Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2001. / Includes bibliographical references (p. 211-215). / by Scott Alan Uebelhart. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2003. / Includes bibliographical references (leaves 197-201). / by David Joe Willis. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2007. / Includes bibliographical references (p. 181-189). / In this thesis, we study a novel hierarchical wireless networking approach in which some of the nodes are more capable than others. In such networks, the more capable nodes can serve as Mobile Backbone Nodes and provide a backbone over which end-to-end communication can take place. The main design problem considered in this thesis is that of how to (i) Construct such Mobile Backbone Networks so as to optimize a network performance metric, and (ii) Maintain such networks under node mobility. In the first part of the thesis, our approach consists of controlling the mobility of the Mobile Backbone Nodes (MBNs) in order to maintain network connectivity for the Regular Nodes (RNs). We formulate this problem subject to minimizing the number of MBNs and refer to it as the Connected Disk Cover (CDC) problem. We show that it can be decomposed into the Geometric Disk Cover (GDC) problem and the Steiner Tree Problem with Minimum Number of Steiner Points (STP-MSP). We prove that if these subproblems are solved separately by y- and 5-approximation algorithms, the approximation ratio of the joint solution is y1+6. Then, we focus on the two subproblems and present a number of distributed approximation algorithms that maintain a solution to the GDC problem under mobility. A new approach to the solution of the STP-MSP is also described. We show that this approach can be extended in order to obtain a joint approximate solution to the CDC problem. Finally, we evaluate the performance of the algorithms via simulation and show that the proposed GDC algorithms perform very well under mobility and that the new approach for the joint solution can significantly reduce the number of Mobile Backbone Nodes. / (cont.) In the second part of the thesis, we address the the joint problem of placing a fixed number K MBNs in the plane, and assigning each RN to exactly one MBN. In particular, we formulate and solve two problems under a general communications model. The first is the Maximum Fair Placement and Assignment (MFPA) problem in which the objective is to maximize the throughput of the minimum throughput RN. The second is the Maximum Throughput Placement and Assignment (MTPA) problem, in which the objective is to maximize the aggregate throughput of the RNs. Due to the change in model (e.g. fixed number of MBNs,general communications model) from the first part of the thesis, the problems of this part of the thesis require a significantly different approach and solution methodology. Our main result is a novel optimal polynomial time algorithm for the MFPA problem for fixed K. For a restricted version of the MTPA problem, we develop an optimal polynomial time algorithm for K < 2. We also develop two heuristic algorithms for both problems, including an approximation algorithm for which we bound the worst case performance loss. Finally, we present simulation results comparing the performance of the various algorithms developed in the paper. In the third part of the thesis, we consider the problem of placing the Mobile Backbone Nodes over a finite time horizon. In particular, we assume complete a-priori knowledge of each of the RNs' trajectories over a finite time interval, and consider the problem of determining the optimal MBN path over that time interval. We consider the path planning of a single MBN and aim to maximize the time-average system throughput. We also assume that the velocity of the MBN factors into the performance objective (e.g. as a constraint/penalty). / (cont.) Our first approach is a discrete one, for which our main result is a dynamic programming based approximation algorithm for the path planning problem. We provide worst case analysis of the performance of the algorithm. Additionally, we develop an optimal algorithm for the 1-step velocity constrained path planning problem. Using this as a sub-routine, we develop a greedy heuristic algorithm for the overall path planning problem. Next, we approach the path-planning problem from a continuous perspective. We formulate the problem as an optimal control problem, and develop interesting insights into the structure of the optimal solution. Finally, we discuss extensions of the base discrete and continuous formulations and compare the various developed approaches via simulation. / by Anand Srinivas. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2012. / Cataloged from department-submitted PDF version of thesis. This electronic version was submitted and approved by the author's academic department as part of an electronic thesis pilot project. The certified thesis is available in the Institute Archives and Special Collections. / Includes bibliographical references (p. 167-176). / The overarching goals of this thesis are to quantify the efficiency loss due to market participant strategic behavior, and to design proper pricing mechanisms that reduce the efficiency loss. The concept of efficiency loss is intimately related to the concept of "price of anarchy," which was advanced by Koutsoupias and Papadimitriou, and compares the maximum social welfare with that achieved at a worst Nash equilibrium. This thesis focuses on the following two topics: (i) For a market with an arbitrary number of participants, how much is the Nash equilibrium close, in the sense of price of anarchy, to a social optimum? (ii) For a resource allocation/pricing mechanism, is the social welfare achieved at an economic equilibrium asymptotically optimal, as the number of market participants goes to infinity? Regarding the first topic, we quantify the efficiency loss in classical Cournot oligopoly games, where multiple oligopolists compete by choosing quantities. We also compare the total profit earned at a Cournot equilibrium to the maximum possible total profit that would be obtained if the suppliers were to collude. For the second topic, related to the efficiency in large economics, we analyze the efficiency of Kelly's proportional allocation mechanism in large-scale wireless communication systems. We study a corresponding Bayesian game in which each user has incomplete information on the state or type of the other users, and show that the social welfare achieved at a Bayes-Nash equilibrium is asymptotically optimal, as the number of users increases to infinity. Finally, for electricity delivery systems, we propose a new dynamic pricing mechanism that explicitly encourages consumers to adapt their consumption so as to offset the variability of demand on conventional units. Through a dynamic game-theoretic formulation, we show that the proposed pricing mechanism achieves social optimality asymptotically, as the number of consumers increases to infinity. / by Yunjian Xu. / Ph.D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1964. / Microfiche copy available in Barker. / Includes bibliographical references (leaves 128-130). / by Fred Marvin Shinnick, III. / M.S.