A computational model of the micro-ion thruster MiXI has been developed, analyzed, and partially verified. This model includes submodels that govern the physical, magnetic, electrostatic, plasma physics, and power deposition of the thruster. Over the past few years, theses have been conducted with the goal of running tests and analyzing the results; this model is used to understand how the thruster components interact so as to make predictions about, and allow for optimization of, the thruster operation. Testing is then performed on the thruster and the results are compared to the output of the code. The magnetic structure of the thruster was analyzed and numerous different configurations generated which were also evaluated by the optimizer and tested. Using the different configurations, models, and optimization tools, the total efficiency of the thruster is theoretically able to reach 69.4%. Operational testing of the thruster at many different throttle settings demonstrated a maximum total efficiency of 45.9 ±24.6%, discharge loss values as low as 109 ±25 eV/ion, and total power required as low as 50.5 ±0.1W to maintain thruster operation with beam extraction. Measurements of the plasma were taken using a Langmuir probe and the interpretation of the tests are used to verify the plasma physics submodel. Power draw measurements and analysis of the throttle inputs during testing are compared to the performance model outputs but were not accurate or consistent enough to fully verify the power deposition and plasma physics models. Analysis of the models and operational testing in this study have led to an increased understanding of the performance and operation of the MiXI-CP-V3 thruster, furthering the effort to create an efficient, flight capable micro-ion thruster.

As satellites become smaller, cheaper, and quicker to manufacture, constellation systems will be an increasingly attractive means of meeting mission objectives. Optimizing satellite constellation geometries is therefore a topic of considerable interest. As constellation systems become more achievable, providing coverage to specific regions of the Earth will become more common place. Small countries or companies that are currently unable to afford large and expensive constellation systems will now, or in the near future, be able to afford their own constellation systems to meet their individual requirements for small coverage regions. The focus of this thesis was to optimize constellation geometries for small coverage regions with the constellation design limited between 1-6 satellites in a Walker-delta configuration, at an altitude of 200-1500km, and to provide remote sensing coverage with a minimum ground elevation angle of 60 degrees. Few Pareto-frontiers have been developed and analyzed to show the tradeoffs among various performance metrics, especially for this type of constellation system. The performance metrics focus on geometric coverage and include revisit time, daily visibility time, constellation altitude, ground elevation angle, and the number of satellites. The objective space containing these performance metrics were characterized for 5 different regions at latitudes of 0, 22.5, 45, 67.5, and 90 degrees. In addition, the effect of minimum ground elevation angle was studied on the achievable performance of this type of constellation system. Finally, the traditional Walker-delta pattern constraint was relaxed to allow for asymmetrical designs. These designs were compared to see how the Walker-delta pattern performs compared to a more relaxed design space. The goal of this thesis was to provide both a framework as well as obtain and analyze Pareto-frontiers for constellation performance relating to small regional coverage LEO constellation systems. This work provided an in-depth analysis of the trends in both the design and objective space of the obtained Pareto-frontiers. A variation on the εNSGA-II algorithm was utilized along with a MATLAB/STK interface to produce these Pareto-frontiers. The εNSGA-II algorithm is an evolutionary algorithm that was developed by Kalyanmoy Deb to solve complex multi-objective optimization problems. The algorithm used in this study proved to be very efficient at obtaining various Pareto-frontiers. This study was also successful in characterizing the design and solution space surrounding small LEO remote sensing constellation systems providing small regional coverage.

