, using the fast solutions of the 1D in uniform zones and the detailed solutions of the FDS in complex areas. The accuracy of the Multiscale is evaluated by comparing it to full 3D simulations. In this case, a tunnel of 4.8m x 4.8m and 600m of length is simulated. The flow velocities and temperature of Multiscale and FDS simulations are compared. The Multiscale model achieves a time saving that is closely proportional to the portion of the domain calculated with the 1D sub-model. And, even when the simulation time is shorter the difference with the outputs obtained by the FDS is small in temperature, velocities and backlayering extension. The presented model is capable of reducing the time necessary to make a tunnel fire simulation without jeopardizing its results. Still, the Multiscale has some areas to improve and develop, as its boundary conditions, which should be improved further in the future

Calculations of fire smokes behaviour in long rail tunnels

In order to simulate fire consequences in complex underground networks, we want to implement a coupling between a ID ventilation code and a CFD model or a zone model. The project consists in 3 main steps: the development of a ID ventilation code whose programming structure will support a coupling with another code, the definition of exchange of boundary conditions between the 2 codes and the validation of this exchange. In this paper we present our new ID code developed in this framework. A case study shows the global reaction of the flow to a fire and proves the interest of keeping into account the whole network instead limiting the calculation domain to a zone closed to the accident

Target Tracking in Confined Environments with Uncertain Sensor Positions

To ensure safety in confined environments such as mines or subway tunnels, a (wireless) sensor network can be deployed to monitor various environmental conditions. One of its most important applications is to track personnel, mobile equipment and vehicles. However, the state-of-the-art algorithms assume that the positions of the sensors are perfectly known, which is not necessarily true due to imprecise placement and/or dropping of sensors. Therefore, we propose an automatic approach for simultaneous refinement of sensors' positions and target tracking. We divide the considered area in a finite number of cells, define dynamic and measurement models, and apply a discrete variant of belief propagation which can efficiently solve this high-dimensional problem, and handle all non-Gaussian uncertainties expected in this kind of environments. Finally, we use ray-tracing simulation to generate an artificial mine-like environment and generate synthetic measurement data. According to our extensive simulation study, the proposed approach performs significantly better than standard Bayesian target tracking and localization algorithms, and provides robustness against outliers.Comment: IEEE Transactions on Vehicular Technology, 201

Innovative Modelling Approaches for the Design, Operation and Control of Complex Energy Systems with Application to Underground Infrastructures

