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Aerospace Systems Design Laboratory (ASDL)
Aerospace Systems Design Laboratory (ASDL)
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ItemA Framework for Selecting Multi-Attribute Optimal Renewable Energy Driven Desalination Architectures(Georgia Institute of Technology, 2021-12-08) Brooks, Joshua DanielThe World is drifting into a near-future of unprecedented water resource management challenges. Growing water demand is projected to be met by limited, unpredictable, and in many locations shifting freshwater resources. Near-future populations are projected to face widespread water stress, most immediately and severely encountered in the form of hydrological drought. Desalination systems offer resilience in the form of additional water supplies which are insensitive to drought. However, desalination systems are currently limited by their costs, water inefficiency, greenhouse gas (GHG) emissions, energy requirements, and quality and environmental impacts, and are thus not used on the wider scale necessary to appropriately mitigate the risk of projected water stress. This work aimed to help overcome desalination’s core barriers to adoption by introducing an original framework for the quantitative performance-based selection of multi-attribute optimal desalination architectures. This framework enables an expansive desalination architecture design space exploration across both desalting and energy subsystems. Desalination architectures were valuated by mapping their barriers to adoption to their quantifiable performance attributes: cost, GHG emissions, and freshwater recovery. A superstructure flowsheet model was constructed to include reverse osmosis, multi-stage flash, multi-effect distillation, and thermal vapor compression desalting technologies. This model was situated inside of an optimization routine and used to both explore an unprecedented desalting design space and to identify designs which often outperformed those identified in similar efforts. An individual desalination architecture alternative in this work is defined as any desalting subsystem alternative connected to an optimal energy subsystem. An energy system model was therefore constructed to include photovoltaic arrays, wind energy converters, concentrated solar power plants, battery energy storage, and a connection to a conventional electrical grid and steam generator. Incorporating renewable energy sources (RES) enabled the identification of energy subsystems which lowered cost, GHG emissions, and water consumption compared to traditional grid and dedicated steam generation systems. High speed metamodels were successfully used to represent the full energy system model in order to make desalination architecture evaluation and optimization exercises computationally tenable. The full desalination architecture evaluation environment, consisting of the integrated desalting and energy subsystem models, was situated within an optimization routine. Cost-driven optimization exercises consistently identified RES-driven desalination alternatives which outperformed conventional alternatives identified in similar efforts. In addition, multiple cases were demonstrated wherein the simultaneous consideration of both energy and desalting subsystem performance in desalination architecture optimization exercises identified alternatives which were uncompetitive using the traditional selection approach. This thesis effort provides decision makers with a quantitative performance-based, tailorable framework for rapidly exploring the desalination architecture design space and selecting multi-attribute optimal systems regarding their unique preferences and system requirements. The constructed framework is flexible enough to accommodate different optimization and decision making techniques, and approaches are discussed for incorporating additional technologies into the desalting and energy subsystem modeling environments. This quantitative architecture selection framework, specifically its capability in allowing novel architectural and conceptual trades, is the core outcome of this work.
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ItemA methodology for capturing the impacts of bleed flow extraction on compressor performance and operability in engine conceptual design(Georgia Institute of Technology, 2015-04-23) Brooks, Joshua DanielThe commercial aviation industry continually faces the challenge of reducing fuel consumption for the next generation of aircraft. This challenge rests largely on the shoulders of engine design teams, who push the boundaries of the traditional design paradigm in pursuit of more fuel efficient, cost effective, and environmentally clean engines. In order to realize these gains, there is a heightened requirement of accounting for engine system and subsystem level impacts from a wide range of variables, earlier in the design process than ever before. One of these variables, bleed flow extraction, or simply bleed, plays an especially greater role; due to the approach engine designers are taking to combat the current state of fuel efficiency. For this reason, this research examined the current state of bleed handling performed during the engine conceptual design process, questioned its adequacy with regards to properly capturing the impacts of this mechanism, and developed a bleed handling methodology designed to replace the existing method. The traditional method of handling bleed in the engine cycle design stage relies on a variety of engine level impacts stemming from zero dimensional thermodynamic analysis, as well as the utilization of a static performance characterization of the engine compression component, the axial flow compressor. The traditional method operates under the assumption that the introduction of additional bleed to the compressor system has created no additional compressor level impact. The methodology developed in this work challenges this assumption in two parts, first by creating a way to evaluate the compressor level impacts caused by the introduction of bleed, and second by implementing the knowledge gained from this compressor level evaluation into the engine cycle design, where the engine level impacts could be compared to those predicted by the traditional method of bleed handling. The compressor level impacts from the addition of bleed were quantified using a low fidelity, multi-stream, meanline analysis. Here, an innovative approach was developed which cross pollinated existing methods used elsewhere in the analysis environment, to account for the bleed impact in the object oriented modeling environment. Implementation of this approach revealed that the addition of bleed negatively and significantly impacts the compressor level performance and operability. With the completion of the above analyses, this newly acquired capability to quantify, or at least qualify, the compressor level bleed impacts was tied into the engine level cycle analysis. This form of component zooming, allows the user to update the bleed flow rate from a number of locations along the compressor, as well as the compressor variable stator vain orientation, within the existing cycle analysis. Utilization of this ability provided engine level performance and operability analyses which revealed a disparity between the traditional and herein developed bleed handling methodology’s predictions. The found results reveal a need for more stringent handling of bleed during the engine conceptual design than the traditional method provides, and suggests that the developed methodology provides a positive step to the realization of this need.