DATA ASSIMILATION BASED NUMERICAL SIMULATIONS TO ASSIST REAL-TIME SMOKE CONTROL MANAGEMENT IN LARGE SPACES

Abstract The work presented in this paper illustrates the concept of numerical simulations for real-time 'Numerical Fire Forecast' (NFF), applied to smoke control management in large spaces. The numerical calculations performed within the Inverse Zone Modelling framework are based on a series of full scale experiments conducted using the Japanese Building Research Institute (BRI) fire test facility. The experimental set-up consists of a large space of 720m 2 floor area and 26.3m ceiling height, equipped with shafts and fans to study different smoke control options. The measurements include the smoke layer interface (from thermocouples, photometers and visual observation), the smoke layer temperature at different heights (using thermocouples) and the mass flows of air and hot smoke through mechanical and natural vents. In the case of natural filling (i.e. no mechanical or natural venting), the assimilation of smoke layer height data within a 30 s window results in more than 4 minutes lead time of the forecast, with a good level of confidence. Predictions are given in terms of smoke layer height and upper layer temperature. The steady-state value of the methanol fire (Q c = 1300 kW) has been estimated after 30 s with less than 10% error. Widening the assimilation window does not improve the forecast. When mechanical ventilation is activated after the assimilation process with a sufficiently high exhaust rate, the forecast shows with a relatively substantial positive lead time, safe levels of smoke interface height. Introduction Fire Safety Engineering is a multi-disciplinary science, which aims at designing fire-safe buildings with appropriate solutions to preserve property and, most importantly, human life. Therefore, before the construction (or the renovation) of a building, architects, fire engineers and regulators need to consider a given set of fire scenarios in order to examine different options and choose the most appropriate one(s). For this purpose, a large amount of tools have been developed across the years in order to provide an answer to various questions that arise when studying the complex phenomenon of a fire. These questions are often related to the integrity of the building (fire resistance of the structure), fire and smoke spread, and evacuation. The tools used range from simple engineering hand-calculations to the more sophisticated computational fluid and solid mechanics. Many fire simulation tools have been developed to provide guidance in a priori studies. The level of complexity already reached in these tools and the required computational resources render their use for real time predictions impossible. Subsequently, fire fighters have to rely on their intuition and experience as to the decisions and actions to take in real fire situations. It is in this context that the concept of sensor assisted fire fighting has emerge

A multi-modal video analysis approach for car park fire detection

In this paper a novel multi-modal flame and smoke detector is proposed for the detection of fire in large open spaces such as car parks. The flame detector is based on the visual and amplitude image of a time-of-flight camera. Using this multi-modal information, flames can be detected very accurately by visual flame feature analysis and amplitude disorder detection. In order to detect the low-cost flame related features, moving objects in visual images are analyzed over time. If an object possesses high probability for each of the flame characteristics, it is labeled as candidate flame region. Simultaneously, the amplitude disorder is also investigated. Also labeled as candidate flame regions are regions with high accumulative amplitude differences and high values in all detail images of the amplitude image's discrete wavelet transform. Finally, when there is overlap of at least one of the visual and amplitude candidate flame regions, fire alarm is raised. The smoke detector, on the other hand, focuses on global changes in the depth images of the time-of-flight camera, which do not have significant impact on the amplitude images. It was found that this behavior is unique for smoke. Experiments show that the proposed detectors improve the accuracy of fire detection in car parks. The flame detector has an average flame detection rate of 93%, with hardly any false positive detection, and the smoke detection rate of the TOF based smoke detector is 88%. © 2012 Elsevier Ltd

Increasing the simulation performance of large-scale evacuations using parallel computing techniques based on domain decomposition

