A simulação numérica de escoamentos reativos, como a combustão, tem um caráter altamente não-linear devido a presença de diversas reações químicas que acontecem entre as espécies que descrevem o processo de oxidação do combustível. Além disso, tais processos ocorrem a nível molecular, tornando o sistema de equações governantes rígido, o que implica na necessidade de esquemas numéricos de alta ordem bem como malhas finas e passo de tempo pequeno, aumentando consideravelmente o custo computacional. Neste sentido, o uso de mecanismos de oxidação detalhados na simulação numérica é proibitivo, e técnicas de redução química são necessárias de modo a desenvolver modelos reduzidos com menos variáveis e rigidez moderado, mantendo a precisão e abrangência do modelo detalhado. O objetivo do presente trabalho é obter uma comparação dos resultados obtidos para duas técnicas de redução química diferentes, Directed Relation Graph - DRG, baseada no desenvolvimento de mecanismos esqueletos, e a Reaction Diffusion Manifolds - REDIM, baseada na separação das escalas de tempo. Como validação dos modelos propostos, simulações numéricas 1D de chamas pré-misturadas e não pré-misturadas, bem como de reatores homogêneos, são desenvolvidas. Além disso, uma estratégia que une as duas técnicas de redução é apresentada, com o objetivo de ser aplicada em mecanismos cinéticos grandes. / Numerical simulation of reactive flows, such as combustion, has a highly non-linear character due to the presence of several chemical reactions that occur among the chemical species that describe the process of fuel’s oxidation. Besides, such processes occur at a molecular level, making the system of governing equations stiff, which implies in the need of high order numerical schemes as well as fine meshes and small time step, enhancing considerably the computational cost. In this sense, the use of detailed oxidation mechanisms in the numerical simulation is prohibitive, and chemical reduction techniques are needed in order to develop reduced models with less variables and moderate stiffness, while maintaining the accuracy and comprehensiveness of the detailed model. The objective of the present works if to obtain a comparison between two chemical reduction techniques, the Directed Relation Graph - DRG, based on the skeletal mechanisms generation, and the Reaction Diffusion Manifolds - REDIM, based on the separation of time scales. As validation of the proposed models, one-dimensional numerical simulations of premixed and non-premixed flames, as well as homogeneous reactors, are carry out. Besides, a coupled methodology between DRG and REDIM is presented, that will provide a useful tool for simulation of fuels with very large detailed kinetic mechanisms.

A simulação numérica de escoamentos reativos, como a combustão, tem um caráter altamente não-linear devido a presença de diversas reações químicas que acontecem entre as espécies que descrevem o processo de oxidação do combustível. Além disso, tais processos ocorrem a nível molecular, tornando o sistema de equações governantes rígido, o que implica na necessidade de esquemas numéricos de alta ordem bem como malhas finas e passo de tempo pequeno, aumentando consideravelmente o custo computacional. Neste sentido, o uso de mecanismos de oxidação detalhados na simulação numérica é proibitivo, e técnicas de redução química são necessárias de modo a desenvolver modelos reduzidos com menos variáveis e rigidez moderado, mantendo a precisão e abrangência do modelo detalhado. O objetivo do presente trabalho é obter uma comparação dos resultados obtidos para duas técnicas de redução química diferentes, Directed Relation Graph - DRG, baseada no desenvolvimento de mecanismos esqueletos, e a Reaction Diffusion Manifolds - REDIM, baseada na separação das escalas de tempo. Como validação dos modelos propostos, simulações numéricas 1D de chamas pré-misturadas e não pré-misturadas, bem como de reatores homogêneos, são desenvolvidas. Além disso, uma estratégia que une as duas técnicas de redução é apresentada, com o objetivo de ser aplicada em mecanismos cinéticos grandes. / Numerical simulation of reactive flows, such as combustion, has a highly non-linear character due to the presence of several chemical reactions that occur among the chemical species that describe the process of fuel’s oxidation. Besides, such processes occur at a molecular level, making the system of governing equations stiff, which implies in the need of high order numerical schemes as well as fine meshes and small time step, enhancing considerably the computational cost. In this sense, the use of detailed oxidation mechanisms in the numerical simulation is prohibitive, and chemical reduction techniques are needed in order to develop reduced models with less variables and moderate stiffness, while maintaining the accuracy and comprehensiveness of the detailed model. The objective of the present works if to obtain a comparison between two chemical reduction techniques, the Directed Relation Graph - DRG, based on the skeletal mechanisms generation, and the Reaction Diffusion Manifolds - REDIM, based on the separation of time scales. As validation of the proposed models, one-dimensional numerical simulations of premixed and non-premixed flames, as well as homogeneous reactors, are carry out. Besides, a coupled methodology between DRG and REDIM is presented, that will provide a useful tool for simulation of fuels with very large detailed kinetic mechanisms.