The ventilations systems play a key role in underground infrastructures for health and safety of occupants during normal operation as well as during accidents. Their performances are affected by selection of the optimal design, operation and control that is investigated by predicting air flow. The calculation of ventilation flows and their interaction with fires can be done with different modelling approaches that differ in the accuracy and in the required resources. The 3D computational fluid dynamics (CFD) tools approximate the flow behaviour with a great accuracy but they require high computational resources. The one dimensional (1D) models allow a compact description of the system with a low computational time but they are unsuitable to simulate thermal fluid-dynamic scenarios characterized by turbulence and gradients. Innovative tools are necessary in order to make the analysis and optimization of these systems possible and accurate in a reasonable time. This can be achieved both with appropriate numerical approaches to the full domain as the model order reduction techniques and with the domain decompositions methods as the multiscale physical decomposition technique. The reduced order mode techniques as the proper orthogonal decomposition (POD) is based on the snapshots method provides an optimal linear basis for the reconstruction of multidimensional data. This technique has been applied to non-dimensional equations in order to produce a reduced model not depending on the geometry, source terms, boundary conditions and initial conditions. This type of modelling is adapted to the optimization strategies of the design and operation allowing to explore several configuration in reduced times, and for the real time simulation in the control algorithms. The physical decomposition achieved through multiscale approaches uses the accuracy of the CFD code in the near field e.g. the region close to the fire source, and takes advantage of the low computational cost of the 1-D model in the region where gradients in the transversal direction are negligible. In last years, the multiscale approach has been proposed for the analysis of tunnel ventilation. Among the several CFD codes used in this field, the Fire Dynamic Simulator (FDS) is suitable for the multiscale modelling. This is an open source CFD package developed by NIST and VTT and presents the HVAC routine in which the conservation equations of mass, energy and momentum are implemented. Currently, the HVAC module does not allow one to consider heat and mass transfer, which significanltly limits the applications. For these reasons a multiscale simulator has been created through the fully integration of a 1D continuity, momentum, energy and mass transport equation in FDS modifying its source codes. The multiscale simulator thus obtained, is based on a direct coupling by means of a Dirichlet-Neumann strategy. At each 1-D-CFD interface, the exchange flow information occurs prescribing thermo-fluid dynamic boundary conditions. The 1-D mass transport equation computes the diffusion of the exhaust gas from the CFD domain and the relative concentration that is particularly interesting in the case of back layering of smoke. The global convergence of the boundary conditions at each 1-D-CFD interface has been analyzed by monitoring the evolution of thermo-fluid dynamic variables (temperature, velocity, pressure and concentration. The multiscale simulator is suitable for parametric and sensitivity studies of the design and the operation ventilation and fire safety systems. This new tool will be available for all the scientific community. In this thesis, Chapter 1 provides a general introduction to the role of the system ventilation in underground infrastructures and to the innovative modelling strategies proposed for these systems. Chapter 2 offers a description of the 1D network modelling, its fluid-dynamic application to the Frejus tunnel and its thermal application to ground heat exchangers. In Chapter 3, the proper orthogonal decomposition method is presented and its application to the optimal control of the sanitary ventilation for the Padornelo Tunnel is discussed. To demonstrate the applicability of POD method in other fields, boreholes thermal energy storage systems have been considered in same chapter. In particular, a multi-objective optimization strategy is applied to investigate the optimal design of these system and an optimization algorithm for the operation is proposed. Chapter 4 describes the multiscale approach and the relative simulator. The new open tool is used for modeling the ventilation system of the Monte Cuneo road tunnel in case of fire. Results show that in the case of the current configuration of the ventilation system, depending on the atmospheric conditions at portals, smoke might not be fully confined. Significant improvements in terms of safety conditions can be achieved through increase of in smoke extraction, which requires the installation of large dumpers and of deflectors on the jet fans. The developed tool shows to be particularly effective in such analysis, also concerning the evaluation of local conditions for people evacuation and fire-brigades operation

Entropy-Preserving Coupling Conditions for One-dimensional Euler Systems at Junctions

This paper is concerned with a set of novel coupling conditions for the $3\times 3$ one-dimensional Euler system with source terms at a junction of pipes with possibly different cross-sectional areas. Beside conservation of mass, we require the equality of the total enthalpy at the junction and that the specific entropy for pipes with outgoing flow equals the convex combination of all entropies that belong to pipes with incoming flow. Previously used coupling conditions include equality of pressure or dynamic pressure. They are restricted to the special case of a junction having only one pipe with outgoing flow direction. Recently, Reigstad [SIAM J. Appl. Math., 75:679--702, 2015] showed that such pressure-based coupling conditions can produce non-physical solutions for isothermal flows through the production of mechanical energy. Our new coupling conditions ensure energy as well as entropy conservation and also apply to junctions connecting an arbitrary number of pipes with flexible flow directions. We prove the existence and uniqueness of solutions to the generalised Riemann problem at a junction in the neighbourhood of constant stationary states which belong to the subsonic region. This provides the basis for the well-posedness of the homogeneous and inhomogeneous Cauchy problems for initial data with sufficiently small total variation.Comment: 17 pages, 2 figure

Fire safety assessment of open wide gangway underground trains in tunnels using coupled fire and evacuation simulation

