Great interest has been shown for the development of an All Electric Aircraft. There are many possible benefits and applications for the development of an All Electric Aircraft, such as monitoring severe weather or exploring the surface of other planets, and ultimately in civil aviation, a zero-emission aircraft. Design of the size and weight of the electrical systems for airplane use is important and a critical factor in this development is the propulsion of the aero-vehicle. One method to increase power density of a motor is to use superconducting components. The development of a superconducting motor that provides enough power for an airplane is discussed. A Cessna-type aircraft is to be powered by a motor that utilizes high temperature superconducting (HTS) components in the inductor. This motor is a novel design that uses both BSCCO (bismuth strontium calcium copper oxide) tape wound in pancake shapes and single domain, bulk YBCO (yttrium barium copper oxide) plates to create powerful magnetic fields capable of meeting requirements for an aircraft. The HTS inductor design generates a magnetic field outward to a rotating, non-superconducting armature. The BSSCO pancakes generate a magnetic field to trap magnetic flux in the YBCO plates via the Field Cooling method (FC). The use of FC creates very powerful magnetic fields but requires a multi-step cooling schedule for the inductor design. To properly trap flux using FC, the BSCCO pancakes must first be cooled to the operating temperature and generate an applied magnetic field while the bulk YBCO plates remain above the critical temperature. The YBCO plates are then cooled near the operating temperature, thus trapping flux in the plates. The current in the pancakes is then reversed and the magnetic fields are generated, then the YBCO plates are further cooled to the steady state temperature. This process of cooling the BSCCO pancakes and then cooling the YBCO plates is called the 3-stage cooling. The cooling of the motor is by conduction due to the mobile application of aero-propulsion. The conduction-cooled inductor is constructed along with a cooling apparatus that includes an aluminum central cylinder attached to a cryocooler, G10 rings, and heaters that aid in the 3-stage cooling process. Simulations were performed that model the heat loads, cooling schedule from room temperature to operational temperature, and the 3-stage cooling to aid in the design. These modeling results show the temperature gradients in the inductor and HTS components and are verified experimentally. A full-scale, mockup inductor has been constructed and is cooled with a cryocooler in a cryostat. The cooling inductor final design is shown with modeling results and the proof-of-principle or a motor utilizing HTS materials in the inductor has been provided. A prototype of the motor should be built and tested based on these electromagnetic and cooling designs. The use of heaters near the YBCO plates is required in the 3-stage cooling design. The YBCO has trapped-flux that is dependent on the operating temperature and the stability of the trapped-flux is critical to the motor design. Work has been done that experimentally tests the stability of trapped flux in YBCO plates. A heat impulse is inputted into a YBCO sample that is fully penetrated in current via FC. The experiments were performed in a sample chamber that has temperature and applied magnetic field controllability. The change in the magnetic field and temperature of the sample is measured and analyzed before and after the heat pulse using Hall probes. The experimental data suggests that there is no thermal runaway loss in the trapped-magnetic flux for a small heat input and an operating temperature for which the sample has maximum stability. To explain the physics of the trends exhibited in the data, two models were developed. The first model uses an analytical approach to capture the overall trends exhibited by the data. The analytical model uses an energy balance based on the stored magnetic energy loss and change in thermal energy before and after the heat pulse is input into the sample. The second model is a finite element analysis approach using commercial software (Comsol) to gain a more in-depth analysis of the internal changes in the sample during the heat pulse. The Comsol model provides a tool to study the effect of the heat pulse on the current density and the effect of the cooling environment surrounding the sample. The models are able to capture the trends suggested by the experiment and provide insight into the fundamental phenomena that happen during the heat pulse. The sample studied in the experiment does indeed have a maximum stability point and it is explained by the modeling work. A cooling apparatus was designed to cool the inductor of a HTS motor. The electro-magnetic design utilizes field cooling to trap flux and this was accomplished with a 3-stage cooling process. The cooling design was validated using simulations and experimental data. The cooling apparatus showed the feasibility of the inductor to trap flux in the plates. The stability of the trapped flux was also studied. Experimental data shows that there is no thermal runaway when heat is inputted into a sample and an operating temperature exists that suggests a maximum stability. The physics of the stability experiment was uncovered using an analytical model and a FEA model. Also shown was the effect of the cooling environment on the sample during the heat impulse. The stability models showed that the data are the results of the cooling environment and the competing effects of current density and specific heat, both functions of temperature. / A Dissertation submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Degree Awarded: Spring Semester, 2009. / Date of Defense: March 30, 2009. / Field Cooling, Trapped-flux magnets, Conduction cooling, HTS motor, Stability / Includes bibliographical references. / Cesar A. Luongo, Professor Directing Dissertation; Pascal Tixador, Outside Committee Member; Steven W. Van Sciver, Committee Member; Thomas L. Baldwin, Committee Member; Philippe J. Masson, Committee Member.

