This thesis describes the implementation of the conditional moment closure (CMC) combustion model in a numerical scheme and its application to the modelling of enclosure fires. Prediction of carbon monoxide (CO) in the upper smoke layer of enclosure fires is of primary interest because it is a common cause of death. The CO concentration cannot be easily predicted by empirical means, so a method is needed which models the chemistry of a quenched, turbulent fire plume and subsequent mixing within an enclosed space. CMC is a turbulent combustion model which has been researched for over a decade. It has provided predictions of major and minor species in jet diffusion flames. The extension to enclosure fires is a new application for which the flow is complex and temperatures are well below adiabatic conditions. Advances are made in the numerical implementation of CMC. The governing combustion equations are cast in a conserved, finite volume formulation for which boundary conditions are uniquely defined. Computational efficiency is improved through two criteria which allow the reduction in the size of the computational domain without any loss of accuracy. Modelling results are compared to experimental data for natural gas fires burning under a hood. Comparison is made in the recirculating, post-flame region of the flow where temperatures are low and reactions are quenched. Due to the spatial flux terms contained in the governing equations, CMC is able to model the situation where chemical species are produced in the high temperature fire-plume and then transported to non-reacting regions. Predictions of CO and other species are in reasonable agreement with the experimental data over a range of lean and rich hood-fire conditions. Sensitivity of results to chemistry, temperature and modelling closures is inves- tigated. Species predictions are shown to be quite different for the two detailed chemical mechanisms used. Temperature conditions within the hood effect the for- mation of species in the plume prior to quenching and subsequently species predic- tions in the post-flame region are also effected. Clipped Gaussian and ß-function probability density functions (PDFs) are used for the stochastic mixture fraction. Species predictions in the plume are sensitive to the form of the PDF but in the post-flame region, where the ß-function approaches a Gaussian form, predictions are relatively insensitive. Two models are used for the conditional scalar dissipation: a uniform model, where the conditional quantity is set equal to the unconditional scalar dissipation across all mixture fraction space; and a model which is consistent with the PDF transport equation. In the plume, predictions of minor species are sensitive to the modelling used, but in the recirculating, post-flame region species are not significantly effected.

Thesis (M.S.) in Forestry--University of Maine, 2004. / Includes vita. Includes bibliographical references (leaves 104-115).