The objective of this research is to examine how to design low-noise transport aircraft using Multidisciplinary Design Optimization (MDO). The subject is approached by designing for low-noise both implicitly and explicitly. The explicit design approach involves optimizing an aircraft while explicitly constraining the noise level. An MDO framework capable of optimizing both a cantilever wing and a Strut-Braced-Wing (SBW) aircraft was developed. The framework employs aircraft analysis codes previously developed at the Multidisciplinary Design and Analysis (MAD) Center at Virginia Tech (VT). These codes have been improved here to provide more detailed and realistic analysis. The Aircraft Noise Prediction Program (ANOPP) is used for airframe noise analysis. The objective is to use the MDO framework to design aircraft for low-airframe-noise at the approach conditions and quantify the change in weight and performance with respect to a traditionally designed aircraft. The results show that reducing airframe noise by reducing approach speed alone, will not provide significant noise reduction without a large performance and weight penalty. Therefore, more dramatic changes to the aircraft design are needed to achieve a significant airframe noise reduction. Another study showed that the trailing-edge (TE) flap can be eliminated, as well as all the noise associated with that device, without incurring a significant weight and performance penalty. To achieve approximately 10 EPNdB TE flap noise reduction the flap area was reduced by 82% while the wing reference area was increased by 12.4% and the angle of attack increased from 7.6 degrees to 12.1 degrees to meet the required lift at approach. The wing span increased by approximately 2.2%. Since the flap area is being minimized, the wing weight suffers only about a 2,000 lb penalty. The increase in wing span provides a reduction in induced drag to balance the increased parasite drag due to a lower wing aspect ratio. As a result, the aircraft has been designed to have minimal TE flaps without any significant performance penalty. If noise due to the leading-edge (LE) slats and landing gear are reduced, which is currently being pursued, the elimination of the flap will be very significant as the clean wing noise will be the next 'noise barrier'. Lastly, a comparison showed that SBW aircraft can be designed to be 10% lighter and require 15% less fuel than cantilever wing aircraft. Furthermore, an airframe noise analysis showed that SBW aircraft with short fuselage-mounted landing gear could have similar or potentially a lower airframe noise level than comparable cantilever wing aircraft. The implicit design approach involves selecting a configuration that supports a low-noise operation, and optimizing for performance. A Blended-Wing-Body (BWB) transport aircraft has the potential for significant reduction in environmental emissions and noise compared to a conventional transport aircraft. A BWB with distributed propulsion was selected as the configuration for the implicit low-noise design in this research. An MDO framework previously developed at the MAD Center at Virginia Tech has been refined to give more accurate and realistic aircraft designs. To study the effects of distributed propulsion, two different BWB configurations were optimized. A conventional propulsion BWB with four pylon mounted engines and two versions of a distributed propulsion BWB with eight boundary layer ingestion inlet engines. A 'conservative' distributed propulsion BWB design with a 20% duct weight factor and a 95% duct efficiency, and an 'optimistic' distributed propulsion BWB design with a 10% duct weight factor and a 97% duct efficiency were studied. The results show that 65% of the possible savings due to 'filling in' the wake are required for the 'optimistic' distributed propulsion BWB design to have comparable $TOGW$ as the conventional propulsion BWB, and 100% savings are required for the 'conservative' design. Therefore, considering weight alone, this may not be an attractive concept. Although a significant weight penalty is associated with the distributed propulsion system presented in this study, other characteristics need to be considered when evaluating the overall effects. Potential benefits of distributed propulsion are, for example, reduced propulsion system noise, improved safety due to engine redundancy, a less critical engine-out condition, gust load/flutter alleviation, and increased affordability due to smaller, easily-interchangeable engines. / Ph. D.

Topology-based optimization techniques and lattice structures are powerful ways to accomplish lightweight components with enhanced mechanical performance. Recent developments in additive manufacturing (AM) have led the way to extraordinary opportunities in realizing complex designs that are derived from topology and lattice-based structural optimization. The main aim of this work is to give a contribution, in the integration between structural optimization techniques and AM, by proposing a setup of a proper methodology for rapid development of optimized medical implants addressing oseeointegration and minimization of stress shielding related problems. The validity of the proposed methodology for a proof of concept was demonstrated in two real-world case studies: a tibia intramedullary implant and a shoulder hemi prosthetics for two bone cancer patients. The optimization was achieved using topology optimization and replacement of solid volumes by lattice structures. Samples of three lattice unit cell configurations were designed, fabricated, mechanically tested, and compared to select the most proper configuration for the shoulder hemi prosthesis. Weight reductions of 30% and 15% were achieved from the optimization of the initial design of the tibia intramedullary implant and the shoulder hemiprosthesis respectively compared to initial designs. Prototypes were fabricated using selective laser melting (SLM) and direct light processing (DLP) technologies. Validation analysis was performed using finite element analysis and compressive mechanical testing. Future work recommendations are provided for further development and improvement of the work presented in this thesis.