Evacuation simulation has the potential to be used as part of a decision support system during large-scale incidents to provide advice to incident commanders. To be viable in these applications, it is essential that the simulation can run many times faster than real time. Parallel processing is a method of reducing run times for very large computational simulations by distributing the workload amongst a number of processors. This paper presents the development of a parallel version of the rule based evacuation simulation software buildingEXODUS using domain decomposition. Four Case Studies (CS) were tested using a cluster, consisting of 10 Intel Core 2 Duo (dual core) 3.16 GHz CPUs. CS-1 involved an idealised large geometry, with 20 exits, intended to illustrate the peak computational speed up performance of the parallel implementation, the population consisted of 100,000 agents; the peak computational speedup (PCS) was 14.6 and the peak real-time speedup (PRTS) was 4.0. CS-2 was a long area with a single exit area with a population of 100,000 agents; the PCS was 13.2 and the PRTS was 17.2. CS-3 was a 50 storey high rise building with a population of 8000/16,000 agents; the PCS was 2.48/4.49 and the PRTS was 17.9/12.9. CS-4 is a large realistic urban area with 60,000/120,000 agents; the PCS was 5.3/6.89 and the PRTS was 5.31/3.0. This type of computational performance opens evacuation simulation to a range of new innovative application areas such as real-time incident support, dynamic signage in smart buildings and virtual training environments

DG-FEM solution for nonlinear wave-structure interaction using Boussinesq-type equations

We present a high-order nodal Discontinuous Galerkin Finite Element Method (DG-FEM) solution based on a set of highly accurate Boussinesq-type equations for solving general water-wave problems in complex geometries. A nodal DG-FEM is used for the spatial discretization to solve the Boussinesq equations in complex and curvilinear geometries which amends the application range of previous numerical models that have been based on structured Cartesian grids. The Boussinesq method provides the basis for the accurate description of fully nonlinear and dispersive water waves in both shallow and deep waters within the breaking limit. To demonstrate the current applicability of the model both linear and mildly nonlinear test cases are considered in two horizontal dimensions where the water waves interact with bottom-mounted fully reflecting structures. It is established that, by simple symmetry considerations combined with a mirror principle, it is possible to impose weak slip boundary conditions for both structured and general curvilinear wall boundaries while maintaining the accuracy of the scheme. As is standard for current high-order Boussinesq-type models, arbitrary waves can be generated and absorbed in the interior of the computational domain using a flexible relaxation technique applied on the free surface variables. (c) 2007 Elsevier B.V. All rights reserved

A new class of glycomimetic drugs to prevent free fatty acid-induced endothelial dysfunction

Background: Carbohydrates play a major role in cell signaling in many biological processes. We have developed a set of glycomimetic drugs that mimic the structure of carbohydrates and represent a novel source of therapeutics for endothelial dysfunction, a key initiating factor in cardiovascular complications. Purpose: Our objective was to determine the protective effects of small molecule glycomimetics against free fatty acid­induced endothelial dysfunction, focusing on nitric oxide (NO) and oxidative stress pathways. Methods: Four glycomimetics were synthesized by the stepwise transformation of 2,5­dihydroxybenzoic acid to a range of 2,5­substituted benzoic acid derivatives, incorporating the key sulfate groups to mimic the interactions of heparan sulfate. Endothelial function was assessed using acetylcholine­induced, endotheliumdependent relaxation in mouse thoracic aortic rings using wire myography. Human umbilical vein endothelial cell (HUVEC) behavior was evaluated in the presence or absence of the free fatty acid, palmitate, with or without glycomimetics (1µM). DAF­2 and H2DCF­DA assays were used to determine nitric oxide (NO) and reactive oxygen species (ROS) production, respectively. Lipid peroxidation colorimetric and antioxidant enzyme activity assays were also carried out. RT­PCR and western blotting were utilized to measure Akt, eNOS, Nrf­2, NQO­1 and HO­1 expression. Results: Ex vivo endothelium­dependent relaxation was significantly improved by the glycomimetics under palmitate­induced oxidative stress. In vitro studies showed that the glycomimetics protected HUVECs against the palmitate­induced oxidative stress and enhanced NO production. We demonstrate that the protective effects of pre­incubation with glycomimetics occurred via upregulation of Akt/eNOS signaling, activation of the Nrf2/ARE pathway, and suppression of ROS­induced lipid peroxidation. Conclusion: We have developed a novel set of small molecule glycomimetics that protect against free fatty acidinduced endothelial dysfunction and thus, represent a new category of therapeutic drugs to target endothelial damage, the first line of defense against cardiovascular disease

