Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2009. / Includes bibliographical references (p. 75-76). / This thesis presents a methodology for the integration of blade row body forces, derived from axisymmetric and three- dimensional flow fields, for use in the stability analysis of axial compressors. The body force database represents the body forces as a function of the local flow coefficient times the overall flow coefficient; doing this overcomes a source of non-uniqueness in the representation. Stability calculations using body force databases from this methodology as well as from a legacy method, applied to axisymmetric streamline curvature calculations, are compared. A procedure for joining body forces extracted from axisymmetric and three-dimensional CFD calculations is presented along with an assessment of the sensitivity of the stall prediction and onset behavior to the shape of the body force curves. The slope of the body force curves near the point corresponding to peak pressure rise, as well as those near zero flow, are found to be important in determining the stall point and inception type. Comparisons to previous work and test data from a single stage research compressor are made. / by Amish A. Patel. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2002. / Includes bibliographical references (p. 120-121). / by Steven R. Braddom. / S.M.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, February 2015. / Cataloged from PDF version of thesis. "October 2014." / Includes bibliographical references (pages 143-149). / This thesis investigates search scenarios in which multiple mobile, self-interested agents, cows in our case, compete to capture targets. The problems considered in this thesis address search strategies that reflect (i) the need to efficiently search for targets given a prior on their location, and (ii) an awareness that the environment in which searching takes place contains other self-interested agents. Surprisingly, problems that feature these elements are largely under-represented in the literature. Granted, the scenarios of interest inherit the challenges and complexities of search theory and game theory alike. Undeterred, this thesis makes a contribution by considering competitive search problems that feature a modest number of agents and take place in simple environments. These restrictions permit an in-depth analysis of the decision-making involved, while preserving interesting options for strategic play. In studying these problems, we report a number of fundamental competitive search game results and, in so doing, begin to populate a toolbox of techniques and results useful for tackling more scenarios. The thesis begins by introducing a collection of problems that fit within the competitive search game framework. We use the example of taxi systems, in which drivers compete to find passengers and garner fares, as a motivational example throughout. Owing to connections with a well-known problem, called the Cow-Path Problem, the agents of interest, which could represent taxis or robots depending on the scenario, will be referred to as cows. To begin, we first consider a one-sided search problem in which a hungry cow, left to her own devices, tries to efficiently find a patch of clover located on a ring. Subsequently, we consider a game in which two cows, guided only by limited prior information, compete to capture a target. We begin by considering a version in which each cow can turn at most once and show this game admits an equilibrium. A dynamic-programming-based approach is then used to extend the result to games featuring at most a finite number of turns. Subsequent chapters consider games that add one or more elements to this basic construct. We consider games where one cow has additional information on the target's location, and games where targets arrive dynamically. For a number of these variants, we characterize equilibrium search strategies. In settings where this proves overly difficult, we characterize search strategies that provide performance within a known factor of the utility that would be achieved in an equilibrium. The thesis closes by highlighting the key ideas discussed and outlining directions of future research. / by Kevin Spieser. / Ph. D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1988. / Includes bibliographical references. / by Nesbitt Ward Hagood IV. / M.S.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1990. / Includes bibliographical references (leaves 50-52). / by Gail Jeanne Standish. / M.S.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1993. / Includes bibliographical references (leaf 147). / by William Edward Gorgen. / M.S.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1999. / Includes bibliographical references (p. 149-151). / The effects of trailing edge blowing on stator unsteady loading were investigated through a set of experiments on a trailing edge blowing fan. Flow field measurements and stator unsteady loading measurements were taken at five radial locations. Reductions in the relative wake harmonics were seen at all spans for the first two multiples of blade passing frequency. The reductions ranged from 59% to 95% for the 1*BPF harmonic and from 19% to 84% for the 2*BPF harmonic. Trailing edge blowing was seen to have significant effects on both the longitudinal and transverse harmonics. The largest reduction (73%) of the 1*BPF transverse harmonic was seen at 37.5% span, while the largest reduction (99%) of the 1*BPF longitudinal harmonic was seen at 75% span. Changes in the stator unsteady loading ranged from -15dB to +7dB at different points along the chord and span. The changes did not correlate well with changes in the wake harmonics. The most notable lack of correlation occurred at 50% span, where the stator unsteady loading increases while the largest overall reductions in wake harmonic amplitude are seen. Two-dimensional steady state analysis of the free stream and wake (maximum velocity deficit) conditions suggests that the effects of the longitudinal and transverse gusts partially cancel each other in the no blowing case at 50% span. Thus, it is likely that trailing edge blowing disturbs the established balance resulting in an unsteady loading increase even though the wake harmonics are reduced. The flow field measurements were used in conjunction with the BBN/PW V072 noise prediction code to obtain stator unsteady loading predictions with and without trailing edge blowing. The predictions correlate to the changes in the wake transverse harmonics and fail to agree with the stator unsteady loading measurements. Because the V072 code only models the effects of transverse gusts and because trailing edge blowing has strong effects on both transverse and longitudinal gusts, the lack of agreement between the predictions and the measurements is understandable. / by Margarita C. Brito. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 157-168). / While creating intelligent agents who can solve stochastic sequential decision making problems through interacting with the environment is the promise of Reinforcement Learning (RL), scaling existing RL methods to realistic domains such as planning for multiple unmanned aerial vehicles (UAVs) has remained a challenge due to three main factors: 1) RL methods often require a plethora of data to find reasonable policies, 2) the agent has limited computation time between interactions, and 3) while exploration is necessary to avoid convergence to the local optima, in sensitive domains visiting all parts of the planning space may lead to catastrophic outcomes. To address the first two challenges, this thesis introduces incremental Feature Dependency Discovery (iFDD) as a representation expansion method with cheap per-timestep computational complexity that can be combined with any online, value-based reinforcement learning using binary features. In addition to convergence and computational complexity guarantees, when coupled with SARSA, iFDD achieves much faster learning (i.e., requires much less data samples) in planning domains including two multi-UAV mission planning scenarios with hundreds of millions of state-action pairs. In particular, in a UAV mission planning domain, iFDD performed more than 12 times better than the best competitor given the same number of samples. The third challenge is addressed through a constructive relationship between a planner and a learner in order to mitigate the learning risk while boosting the asymptotic performance and safety of an agent's behavior. The framework is an instance of the intelligent cooperative control architecture where a learner initially follows a safe policy generated by a planner. The learner incrementally improves this baseline policy through interaction, while avoiding behaviors believed to be risky. The new approach is demonstrated to be superior in two multi-UAV task assignment scenarios. For example in one case, the proposed method reduced the risk by 8%, while improving the performance of the planner up to 30%. / by Alborz Geramifard. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2004. / Includes bibliographical references (leaves 95-97). / Airlines maximize the use of their resources by minimizing the time between consecutive flight legs in their aircraft and crew schedules. As a result, bad weather or unscheduled aircraft maintenance events can have a significant impact on an airline's operations. The consequences of these disruptions are major costs to airlines, passengers and, ultimately, to the economy itself. In this thesis, the steps taken to implement an airline schedule recovery model in a realistic simulation of the U.S. airspace system are presented. The MIT Extensible Network Simulation (MEANS), an event based queueing model of the U.S. National Airspace System, can be used for tactical decision making, long term decision making and post priori event analysis. Thus, the addition of a recovery model is critical to obtain accurate simulation results. The airline recovery model consists of an optimized aircraft re-scheduling model, a crew re-assigning model and a heuristic passenger itinerary search model. The model was used to simulate airline recovery procedures over the course of a day of operations for different scenarios. / by Fábio Faizi Rahnemay Rabbani. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2005. / "CSDL-T-1503, digital appendix"--CDROM label. Appendix B of thesis text contains an index to the CDROM. / Includes bibliographical references (p. 113-114). / Currently, Draper Laboratory is in the development stages of a gliding autogyro airdrop system. The goal of the project is to design a platform capable of placing small, high value items into urban terrain. Theoretically, autogyros can achieve descent rates and glide slopes similar to current parafoil based systems, but do so with greater precision. Over the past half-century most rotorcraft research has focused on helicopter design, only viewing autorotation as a means of achieving emergency landings. In contrast, this project utilized early rotor theory to develop algorithms which can predict unpowered rotor performance across the entire flight envelope. To validate these predictions, a vertical wind tunnel capable of testing rotors up to 4 feet in diameter at descent rates of up to 25 ft/s was constructed. Emphasis was also placed on developing deployment sequences that would allow the system to achieve stable autorotation autonomously. By varying parameters such as blade pitch angle and rotor solidity, it is shown that in the proper configuration, rotor based systems can match and even surpass parafoils in areas such as descent rate and glide slope. The autogyro also has the added capability of varying its lift-to-drag ratio in flight while maintaining reasonable descent speeds, allowing for more precise control to the target. Possible deployment sequences are displayed, proving that relatively simple configurations can be brought into stable autorotation. The algorithms developed and vertical wind tunnel constructed for this project can be used to gain further knowledge of autogyro performance. / by Michael Oliver. / S.M.