<p>The study of canonical flows, such as channels, pipes, or boundary layers, is essential for a deeper understanding of the physical mechanisms present in wall-bounded turbulence. Of particular importance in flows delimited by solid walls is the near-wall region where a large fraction of the drag stems from velocity fluctuations in a thin boundary layer adjacent to surfaces. In that context it is interesting to recognize that globally about 10% of all energy is used to overcome turbulent drag in one way or another. The goal of this study is to clarify our understanding in these areas by combining computations and experiments of turbulent duct flows and boundary layers. Oil film interferometry (OFI) and static pressure measurements were carried out over the range 200 &lt; <i>Re</i>_&tau; &lt; 800 (where <i> Re</i>_&tau; is the friction Reynolds number, based on duct half-height <i>h</i> and friction velocity <i>u</i>_&tau;) in an adjustable-geometry duct flow facility. Three-dimensional effects were studied by considering different aspect ratio (AR) configurations. Contrary to the accepted understanding in the field of turbulence research, we found that an aspect ratio of at least 24 is required in order to obtain "high-AR duct conditions" , and a development length of around 200 duct full-heights (for low and intermediate Reynolds numbers) is necessary for appropriate flow development. </p><p> The three-dimensional effects present in the flow, i.e., side-wall boundary layers and secondary motions, are also studied by means of direct numerical simulations (DNSs). The spectral element code Nek5000, developed by Fischer <i> et al.</i> (2008), is used to compute turbulent duct flows with aspect ratios from 1 to 10 in streamwise-periodic boxes of length 25<i>h</i> (long enough to capture the longest streamwise structures) and Reynolds numbers <i> Re</i>_&tau;,c = 180 and 330. While preparing the duct simulations, we also considered the necessary averaging times for converged statistics in simulations of wall turbulence; as a result, a set of guidelines regarding sampling times and intervals is also given. We find that the conditions often computed in z-periodic channels cannot be reproduced experimentally, even at very high aspect ratios such as 48, and therefore conclude that "computational channels" and "experimental high-AR ducts" are two different flows. The implications of these findings on wind tunnel experiments (with aspect ratios typically ranging from 3 to 16), and the large volume of available "two-dimensional" zero pressure gradient boundary layer data, are also assessed in this study. We therefore recommend the computational and experimental study of turbulent pipe flows, since this is the only case where matching canonical conditions can be obtained both in DNS computations and experimental facilities. </p><p> In addition, we re-analyze currently available Pitot tube corrections for ZPG turbulent boundary layer measurements, and propose new forms with coefficients dependent on inner-scaled Pitot tube diameter, [special characters omitted]. Reynolds number and probe size effects are both introduced in these coefficients, yielding excellent collapse of data over a much wider range of Pitot tube diameters (from 0.2 to 12.82 mm), and very good agreement with reference hot-wire and PIV data. We developed a new correcting scheme, called &kappa;<i> B</i>&mdash;Musker, which is able to provide the highest possible accuracy in probe position when applied to profile measurements of wall-bounded flows. </p>

<p> A DC&ndash;thermal plasma jet is proposed as a reliable ignition source for reaction control system (RCS) thrusters employing oxygen with hydrocarbons, like methane. Industrial plasma torch systems are analyzed to understand the behavioral characteristics of DC&ndash;thermal plasmas. Nitrogen is used as a working gas for the source of plasma jet to understand the general mechanism of thermal plasma formation. DC&ndash;thermal plasmas require high electrical energy to maintain their arc discharge status which presents challenges in space systems. The purpose of this study is, therefore, to find a suitable configuration which minimizes power consumption.</p><p> Various physical and electrical conditions relate to a thermal plasma formation. In this study, the input voltage (221&ndash;332V) and pressure (5&ndash;15 psi) are applied as initial conditions. The DC&ndash;power module and starter module are designed as plasma drivers and a commercial off&ndash;the&ndash;shelf torch head is used for this research. The normalized method is developed to estimate the arc temperature. Test results show that the lowest power consumption and arc&ndash;starting voltage are 1,321W and 248.8 VDC, respectively. In addition, it is found that the current is a major factor for varying the mass flow rate.</p><p> Since the lowest power consumption is still high, future improvements and research should focus on integrating a high&ndash;power and lightweight energy source, developing a high&ndash;frequency and half&ndash;duty cycle power system, and incorporating a composite cathode. In addition, a new conceptual torch design is proposed to be considered as an igniter for RCS thrusters. The next step would be to repeat the plasma torch tests with the new configuration at ambient and vacuum conditions. These would be followed by combustion tests to verify the actual functionality of the plasma igniter for RCS thrusters with various oxidizer and fuel mixture ratios. In parallel, research should focus on miniaturization of the electrical system.</p>