Intérêt des modèles des plus proches voisins pour le contrôle de l'hétérogénéité spatiale : application à un essai de provenances de pin d'Alep (pinus halepensis mill.) en Tunisie

peer reviewedTo study the importance of the spatial analysis in the control of soil heterogeneity in experiment on field, three approaches of statistical analysis were applied to a total height of trees measured at 29 years of age in a comparative test of thirty origins of Aleppo pine (Pinus halepensis Mill.), autochtonous and introduced in Tunisia. Analysis without control of heterogeneity (totally random), with a global control of heterogeneity (complete blocks) and with a local control of heterogeneity (nearest neighbour models) were used. For this last approach using to estimate the plot fertility the one of the nearby plots, various combinations of neighbour were tested with one or two coefficients of regression. The obtained results showed that the reduction of the residual mean square by comparison to the analysis without control of heterogeneity is 30 % to the complete blocks analysis and varied between 66 and 79 % for spatial analysis. Significant positive correlations between plots residues and the average of the residues of the nearby plots were observed before adjustment of data. After adjustment of data by the nearest neighbour models, these correlations were registered a reduction from 92 to 95 % according to the used model. Among the six nearest neighbour models studied, the model bringing in eight neighbours with two coefficients of regression showed itself the most effective. It also seemed that after adjustment of data by nearest neighbour models, using the structure of blocks does not produce a reduction of the residual mean square.Afin d'étudier l'importance des analyses spatiales dans le contrôle de l'hétérogénéité du terrain en expérimentation sur champ, trois approches d'analyses statistiques ont été appliquées à la hauteur totale des arbres mesurée à 29 ans d'âge dans un essai comparatif d'une trentaine de provenances de pin d'Alep (Pinus halepensis Mill.) autochtones et introduites en Tunisie. Il s'agit des analyses sans contrôle d'hétérogénéité (Complètement aléatoire - CA), avec un contrôle globa de l'hétérogénéité (Blocs Aléatoires Complets - BAC) et avec un contrôle local de l'hétérogénéité du terrain (Modèles des Plus Proches Voisins - MPPV). Pour cette dernière approche qui consiste à utiliser pour l'estimation de la performance propre de chaque parcelle celles des parcelles voisines, différentes combinaisons des voisins les plus proches ont été testées avec chaque fois un ou deux coefficients de régression. Les résultats obtenus ont montré que la réduction de la variance résiduelle par rapport à l'analyse sans contrôle d'hétérogénéité est de l'ordre de 30 % pour l'analyse en BAC et varie de 66 à 79 % pour les MPPV. Des corrélations positives très hautement significatives entre les résiduelles des différentes parcelles et la moyenne des résiduelles des parcelles voisines ont été observées avant ajustement des données à l'effet terrain. Après ajustement des données à l'aide des MPPV, ces corrélations ont enregistré une réduction de l'ordre de 92 à 95 % selon le modèle utilisé. Parmi les six modèles des plus proches voisins étudiés, le modèle faisant intervenir les huit voisins avec deux coefficients de régression s'est montré le plus efficace. Il est apparu également qu'après ajustement des données à l'aide des MPPV, la prise en compte de la structure en blocs n'entraîne pas une réduction de la variance résiduelle

Large Eddy Simulations of a Set of Experiments with Water Spray-Hot Air Jet Plume Interactions

© 2019, Springer Nature B.V. Large eddy simulations of water spray-hot air jet plume interactions, as obtained with FireFOAM 2.2.x, are presented. Three hot air jet plumes, with thermal powers of 1.6, 2.1 and 2.6 kW, are examined, interacting with a water spray with discharge rate of 0.084 lpm. A systematic comparison between simulations and experiments involving only the hot air jet plumes, the water spray alone and the combination of the two has been performed in order to evaluate the predictive capabilities of FireFOAM. Overall, the code is capable of predicting well the mean values of the hot air jet plumes but deviations are evident for the rms values. Discrepancies in the predictions of the volume fluxes in the near-field for the water spray alone case are observed if the experimentally reported injection angle is used. Improvements are observed if the injection angle is modified based on the experimentally reported data in the near-field. The interactions between the hot air jet plumes and water sprays, are characterized by the location of the interaction region. The interaction boundary moves up from the base of the plume by increasing the convective heat release rates. The simulation results follow the experimental trend but deviate up to 26% due to the differences in the predicted hot air jet plumes and spray characteristics.status: publishe