Graduation date: 1999

La mayoría de los bosques del planeta, exceptuando, quizá, el cinturón más húmedo del trópico, han sufrido perturbaciones recurrentes por incendios, desde hace miles de años. Sin embargo, en el último siglo, la combinación de factores socio-económicos y ambientales han alterado la frecuencia y distribución de incendios en casi todos los ecosistemas forestales. Esta mala distribución del fuego ha conllevado la acumulación de este elemento perturbador en ecosistemas poco adaptados a su presencia (e.g. bosques tropicales húmedos), mientras que otros ecosistemas han sufrido los efectos de las políticas de supresión de incendios (e.g. bosques templados norteamericanos). Entre las consecuencias de estas alteraciones, algunas se refieren a variaciones en el régimen de incendios, con implicaciones en términos de conservación forestal, impacto ecológico, económico y social. La presente tesis analiza la influencia de factores ambientales y socio-económicos en algunas características del régimen de incendios en ecosistemas tropicales y mediterráneos. En el ámbito tropical, la zona de estudio es el Estado mexicano de Chiapas, y los objetivos son básicamente dos: 1) caracterizar el régimen de incendios en el Estado, en términos de frecuencia de incendios, distribución, áreas y ecosistemas afectados, tipología de incendios, causalidad, y su interacción con algunos factores como el fenómeno de El Niño, la distribución de la tenencia de la tierra o la variación de las precipitaciones. 2) Analizar la influencia relativa de factores ambientales frente a factores socio-económicos, en años de condiciones climáticas normales y años de El Niño. El objetivo último era determinar variaciones en la afectación de los principales ecosistemas y listar los factores más importantes a considerar, a nivel de gestión forestal contra incendios. A nivel de ecosistemas mediterráneos, se seleccionó el incendio del Solsonés 1998, como caso estudio, siendo los principales objetivos: 3) Seleccionar la metodología de clasificación post-incendio más eficiente entre varias técnicas analizadas (teledetección y muestreo de campo). 4) Analizar la influencia de diversos factores ambientales en la formación de islas de vegetación en un gran incendio, empleando las laderas como unidad espacial. 5) Verificar la importancia de la estructura forestal y la continuidad del combustible en la heterogeneidad final de las severidades de afectación de un incendio. En relación a estos objetivos, las principales aportaciones de este estudio han sido, en lo referente a ecosistemas tropicales: La descripción de los incendios en Chiapas como mayoritariamente superficiales, afectando principalmente a estratos no arbóreos, de grandes dimensiones, de origen antrópico y con cierta propensión a afectar zonas protegidas. La aportación clave sin embargo, hace referencia a la demostración de la importancia de El Niño en la afectación de los ecosistemas tropicales húmedos, principalmente influenciado por la presencia de pastos alrededor de bosques fragmentados. El cambio de importancia relativa de los factores ambientales en años de no-ENSO frente a la mayor importancia de los factores socio-económicos en años de ENSO. También se puede remarcar el cambio de ecosistema afectado condicionado por el tipo de año (condiciones climáticas normales o extremas, ENSO o no ENSO: pino-encino versus bosques tropicales húmedos). En relación a los bosques mediterráneos, las técnicas más sencillas de teledetección resultaron las adecuadas para la identificación de islas. La formación de estas islas se ve condicionada por el tamaño y orientación y pendiente de las laderas, así como la cantidad y madurez de los rodales afectados, siendo las laderas más extensas, de orientación noroeste, de mayor pendiente, con mayores extensiones forestales y bosques más maduros (en términos de mayores tamaños), las más propicias a formar islas. Las características estructurales de los rodales fue de gran importancia para predecir la supervivencia forestal en zonas de condiciones climáticas moderadas. / The great majority of the forests of the world, excepting perhaps, the wettest belt of the tropics, have been burned over, at more or less frequent intervals, for many thousands of years. In the last century however, a combination of human and environmental factors have altered the frequency and distribution of fire, almost everywhere. This maldistribution of fire has resulted in an accumulation of this element in ecosystems not adapted to high frequencies of fire (i.e. tropical and sub-tropical areas), while other ecosystems have suffered the effects of fire suppression policies (i.e. north American temperate forests). Among the consequences of these alterations, some of them refer to variations in fire regimes, with implications in terms of forest conservation, ecological, economic and social impact. The present thesis analyses the influence of environmental and socio-economic factors for certain elements of the fire regime in tropical and Mediterranean ecosystems. In tropical areas, the study case relates to the tropical Mexican State of Chiapas, and the objectives are basically two: 1) to characterize the fire regime in the State, in terms of frequency of fires, fire distribution, areas and ecosystems affected, type of fires, causality, and their interaction with some factors like the phenomenon of El Niño, the land distribution, or the variation of rainfall values. 2) To analyse the relative influence of environmental factors versus socio-economic factors, in years of normal climatic conditions and years of El Niño. The final objective is to detect variations in the affectation of the major ecosystems and to list the most important factors to consider for forest fire management. For the Mediterranean ecosystems, the fire of Solsonés 1998 was selected as case study. Main objectives are: 3) To select the most efficient methodology for post-fire classification among several techniques: image classification and field survey. 4) To determine the influence of diverse environmental factors in the formation of vegetation islands inside a large forest fire, using "slope", as the spatial unit. 5) To verify the importance of forest structure and fuel continuity in the final heterogeneity of fire severities in a large fire. In relation to these objectives, the main contributions of this study are, with respect to tropical ecosystems: The characterization of fires in Chiapas, as in other tropical areas, mainly as superficial fires, frequently affecting non-arboreal layers. Major problems focus on large forest fires, which are responsible for the major burned areas. Fires are mainly human related and display certain propensity to affect protected zones. The key contribution nevertheless, refers to the major importance of El Niño in the affectation of humid tropical ecosystems. This is specially enhanced by the presence of cattle pasture surrounding the fragmented forests. The shift on the importance of environmental factors in years of no-ENSO versus the greater importance of socio-economic factors in years of ENSO, is also a major achievement. Moreover, shifts in ecosystem affectation have also been observed depending on the climatic conditions: pine-oak in no-ENSO years versus humid tropical forests in ENSO years. Regarding the Mediterranean forests, the simplest techniques of teledetection were the best performing ones for island identification. The formation of these islands is conditioned by the size and aspect of the slopes, as well as by the amount and maturity of the affected patches. Most extensive slopes, north-western orientations, more abrupt, larger forest extensions per slope, and more mature forests (in terms of greater sizes), are the most suitable combination of factors to form islands. This formation of islands does not have, therefore, a random distribution. Besides, the structural characteristics of the forest patches was confirmed to be of great importance to predict the forest survival in areas were fire burned under moderate climatic conditions. Larger patches and larger trees are the ones that will survive fire the best.

Thesis (M.S.)--Boise State University, 2009. / Includes abstract. Includes bibliographical references (leaves 81-91).

Title from PDF of title page (University of Missouri--Columbia, viewed on Feb 18, 2010). The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Thesis advisor: Dr. Mark R. Ryan and Mike Hubbard. Includes bibliographical references.

published_or_final_version / Botany / Doctoral / Doctor of Philosophy

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