Richtmyer-Meshkov (R-M) instability occurs when two different density fluids are impulsively accelerated in the direction normal to their nearly planar interface. The instability causes perturbations on the interface to grow and to possibly become turbulent. R-M instability is a fundamental fluid instability that is important to fields ranging from astrophysics to high-speed combustion. For example, R-M instability is currently one of the limiting factors in achieving a positive net yield in laser driven inertial confinement fusion experiments. This experimental study investigates the instability of an interface between incompressible, miscible liquids with an initial sinusoidal perturbation. After undergoing a nearly impulsive acceleration, the initial perturbation quickly inverts and then grows in amplitude. The vorticity on the interface eventually coalesces into a series of alternating signed vortices. Disturbance amplitudes are measured and compared to theoretical predictions. Linear stability theory gives excellent agreement with the measured initial perturbation growth rates, while the predicted amplitudes differ by less than 10% from experimental measurements up to a nondimensional time kȧ₀t = 0.7. Fourth order, single-mode perturbation theory extends the 1.0% amplitude agreement up to a nondimensional time kȧ₀t = 1.3. A discrete vortex model and a combined model equation are within 10% of the experimental amplitude measurements up to the maximum experimental nondimensional time kȧ₀t = 30. The effects of Reynolds number (based on circulation) on the vortex core evolution and overall growth rate of the interface are also investigated. In addition, an instability in the vortex cores is observed for the first time and criteria established for its occurrence.

This study involves an experimental and analytical investigation of low-velocity impact phenomenon in sandwich composite structures. The analytical solution of a three-dimensional finite-geometry multi-layer specially orthotropic panel subjected to static and transient transverse loading cases is presented. The governing equations of the static and dynamic formulations are derived from Reissner's functional and solved by enforcing the continuity of traction and displacement components between adjacent layers. For the dynamic loading case, the governing equations are solved by applying Fourier or Laplace transformation in time. Additionally, the static solution is extended to solve the contact problem between the sandwich laminate and a rigid sphere. An iterative method is employed to determine the sphere's unknown contact area and pressure distribution. A failure criterion is then applied to the sandwich laminate's stress and strain field to predict impact damage. The analytical accuracy of the present study is verified through comparisons with finite element models, other analyses, and through experimentation. Low-velocity impact tests were conducted to characterize the type and extent of the damage observed in a variety of sandwich configurations with graphite/epoxy face sheets and foam or honeycomb cores. Correlation of the residual indentation and cross-sectional views of the impacted specimens provides a criterion for the extent of damage. Quasi-static indentation tests are also performed and show excellent agreement when compared with the analytical predictions. Finally, piezoelectric polyvinylidene fluoride (PVF2) film sensors are found to be effective in detecting low-velocity impact.

Solid oxide electrolysis of a mixture of water and carbon dioxide has many applications in space exploration. It can be implemented in propellant production systems that use Martian resources or in closed-loop life support systems to cleanse the atmosphere of facilities in extraterrestrial bases and of cabin spacecrafts. This work endeavors to quantify the performance of combined water and carbon dioxide electrolysis, referred to as "combined electrolysis", and to understand how it works so that the technology can be best applied. First, to thoroughly motivate the research, system modeling is presented that demonstrates the competitiveness of the technology in terms of electrolysis power requirements and consequential system mass savings. Second, to demonstrate and quantify the performance of the technology, experimental results are presented. Electrolysis cells were constructed with 8% by mol yttria-stabilized zirconia electrolytes, 50/50 by weight platinum/yttria-stabilized zirconia electrodes and chromium-alloy or alumina manifolds and tubing. Performance and gas chromatograph data from electrolysis of many different gas mixtures, including water, carbon dioxide, and a combined mixture of both, are presented. Third, to explain observations made during experiments and theorize about the phenomena governing combined electrolysis, data analyses and thermodynamic modeling are applied. Conclusions are presented regarding the transient response of combined electrolysis, the relative performance of it to that of other mixtures, how its performance depends on the water to carbon dioxide ratio, its effect on cell health, and its preference to water versus carbon dioxide. Procedures are also derived for predicting the composition of combined electrolysis exhaust for a given oxygen production rate, humidity content, and inlet flow rate. The influence of the two cell materials proves to be significant. However, in both cases it is proven that combined electrolysis does not encourage carbon deposition and the makeup of its products is governed by the water gas shift reaction. It is shown that the chromium-alloy system achieves water gas shift reaction equilibrium whereas the alumina system does not. Experimental observations support the argument that chromium oxide inside the chromium alloy cell forces its water gas shift reaction to equilibrium during electrolysis, influencing combined electrolysis performance.