Practically all engineering applications require knowledge of uncertainty. Accurately quantifying uncertainty within engineering problems supports model development, potentially leading to identification of key risk factors or cost reductions. Often the full problem requires modeling behavior of materials or structures from the quantum scale all the way up to the macroscopic scale. Predicting such behavior can be extremely complex, and uncertainty in modeling is often increased due to necessary assumptions. We plan to demonstrate the benefits of performing uncertainty analysis on engineering problems, specifically in the development of constitutive relations and structural analysis of smart materials and adaptive structures. This will be highlighted by a discussion of ferroelectric materials and their domain structure interaction, as well as dielectric elastomers’ viscoelastic and electrostrictive properties. / A Dissertation submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Summer Semester 2017. / June 22, 2017. / Electrostriction, Ferroelectricity, Parameter Estimation, Uncertainty Quantification, Viscoelasticity / Includes bibliographical references. / William Oates, Professor Co-Directing Dissertation; M. Yousu Hussaini, Professor Co-Directing Dissertation; Changchun Zeng, University Representative; Kunihiko Taira, Committee Member; Shangchao Lin, Committee Member; Ralph Smith, Committee Member.

Azobenzene is a photo responsive polymer which undergoes molecular change under exposure to certain wavelengths of light. This molecular shape change can cause an overall macroscopic shape change in an azobenzene polymer network. This promising photostrictive behavior has broad range of applications in flow control, robotics and energy harvesting applications. The conversion of solar energy directly into mechanical work provides unique capabilities in adaptive structures. In this thesis, stress measurements show that irradiated azo-LCN experience photochemical and thermomechanical stress. Experimental results show that stress response depends highly on the range of pre-stress applied and the threshold pre-stress differs for different polarization directions. / A Thesis submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of Master of Science. / Spring Semester 2017. / March 30, 2017. / azobenzene, light intensity, polarization, pre-stress / Includes bibliographical references. / William S. Oates, Professor Directing Thesis; Shangchao Lin, Committee Member; Juan C. Ordonez, Committee Member.

Global energy demands are on the rise, and the current technology used to generate, transmit, and distribute electricity will not be able to meet the growth due to the bottlenecks in densely populated areas and the inefficiencies throughout the electrical grid. Soon, new technologies will be required to relieve the constraints on the grid while being cost effective, reliable, and environmentally acceptable. High temperature superconducting (HTS) technology being developed has the means to provide ways to overcome the challenges faced by electric utility companies. Other applications including all-electric ships and aircrafts would also benefit greatly from the use of HTS power devices in meeting the increasing electrical power requirements at high power densities. HTS power technology is relatively complex, and it involves multiple technological and scientific disciplines besides the materials being expensive currently to enable cost-effective applications. Therefore, intensive numerical modeling efforts are necessary to improve the designs and system level optimizations so that the technology will be commercially viable. The goal of the research described here is to investigate and develop effective methods of modeling and simulating HTS power devices cooled with gaseous helium (GHe) circulation. The technique of GHe-cooled HTS power systems is relatively new, and there is much room for improvements in designs, particularly integrating the superconducting and cryogenics systems. Benefits of modeling the systems in detail include reduced cost and time and the ability to perform optimizations; each of which would allow faster development cycles at lower cost. These benefits arise from the fact that it’s more efficient to design complex systems using bits as opposed to atoms. A 30-m long HTS power cable including the cable terminations and the cryogenic helium circulation system is the primary system studied in this work. GHe offers some important benefits over liquid nitrogen including improved safety in confined spaces and lower operating temperatures especially for superconducting applications that require high power densities such as those to be used on all-electric Navy ships. However, there are still some challenges that need to be addressed. GHe possesses lower heat capacity per unit volume compared to liquid cryogens, and its weak dielectric strength currently restricts its use in HTS power cables at low and medium voltage applications. This dissertation describes numerical modeling techniques including volume element methods and finite element methods that were developed to visualize the physics of several different HTS cable system components. The modelling techniques developed were further utilized for transient analysis of the cryogenic thermal and electrical behavior under various scenarios and system operational contingencies to assess the limitations of the technology and to devise methods for mitigating the contingencies. / A Dissertation submitted to the Department of Mechanical Engineering in partial fulfillment of the Doctor of Philosophy. / Summer Semester 2017. / July 20, 2017. / cryogenics, helium gas, numerical modeling, superconductivity / Includes bibliographical references. / Juan Ordonez, Professor Co-Directing Dissertation; Sastry Pamidi, Professor Co-Directing Dissertation; Hui "Helen" Li, University Representative; Wei Guo, Committee Member; Patrick Hollis, Committee Member.

