<p>  </p> <p>With rising concerns over commercial aviation’s contribution to global carbon emissions, there exists a tremendous pressure on the aviation industry to find advanced technological solutions to reduce its share of CO2 emissions. Single-aisle (or narrowbody) aircraft are the biggest contributors to CO2 emissions by number of operations, insisting a need to reduce / eliminate their aircraft-level fuel consumption as soon as possible. A potential solution for this is to operate fully-electric single-aisle aircraft; however, the limitations of the current (and predicted future) battery technology is forcing the industry to explore hybrid-electric aircraft as a possible mid-term solution.</p> <p>Modeling hybrid-electric aircraft comes with its own challenges due to the presence of two different propulsion sources – gas turbine engines (powered by Jet-A fuel) and electric motors (powered by batteries). Since traditional sizing approaches and legacy sizing tools do not seem to work well for hybrid-electric aircraft, this work presents a “flight-mechanics-based” conceptual sizing tool for hybrid-electric aircraft, set up as a Multidisciplinary Design Optimization (MDO) toolbox. Some of the key features of the sizing tool include concurrently sizing the electric motors and downsizing the gas turbine engines while meeting the one-engine-inoperative (OEI) and top-of-climb constraints, and re-sizing the fuselage to account for the volumetric constraints associated with required batteries.</p> <p>Current work considers a parallel hybrid-electric single-aisle aircraft with a 900 nmi design range, with electric power augmentation (with electric motors operating at full throttle) available only for the takeoff and climb segments when sizing the aircraft. Four hybrid-electric propulsion technology cases are considered, and the resulting hybrid-electric aircraft show 15.0% to 22.5% reduction in fuel burn compared to a Boeing 737-800 aircraft.</p> <p>Another challenge with modeling hybrid-electric aircraft is determining their off-design performance characteristics (considering a different payload or mission range, or both). This work presents an energy management tool – set up as a nonlinear programming optimization problem – to minimize the fuel burn for a payload-range combination by identifying the optimal combination of throttle settings for the gas turbine engines and the electric motors during takeoff, climb, and cruise, along with identifying an optimal flight path. The energy management tool enables fuel savings of at least of 2%, with actual savings ranging from 142.1 lbs to 276.1 lbs per trip for a sample route (LGA–ORD) at a 80% load factor.</p> <p>Although the hybrid-electric aircraft sizing and performance analysis studies show encouraging results about the potential reduction in carbon emissions at an aircraft level, the future fleet-level carbon emissions are not expected to reduce proportionally to these aircraft level emission reductions. This work predicts the fleet-level environmental impacts of future single-aisle parallel hybrid-electric aircraft by modeling the behavior of a profit-seeking airline (with a mixture of conventional all Jet-A fuel burning and hybrid electric aircraft in its fleet) using the Fleet-Level Environmental Evaluation Tool (FLEET). FLEET’s model-based predictions rely upon historically-based information about US-touching airline routes and passenger demand served by US flag-carrier airlines from the Bureau of Transportation Statistics to initiate model-based predictions of future demand, aircraft fleet mix, and aircraft operations. Using the aircraft performance coefficients from the energy management tool to represent the behavior of a single-aisle parallel hybrid-electric aircraft, the FLEET simulation predicts the changes in the fleet-wide carbon emissions due to the introduction of this new aircraft in an airline fleet in the year 2035. By 2055, FLEET results predict that the fleet-wide CO2 emissions with hybrid-electric aircraft in the fleet mix are at least 1.2% lower than the fleet-wide CO2 emissions of a conventional (all Jet-A fuel burning) aircraft-only airline. The rather limited reduction in emissions is an attribute of the reduced range capability and higher operating cost of the hybrid-electric aircraft (relative to a conventional aircraft of similar size). This causes the airline to change the usage, acquisition and retirement of its conventional aircraft when hybrid-electric aircraft are available; this is most notable to serve passenger demand on certain predominantly single-aisle service routes that cannot be flown by the future single-aisle hybrid-electric aircraft. </p>

