<p> With the increasing size of wind turbines and the use of flexible and light materials in aerodynamic applications, aeroelastic tailoring for power generation and blade stability has become an important subject in the study of wind turbine dynamics. To this day, coupling of bending and torsion in wind turbine rotor blades has been studied primarily as an elastic mechanism due to a coupling laminate construction. In this report, inertial coupling of bending and torsion, due to offset of axis of elasticity and axis of center of mass, is investigated and numerical simulations are performed to test the validity of the constructed model using an in-house developed aeroelastic numerical tool. A computationally efficient aeroelastic numerical tool, based on Goldstein's helicoidal vortex model with a prescribed wake model and modal coupling of bending and torsion in the blades, is developed for 2-bladed horizontal axis wind turbines and a conceptual study is performed in order to argue the validity of the proposed formulation and numerical construction. The aeroelastic numerical tool, without bending-torsion coupling, was validated (Chattot 2007) using NREL Phase VI wind turbine data, which has become the baseline model in the wind turbine community. Due to novelty of the proposed inertial bending-torsion coupling in the aeroelastic model of the rotor and lack of field data, as well as, other numerical tools available for code to code comparison studies, a thorough numerical investigation of the proposed formulation is performed in order to validate the aeroelastic numerical tool Finally, formulations of geometrically nonlinear beams, elastically nonlinear plates and shells, and a piecewise linear, two degree of freedom, quasi steady, aerodynamic model are presented as an extension for nonlinear wind turbine aeroelastic simulations. Preliminary results of nonlinear beams, plates, shells, and 2 DOF NACA0012 aeroelastic model are presented.</p>

The take-off and landing of an Unmanned Aerial Vehicle (UAV) is often the most critical and accident prone portion of its mission. This potential hazard coupled with the time and resources necessary to train a remote UAV pilot makes it desirable to have autonomous take-off and landing capabilities for UAVs. However, a robust, reliable, and accurate autonomous takeoff and landing capability for fixed-wing aircraft is not an available feature in many low-cost UAV flight control systems. This thesis describes the design of an autonomous take-off and landing algorithm implemented on an existing low-cost flight control system for a small fixed wing UAV. This thesis also describes the autonomous takeoff and landing algorithm development and gives validation results from hardware in the loop simulation.

<div>Mission designs have been focused on using proven orbital maneuvers (i.e., propulsive maneuvers and gravity-assist) to deliver spacecraft to planetary destinations. Aeroassist maneuvers, despite their potential benefits, have not been given serious considerations due to the perceived risk and complexity. As entry technologies mature, aeroassist maneuvers need to be considered more extensively. Currently, there is no tool available that can perform rapid preliminary mission designs using aeroassist maneuvers. In this dissertation, integrated design methodologies for aerocapture and aerogravity-assist are developed, which can be readily converted to design tools that enable rapid mission concept formulations. </div><div> </div><div>The aerocapture design methodology is used to develop extensive design rules and relations for aerocapture missions to Titan, Venus, and Uranus, considering a wide range of vehicle parameters and interplanetary trajectories. These design rules and relations are intended as a convenient resource for mission designers and system engineers to evaluate the feasibility of aerocapture (e.g., effects of V-infinity on aerocapture missions) and the relevant design requirements, such as choices for vehicle characteristics and TPS materials. In addition, potentials for inclination change for Titan aerocapture are also quantified, presenting additional benefits of using aerocapture. Given the unusual orientation of Uranus, the changes in inclination and shift of line of apsides are also quantified for Uranus aerocapture. </div><div> </div><div>A novel design methodology is developed for Saturn system missions using nontraditional aerogravity-assist maneuvers at Titan. Compared with the existing literature, the novel methodology explores a comprehensive design space by integrating design considerations for interplanetary trajectories, atmospheric trajectories, arrival geometries at Titan, and vehicle designs. The methodology enables preliminary design trades and allows the mission designer to assess the feasibility of Titan aerogravity-assist and quickly develop requirements for trajectory designs and vehicle designs. The methodology also identifies potential Saturn and Titan arrival conditions. Results for an example Enceladus mission and Saturn system mission are presented, showing that a Saturn arrival V-infinity of 7 km/s renders Titan aerogravity-assist feasible for an Enceladus mission, while using the current entry technology. </div><div> </div><div>Bank modulation and drag modulation have been considered separately for aeroassist vehicles in the literature. The investigation combines bank modulation and drag modulation to improve the control authorities for aeroassist vehicles and such improvements are quantified using numerical simulations for a wide range of vehicle design configurations. The results show the potential of using a low-L/D vehicle for aerocapture at Uranus using combined bank and drag modulation. </div><div><br></div>

