Thesis--Wisconsin. / Includes bibliographical references (leaves 105-110).

Thesis (Ph. D. in Chemical Engineering)--Vanderbilt University, Dec. 2009. / Title from title screen. Includes bibliographical references.

Bibliography: leaves 190-212. / xxiii, 240 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / This thesis describes a thrust vectoring nozzle (TVN) which produces a jet which may be deflected at angles in excess of 80o from the nozzle axis by fluid dynamic means, while maintaining total thrust efficiency of the order of 50%, or at 50o with an efficiency of the order of 70%. The thrust vectoring by fluid dynamic means is achieved by injecting secondary fluid at the nozzle throat and partially separating the primary jet causing it to deform. / Thesis (Ph.D.)--University of Adelaide, Dept. of Mechanical Engineering, 1995

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1992. / Vita. Abstract. Includes bibliographical references (leaves 209-216). Also available via the Internet.

Les travaux de recherche présentés dans cette thèse concernent la mise au point et l’étude de résines polysiloxanes et de matériaux sol-gel hybrides permettant de développer de nouveaux revêtements de protection pour des applications spatiales. Il s’agit notamment d’assurer le contrôle thermique des véhicules spatiaux et la protection des polymères vis-à-vis de l’oxygène atomique pour les applications en orbite basse. Outre la stabilité en environnement spatial et les contraintes de mise en œuvre, les revêtements doivent présenter des caractéristiques innovantes (température de polymérisation modérée) et être élaborés à partir de matières premières facilement approvisionnables pour éviter tout risque d’obsolescence. / This work presents the formulation and the study of polysiloxane resins and hybrid sol-gel materials to develop new protective coatings resistant to space environment. Spacecraft thermal control and polymer protection towards atomic oxygen are required in Low Earth Orbit applications. Besides the stability in the space environment and the process requirements, the coatings have to exhibit innovative properties (such as a low curing temperature) and be composed of raw materials with easy supply in order to avoid any risk of obsolescence.

This dissertation is concerned with the position and vibration control of flexible articulated space robots consisting of a rigid platform, two flexible arms, and a rigid end-effector carrying a payload, all components being serially connected through revolute joints. The mission is to carry a payload over a prescribed trajectory in the inertial space, while suppressing the elastic vibration of the arms and the rigid-body perturbations. The equations of motion governing the robot dynamics are derived by means of Lagrangian mechanics and they include actuator dynamics. Based on the assumption that the elastic deformations and the rigid-body perturbations are small relative to the nominal trajectory-following rigid-body motions, a perturbation approach is adopted to separate the equations into nonlinear rigid-body equations and linear perturbation equations. The nominal trajectory is planned to conserve the limited actuator resources and keep the platform attitude stationary, by eliminating the inherent kinematic redundancy of the manipulator. By assuming perfect sensing, i.e., all the states are completely accessible, two kinds of controls are designed in discrete-time. First, a feedforward control is designed to minimize the persistent disturbance resulting from the nominal motions. Next, a feedback control is synthesized based on the Linear Quadratic Regulator (LQR) theory with a prescribed degree of stability to make the system stable and further enhance the disturbance-rejection performances. These controls are subsequently applied to the case in which only the sensor outputs are available, and they are noisy. A finite number of sensors is assumed. A Kalman filter is designed to estimate the state on the assumption of zeromean Gaussian white plant and measurement noise. In the real situation, controls are applied to the original plant rather than the linearized model, so that the Linear Quadratic Gaussian (LQG) control combined with robustness recovery methods is tested on the plant. Due to difficulties in implementing a Kalman filter, a Maximum Likelihood Estimator (MLE) is proposed. A numerical example illustrates the approach. / Ph. D.

The objectives of this study were to characterize the effects of the space environment on the compressive behavior of T300/934 graphite/epoxy composite material and on the tensile properties of the neat (unfilled) epoxy matrix material. Both materials were tested in the baseline state and after exposure to electron radiation (total dose of 10,000 Mrads of 1 MeVelectrons at a dose rate of 50 Mrads/hr). Irradiation was conducted under vacuum and simulates 30 year, "worst case", exposure in geosynchronous earth orbit. A compressive test method was developed to characterize thin (8-ply) unidirectional coupons. Compression tests were conducted at cryogenic (-250°F; -157°C), room, and elevated (250°F; 121°C) temperatures. Elastic and strength properties were obtained in the principal material directions (E₁, E₂, v₁₂, v₂₁, X_c, Y_c). Tensile specimens of the neat Fiberite 934 epoxy resin were fabricated and tests were conducted at room and elevated (250°F; 121°C) temperatures. Elastic and strength properties (E, ν, δ_ult) were obtained. Irradiation and temperature were found to have a significant effect on composite and neat resin properties. Properties tended to improve at cryogenic temperature and degrade at elevated temperature. Irradiation degraded properties at all temperatures, with the degradation being most severe at elevated temperature. / M.S.