No description available.

<p dir="ltr">Design under uncertainty (DUU) for spacecraft is crucial in ensuring mission success, especially given the criticality of their failure. To obtain a more realistic understanding of space systems, it is beneficial to holistically couple the modeling of the spacecraft and its trajectory as a multidisciplinary analysis (MDA). In this work, a MDA model is developed for an Earth-Mars mission by employing the general mission analysis tool (GMAT) to model the mission trajectory and rocket propulsion analysis (RPA) to design the engines. By utilizing this direct MDA model, the deterministic optimization (DO) of the system is performed first and yields a design that completed the mission in 307 days while requiring 475 kg of fuel. The direct MDA model is also integrated into a Monte Carlo simulation (MCS) to investigate the uncertainty quantification (UQ) of the spacecraft and trajectory system. When considering the combined uncertainty in the launch date for a 20-day window and the specific impulses, the time of flight ranges from 275 to 330 days and the total fuel consumption ranges from 475 to 950 kg. The spacecraft velocity exhibits deviations ranging from 2 to 4 km/s at any given instance in the Earth inertial frame. The amount of fuel consumed during the TCM ranges from 1 to 250 kg, while during the MOI, the amount of fuel consumed ranges from 350 to 810 kg. The usage of the direct MDA model for optimization and uncertainty quantification of the system can be computationally prohibitive for DUU. To address this challenge, the effectiveness of utilizing surrogate-based approaches for performing UQ is demonstrated, resulting in significantly lower computational costs. Gaussian processes (GP) models trained on data from the MDA model were implemented into the UQ framework and their results were compared to those of the direct MDA method. When considering the combined uncertainty from both sources, the surrogate-based method had a mean error of 1.67% and required only 29% of the computational time. When compared to the direct MDA, the time of flight range matched well. While the TCM and MOI fuel consumption ranges were smaller by 5 kg. These GP models were integrated into the DUU framework to perform reliability-based design optimization (RBDO) feasibly for the spacecraft and trajectory system. For the combined uncertainty, the DO design yielded a poor reliability of 54%, underscoring the necessity for performing RBDO. The DUU framework obtained a design with a significantly improved reliability of 99%, which required an additional 39.19 kg of fuel and also resulted in a reduced time of flight by 0.55 days.</p>

Research in the field of reliability based design is mainly focused on two sub-areas: The computation of the probability of failure and its integration in the reliability based design optimization (RBDO) loop. Four papers are presented in this work, representing a contribution to both sub-areas. In the first paper, a new Second Order Reliability Method (SORM) is presented. As opposed to the most commonly used SORMs, the presented approach is not limited to hyper-parabolic approximation of the performance function at the Most Probable Point (MPP) of failure. Instead, a full quadratic fit is used leading to a better approximation of the real performance function and therefore more accurate values of the probability of failure. The second paper focuses on the integration of the expression for the probability of failure for general quadratic function, presented in the first paper, in RBDO. One important feature of the proposed approach is that it does not involve locating the MPP. In the third paper, the expressions for the probability of failure based on general quadratic limit-state functions presented in the first paper are applied for the special case of a hyper-parabola. The expression is reformulated and simplified so that the probability of failure is only a function of three statistical measures: the Cornell reliability index, the skewness and the kurtosis of the hyper-parabola. These statistical measures are functions of the First-Order Reliability Index and the curvatures at the MPP. In the last paper, an approximate and efficient reliability method is proposed. Focus is on computational efficiency as well as intuitiveness for practicing engineers, especially regarding probabilistic fatigue problems where volume methods are used. The number of function evaluations to compute the probability of failure of the design under different types of uncertainties is a priori known to be 3n+2 in the proposed method, where n is the number of stochastic design variables. / <p>QC 20160317</p>

