Forest fire modelling

2011 - 2012Wildland fires have always been undesired and dangerous events. The danger includes the destruction of a renewable natural resource, damage of the atmospheric environment through the emissions of pollutant gases, which contribute to the greenhouse effect, and threat to the lives of people living in the areas surrounding the place where fire occurs and of the members of firefighting teams. To cope with all this, it is necessary to know the behaviour of the fire in order to be able to make adequate and proper decisions that will assist activities implemented in fire suppression and prevention. In this context, fire behaviour modelling is utilized to determine these characteristics and to simulate fire propagation in a variety of vegetations, under diverse climatic and topographic conditions. In this context, the aim of the thesis work was to study and describe the fire propagation under different fuel features and boundary conditions with particular attention to terrain configurations where fire propagation may be characterized by abrupt variations in intensity and propagation rate. These areas include double-slope domain and canyons where such a phenomena (commonly identified as eruptive behaviour) occurs without any change in the main factors governing the fire propagation (i.e. atmospheric condition, vegetative fuel, domain topography). This work aims to provide an increase of knowledge in the fire spreading, currently still limited, thanks to the adoption of a physically-based code (WFDS) to model flame propagation; in fact, through the numerical resolution of the fundamental balance equation describing the fire phenomenon, it offers a way to analyze the fire behaviour on a scientific basis. To purse this target different aspects, reported in different chapters, were considered in this work. The first part examines shortly the social, economical and ecological impact of wildland fires on a global scale and for the countries of the Euro–Mediterranean region. The role of fire behaviour modelling as a tool for fire fighting activities and prevention management is put in evidence and discussed. The second part endeavours a short review of the main surface fire spread models developed since 1990 with particular attention to physically-based codes. These models are alternative to empirical or quasi-empirical models, which do not have physical basis and are only statistical in nature or make use of some form of physical framework upon which to base the statistical modelling chosen. A comparison between the most frequently used simulation codes is accomplished and the advantages to consider a physical code - for instance WFDS - rather than an empirical or quasi-empirical one is highlighted. [edited by Author]XI n.s

The role of the terrain geometry on the flames propagation through a vegetative fuel bed

When a wildland fire occurs the domain geometry is a key parameter in governing the way the fire spreads across the terrain. The effect of this variable on the rate of flames propagation was investigated in this work by means of a computational fluid dynamics software specifically designed to simulate fires in wildland environment. The physics-based model - i.e. relied on the laws of conservation of momentum, energy and mass – was adopted under two different domain configurations (double-slope domains and canyon); the capability of the computational code to correctly predict the fire behaviour was verified by comparison with results of experimental tests available in the literature

Modelling of a Catalytic Micro-Reactor Coupling Endothermic Methane Reforming and Combustion

In this study the mathematical modelling of a catalytic microstructured plate reactor for the production of hydrogen was performed in 2D and 3D geometry. The proposed reacting system uses the heat generated by an exothermic reaction (combustion) to sustain endothermic reforming reactions. Therefore, it pertains to those devices useful for producing the feed for fuel cell system for the remote generation of electrical power. However, because of the compactness of the reacting system it can also be considered in the context of apparatus aiming at process intensification. Within this frame the catalytic contribution of both exothermic and endothermic reactions was modeled considering the classic Langmuir- Hinshelwood surface kinetic theory. The advantage of using a real 3D geometry configuration consists in the possibility of considering the importance of the entering and boundary effects with particular attention to fluid stagnation and heat hot spots. The trade off of such a choice is certainly the huge increase of computing time and/or of the power of the computing facility. With respect to other works performed with similar reactor geometry and reacting systems this does not use simplifying assumptions such as catalyst layers modeled by one-dimensional approach, fully developed laminar flow or transverse heat and mass transfer taken into account through lumped heat and mass transfer coefficients. Results of simulations presented here concentrates on the comparisons between results of: countercurrent (CTC) and concurrent (CNC) flow patterns of the reactant streams; of simulations carried out with 2D and 3D models and of the influence of the thickness of the catalytic layers on the reactor performance. Simulations indicates that CNC flow pattern of reactants streams allows a better performance of the reactor since positive temperature differences between the catalyst layers and the gas in the channels maintain along the whole reactor and, consequently, there are not heat flux inversions, which occur under CTC flow pattern. Results also showed that as concerns an adiabatic reactor, whatever the operating conditions, 2D and 3D models yield substantially the same results. Finally, modelling demonstrated that for a realistic catalyst layer configuration thicknesses larger than 50 _m are useless for enhancing the reactor performance. The feasibility of the model proposed may show its potential in fast and easy implementation of several combustion and reforming fuels so to significantly enhance the performance prediction of real processes

