Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1997. / Includes bibliographical references (p. 172-173). / by Mark Eric Bury. / M.S.

Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2013. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Cataloged from student-submitted PDF version of thesis. / Includes bibliographical references (pages 167-169). / This project is focused on modeling the internal ow in centrifugal compressors for the purpose of assessing the onset of rotating stall and surge. The current methods to determine centrifugal compressor stability limits are based on empirical data and often, experiments. Unsteady full wheel simulations have become feasible due to the increase in computation power but the prediction of the stability limit still remains a challenge. The presented methodology is based on the idea of body forces and a blade passage model suitable for centrifugal compressors is derived. Previous work has shown that blade passage models are capable of capturing the response to inlet ow distortions and the onset of instability in axial compressors. In this thesis, a blade passage model is developed for centrifugal compressors with the goal of capturing the three-dimensional through-ow computed by steady RANS simulations. The model consists of three main elements, a normal force model, a viscous parallel force model, and a blade metal blockage model. The work demonstrates the model's capabilities on a radial impeller with prismatic blades where the total-to-static pressure rise coefficient and stage loading coefficient are in agreement with RANS calculations within 6.75% and 5%, respectively. While the model denition is shown to be consistent with other blade passage models for axial compressors, its application to a transonic axial compressor rotor and a high-speed centrifugal compressor stage revealed numerical convergence problems. It is thought that the model derivation and denition are sound and that these issues are due to implementation errors. The methodology and related modeling process are investigated step by step for three-dimensional blade geometries and, where applicable, verified with direct numerical calculation. The model limitations and potential implementation error are discussed at length so as to guide future work required to complete the demonstration of this blade passage model for axial and centrifugal compressors with three-dimensional blade shapes. / by Anjaney Pramod Kottapalli. / S.M.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1989. / Includes bibliographical references (leaves 48-49). / by Jayant Sharma. / M.S.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2004. / Includes bibliographical references (p. 120-123). / The introduction of concurrent design practices to the aerospace industry has greatly increased the efficiency and productivity of engineers during design sessions. Teams that are well-versed in such practices such as JPL's Team X are able to thoroughly examine a trade space and develop a family of reliable point designs for a given mission in a matter of weeks compared to the months or years sometimes needed for traditional design. Simultaneously, advances in computing power have given rise to a host of potent numerical optimization methods capable of solving complex multidisciplinary optimization problems containing hundreds of variables, constraints, and governing equations. Unfortunately, such methods are tedious to set up and require significant amounts of time and processor power to execute, thus making them unsuitable for rapid concurrent engineering use. In some ways concurrent engineering and automated system-level optimization are often viewed as being mutually incompatible. It is therefore desirable to devise a system to allow concurrent engineering teams to take advantage of these powerful techniques without hindering the teams' performance. This paper proposes such an integration by using parametric approximations of the subsystem models. These approximations are then linked to a system-level optimizer that is capable of reaching a solution more quickly than normally possible due to the reduced complexity of the approximations. The integration structure is described in detail and applied to a standard problem in aerospace engineering. Further, a comparison is made between this application and traditional concurrent engineering through an experimental trial with two groups each using a different method to / (cont.) solve the standard problem. Each method is evaluated in terms of optimizer accuracy, time to solution, and ease of use. The results suggest that system-level optimization, running as a background process during integrated concurrent engineering, is potentially advantageous as long as it is judiciously implemented from a mathematical and organizational perspective. / by Todd Schuman. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2006. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Includes bibliographical references (leaves 93-95). / With the advance in the fields of computer science, control and optimization, it is now possible to build aerial vehicles which do not need pilots. An important capability for such autonomous vehicles is to be able to generate their own path to navigate in a constrained environment and accomplish mission objectives, such as reaching waypoints in minimal time. To account for dynamic changes in the environment, perturbations, modeling errors and modifications in the mission scenario, the trajectory needs to be continuously re-optimized online based on the latest available updates. However, to allow for high update rates, the trajectory optimization problem needs to be simple enough to be solved quickly. Optimizing for a continuous trajectory of a dynamically-constrained vehicle in the presence of obstacles is an infinite-dimension nonlinear optimal control problem. Such a problem is intractable in real-time and simplifications need to be made. In this thesis, the author presents the mechanisms used to design a path-planner with real-time and long-range capabilities. The approach relies on converting the optimal control problem into a parameter optimization one whose horizon can be reduced by using a global cost-to-go function to provide an approximate cost for the tail of the trajectory. / (cont.) Thus only the short-term trajectory is being constantly optimized online based on a mixed integer linear programming formulation that accounts for the vehicle's performance. The cost-to-go function presented in this thesis has the feature to be tailored to both the environment and the vehicle's maneuvering capabilities. The author then implements and demonstrates a path-planner software based on the presented approach for a real unmanned helicopter, the Renegade, that flew within the DARPA SEC program. A full description of the capabilities and functions supported by the planner software are provided. Hardware-in-the-loop simulation results are provided to illustrate the performance of the system. / by Olivier Toupet. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2005. / Includes bibliographical references. / The primary aim of this thesis is to advance the theory of advanced locomotion mechanical counter pressure (MCP) spacesuits by studying the changes in the human body shape during joint motion. Two experiments take advantage of three-dimensional laser scan technology to measure the shape changes of the human body. The first experiment is an analysis of the surface area and volume of the thigh, knee, calf, and entire leg during knee flexion. The second experiment is an analysis of the full-field strain on the skin surface of the leg during knee flexion. A repeatable and quantitative technique for mapping the leg skin strain field is developed. The results of the algorithm indicate the magnitude of strain over the entire surface of the leg, as well as the direction of minimum leg skin stretching during knee flexion. For 88% of the leg surface, knee flexion causes skin strain between -0.3 and 0.3 (less than 30% contraction or extension). However, just below the patella, longitudinal strain is as high as 0.7, and at the knee hollow, it is as low as -0.6. Circumferential strain values are as high as 1.0 and 0.5 just below the patella and over the calf muscle, respectively, and along the anterior surface of the lower leg, they are as low as -0.7. The leg area, volume, and skin strain results lead to quantitative design requirements for highly mobile second skin spacesuits, and they inspire two prototype MCP leg sleeves: a hybrid urethane-foam bladder garment and a skintight nylon fiber lines of non-extension garment. These two prototypes are constructed and tested for mobility and skin surface pressure. Pressurization of the hybrid foam prototype inhibits leg mobility. / (cont.) However, the nylon lines of non-extension prototype shows promise as an advanced locomotion spacesuit design concept. During pressurization to leg surface pressure of 7.5 kPa (56 mmHg, 1.1 psi), the prototype preserves easy mobility to 90 degrees of knee joint flexion. Recommendations are made for improving its pressure production performance to the desired 30 kPa (222 mmHg, 4.3 psi) level. / by Kristen Bethke. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2007. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Includes bibliographical references (p. 231-239). / Electric thrusters are being developed for in-space propulsion needs of spacecraft as their higher specific impulse enables a significant reduction in the required propellant mass and allows longer duration missions. Over the last few decades many different electric propulsion concepts have been proposed and studied. In studying the electric thrusters, in order to improve the thruster performance as well as to understand the underlying physics of thruster's operation, various diagnostics methods were employed. As one unique method, emission spectroscopy provides a non-invasive, fast and economical diagnostic allowing also the ability to access hard to reach locations. In this study, emission spectroscopy is employed as a means to determine the trends in thruster operations as well as diagnosing the plasma parameters. This study presents the spectral measurement results of three different electric thrusters and plasma sources. First, the BHT-200 Hall thruster emission spectra measurements are presented for varying discharge voltage and for various regions of observation. / (cont.) Second, spectral measurements of a TAL type laboratory mini-Hall thruster, MHT-9, were presented. Third, radiation emission measurements of an experimental Helicon plasma source being studied to assess the possibility of using Helicon discharge as a propulsive system are presented and the trends are discussed. Two collisional-radiative (C-R) models are developed for Argon and Xenon plasmas to analyze the experimental spectra. In the C-R models, electron induced excitation, deexcitation and ionization collisions, and spontaneous radiative de-excitation transitions are simulated for neutral and singly charged ion species. The models are validated against measured spectra obtained using different experimental setups. The BHT-200 Hall thruster has insulator ceramic annular walls made of Boron-Nitride (BN). Erosion of ceramic walls is one of the major life limiting factors for Hall thrusters. Emission spectroscopy is used as a means to determine the trends in the thruster wall erosion rate by measuring the radiation emission of the Boron neutral 249.68nm and 249.77nm lines. Discussion about the spectral measurements and relevant analysis are presented. / by Murat Çelik. / Ph.D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1994. / Includes bibliographical references (p. 159-162). / by Brett P. Masters. / M.S.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2009. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 99-100). / This thesis presents a path planning and control strategy that enables an unmanned non-holonomic vehicle to intercept a fast moving object. The path planning is performed under model uncertainty, with respect to the vehicle's maneuverability, as well as uncertainty in the estimation of the object's future trajectory and position. This problem involves the tracking of the dynamic object in a cluttered environment and the accurate estimation of its future position in the presence of noisy measurements. The ground vehicle (interceptor) is required to intercept the dynamic object at a predicted (catch) location in a finite amount of time. This time restriction presents quite a challenge given the inherent limitation in the vehicle's steering and maneuverability. The solution strategy is divided into three sub-problems: 1) prediction, 2) path planning and 3) control. The prediction of the parameters that describe the dynamic's object in space is accomplished via Kalman Filtering which, in conjunction with an impact predictor, provide the waypoints needed to construct a reference path that will place the interceptor on a collision course with the dynamic object (target.) A pure pursuit algorithm was used to steer the interceptor along a reference trajectory, which was designed to make the vehicle engage the dynamic object on a near tail-on aspect. In the endgame, the pure pursuit algorithm was modified to ensure arrival to the catch point while a position controller was added to ensure timely arrival to the predicted catch location. The problem statement was then augmented to include obstacle avoidance. / (cont.) The dynamic object was required to navigate around fixed obstacles in order to catch the dynamic object. Results will show that the proposed strategy performed very well in the absence of obstacles and was well suited to handle the maneuverability constraints of the non-holonomic vehicle. Results also will show that, with minor modifications to the path planner, the interceptor successfully managed to avoid obstacles and catch the dynamic object although at a slightly lower success rate. The proposed solution was first demonstrated in simulation and then tested using MIT's RAVEN testbed. / by Sergio A. Cafarelli. / S.M.

Massachusetts Institute of Technology. Dept. of Aeronautics and Astronautics. Thesis. 1970. M.S. / MICROFICHE COPY ALSO AVAILABLE IN AERONAUTICS LIBRARY. / Bibliography: p. 98-100. / M.S.