The success of the Hubble Space Telescope created a great interest in the next generation of space telescopes. To address this need, the University of Arizona (UA) has designed and built several lightweight prototype mirrors ranging in size from 0.5 m to 2 m in diameter. These mirrors consist of three key components: a thin, lightweight glass substrate holds the reflective surface; the surface accuracy is maintained by an array of position actuators; and the stiffness is maintained by a lightweight carbon-fiber/epoxy support structure. The UA mirrors are different from conventional mirrors in that they are actively-controlled: their figure may be changed after they leave the optics shop. This dissertation begins with an overview of the technical issues for placing large optics in space, and I also discuss the current state-of-the-art in active mirror design. Chapters 3 and 4 discuss ways to design mirrors such that the optical performance is maximized while the mass is minimized. Chapter 3 looks at the best way to distribute the mass between the reflective substrate and the actuators, and Chapter 4 looks at the optimum geometries for structured mirrors. The second half of this work looks at the practical aspects of controlling active mirrors. Chapter 5 discusses the University of Arizona's 2 m NMSD prototype mirror. Specifically, I review the system that I developed to measure and control the mirror. I also provide some details on using a least-squares solution to solve for the actuator commands. Chapter 6 discusses the UA ultralightweight 0.5 m prototype mirror. I describe the techniques that I developed for attaching loadspreaders to the reflective surface, the metrology system, and a software package used to remotely-control the mirror.

In order to eliminate thermodynamic limitations during H₂ and CO reduction processes, a novel carbothermal reduction process is proposed to generate lunar oxygen for propellant and life support on the lunar surface. The kinetics and mechanism of the carbothermal reduction of synthetic ilmenite and fayalite (simulants for lunar ilmenite and fayalite) were investigated in the present study. Carbothermal reduction of ilmenite with charcoal powder was studied between 975°C and 1100°C. It was found that the reduction process is controlled by the carbon gasification reaction instead of by the rate of ilmenite reduction with carbon monoxide, which has been claimed to be the rate limiting step by several prior researchers. The activation energy obtained using a simplified carbon gasification model for this reduction is 27.2 kcal/mole. The reduction products were studied by SEM and XRD and it was found that the major products are α-Fe and TiO₂ at temperatures below 1000°C; at 1050°C, α-Fe and Ti₉O₁₇ were observed; at 1100°C, α-Fe and Ti₄O₇ were observed. Iron is completely segregated from the titanium oxides in the product. Carbothermal reduction of ilmenite with deposited carbon was investigated between 775°C and 1000°C. An extremely fast reduction rate (more than ten times faster than charcoal powder reduction) was observed. The reduction rate-limiting step is believed to be the ilmenite reduction with carbon monoxide. The activation energy calculated by a simplified model is 50 kcal/mole between 775°C and 900°C, and 17.6 kcal/mole above 900°C. It was also found that TiO₂ can be reduced to much lower oxygen content titanium oxides than during powdered charcoal reduction. The temperature and particle size effects during carbothermal reduction of synthetic fayalite were investigated. The product morphology of this reduction showed that α-Fe and α-cristobalite are the main products at temperatures above 1100°C, at lower temperatures, α-Fe, α-quartz and amorphous silica are the main products. The iron produced by reduction is segregated from the SiO₂ phases and agglomerates in large particles, which is different from the product morphology observed during hydrogen reduction of fayalite. In order to better understand the mechanism and kinetics of the carbothermal reduction process, a mathematical model was developed to simulated the CO₂/CO ratio, CO and CO₂ partial pressure distributions, conversion, etc. during the reduction process. Using the model to treat the reduction of ilmenite with charcoal powder reproduces experimental results very well.

Although it has been used for many years, an existing computer code, developed to simulate the laminar opposed-jet diffusion flame (LOJDF), was found not to be written in an user-friendly fashion. This was especially true for the portion dealing with calculation of thermochemical properties. The purpose of this research was to replace the appropriate portions of the existing program by the corresponding portions of the CHEMKIN package. CHEMKIN has become a recognized standard in inputing chemical kinetics data into program, since the inputing is almost format free and easy to manipulate. A series of test cases show that the updated code is now better structured, user-friendly, and ready to use. The previous LOJDF model, in addition, is modified by adding source terms for species generation in the governing equations. The source-contained LOJDF model has proven to be useful in evaluating the numerical relation of the fate of an impurity to its location and strength.

The first objective of this study was to determine and compare the fatigue damage from two different vibration events versus the fatigue damage from an envelope of both events. The second objective was to determine and compare the fatigue damage from the equipment test versus the fatigue damage from a section test while using the same vibration envelope. Both objectives were accomplished using NASTRAN models to calculate internal loads for use in the fatigue analysis. This study proved that the vibration envelope produced three times more fatigue damage than the worst vibration event, and two times more fatigue damage than both events applied sequentially. When the same vibration envelope was used in an equipment test and a section test, the analytical results showed the internal loads were quite different. Furthermore, this study demonstrated the need to validate and update analytical models with actual test data to derive accurate equipment loads.