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 154-165). / Transportation represents one of the largest contributors to anthropogenic air pollution and global climate change. This thesis aims to quantify three specific environmental impacts from transportation fuel combustion and production: 1) Health impacts from transportation combustion emissions in the United States. A multiscale air quality model is applied to assess health impacts from PM 2.5 and ozone concentrations attributable to different transportation modes and other sectors in the U.S. Road transportation is found to be the largest contributor for both pollutant-related mortalities, causing overall 58,000 (90% Cl: 22,800 107,100) early deaths per year. Shipping accounts for 8,800 (90% Cl: 3,700 - 16,100) premature mortalities per year, and rail transportation for 5,000 (90% Cl: 1,900 - 9,300) early deaths. Aviation emissions are responsible for 2,500 (90% Cl: 1,400 - 3,700) early deaths per year in the U.S. 2) Climate effects of albedo changes due to biofuel production. An augmented lifecycle framework is developed to quantify the effects of albedo variations induced by biomass cultivation, and applied to eleven land-use change (LUC) scenarios. Two scenarios are found to have a warming effect, the largest of which is for replacement of desert land with salicornia cultivation. This corresponds to 222 gCO₂e/MJ, equivalent to 3890% and 247% of the lifecycle greenhouse gas (GHG) emissions of fuels derived from salicornia and crude oil, respectively. Nine LUC scenarios exhibit a cooling effect, the largest of which is for the replacement of tropical rainforest with soybean cultivation. This corresponds to -161 gCO₂e/MJ, or -28% and -178% of the lifecycle GHG emissions of fuels derived from soybean and crude oil. 3) Climate impacts from changes in radiative forcing (RF) generated by contrails and contrail cirrus in the scenario of a widespread use of alternative jet fuels in the U.S. The Contrail Evolution and Radiation Model (CERM) is developed to simulate contrail and contrail cirrus cover, properties and radiative forcing over the United States. The results show that the use of alternative jet fuels in the U.S. generates 8% more contrails with respect to conventional jet fuels, due to the enhanced engine water vapor emissions. Contrails from alternative fuels are optically thinner (-35% in optical depth), and formed by larger and fewer ice crystals (+58% in diameter and -73% in number concentration), due to the lower emissions. These differences are responsible for a lower albedo (-36%) from contrails forming as a consequence of alternative fuels emissions. The cooling impact of having optically thinner contrails and is contrasted by the warming effects of having contrails less reflective of the incoming sunlight and in larger number, thus determining a small difference (+0.6%) in the net RF by contrails and contrail cirrus in case of alternative fuels use with respect to conventional jet use. CERM simulations are also performed to quantify for the first time impacts on contrails and contrail cirrus radiative impacts of both combustor technology and ambient conditions, in terms of available concentrations ice nuclei (IN). The results of this thesis offer new insights into the environmental impacts of transportation. The air quality and climate impacts of this sector can be potentially reduced by fostering the use of alternative fuels, but only when previously overlooked effects (such as changes in surface albedo for biofuel production, or ambient concentrations of ice nuclei affecting contrail properties) are taken into account. / by Fabio Caiazzo. / Ph. D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2006. / Includes bibliographical references (p. 137). / Numerical experiments have been implemented to characterize the unsteady loading on the rotating impeller blades in a modem centrifugal compressor. These consist of unsteady Reynolds-averaged Navier Stokes simulations of three-dimensional and quasi-two dimensional approximate models. The interaction between the rotating impeller and the stationary downstream diffuser has been identified as strong source of unsteady loading on the impeller blades. First of a kind unsteady calculations haven been carried out to elucidate an upstream manifestation of a downstream stimulus experienced in a particular centrifugal compressor stage. Here the upstream manifestation is the considerable unsteady loading in the splitter blade leading edge while the downstream stimulus is the unsteady impeller-diffuser interaction Three key parameters that control the level and extent of the unsteady loading are the impeller-diffuser gap, stage loading, and the impeller passage relative Mach number. Impeller-diffuser gap has been shown to control the peak level of unsteady loading on the blade. Stage loading has been shown to control the upstream attenuation of the loading. / (cont.) A hypothesis has been put forward that increased diffusion associated with increased stage loading increases the impeller sensitivity to the downstream disturbance. The relative Mach number has been shown to set the chordwise distribution of the unsteady load on the blade. Unsteady blade loading has been computed through a quasi two-dimensional model in which an unsteady pressure boundary condition is imposed at the impeller exit to approximate the presence of the downstream diffuser. Results of this approximate model have been shown to yield unsteady loading characteristics that are in accord with the full three-dimensional unsteady model. An implied utility of this result is that a quasi-2D approximation could be used during the design phase to approximate the unsteady loading in a timeframe that is compatible with the design environment. The effect of unsteady flow on mass flow capacity of a fluid device is eliminated as a source for over-predictions in mass flow when a steady-state approximation is used. / by Kenneth A. Gould. / S.M.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1993. / Includes bibliographical references (leaves 79-80). / by Sabine Anne Vermeersch. / M.S.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1994. / Includes bibliographical references (p. 207-217). / by Ronald L. Spangler, Jr. / Ph.D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1992. / Includes bibliographical references (leaves 112-113). / by Olivier Etchevers. / M.S.