This work investigates three main topics. The first of these is the development and comparison of time integration schemes on two-dimensional unstructured meshes. Both explicit and implicit solution algorithms for the two-dimensional Euler equations on unstructured grids are presented. Cell-centered and cell-vertex finite volume upwind schemes utilizing Roe’s approximate Riemann solver are developed. For the cell-vertex scheme, a four stage Runge-Kutta time integration with and without implicit residual averaging, a point Jacobi method, a symmetric point Gauss-Seidel method, and two methods utilizing preconditioned sparse matrix solvers are investigated. For the cell-centered scheme, a Runge-Kutta scheme, an implicit tridiagonal relaxation scheme modeled after line Gauss-Seidel, a fully implicit LU decomposition, and a hybrid scheme utilizing both Runge-Kutta and LU methods are presented. A reverse Cuthill-McKee renumbering scheme is employed for the direct solver in order to decrease CPU time by reducing the fill of the Jacobian matrix. Comparisons are made for both first-order and higher-order accurate solutions using several different time integration algorithms. Higher-order accuracy is achieved by using multi-dimensional monotone linear reconstruction procedures. Results for flow over a transonic circular arc are compared for the various time integration methods. The second topic involves an interactive adaptive remeshing algorithm. The interactive adaptive remeshing algorithm utilizing a frontal grid generator is compared to a single grid calculation. Several device dependent interactive graphics interfaces have been developed along with a device independent DI-3000 interface which can be employed on any computer that has the supporting software including the Cray-2 supercomputers Voyager and Navier. Solutions for two-dimensional, inviscid flow over a transonic circular arc and a Mach 3.0 internal flow with an area change are examined. The final topic examined in this work is the capabilities developed for a structured three-dimensional code called GASP. The capabilities include: generalized chemistry and thermodynamic modeling, space marching, memory management through the use of binary C Input/Output, and algebraic and two-equation eddy viscosity turbulence modeling. Results are given for a Mach 1.7 three-dimensional analytic forebody, a Mach 1.38 axisymmetric nozzle with hydrogen-air combustion, a Mach 14.1 15° ramp, and Mach 0.3 viscous flow over a flat plate. The incorporation of these capabilities and the two-dimensional unstructured time integration schemes into a three-dimensional unstructured solver is also discussed. / Ph. D.

The objective of the proposed research is to study the integration of humans and automation for the operation of regenerative life support systems (RLSS). RLSS combine physico-chemical and biological processes with the purpose of increasing the autonomy of space habitats and the life quality of their living organisms by properly reusing byproducts and regenerating consumable resources. However, these processes require energy and time to transform chemical compounds and organic wastes into nutrients, consumables, and edible products. Consequently, the maintenance of RLSS imposes a considerable workload on human operators. In addition, the uncertainties introduced by unintended chemical reactions promoted by material loop closure may create unexpected situations that, if unattended, could translate into performance deterioration, human errors, and failures. The availability of novel chemical and biological sensors together with computational resources enable the development of monitoring and automation systems to alleviate human workload, help avoid human error, and increase the overall reliability of these systems. This research aggregates sensor data and human-expert situation assessments to create a representation of their situation knowledge base (\gloss{skb}). The representation is used in a switched control approach to the automation of RLSS, for decision support, and human-automation coordination. The aggregation method consists of an optimization process based on particle swarms. The purpose of this work is to contribute to the methodological development of situation-oriented and user-centered design approaches to human-automation systems. Experiments and simulations are supported on the process of respiration in an aquatic habitat acting as a RLSS.

Application of power MOSFETs in spaceborne power converters was simulated by exposing devices to low-dose-rate ionizing radiation. Both radiation-hardened and nonhardened devices were tested with constant and switched gate biases during irradiation. In addition, some of the devices were under load. The threshold-voltage shifts were strongly bias dependent. The threshold-voltage shift of the nonhardened parts was approximately dose-rate independent, while the hardened parts exhibited significant dose-rate dependence. A pre-anneal dose-rate dependence was found for the interface-state buildup of the switched and positively biased devices, but the results for the switched devices were qualitatively different than those for the positively biased devices. The buildup of interface trapped charge was found to be the primary contributor to mobility degradation, which results in reduced drive capability and slower operation of the devices. These results indicate that new methods need to be utilized to accurately predict the performance of power MOSFETs in space environments.