Micro-Scale Catalytic Reactor for Syngas Production

This paper presents both experimental and modeling investigations of a catalytic wall fuel processor consisting of coupled methane reforming and methane combustion sections. The reacting systems are both catalytic and the latter generates the heat required for the occurrence of the former. The catalytic wall reactor was examined for light-off behavior and for steady-state product distribution. On one hand, the analysis of the reaction products distribution after catalyst ignition indicated that in both combustion and reforming sections catalysts undergo to a relatively long transient (about 40 min) before reaching steady state conditions. On the other hand, a much longer reactor thermal transient was observed and the two transient behaviors appear independent of each other. Analysis of the reactor operating under real conditions (nonadiabatic) showed that a 3D model is needed to accurately predict the reactor performance because a 2D model, although much more convenient, cannot allow for the whole heat loss thereby yielding unreliable results

Fire behaviour in canyons due to symmetric and asymmetric ignitions

The eruptive propagation of a fire is a particular behaviour characterized by a sudden increase in the rate of spread and intensity without any change in the external driving forces such as wind velocity and ambient temperature, vegetation type and moisture content. It is, therefore, a local or internal dynamic connected with the terrain configuration and the ignition position that regulates fire spreading and causes its acceleration. This phenomenon is particularly evident and common in canyons. This work aims to study the effect ignition position on the fire propagation in a canyon by means of a physically-based computational code. The code WFDS was shown to be effective to describe the fire behaviour throughout such a terrain configuration

The effects of psychoeducational family intervention on coping strategies of relatives of patients with bipolar i disorder: Results from a controlled, real-world, multicentric study

Background: Psychoeducational family intervention (PFI) has been proven to be effective in improving the levels of family burden and patients\u2019 personal functioning in schizophrenia and bipolar disorders (BDs). Less is known about the impact of PFI on relatives\u2019 coping strategies in BD. Methods: A multicenter, controlled, outpatient trial funded by the Italian Ministry of Health and coordinated by the Department of Psychiatry of the University of Campania \u201cLuigi Vanvitelli\u201d has been conducted in patients with bipolar I disorder (BD-I) and their key relatives consecutively recruited in 11 randomly selected Italian community mental health centers. We aim to test the hypothesis that PFI improves problem-oriented coping strategies in relatives of BD-I patients compared to the Treatment As Usual (TAU) group. Results: The final sample was constituted of 123 patients and 139 relatives. At baseline assessment (T0), the vast majority of relatives already adopted problem-oriented coping strategies more frequently than the emotion-focused ones. At the end of the intervention, relatives receiving PFI reported a higher endorsement of adaptive coping strategies, such as \u201cmaintenance of social interests\u201d (odds ratio [OR]=0.309, CI=0.04\u20130.57; p=0.023), \u201cpositive communication with the patient\u201d (OR=0.295, CI=0.13\u20130.46; p=0.001), and \u201csearching for information\u201d (OR=0.443, CI=0.12\u20130.76; p=0.007), compared to TAU relatives, after controlling for several confounders. As regards the emotion-focused coping strategies, relatives receiving the experimental intervention less frequently reported to adopt \u201cresignation\u201d (OR=-0.380, CI=-0.68 to -0.08; p=0.014) and \u201ccoercion\u201d (OR=-0.268, CI=-0.46 to -0.08; p=0.006) strategies, compared to TAU relatives. Conclusion: PFI is effective in improving the adaptive coping strategies of relatives of BD-I patients, but further studies are needed for evaluating the long-term benefits of this intervention