This study is devoted to some of the most important issues for advancing inkjet printing for possible application in the coating industry with a focus on piezoelectric droplet on demand (DOD) inkjet technology. Current problems, as embodied in liquid filament breakup along with satellite droplet formation and reduction in droplet sizes, are discussed and then potential solutions identified. For satellite droplets, it is shown that liquid filament break-up behavior can be predicted by using a combination of two pi-numbers, including the Weber number, We and the Ohnesorge number, Oh, or the Reynolds number, Re, and the Weber number, We. All of these are dependent only on the ejected liquid properties and the velocity waveform at the print-head inlet. These new criteria are shown to have merit in comparison to currently used criteria for identifying filament physical features such as length and diameter that control the formation of subsequent droplets. In addition, this study performs scaling analyses for the design and operation of inkjet printing heads. Because droplet sizes from inkjet nozzles are typically on the order of nozzle dimensions, a numerical simulation is carried out to provide insight into how to reduce droplet sizes by employing a novel input waveform impressed on the print-head liquid inflow without changing the nozzle geometry. A regime map for characterizing the generation of small droplets based on We and a non-dimensional frequency, Ω is proposed and discussed. In an attempt to advance inkjet printing technology for coating purposes, a prototype was designed and then tested numerically. The numerical simulation successfully proved that the proposed prototype could be useful for coating purposes by repeatedly producing mono-dispersed droplets with controllable size and spacing. Finally, the influences of two independent piezoelectric characteristics - the maximum head displacement and corresponding frequency, was investigated to examine the quality of filament breakup quality and favorable piezoelectric displacements and frequencies were identified.

Approved for public release, distribution is unlimited / Numerous optimization problems involve systems with multiple and often contradictory criteria. Such contradictory criteria have been an issue for marine/naval engineering design studies for many years. This problem becomes more important when one considers novel ship types with very limited or no operational record. A number of approaches have been proposed to overcome these multiple criteria design optimization problems. This Thesis follows the Parameter Space Investigation (PSI) technique to address these problems. The PSI method is implemented with a software package called MOVI (Multi-criteria Optimization and Vector Identification). Two marine/naval engineering design optimization models were investigated using the PSI technique along with the MOVI software. The first example was a bulk carrier design model which was previously studied with other optimization methods. This model, which was selected due to its relatively small dimensionality and the availability of existing studies, was utilized in order to demonstrate and validate the features of the proposed approach. A more realistic example was based on the "MIT Functional Ship Design Synthesis Model" with a greater number of parameters, criteria, and functional constraints. A series of optimization studies conducted for this model demonstrated that the proposed approach can be implemented in a naval ship design environment and can lead to a large design parameter space exploration with minimum computational effort. / Lieutenant Junior Grade, Turkish Navy

This research addresses problems in designing analog and mixed-signal (AMS) systems by bridging the gap between system-level and circuit-level simulation by making simulations fast like system-level and accurate like circuit-level. The tools proposed include metamodel integrated Verilog-AMS based design exploration flows. The research involves design centering, metamodel generation flows for creating efficient behavioral models, and Verilog-AMS integration techniques for model realization. The core of the proposed solution is transistor-level and layout-level metamodeling and their incorporation in Verilog-AMS. Metamodeling is used to construct efficient and layout-accurate surrogate models for AMS system building blocks. Verilog-AMS, an AMS hardware description language, is employed to build surrogate model implementations that can be simulated with industrial standard simulators. The case-study circuits and systems include an operational amplifier (OP-AMP), a voltage-controlled oscillator (VCO), a charge-pump phase-locked loop (PLL), and a continuous-time delta-sigma modulator (DSM). The minimum and maximum error rates of the proposed OP-AMP model are 0.11 % and 2.86 %, respectively. The error rates for the PLL lock time and power estimation are 0.7 % and 3.0 %, respectively. The OP-AMP optimization using the proposed approach is ~17000× faster than the transistor-level model based approach. The optimization achieves a ~4× power reduction for the OP-AMP design. The PLL parasitic-aware optimization achieves a 10× speedup and a 147 µW power reduction. Thus the experimental results validate the effectiveness of the proposed solution.