<p> Disengaged employees cost U.S. companies billions of dollars annually in lowered productivity, a cost which has been compounded by the difficult economic situations in the country. The potential for increasing productivity through increased employee engagement was examined in this study. Using personal engagement theory and the theory of planned behavior, the purpose of this phenomenological study was to explore how the experiences of salaried aerospace employees affected productivity and the financial performance of an organization. Interviews were conducted with a purposive sample of 20 aerospace employees whose responses were codified and analyzed to identify themes. The analysis indicated that (a) the lived experiences of employees influenced employee engagement, (b) employee engagement affects organizational commitment and performance, and (c) trust and respect and leadership are essential components to keep employees engaged. Eighty percent of the participants indicated that as employee engagement increases so too does organizational performance. The implications for positive social change include new insights for leaders seeking to increase productivity and financial performance, and to support employee engagement for maintaining sustainability, retaining talent, increasing profits, and improving the economy.</p>

<p> I present the development of instrumentation and methods for the measurement of coastal processes, ocean surface phenomena, and air-sea interaction in two parts. In the first, I discuss the development of a portable scanning lidar (light detection and ranging) system for manned aircraft and demonstrate its functionality for oceanographic and coastal measurements. Measurements of the Southern California coastline and nearshore surface wave fields from seventeen research flights between August 2007 and December 2008 are analyzed and discussed. The October 2007 landslide on Mt. Soledad in La Jolla, California was documented by two of the flights. The topography, lagoon, reef, and surrounding wave field of Lady Elliot Island in Australia's Great Barrier Reef were measured with the airborne scanning lidar system on eight research flights in April 2008. Applications of the system, including coastal topographic surveys, wave measurements, ship wake studies, and coral reef research, are presented and discussed. </p><p> In the second part, I detail the development of instrumentation packages for small (18 &ndash; 28 kg) unmanned aerial vehicles (UAVs) to measure momentum fluxes and latent, sensible, and radiative heat fluxes in the atmospheric boundary layer (ABL), and the surface topography. Fast-response turbulence, hygrometer, and temperature probes permit turbulent momentum and heat flux measurements, and short- and long-wave radiometers allow the determination of net radiation, surface temperature, and albedo. Careful design and testing of an accurate turbulence probe, as demonstrated in this thesis, are essential for the ability to measure momentum and scalar fluxes. The low altitude required for accurate flux measurements (typically assumed to be 30 m) is below the typical safety limit of manned research aircraft; however, it is now within the capability of small UAV platforms. Flight tests of two instrumented BAE Manta UAVs over land were conducted in January 2011 at McMillan Airfield (Camp Roberts, CA), and flight tests of similarly instrumented Boeing-Insitu ScanEagle UAVs were conducted in April 2012 at the Naval Surface Warfare Center, Dahlgren Division (Dahlgren, VA), where the first known direct flux measurements were made from low-altitude (down to 30 m) UAV flights over water (Potomac River). During the October 2012 Equatorial Mixing Experiment in the central Pacific aboard the R/V <i>Roger Revelle</i>, ship-launched and recovered ScanEagles were deployed in an effort to characterize the marine atmospheric boundary layer structure and dynamics. I present a description of the instrumentation, summarize results from flight tests, present preliminary analysis from UAV flights off of the <i>Revelle</i>, and discuss potential applications of these UAVs for marine atmospheric boundary layer studies.</p>

<p> The design of control mixing algorithms for launch vehicles with multiple vectoring engines yields competing objectives for which no straightforward solution approach exists. The designer seeks to optimally allocate the effector degrees of freedom such that maneuvering capability is maximized subject to constraints on available control authority. In the present application, such algorithms are generally restricted to linear transformations so as to minimize adverse control-structure interaction and maintain compatibility with industry-standard methods for control gain design and stability analysis. Based on the application of the theory of ellipsoids, a complete, scalable, and extensible framework is developed to effect rapid analysis of launch vehicle capability. Furthermore, a control allocation scheme is proposed that simultaneously balances attainment of the maximum maneuvering capability with rejection of internal loads and performance losses resulting from thrust vectoring in the null region of the admissible controls. This novel approach leverages an optimal parametrization of the weighted least squares generalized inverse and exploits the analytic properties of the constraint geometry so as to enable recovery of more than ninety percent of the theoretical capability while maintaining linearity over the majority of the attainable set.</p>