At high angles of attack, asymmetric vortices are formed on the leeward side of flight vehicles with pointed forebodies due to the random surface imperfections near the forebody apex. These vortices induce adverse side forces and yaw moments. The forces generated are too large to be controlled using conventional control surfaces and can result in flight instability and loss of control. Although many studies have reported that random surface imperfections trigger vortex asymmetry, there is a lack of understanding of how these imperfections directly correlate to the varying side force with roll orientation. The present study is aimed at gaining a better insight into the underlying flow physics of vortex asymmetry. This is accomplished by performing flow field measurements using Particle Image Velocimetry and force measurements using a six-component strain gage balance on an unpolished and a highly-polished 12° semi-apex angle cone at subsonic speeds. Measurements were carried out with and without the implementation of controlled surface imperfections. All experiments were performed at a fixed Reynolds number of 0.3 × 10^6 based on the base diameter of the cone model. The force measurements indicate that the vortices caused by the random surface imperfections are highly dependent on the magnitude of surface roughness. The results show that the side force was significantly reduced and was relatively less dependent on roll orientation for the polished cone. Flow field results show that the ratio of imperfection height to the local cross-flow boundary layer thickness was observed to be critical in influencing the vortex location and growth. Furthermore, the region of incipient boundary layer separation was highly sensitive to the controlled imperfections. / A Thesis submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of Master of Science. / Summer Semester 2017. / July 14, 2017. / Thermal Fluids / Includes bibliographical references. / Rajan Kumar, Professor Directing Dissertation; William S. Oates, Committee Member; Kourosh Shoele, Committee Member.

Wingtip vortices develop at the tips of aircraft wings due to a pressure imbalance during the process of generating lift. These vortices significantly increase the total aerodynamic drag of an aircraft at high-lift flight conditions such as during take-off and landing. The long trailing vortices contain strong circulation and may induce rolling moments and lift losses on a trailing aircraft, making them a major cause for wake turbulence. A mandatory spacing between aircraft is administered by civil aviation agencies to reduce the probability of hazardous wake encounters. These measures, while necessary, restrict the capacity of major airports and lead to higher wait times between take-off and landing of two aircraft. This poses a major challenge in the face of continuously increasing air traffic volume. Wingtip vortices are also known as a potent source of aerodynamic vibrations and noise. These negative effects have made the study of wingtip vortex attenuation a critical area of research. The problem of induced drag has been addressed with the development of wingtip device, like winglets. Tip devices diffuse the vortex at its very onset leading to lower induced drag. The problem of wake turbulence has been addressed in studies on vortex interactions and co-operative instabilities. These instabilities accelerate the process of vortex breakdown, leading to a lower lifetime in the wake. A few studies have tried to develop active mechanisms that can artificially excite these instabilities. The aim of the present study is to develop a device that can be used for both reducing induced drag and exciting wake instabilities. To accomplish this objective, an active winglet actuator has been developed with the help of piezoelectric Macro-Fiber Composite (MFC). The winglet is capable of oscillating about the main wing-section at desired frequency and amplitude. A passive winglet is a well-established drag reducing device. An oscillating winglet can introduce perturbations that can potentially lead to instabilities and accelerate the process of vortex breakdown. A half-body model of a generic aircraft configuration was fabricated to characterize and evaluate the performance of actuated winglets. Two winglet models having mean dihedral orientations of 0° and 75° were studied. The freestream velocity for these experiments was 20 m/s. The angle of incidence of the wing-section was varied between 0° and 8°. The Reynolds number based on the mid-chord length of the wing-section is 140000. The first part of the study consisted of a detailed structural characterization of the winglets at various input excitation and pressure loading conditions. The second part consisted of low speed wind tunnel tests to investigate the effects of actuation on the development of wingtip vortices at different angles of incidence. Measurements included static surface pressure distributions and Stereoscopic (ensemble and phase-locked) Particle Image Velocimetry (SPIV) at various downstream planes. Modal analysis of the fluctuations existing in the baseline vortex and those introduced by actuation is conducted with the help of Proper Orthogonal Decomposition (POD) technique. The winglet oscillations show bi-modal behavior for both structural and actuation modes of resonance. The oscillatory amplitude at these actuation modes increases linearly with the magnitude of excitation. During wind tunnel tests, fluid structure interactions lead to structural vibrations of the wing. The effect of these vibrations on the winglet oscillations decreases with the increase in the strength of actuation. At high input excitation, the actuated winglet is capable of generating controlled oscillations suitable for perturbing the vortex. The vortex associated with a winglet is stretched along its axis with multiple vorticity peaks. The center of the vortex core is seen at the root of the winglet while the highest vorticity levels are observed at the tip. The vortex core rotates and becomes more circular in shape while diffusing downstream. The shape, position, and strength of the vorticity peaks are found to vary periodically with winglet oscillation. Actuation is even capable of disintegrating the single vortex core into two vortices. The most energetic POD fluctuation modes, at the center of the baseline vortex core, correspond to vortex wandering at the initial downstream planes. At the farthest planes, the most energetic modes can be associated with core deformation. High energy fluctuations in the actuated vortex correspond to spatial oscillations and distortions produced by the winglet motion. / A Dissertation submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Summer Semester 2017. / June 22, 2017. / Flow control, MFC, PIV, POD, Winglet, Wingtip vortex / Includes bibliographical references. / Rajan Kumar, Professor Directing Thesis; Richard Liang, University Representative; William S. Oates, Committee Member; Farrukh S. Alvi, Committee Member.