<p> Parts machined from relatively large thickness cross sections can experience significant deformations from high residual stresses that develop in the part during the heat treatment used to form the aluminum alloy. Uphill quenching is a process that can create a part with low residual stress and stable dimensions when the process is controlled properly. The uphill quenching process involves a solution heat treat, quench, cool to liquid nitrogen, steam blast, and then age to final temper. </p><p> In this thesis two parts were modeled using ANSYS. The first part underwent the uphill quench process in the rough machined state. The second part was modeled in the stock material shape and only underwent a solution heat treat, quench, and age to final temper. After the residual stress in the second part was predicted the excess material was removed by killing the associated elements and the deformation of the final machined part was predicted. For both parts analyzed measurements were made and compared against predictions with fairly good results.</p>

<p> Cold-start performance enhancement of a pump-assisted, capillary-driven, two-phase cooling loop was attained using proportional integral and fuzzy logic controls to manage the boiling condition inside the evaporator. The surface tension of aqueous solutions of n-Pentanol, a self-rewetting fluid, was also investigated for enhancing heat transfer performance of capillary driven (passive) thermal devices was also studied. A proportional-integral control algorithm was used to regulate the boiling condition (from pool boiling to thin-film boiling) and backpressure in the evaporator during cold-start and low heat input conditions. Active flow control improved the thermal resistance at low heat inputs by 50% compared to the baseline (constant flow rate) case, while realizing a total pumping power savings of 56%. Temperature overshoot at start-up was mitigated combining fuzzy-logic with a proportional-integral controller. A constant evaporator surface temperature of 60&deg;C with a variation of &plusmn;8&deg;C during start-up was attained with evaporator thermal resistances as low as 0.10 cm<i>2</i>&ndash;K/W. The surface tension of aqueous solutions of n-Pentanol, a self-rewetting working fluid, as a function of concentration and temperature were also investigated. Self-rewetting working fluids are promising in two-phase heat transfer applications because they have the ability to passively drive additional working fluid towards the heated surface; thereby increasing the dryout limitations of the thermal device. Very little data is available in literature regarding the surface tension of these fluids due to the complexity involved in fluid handling, heating, and experimentation. Careful experiments were performed to investigate the surface tension of n-Pentanol + water. The concentration and temperature range investigated were from 0.25%wt. to1.8%wt and 25&deg;C to 85&deg;C, respectively. </p>

<p> The current fiscally austere environment prevalent in the military and industry is driving extreme measures to save money. In the United States Air Force, this has driven enormous efforts to trim sustainment spending on extended life aircraft. The challenge to the aerospace engineer is to ensure flight safety in the midst of this economic pressure. </p><p> One method of cutting costs is to increase the time an aircraft is in service by delaying the point when the aircraft is taken out of service for depot maintenance. To ensure flight safety, in depth fatigue and fracture analysis needs to be accomplished to assess increasing the inspection interval. </p><p> The purpose of this study was to determine the sensitivity of Aluminum 2024-T351 alloy, a common material used in tension dominated aerospace applications, to two different loading spectra&mdash;one that is aggressive and the other that is benign. This was accomplished by conducting five different combinations of the two spectra, developing computer simulations using the AFGROW software and comparing with the measured data. The results showed that the material demonstrated significantly different behavior between the two spectra. These results provide a valuable tool for the aerospace engineer for fatigue life prediction and inspection interval evaluation.</p>

<p> A software prototype for autonomous 3D scanning of uncooperatively rotating orbital debris using a point cloud sensor is designed and tested. The software successfully generated 3D models under conditions that simulate some on-orbit orbit challenges including relative motion between observer and target, inconsistent target visibility and a target with more than one plane of symmetry. The model scanning software performed well against an irregular object with one plane of symmetry but was weak against objects with 2 planes of symmetry. </p><p> The suitability of point cloud sensors and algorithms for space is examined. Terrestrial Graph SLAM is adapted for an uncooperatively rotating orbital debris scanning scenario. A joint EKF attitude estimate and shape similiarity loop closure heuristic for orbital debris is derived and experimentally tested. The binary Extended Fast Point Feature Histogram (EFPFH) is defined and analyzed as a binary quantization of the floating point EFPFH. Both the binary and floating point EPFH are experimentally tested and compared as part of the joint loop closure heuristic.</p>

<p> Inverse optimal control is the problem of computing a cost function with respect to which observed state input trajectories are optimal. We present a new method of inverse optimal control based on minimizing the extent to which observed trajectories violate first-order necessary conditions for optimality. We consider continuous-time deterministic optimal control systems with a cost function that is a linear combination of known basis functions. We compare our approach with three prior methods of inverse optimal control. We demonstrate the performance of these methods by performing simulation experiments using a collection of nominal system models. We compare the robustness of these methods by analyzing how they perform under perturbations to the system. We consider two scenarios: one in which we exactly know the set of basis functions in the cost function, and another in which the true cost function contains an unknown perturbation. Results from simulation experiments show that our new method is computationally efficient relative to prior methods, performs similarly to prior approaches under large perturbations to the system, and better learns the true cost function under small perturbations. We then apply our method to three problems of interest in robotics. First, we apply inverse optimal control to learn the physical properties of an elastic rod. Second, we apply inverse optimal control to learn models of human walking paths. These models of human locomotion enable automation of mobile robots moving in a shared space with humans, and enable motion prediction of walking humans given partial trajectory observations. Finally, we apply inverse optimal control to develop a new method of learning from demonstration for quadrotor dynamic maneuvering. We compare and contrast our method with an existing state-of-the-art solution based on minimum-time optimal control, and show that our method can generalize to novel tasks and reject environmental disturbances. </p>