The main objective of this study is to develop a modeling methodology that facilitates incorporating the plant pathway into environmental contamination models recognizing the fact that plants are dynamic entities that regulate their life cycle according to natural and anthropogenic environmental conditions. A modeling framework that incorporates the plant pathway into an integrated water flow and contaminant transport model in terrestrial systems is developed. The modeling framework is aimed to provide a tool to analyze the plant pathway of exposure to contaminants. The model developed using this framework describes the temporal and spatial variation of the contaminant concentration within the plant as it is interacting with the soil and the atmosphere. The first part of the study focuses on the integration of the dynamics of water and contaminant distribution and plant related processes within the vadose zone. A soil-plant system model is developed by coupling soil-water flow, contaminant transport, plant life-cycle, and plant pathway models. The outcome unifies single media continuous models with multimedia compartmental models in a flexible framework. The coupling of the models was established at multiple interfaces and at different levels of solution steps (i.e. model development phase vs. numerical solution phase). In the second part of the study, the soil-plant system model is extended to cover large spatial areas by describing the environmental system as a collection of soil-plant systems connected through overland flow and transport processes on the ground surface and through lateral interactions in the subsurface. An overland flow model is integrated with the previously coupled model of unsaturated zone soil-water flow and plant life-cycle by solving the flow model equations simultaneously within a single global matrix structure. An overland / subsurface interaction algorithm is developed to handle the ground surface conditions. The simultaneous solution, single-matrix approach is also adopted when integrating the overland transport model with the previously coupled models of vadose zone transport and plant pathway. The model developed is applied to various environmental contamination scenarios where the effect of the presence of plants on the contaminant migration within environmental systems is investigated.

Submitted by Johnny Rodrigues (johnnyrodrigues@ufcg.edu.br) on 2018-09-05T19:13:02Z No. of bitstreams: 1 HUGO MORAIS DE ALCÂNTARA - TESE PPGRN 2013..pdf: 10749707 bytes, checksum: 042c63fe46b2820168cc4a2b33b2f966 (MD5) / Made available in DSpace on 2018-09-05T19:13:02Z (GMT). No. of bitstreams: 1 HUGO MORAIS DE ALCÂNTARA - TESE PPGRN 2013..pdf: 10749707 bytes, checksum: 042c63fe46b2820168cc4a2b33b2f966 (MD5) Previous issue date: 2013-08-29 / Em regiões tropicais, como o semiárido brasileiro, a redução de áreas de florestas por meio da extração de lenha, da agricultura e pecuária de subsistência, associada à variabilidade espacial e temporal dos regimes climático e hidrológico, têm contribuído significativamente para a degradação ambiental de extensas áreas. Estudos em bacias experimentais têm evidenciado o papel da cobertura vegetal sobre a redução da erosão como um dos principais fatores para a conservação de pequenas bacias rurais, mas em geral não consideram as relações do homem com o ambiente. Esta tese tem como o principal problema de pesquisa a conservação e/ou recuperação ambiental de pequenas bacias hidrográficas rurais na região do semiárido brasileiro. A hipótese que norteia o trabalho é que uma metodologia que considere cenários futuros de uso e ocupação do solo e as relações do homem com o meio ambiente resultará em uma maior possibilidade de implementação das estratégias conservacionistas. O objetivo deste trabalho é a proposição de metodologia para a seleção de estratégias de conservação e/ou recuperação de pequenas bacias hidrográficas do semiárido, na perspectiva dos recursos hídricos, através de modelagem ambiental, considerando a aceitabilidade social dessas estratégias pelas comunidades rurais que ocupam as bacias. A metodologia proposta enfatiza a necessidade de uma caracterização ambiental considerando fatores climáticos, hidrológicos, políticos, econômicos e sociais, para embasar um planejamento conservacionista realista, viável e que esteja em sintonia com as necessidades dos produtores rurais. Advoga-se o uso de entrevistas e reuniões com os produtores e de modelos de simulação ambiental como ferramental. Os modelos podem contribuir na localização