<p>Various engineering systems have become rapidly automated and intelligent as sensing, communication, and computing technologies have been increasingly advanced. The dynamical behaviors of such systems have also become complicated as they need to meet requirements on performance and safety in various operating conditions. Due to the heterogeneity in its behaviors for different operating modes, it is not appropriate to use a single dynamical model to describe its dynamics, which motivates the development of the stochastic hybrid system (SHS). The SHS is defined as a dynamical system which contains interacting time-evolving continuous state and event-driven discrete state (also called a mode) with uncertainties. Due to its flexibility and effectiveness, the SHS has been widely used for modeling complex engineering systems in many applications such as air traffic control, sensor networks, biological systems, and etc.</p><p>One of the key research areas related to the SHS is the inference or estimation of the states of the SHS, which is also known as the hybrid state estimation. This task is very challenging because both the continuous and discrete states need to be inferred from noisy measurements generated from mixed time-evolving and event-driven behavior of the SHS. This becomes even more difficult when the dynamical behavior or measurement contains nonlinearity, which is the case in many engineering systems that can be modeled as the SHS.</p><p>This research aims to 1) propose a stochastic nonlinear hybrid system model and develop novel nonlinear hybrid state estimation algorithms that can deal with the aforementioned challenges, and 2) apply them to safety-critical applications in air traffic control systems such as aircraft tracking and estimated time of arrival prediction, and unmanned aircraft system traffic management.</p>

Orbital rendezvous enables spacecraft to perform missions to service satellites, remove space debris, resupply space stations, and return samples from other planets. These missions are often considered high risk due to concerns that the two spacecraft will collide if the maneuvering capability of one spacecraft is compromised by a fault.<br>In this thesis, a passive safety analysis is used to evaluate the probability that a fault that compromises maneuvering capability results in a collision. For a rendezvous<br>mission, the chosen approach trajectory, state estimation technique, and probability of collision calculation each impact the total collision probability of the mission. This<br>thesis presents a modular framework for evaluating the comparing the probability of collision of rendezvous mission design concepts.<br>Trade studies were performed using a baseline set of approach trajectories, and a Kalman Filter for relative state estimation and state estimate uncertainty. The state covariance matrix following each state update was used to predict the resulting probability of collision if a fault were to occur at that time. These trade studies emphasize that the biggest indicator of rendezvous mission risk is the time spent on a nominal intercept trajectory.

