Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item Extracting capacity metrics for General Aviation airports from ADS-B data(2021) Mitkas, Danae Zoe; Lovell, David J; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)General Aviation airports play a pivotal role in the aviation system of the US, with over 5000 small airports existing and operating across the country. Serving almost exclusively small aircraft, these airports have a unique activity profile, compared to larger commercial airports. Like their larger cousins, they occasionally see the need to apply for federal funding for capacity enhancement projects, a process that requires rigorous documentation of the demand and capacity situation at the airport. Existing models for capacity estimation have been calibrated to reflect the much larger scale features that dominate large airports. The main challenge is to develop a method to provide precise data for small airports that operate mainly with small single or multi-engine aircraft. These airports are typically not towered and, hence, do not benefit from traditional automated data collection technologies. This research addresses the issues of a) collecting aircraft data at local airport environments from aircraft equipped with Automated Dependent Surveillance – Broadcast (ADS-B) technology, b) processing the data to determine and classify flights, and c) assessing elements of the operational performance of these aircraft. The thesis proposes a method to extract aircraft approach speeds and runway occupancy times, which are important contributors to capacity estimation. We applied and validated our method in three small airports.Item SUSTAINING THE PACIFIC CARRIER AIR WAR: THE DEVELOPMENT OF U.S. NAVAL AVIATION MAINTENANCE AND THE ENLISTED AIRCRAFT TECHNICIAN IN WORLD WAR II(2019) Fisher, Stanford Edward; Sumida, Jon T; History; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The ability of the United States Navy to fight a protracted war throughout the Pacific Ocean in World War II was not solely the result of technology, tactics, or admiralship. Naval aviation maintenance played a major role in the U.S. victory over Japan. Naval aviation leadership throughout the period between World War I and World War II focused on the improvement of technology and tactics rather than training a new, and in the event of war, necessarily large cohort of enlisted personnel. Aircraft maintenance was an afterthought for much of the era because of the small number of carriers and aircraft. When the United States realized a two-ocean naval war was imminent and a drastic increase in the size of its aviation fleet was ordered, the navy was forced to reconsider its earlier practices and forge new polices and processes. The U.S. naval air war against Japan did not achieve sustained success until enough aircraft technicians were in place to support the doctrine of the Fast Carrier Task Force. The United States Navy was not ready to fight a protracted war at sea until its carrier aircraft technicians were trained and in place. The historiography of U.S. naval warfare in the modern era lacks any comprehensive study on the subject of naval aviation maintenance. This dissertation demonstrates the importance of considering all elements of the military institution, not just those that correspond to operational-battle history when studying the full dimensions of modern naval war in the age of the aircraft carrier. Recognizing the drastic institutional changes that accompanied an increase in maintenance personnel from less than 10,000 to nearly 250,000 over four years, a complete restructuring of the aviation navy’s technical educational system, and the development of highly specialized skilled labor force on board the aircraft carrier are essential to creating a more complete historiography World War II naval warfare. Analyzing the effect that aircraft maintenance and the aircraft technician had on carrier warfare is an added layer to the complex study of war that should not be overlooked. Even in the era of modern-technologically advanced warfare, people still matter.Item An Experimental and Analytical Investigation of Hydrogen Fuel Cells for Electric Vertical Take-Off and Landing (eVTOL) Aircraft(2019) Ng, Wanyi; Datta, Anubhav; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The objective of this thesis is a comprehensive investigation of hydrogen fuel cells for electric vertical take-off and landing (eVTOL) aircraft. The primary drawback of battery powered eVTOL aircraft is their poor range and endurance with practical payloads. This work uses simulation and hardware testing to examine the potential of hydrogen fuel cells to overcome this drawback. The thesis develops steady state and transient models of fuel cells and batteries, and validates the models experimentally. An equivalent circuit network model was able to capture the waveforms and magnitudes of voltage as a function of current. Temperature and humidity corrections were also included. Examination of the results revealed that the transient behavior of batteries and fuel stacks are significant primarily shortly after startup of the fuel stack and at the limiting ranges of high and low power; for a nominal operating power and barring faults, steady state models were adequate. This work then demonstrates fuel cell and battery power sharing in regulated and unregulated parallel configurations. It details the development of a regulated architecture, which controls power sharing, to achieve a reduction in power plant weight. Finally, the thesis outlines weight models of motors, batteries, and fuel cells needed for eVTOL sizing, and carries out sizing analysis for on-demand urban air taxi missions of three different distances -- 50, 75, and 150~mi of cruise and 5~min total hover time. This revealed that for ranges within 75 mi, a light weight (5000-6000~lb gross weight) all-electric tilting proprotor configuration achieves a practical payload (500~lb or more) with current levels of battery specific energy (150~Wh/kg) if high burst C-rate batteries are available (4-10~C for 2.5~min). Either a battery-only or battery-fuel cell (B-FC) hybrid power plant is ideal depending on the range of the mission: For inter-city ranges (beyond