High Temperature superconductors (HTS) are the only way to achieve elds with superconducting magnets higher than the 25 T of Low Temperature Superconductors (LTS). No-Insulation (NI) REBCO magnets using REBa2Cu3Ox as the superconductor require less copper stabilizer than insulated magnets and thin (30 m) substrates have now become available. In our recent small coil attack on elds greater than 40 T, we have seen that overstrain damage can easily occur even at frequently used design strain of 0.4%. Here we present an experimental study of the uniaxial stress () characteristics of SuperPower and SuNAM coated conductors and also do strain-critical current (Ic()) measurements to nd the onset of permanent damage to Ic. We found considerable variability in their 77 K mechanical properties. The cold-rolled Hastelloy C-276 substrate of the SuperPower is much stronger than the cold-rolled 310 stainless steel substrate used by SuNAM, but of more concern is the variability of the strength of dierent batches of SuNAM tape. Mechanical variability in the dierent SuNAM batches creates a challenge when designing for magnets. We also examined the eects of strain on critical current performance, nding that the critical current of the SuNAM conductor becomes irreversible over a wide range of strains from 0.3-0.6%. Suspecting that some annealing of the substrates occurs during REBCO deposition in the vicinity of 750 C, we performed short heat treatments at 700, 750, and 800 C of samples of the as-delivered substrates used by manufacturers. We found that there was little change to strength of the Hastelloy used by SuperPower but substantial change to the 310 stainless steel used by SuNAM. Our results show that any high eld operation at strains of 0.4% or more requires detailed knowledge of the mechanical properties of the tapes being used, especially for magnets using SuNAM tapes with cold-rolled 310 stainless steel substrates. / A Thesis submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of Master of Science. / Fall Semester 2018. / November 15, 2018. / Includes bibliographical references. / Seungyong Hahn, Professor Directing Thesis; David C. Larbalestier, Committee Member; Lance D. Cooley, Committee Member.

Computational material modeling has a history supporting of engineering applications. This dissertation presents two focal areas of research. The first is modeling and characterizing ultrafast laser machining of sapphire. A three dimensional model of laser machining is presented as an extension to a previously published one dimensional model. The bulk of the work focuses on finite element modeling of nanoindetation of laser machined and pristine sapphire specimen in order to quantify material differences due to laser machining. Discussions on generalized plasticity and finite element modeling are including before presenting results, As the second focal point, this dissertation presents applications of network theory to atomistic material models. A novel method of representing materials as weighted graphs is developed. We believe this approach extends the use of networks beyond their traditional use in chemistry. Within the weighted network approach we show that spectral sparsification is an excellent tool that reduces complex force interactions while maintaining minimal errors. The results are shown to be particularly useful for approximating long range potentials. We also present preliminary work which suggest the network based approach may be suitable for detecting defects and developing macroscale consitutive laws. / A Dissertation submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of Doctorate of Philosophy. / Fall Semester 2018. / November 13, 2018. / finite element, high temperature materials, molecular dynamics, multiscale modeling, sensing / Includes bibliographical references. / William Oates, Professor Directing Thesis; Kyle Gallivan, University Representative; Kunihiko Taira, Committee Member; Shangchao Lin, Committee Member; Jose Mendoza-Cortes, Committee Member.