Fiber-reinforced polymer composites (FRPCs) have a variety of applications in diverse industries. However, predicting the failure of FRPCs is more difficult than predicting the failure of more traditional materials like steel. Furthermore, composites can suffer extreme internal damage, but show little if any external indication that damage has occurred. This study investigated the potential for integrated structural health monitoring and self-healing for polymer composites utilizing triboluminescent (TL) materials. This study followed three phases. In Phase 1, the effects of enhancing resins with TL zinc sulfide manganese (ZnS:Mn) and europium dibenzoylmethide triethylamine (EuD4TEA) phosphors were investigated, including optimization of the EuD4TEA synthesis process and development of a model for tensile modulus based on TL inclusion and type of resin. EuD4TEA should be synthesized using at minimum 80 mmol/L europium nitrate and 260 mmol/L DBM, with at least 80 mmol/L TEA. ZnS:Mn was observed to increase elastic modulus of vinyl ester and light-curable polyurethane, by 103% and 60%, respectively. The larger EuD4TEA crystals decreased vinyl ester’s (VE’s) elastic modulus by 11%, at least partly due to particle size. EuD4TEA-enhanced light-curing polyurethane suffered a 95% decrease in elastic modulus, mostly due to incomplete cure. Inclusion of EuD4TEA in the VE resin resulted in the formation of voids, approximately the size of the EuD4TEA crystals. Protecting the EuD4TEA crystals from the heat of cure reduced the formation of bubbles, and improved TL emissions. Thermogravimetric analysis indicated the NHEt3 group was lost as EuD4TEA was heated above 100 °C. In Phase 2, a new measurement system was developed to evaluate luminescence and longevity of TL-enhanced resins. Optical fibers with a tip coating of TL-enhanced resin both provided a stage for the sample and directed the TL emissions into a light sensor. This tip-coated optical fiber method results in less variation in TL signal for ZnS:Mn-enhanced VE and sucrose-enhanced VE samples than impacts on loose ZnS:Mn and sucrose crystals. The intensity of TL emissions may be increased sevenfold by exposing the TL-enhanced sample to ultraviolet light immediately prior to TL testing. In Phase 3, the potential for TL-induced polymerization (and, by extension, TL-induced healing) was assessed. The results show polymers may be cured with visible light, even low-intensity photoluminescence, indicating feasibility of TL-induced healing. / A Dissertation submitted to the Department of Industrial and Manufacturing Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Spring Semester 2018. / March 28, 2018. / mechanoluminescence, polymer composites, self-healing, structural health monitoring, triboluminescence / Includes bibliographical references. / Okenwa Okoli, Professor Directing Dissertation; John Sobanjo, University Representative; Biwu Ma, Committee Member; Zhibin Yu, Committee Member; Tarik Dickens, Committee Member.

Over the past few decades, surface dielectric barrier discharge (SDBD) actuators have been studied extensively as aerodynamic flow control devices. There has been extensive research on producing SDBD plasmas through excitation by sinusoidal high voltage in low-speed flows, resulting in local acceleration of the flow through the electrohydrodynamic (EHD) effect. However, high-speed flow control using SDBD actuators has not been considered to the same extent. Control through thermal perturbations appears more promising than using EHD effects. SDBDs driven by nanosecond repetitively pulsed (NRP) discharges (NRP SDBDs) can produce rapid localized heating and have been used to produce better flow reattachment in high-speed flows. While surface actuators based on NRP DBDs appear promising for high-speed flow control, the physics underlying the plasma/flow coupling are not well understood and the actuators have yet to be fully characterized or optimized. In particular, methods for tailoring the plasma characteristics by varying the actuator’s electrical or geometrical characteristics have not been thoroughly explored.<div>In the current work, NRP SDBD actuators for control of high-speed flows are developed and characterized. As discussed previously, it is believed that the mechanism for high-speed flow control by these plasmas is thermal perturbations from rapid localized heating. Therefore, the goal is to design actuators that produce well-defined filamentary discharges which provide controlled local heating. The electrical parameters (pulse duration, PRF, and polarity) and electrode geometries are varied and the optimal configurations for producing such plasma filaments over a range of ambient pressures are identified. In particular, single and double sawtooth shaped electrodes are investigated since the enhanced electric field at the electrode tips may permit easier production of “strong” (i.e. higher temperature) filaments with well-defined spacing, even at low pressure. Time-resolved measurements of the gas temperature in the plasma will be obtained using optical emission spectroscopy (OES) to assess the thermal perturbations produced by the actuators. To the author’s knowledge, these will be the first such measurements of temperature perturbations induced by NRP SDBDs. The plasma structure and temperature measurements will be correlated with schlieren visualization of the shock waves and localized flow field induced by the discharges. Finally, the optimized actuators will be integrated into a high-speed flat plate boundary layer and preliminary assessment of the effect of the plasma on the boundary layer will be conducted.<br></div>