approximately 50~mi), the mission is impossible with batteries alone, and fuel cells are a key enabling technology; a VTOL aircraft with a B-FC hybrid powerplant, an aircraft with 6200~lb gross take-off weight, 10~lb/ft$^2$ disk loading, and 10~C batteries, could be sized to carry a payload of 500~lb for a range of 75~mi. For this inter-city range, the research priority centers of fuel cells, as they appear to far surpass future projections of Li-ion battery energy levels based on performance numbers (at a component level), high weight fraction of hydrogen storage due to the short duration of eVTOL missions, and lack of a compressor due to low-altitude missions, with the added benefit of ease of re-fueling. However, for an intra-city mission (within approximately 50~mi), the B-FC combination provides no advantage over a battery-only powerplant; a VTOL aircraft with a battery-only powerplant with the same weight and disk loading as before, and 4~C batteries, can carry a payload of 800~lb for a range of 50~mi. For this mission range, improving battery energy density is the priority.Item Mechanisms for Trajectory Options Allocation in Collaborative Air Traffic Flow Management(2018) Mohanavelu Umamagesh, Prithiv Raj; Lovell, David J; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Flight delays are primarily due to traffic imbalances caused by the demand for airspace resource exceeding its capacity. The capacity restriction might be due to inclement weather, an overloaded air traffic sector, or an airspace restriction. The Federal Aviation Administration (FAA), the organization responsible for air traffic control and management in the USA, has developed several tools known as Traffic Management Initiatives (TMI) to bring the demand into compliance with the capacity constraints. Collaborative Trajectory Option Program (CTOP) is one such tool that has been developed by the FAA to mitigate the delay experienced by flights. Operating under a Collaborative Decision Making (CDM) environment, CTOP is considered as the next step into the future of air traffic management by the FAA. The advantages of CTOP over the traditional the TMIs are unequivocal. The concerns about the allocation scheme used in the CTOP and treatment of flights from the flight operators/airlines have limited its usage. This research was motivated by the high ground delays that were experienced by flights and how the rerouting decisions were made in the current allocation method used in a CTOP. We have proposed four alternative approaches in this thesis, which incorporated priority of flights by the respective flight operator, aimed at not merely reducing an individual flight operator’s delay but also the total delay incurred to the system. We developed a test case scenario to compare the performances of the four proposed allocation methods against one another and with the present allocation mechanism of CTOP.Item AVIATION CONGESTION MANAGEMENT IMPROVEMENTS IN MODELING THE PREDICTION, MITIGATION, AND EVALUATION OF CONGESTION IN THE NATIONAL AIRSPACE SYSTEM(2014) Vlachou, Kleoniki; Lovell, David J.; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The air transportation system in the United States is one of the most complex systems in the world. Projections of increasing air traffic demand in conjunction with limited capacity, that is volatile and affected by exogenous random events, represent a major problem in aviation system management. From a management perspective, it is essential to make efficient use of the available resources and to create mechanisms that will help alleviate the problems of the imbalance between demand and capacity. Air traffic delays are always present and the more air traffic increases the more the delays will increase with very unwanted economic impacts. It is of great interest to study them further in order to be able to more effectively mitigate them. A first step would be to try to predict them under various circumstances. A second step would be to develop various mechanisms that will help in reducing delays in different settings. The scope of this dissertation is to look closer at a threefold approach to the problem of congestion in aviation. The first effort is the prediction of delays and the development of a model that will make these predictions under a wide variety of distributional assumptions. The work presented here is specifically on a continuum approximation using diffusion methods that enables efficient solutions under a wide variety of distributional assumptions. The second part of the work effort presents the design of a parsimonious language of exchange, with accompanying allocation mechanisms that allow carriers and the FAA to work together quickly, in a Collaborative Decision Making environment, to allocate scarce capacity resources and mitigate delays. Finally, because airlines proactively use longer scheduled block times to deal with unexpected delays, the third portion of this dissertation presents the assessment of the monetary benefits due to improvements in predictability as manifested through carriers' scheduled block times.Item IMPACT ASSESSMENT OF DYNAMIC SLOT EXCHANGE IN AIR TRAFFIC MANAGEMENT(2004-12-09) Sankararaman, Ravi; Ball, Michael; Decision and Information Technologies; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Since the inception of Collaborative Decision Making (CDM), the Federal Aviation Administration and the airlines have been striving to improve utilization of critical resources such as arrival slots and reduce flight delays during Ground Delay Programs. Two of the mechanisms that have been implemented for increasing utilization at resource-constrained airports are those of Compression and Slot Credit Substitution (SCS). SCS is a conditional, dynamic means of inter-airline slot exchange while compression can be considered a static means of achieving slot utilization. This thesis will be an attempt to develop theoretical models to understand the performance of compression to slot exchange requests from airlines. This thesis will also address the trends in these slot exchange procedures, the benefits in terms of delay savings realized by the airlines, and avenues for future applications for improving efficiency of the National Airspace System.