<p> There are significant challenges involved in regulating the growing commercial human spaceflight industry. The safety of the crew and passengers should be protected; however, care should be taken not to overburden the industry with too many or too stringent, or perhaps inapplicable, regulations. </p><p> An improvement in launch success would improve the safety of the crew and passengers. This study explores the effectiveness of Mission Assurance policies to guide regulations and standards. There is a severe lack of data regarding commercial human space flights. This means that a direct test of effectiveness by looking at historical commercial human space flight data is not possible. Historical data on current expendable commercial launchers have been used in this study. The National Aeronautics and Space Administration (NASA) has strong Mission Assurance policies for its launch of civil payloads. The Office of Commercial Space Transportation at the Federal Aviation Administration (FAA/AST) regulations of commercial launches are more safety oriented. </p><p> A comparison of launches between NASA and the FAA/AST is used to gauge the effectiveness of Mission Assurance policies on launch success. Variables between the two agencies are reduced so that Mission Assurance policies are isolated as the main difference between launches. Scenarios pertinent to commercial human space flight are used so results can be applicable.</p>

<p> An experimental study will be carried out to determine the suitability of Green Natural Fiber Reinforced Polymer plates (GNFRP) manufactured with hemp fibers, with the purpose of using them as structural materials for the flexural strengthening of reinforced concrete (RC) beams. Four identical RC beams, 96 inches long, are tested for the investigation, three control beams and one test beam. The first three beams are used as references; one unreinforced, one with one layer of Carbon Fiber Reinforced Polymer (CFRP), one with two layers of CFRP, and one with n layers of the proposed, environmental-friendly, GNFRP plates. The goal is to determine the number of GNFRP layers needed to match the strength reached with one layer of CFRP and once matched, assess if the system is less expensive than CFRP strengthening, if this is the case, this strengthening system could be an alternative to the currently used, expensive CFRP systems.</p>

<p> Aero-optical distortions are detrimental to airborne optical systems. To study distortion mechanisms, compressible large-eddy simulations are performed for a Mach 0.5 turbulent boundary layer and a separated shear layer over a cylindrical turret with and without passive control in the upstream boundary layer. Optical analysis is carried out using ray tracing based on the computed density field and Gladstone-Dale relation.</p><p> In the flat-plate boundary layer, the effects of aperture size, Reynolds number, small-scale turbulence, different flow regions and beam elevation angle are examined, and the underlying flow physics is analyzed. Three momemtum-thickness Reynolds numbers, <i>Re</i>_&thetas; = 875, 1770 and 3550, are considered. It is found that the level of optical distortions decreases with increasing Reynolds number within the Reynolds number range considered. The contributions from the viscous sublayer and buffer layer are small, while the wake region plays a dominant role followed by the logarithmic layer. By low-pass filtering the fluctuating density field, it is shown that small-scale turbulence is optically inactive. Consistent with previous experimental findings, the distortion magnitude is dependent on the propagation direction due to anisotropy of the boundary-layer vortical structures. Density correlations and length scales are analyzed to understand the elevation-angle dependence and its relation to turbulence structures. The applicability of Sutton's linking equation to boundary-layer flows is examined, and excellent agreement between linking equation predictions and directly integrated distortions is obtained when the density length scale is appropriately defined.</p><p> The second case studied involves a separated shear layer over a cylindrical turret with a flat window, with inflow from a flat-plate boundary layer with and without passive control devices. The flow and optical results show reasonable agreement with experimental data for the baseline case without control. Aperture size effect, frequency spectra of OPD and two-point spatial correlations of OPD are investigated. The similarities and differences of distortion characteristics compared to those induced by turbulent boundary layers are discussed. The distortions by a separated shear layer are much larger in magnitude and spatially less homogeneous than those induced by an attached boundary layer. It is found that pressure fluctuations are significant and play a dominant role in inducing density fluctuations and associated optical distortions in a separated shear layer, in contrast to the dominant role of temperature fluctuations in a turbulent boundary layer. When passive control is applied using a row of thin and tall pins in the upstream boundary layer, the numerical results confirm key experimental findings. The flow above the optical window is characterized by two distinct shear layers, whose combined effect leads to a significant reduction of density fluctuation magnitude in the main shear layer and associated optical distortions compared to the uncontrolled flow with a single strong shear layer.</p>