Oxygen free high conductivity (OFHC) copper was processed using equal channel angular extrusion (ECAE), drawing, swaging, or ECAE plus either drawing or swaging to a strain of 4. All processing was carried out at room temperature. The ECAE processing was carried out using route Bc with a die of 90° channel intersections. The influence of deformation path on the evolution of texture and microstructure in the as-deformed and annealed (at 250°C for 1 hour) conditions was documented using orientation imaging microscopy (OIM), X-ray diffraction, and Vickers hardness testing. Processing by ECAE alone produced very fine and feathery microstructure (~ 1.2µm thickness) with weak - texture. Elongated grains parallel to the deformation direction were observed in wires processed by either drawing or swaging alone. Their texture was similar and can be described as +. Processing the wire by ECAE to a strain (ε) of ~3 followed by drawing or swaging to a cumulative strain of ~4 resulted in a + duplex texture. The texture in the ECAE plus swage wire was stronger than that of ECAE plus drawing. The Vickers hardness values for wires varied from 108 to 142 Hv, and difference in hardness was attributed to the variation in the substructure, which was minimal in the wires that underwent any form of swaging. Although the grain boundary character distribution (GBCD) of the wires in the as-processed condition was similar, the misorientation distribution function (MDF) was dependent on the processing method. While a high concentration of boundaries with 60 deg were found in the swaged wires, it was relatively absent in other wires, which had lots of 30-45 deg boundaries instead. Subsequent annealing of these wires at 250 deg C produced diverse results: recovered microstructure in any form of swaged wires, partially recrystallized in drawn or ECAE+drawn wires and fully recrystallized in materials processed by ECAE alone. The annealing behavior of these wires were correlated with the density of substructure and the ratio of the mobile (60 deg ) to immobile (30-45 deg ) boundaries. A ratio of mobile boundaries to immobile boundaries was greater than or equal to one resulted in a fully to partially recrystallized microstructure upon annealing, while a ratio less than 1 resulted in limited to no recrystallization upon annealing. / A Thesis submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of Master of Science. / Degree Awarded: Spring Semester, 2009. / Date of Defense: February 25, 2009. / Copper, ECAE, Drawing, Swaging, Recrystallization, Inhibit Grain Growth, Processing Routes, High Strain Deformation / Includes bibliographical references. / Peter N. Kalu, Professor Co-Directing Thesis; Daudi Waryoba, Professor Co-Directing Thesis; Carl Moore, Committee Member; William Oates, Committee Member.

This study is mainly focused on applying the Particle Image Velocimetry (PIV) technique to the unique fluid system of He II. Challenges associated with the application are identified and discussed in the context of the exceptional physical properties and experimental environment of He II. The particle dynamics in He II is studied, and two important parameters, slip velocity and relaxation time, are derived. Based on this information, the tracking characteristics of a variety of candidate tracer particles, including commercially available solid particles and particles generated by freezing liquids and gases, are discussed, as well as their potential applications to liquid helium. It is indicated that polymer particles with a mean diameter of 1.7 μm and specific gravity of 1.1 are the most suitable for tracking the thermal counterflow in our experiments. To introduce these very fine particles into liquid helium, a simple seeding method based on the two-phase fluidized bed technology was developed. The seeding results show an adequate concentration and also a quite uniform spatial distribution of seeded particles. Using the PIV technique, velocity fields of He II thermal counterflow in steady state have been measured in a range of bath temperatures from 1.61 K to 2.0 K and applied heat fluxes from about 1.1 kW/m2 up to 13.7 kW/m2. A significant discrepancy between the measured particle velocity vp,a and theoretical normal fluid velocity vn,t is present at all the temperatures, and the ratio of vp,a/vn,t is most likely a temperature-independent constant around 0.5. Careful analysis suggests that this velocity discrepancy may be caused by an additional force from the superfluid component. A semi-empirical correlation for this force is developed. By adding the force to the particle dynamics equation, the analytical results are shown to be consistent with the experimental results. Also, the propagation of second sound shock and heat diffusion has been studied by measuring the instantaneous velocity fields of induced transient thermal counterflow. The arrival of shock front, effect of expansion fan, passage of shock tail, and the onset of heat diffusion are clearly observed from the particle velocity profiles versus time. The generated particle velocity profiles are compared and discussed in respect of the critical energy flux for the onset of quantum turbulence, and the additional force from the superfluid component is further addressed regarding its application to the transient state. / A Dissertation submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Degree Awarded: Spring Semester, 2004. / Date of Defense: March 24, 2004. / Helium II, PIV, Thermal Counterflow / Includes bibliographical references. / Steven W. Van Sciver, Professor Directing Dissertation; Stephen J. Gibbs, Outside Committee Member; Chiang Shih, Committee Member; David Cartes, Committee Member.