A series of experiments into the behavior of underexpanded jet flows has been conducted at NASA Langley Research Center. This work was conducted in support of the Return to Flight effort following the loss of the Columbia. The tests involved simulating flow through a hypothetical breach in the leading edge of the Space Shuttle Orbiter along its reentry trajectory, with the goal of generating a data set with which other researchers can test and validate computational modeling tools. Two nozzles supplied with high-pressure gas were used to generate axisymmetric underexpanded jets exhausting into a low-pressure chamber. These nozzles had exit Mach numbers of 1 and 2.6. Reynolds numbers based on nozzle exit conditions ranged from about 200 to 35,000, and nozzle exit-to-ambient jet pressure ratios ranged from about 1 to 37. Both free and impinging jets were studied, with impingement distances ranging from 10 to 40 nozzle diameters, and impingement angles of 45??, 60??, and 90??. For the majority of cases, the jet fluid was a mixture of 99.5% nitrogen seeded with 0.5% nitric oxide (NO).;Planar laser-induced fluorescence (PLIF) of NO was used to non-intrusively visualize the flow with a temporal resolution on the order of lets. PLIF images were used to identify and measure the location and size of flow structures. PLIF images were further used to identify unsteady jet behavior in order to quantify the conditions governing the transition to turbulent flow. This dissertation will explain the motivation behind the work, provide details of the laser system and test hardware components, discuss the theoretical aspects of laser-induced fluorescence, give an overview of the spectroscopy of nitric oxide, and summarize the governing fluid mechanical concepts. It will present measurements of the size and location of flow structures, describe the basic mechanisms and origins of unsteady behavior in these flows, and discuss the dependence of such behavior on particular flow structures. Finally, correlations describing the relationship between flow conditions and the degree of flow unsteadiness at a given location along the jet axis will be presented.

A hybrid rocket is a propulsion system that uses propellants in two different phases, typically a solid fuel inside the combustion chamber and a separate gaseous or liquid oxidizer stored in a tank. Hybrid rockets are an area of research interest because of their low explosive risk, inexpensive components, and high degree of reliability. In the Propulsion Research Laboratory at Utah State University, pure oxygen is among the top choice for hybrid rocket oxidizers due to its low cost and ease of storage. When paired with a solid fuel known as ABS (acrylonitrile butadiene styrene) plastic, specific impulse values exceed 200 seconds at one atmosphere. This metric outperforms hydrazine, which is a propellant standard for in-space propulsion that exhibits high vapor toxicity and explosive hazards. However, due to the low density of oxygen, propulsion applications require storage pressures up to 3000 psig. At this high pressure, the use of oxygen can present a fire hazard. As a result, this thesis investigates the feasibility of replacing oxygen with a moderately enriched compressed air containing oxygen levels up to 40%, while maintaining performance metrics equal to or above hydrazine. To demonstrate the performance of moderately enriched air as a hybrid rocket oxidizer, comparisons to tests using pure oxygen are presented.

Hybrid rockets motors provide distinct safety advantages when compared to traditional liquid or solid propellant systems, due to the inherent stability and relative inertness of the propellants prior to established combustion. As a result of this inherent propellant stability, hybrid motors have historically proven dicult to ignite. State of the art hybrid igniter designs continue to require solid or liquid reactants distinct from the main propellants. These ignition methods however, reintroduce to the hybrid propulsion system the safety and complexity disadvantages associated with traditional liquid or solid propellants. The results of this study demonstrate the feasibility of a novel direct electrostatic arc ignition method for hybrid motors. A series of small prototype stand-alone thrusters demonstrating this technology were successfully designed and tested using Acrylonitrile Butadiene Styrene (ABS) plastic and Gaseous Oxygen (GOX) as propellants. Measurements of input voltage and current demonstrated that arc-ignition will occur using as little as 10 watts peak power and less than 5 joules total energy. The motor developed for the stand-alone small thruster was adapted as a gas generator to ignite a medium-scale hybrid rocket motor using nitrous oxide /and HTPB as propellants. Multiple consecutive ignitions were performed. A large data set as well as a collection of development 'lessons learned' were compiled to guide future development and research. Since the completion of this original groundwork research, the concept has been developed into a reliable, operational igniter system for a 75mm hybrid motor using both gaseous oxygen and liquid nitrous oxide as oxidizers. A development map of the direct spark ignition concept is presented showing the ow of key lessons learned between this original work and later follow on development.