A new type of train configuration, known as Open Wide Gangway (OWG) is becoming popular, particularly in underground environments. Previous fire modelling analysis demonstrated that the OWG configuration was considered safe as or safer than conventional configurations as it reduced the likelihood of flashover. However, these studies have ignored the impact on evacuation of the spread of fire effluent to non-fire cars. Here we explore the fire safety offered by conventional and OWG configurations using coupled fire and evacuation modelling techniques. Two tunnel train situations are considered; one in which the car side doors are available for evacuation (train in a wide tunnel) and the other in which only the end cab doors are available (train in a narrow tunnel). Two population configurations are considered, fully and half loaded. Two ignition sources are also considered, one representing an accidental fire and the other an arson fire. The analysis demonstrates that while the OWG configuration may produce improved fire performance in the car of fire origin compared to the conventional configuration, if the interaction of the fire effluent with the evacuating passengers is considered, the OWG configuration results in a significantly greater number of casualties in virtually all the scenarios considered

Experimental approach of the fire hazard in closed spaces : laboratory and full-scale tests

This presentation is intended to open technical discussions at the workshop devoted to fire testing and modelling with regard to the specificity of the fire hazard in various enclosures that are liable to drive the fire scenario (tunnels, warehouses, technical rooms, underground structures). More particularly, the paper outlines INERIS views on the role that can be played by fire tests, from lab-scale to real scale, at the light of a brief historical review and from its own experience. The purpose is illustrated by a number of examples where INERIS has contributed to analyse or solve fire problems, evaluate fire protection systems or potential consequences to the environment or more generally understand related phenomena that can be encountered in closed structures. Eventually, the paper stresses the opportunity and advantages from conjugated use of testing and modelling techniques

Metro systems : Construction, operation and impacts

Peer reviewedPublisher PD

Fire Risk Assessment: A Systematic Review of the Methodology and Functional Areas

Fire is a physical and social phenomenon that affects both individuals and the environment. Fire risk assessment is a critical part of a fire prevention program. In this process, the fire risk associated with the possibility of occurrence and severity of damage resulting from the fire is estimated and calculated. In this paper, a classification scheme and a systematic literature review are presented in order to classify and interpret the current researches on fire risk assessment methodologies and applications. Based on the scheme, 93 scholarly papers from 13 journals are categorized into application areas and other categories. The application areas include the papers on the topics of environmental impact, production and industry, transportation, buildings, power industry, oil and gas industry, urban fires and other topics. Scholarly papers are also classified by (1) year of publication, (2) journal of publication, (3) year of publication and application areas and (4) authors’ nationality. The survey results show that the largest number of papers was published during the period 2010-2012 with 31 (33.33%), the most of the studies have been carried out on environmental impact (47.31%), the journal of Forest Ecology and Management had the highest percentage of articles with 26.88%. It is hoped that the paper can meet the needs of researchers for easy references of fire risk assessment methodologies and applications. Therefore, this work would be able to provide useful insights into the anatomy of the fire-risk assessment methods, and suggest academic researchers and experts a framework for future attempts and researches

The use of multi-zone modelling for tunnel fire risk analysis

Tunnel fire risk analysis are a useful tool to ensure adequate safety levels in tunnels. This report presents the work conducted to integrate a multi-zone modelling approach into a fire risk assessment tool, called ARTU. This work was performed to improve its fire modelling predictive capabilities compared to the currently adopted 1D fire modelling representation. This is deemed to allow for the use of multi-scale modelling, i.e., to select among different modelling approaches in relation to the scenarios under consideration. The multi-zone model integrated within ARTU is based on an existing tool, i.e., the MZ Fire model developed for large spaces which has been updated and adapted for tunnel environments. The integration of MZ Fire model into ARTU involved a set of developments needed specifically for tunnel fire scenarios (e.g. considering tunnel gradient, tunnel section representations, customization of outputs for use in a tunnel fire risk assessment tool, etc.). Those new features are here presented along with a sensitivity analysis looking at zone size. Benchmarking of the results produced is performed through comparison with data from the 2006 BeNeLux tunnel experiments and the 2015 Runehamar experiments. The multi-zone model results were also compared against results from the Fire Dynamics Simulator (FDS) for a set of tunnel configurations