de áreas críticas e fornecer subsídios para a identificação de potenciais estratégias para a redução dos processos erosivos em diferentes escalas espaciais. A metodologia foi aplicada em uma pequena bacia hidrográfica do semiárido do estado da Paraíba. Estratégias candidatas de conservação e recuperação da bacia foram identificadas por meio de reuniões com grupos focais de produtores rurais. O modelo hidrossedimentológico SWAT foi usado com o objetivo de estimar a produção de sedimentos e a lâmina escoada. Foram simulados, com dados climáticos do período de 1998 a 2012, quatro cenários de uso e ocupação do solo montados de acordo com o levantamento de opiniões dos produtores rurais, tendo sido contempladas as estratégias com maior aceitabilidade social. O envolvimento da sociedade nas discussões e negociações ajuda a incorporar, no planejamento de uso dos recursos naturais, aspectos ambientais, culturais e sociais. Os resultados das simulações indicam uma estimativa anual da produção de sedimentos para o cenário atual de uso e ocupação do solo superando de 1,7 a 2,7 vezes os limites de tolerância de perda de solo estabelecidos em nível mundial, porém as estratégias de alterações de uso e ocupação do solo podem reduzir quase totalmente a produção anual de sedimentos e aumentar a produção de água na bacia em até 55,0%. Uma vantagem da metodologia proposta é que, através de uma lista de indicadores socioeconômicos e ambientais, a comunidade pode participar ativamente da pesquisa de campo, tornando-se parte integrante do gerenciamento dos recursos naturais. / In tropical regions, such as the Brazilian semiarid region, the reduction of forest areas by extracting firewood, subsistence agriculture and livestock, associated with spatial and temporal variability of the climatic and hydrological regimes, have significantly contributed to environmental degradation of extensive areas. Research in experimental basins have shown the role of vegetation on erosion reduction as a major factor for the conservation of small rural basins, but generally do not consider the relationship between human society and the environment. This thesis has as its main research problem the conservation and/or environmental remediation of small rural watersheds in the semiarid region of Brazil. The hypothesis that guides the work is that a methodology that considers future scenarios of land use and occupation and the communities’ relationships with the environment will result in a greater possibility of implementation of conservation strategies. The objective of this work is to propose a methodology for the selection of strategies for conservation and/or restoration of small watersheds, from a water resources viewpoint through environmental modeling, considering the social acceptability of these strategies by rural communities that occupy the basins. The methodology emphasizes the need for environmental characterization considering climatic, hydrological, political, economic and social aspects, to support a realistic and feasible conservation planning, considering the farmers’ needs. It advocates the use of interviews and meetings with farmers and environmental simulation models as methodological tools. Models can help in locating critical areas and provide tools for identifying potential strategies to reduce erosion at different spatial scales. The methodology was applied in a small watershed in semiarid region of the State of Paraíba. Candidate strategies for the conservation and restoration of the basin were identified through meetings with focus groups of farmers. The SWAT hydrological model was used to estimate sediment production and runoff. Four scenarios of land use and occupation were simulated using climate data for the period 1998-2012. The scenarios were selected according to the opinions of farmers, having been contemplated strategies with greater social acceptability. Society involvement in the discussions and negotiations helps to incorporate environmental, cultural and social aspects in the planning process. Simulation results show an estimate of annual sediment yield at the current scenario of the use and occupation of land exceeding 1.7 to 2.7 times the tolerance limits established for soil loss worldwide, but the restoration strategies can reduce almost totally the annual sediment yield and increase water production in the basin up to 55.0%. An advantage of the proposed methodology is that through a list of socioeconomic and environmental indicators, the community can actively participate in the field research, becoming an integral part of natural resource management.