A simulação numérica de escoamentos reativos, como a combustão, tem um caráter altamente não-linear devido a presença de diversas reações químicas que acontecem entre as espécies que descrevem o processo de oxidação do combustível. Além disso, tais processos ocorrem a nível molecular, tornando o sistema de equações governantes rígido, o que implica na necessidade de esquemas numéricos de alta ordem bem como malhas finas e passo de tempo pequeno, aumentando consideravelmente o custo computacional. Neste sentido, o uso de mecanismos de oxidação detalhados na simulação numérica é proibitivo, e técnicas de redução química são necessárias de modo a desenvolver modelos reduzidos com menos variáveis e rigidez moderado, mantendo a precisão e abrangência do modelo detalhado. O objetivo do presente trabalho é obter uma comparação dos resultados obtidos para duas técnicas de redução química diferentes, Directed Relation Graph - DRG, baseada no desenvolvimento de mecanismos esqueletos, e a Reaction Diffusion Manifolds - REDIM, baseada na separação das escalas de tempo. Como validação dos modelos propostos, simulações numéricas 1D de chamas pré-misturadas e não pré-misturadas, bem como de reatores homogêneos, são desenvolvidas. Além disso, uma estratégia que une as duas técnicas de redução é apresentada, com o objetivo de ser aplicada em mecanismos cinéticos grandes. / Numerical simulation of reactive flows, such as combustion, has a highly non-linear character due to the presence of several chemical reactions that occur among the chemical species that describe the process of fuel’s oxidation. Besides, such processes occur at a molecular level, making the system of governing equations stiff, which implies in the need of high order numerical schemes as well as fine meshes and small time step, enhancing considerably the computational cost. In this sense, the use of detailed oxidation mechanisms in the numerical simulation is prohibitive, and chemical reduction techniques are needed in order to develop reduced models with less variables and moderate stiffness, while maintaining the accuracy and comprehensiveness of the detailed model. The objective of the present works if to obtain a comparison between two chemical reduction techniques, the Directed Relation Graph - DRG, based on the skeletal mechanisms generation, and the Reaction Diffusion Manifolds - REDIM, based on the separation of time scales. As validation of the proposed models, one-dimensional numerical simulations of premixed and non-premixed flames, as well as homogeneous reactors, are carry out. Besides, a coupled methodology between DRG and REDIM is presented, that will provide a useful tool for simulation of fuels with very large detailed kinetic mechanisms.

This research aims to improve the design and placement of runway exits at airports through analysis and modeling of the effects that exogenous causal factors have on pilots' landing behavior and exit selections. Incorporating these factors into modeling software will strengthen the software's utility by providing project teams the ability to specify which pilot motivational causal factors apply to a new or existing runway. The main findings suggest pilots' exit selections are deterministic but dependent on the presence (or absence) of six (6) causal factors. A model and two (2) case studies are presented and compared against predictions generated by existing modeling software. The results support a finding that the causal factor model improves motivation-based predictions over current modeling techniques, which are drawn from stochastic distributions. The accuracy of this model enables designers to optimize runway exit placement and geometry to maximize runway capacity. / Master of Science / Airport design engineers currently plan the locations and geometric characteristics of runway exits by balancing the expected fleet mix of aircraft on that runway with the capacity and delay effects that the number and placement of these exits might cause. This technique originated from research beginning in the early 1970s, which found that pilots' exit motivations primarily resulted from the capabilities and limitations of their aircraft. Since pilots tend to "fly by the numbers" (i.e., exhibit predictable approach airspeeds, power levels, wing flaps, touchdown locations, landing speeds, and braking efforts), engineers thus employed design principles in which the numbers, locations and geometries of exits were primarily functions of the physical and performance-based characteristics of the specific types of aircraft expected to utilize the runway. However, in studying more than 4 million landings by a single aircraft type (the Boeing 737-800) at 42 U.S. airports, the evidence in this thesis shows that pilots' exit selections are behaviorally motivated by more than the physics of motion. This thesis aims to refine previous research and engineering methods by showing evidence that pilots' exit selections have as much to do with the presence (or absence) of certain environmental factors within the landing system. These factors (described in detailed within) are unique to each airport's overall physical network of interconnected runways, exits, taxiways, terminals and other features. Within this network, a pilot's landing behavior and exit selection depends on the locational and relational interactions that each exit choice will have on the time and distance to their apron (gate) assignment. These "interactions" are referred to as causal factors – defined as physical features within a landing environment that pilots have little-to-no control over – but which nevertheless influence their specific exit selections. Two (2) runway case studies provided in this thesis evidence a finding that a causal factor model reliably predicts pilots' exit selections better than current modeling techniques, which are drawn from probability-based statistical distributions. The stability and accuracy of the new model enables engineering design and project teams to optimize runway exit placement and geometry to maximize runway capacity, and can be adopted for use in both existing and future runways.