Aerospace Engineering Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2737
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Item EXPERIMENTAL INVESTIGATION OF BOUNDARY LAYER TRANSITION ON CONE-FLARE GEOMETRIES AT MACH 4(2024) Norris, Gavin; Laurence, Stuart J; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This study investigates supersonic boundary layer transition on a cone-flarewith a 5° half-angle straight cone and flared bases of +5°, +10°, and +15°. The experiments used the University of Maryland's Multiphase Flow Investigations Tunnel (MIST), a Mach 4 Ludweig tube. Experiments were performed “dry”, without aerosols or droplets, and focus on the first-mode (Tollmien-Schlichting) boundary layer instability waves and their interaction with the compression corner. Using high-speed Schlieren imaging, the boundary layer dynamics on the cone-flare's top surface were analyzed. The data were processed through Power Spectral Density (PSD) and Spectral Proper Orthogonal Decomposition (SPOD) techniques to study the behavior of the first-mode waves and the transition location changes. The findings reveal coherent wave packets within the boundary layer at frequencies characteristic of the first-mode. The wave packets power increased along the cone and peaked near the compression corner before dissipation on the flare. These findings contribute to the understanding of first-mode boundary layer transition mechanisms in hypersonic flows for the cone-flare geometry.Item Deployment of Large Vision and Language Models for Real-Time Robotic Triage in a Mass Casualty Incident(2024) Mangel, Alexandra Paige; Paley, Derek; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In the event of a mass casualty incident, such as a natural disaster or war zone, having a system of triage in place that is efficient and accurate is critical for life-saving intervention, but medical personnel and resources are often strained and struggle to provide immediate care to those in need. This thesis proposes a system of autonomous air and ground vehicles equipped with stand-off sensing equipment designed to detect and localize casualties and assess them for critical injury patterns. The goal is to assist emergency medical technicians in identifying those in need of primary care by using generative AI models to analyze casualty images and communicate with the victims. Large language models are explored for the purpose of developing a chatbot that can ask a casualty where they are experiencing pain and make an informed assessment about injury classifications, and a vision language model is prompt engineered to assess a casualty image to produce a report on designated injury classifiers.Item Urban Air Mobility: Effects of increasing three-dimensionality on fixed and rotary wings in unsteady aerodynamic environments(2024) Wild, Oliver Dominik; Jones, Anya; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The rapidly growing field of electric vertical takeoff and landing aircraft, air taxis, and urban air mobility vehicles promises transformative solutions to alleviate urban congestion, accelerate deliveries, and revolutionize transportation systems. Central to the successful integration of these futuristic modes of transportation is a comprehensive understanding of their aerodynamics, particularly in the context of unsteady airflow encountered in urban environments. This work explores the foundational aspects essential for achieving efficient and safe urban air mobility operation. The focus lies on the integration of rotary and translatory wings in gusty and unsteady flow environments since – unlike conventional fixed-wing aircraft – many urban air vehicles utilize rotor systems for both vertical takeoff and forward flight. The research framework is structured around three interconnected pillars: advancing rotary wings, fixed-wing-gust encounters, and the synthesis of rotary wings in gusty conditions. The combined results from these three pillars are fundamental in reaching the future goal of efficient and safe urban air mobility. The first pillar investigates the aerodynamic characteristics of advancing rotary wings, particularly concerning flow structures, blade loading, and the influence of the trailing edge geometry using experimental, numerical, and modeling techniques. A comparison between a standard NACA0012 airfoil profile and an elliptical profile is conducted at advance ratios ranging from 0.00 to 1.00 at pitch angles from 7 deg to 25 deg. Four main vortex structures were detected in reverse flow. At the aerodynamic leading edge, a strong interference of the tip vortex with the reverse flow dynamic stall vortex was identified when blade flapping was restricted. Dynamic stall vortices advect closer to the blade surface for the blunt elliptical airfoil, thus reducing the wake area in reverse flow. Overall, the vortex structures that form on the ellipse are more coherent than those on the NACA0012. A 29% pitching moment increase was measured in the reverse flow region with sharp trailing-edged blades compared to blunt blades. The blunt trailing-edged blade delayed flow separation and thus prevented the formation of a reverse flow dynamic stall vortex, reducing the pitching moment. The second pillar delves into the three-dimensional dynamics of fixed-wing-gust encounters, aiming to understand the formation of leading-edge vortices and their impact on lift generation. Emphasis is placed on exploring strong transverse gust encounters and the effects of sideslip angle on leading edge vortex formation, with the objective of devising predictive models for lift generation under varied gust scenarios. Experimental investigations in a towing tank and the employment of a strip theory Küssner model show a peak lift coefficient decrease with decreasing gust ratios and increasing sideslip angles. The model accurately predicts the experimental results at gust entry as well as within the gust. Flow reattachment is delayed due to the formation of a leading-edge vortex inducing reverse flow on the wing suction side, resulting in a non-zero wing forcing at gust exit. The third pillar examines the effects of gusts on both hovering and advancing rotors. It synthesizes the findings from the previous two pillars, mirroring real-world conditions occurring on urban air mobility vehicles. Gusts cause an increase in blade flapping and lagging moments, and a nose-down pitching moment in both hovering and advancing rotors. In forward flight, the moment response mirrors a wing-gust encounter. A lower advance ratio broadens the moment peaks. Reverse flow shows a smaller moment response but a wider azimuth angle impact. Increased gust and advance ratios amplify moment disturbances, with gust encounters on the retreating blade more sensitive to gust ratio changes. By integrating insights from rotary wings and gust encounters, this research provides a comprehensive understanding of aerodynamic phenomena crucial for the development of efficient and safe urban flight vehicles. Through this multidisciplinary approach, this thesis contributes to advancing the fundamental understanding of aerodynamic challenges in urban air mobility, paving the way for the development of innovative solutions to propel the future of urban air mobility.Item MEASURING AND MODELING ELECTROMAGNETIC FORCES THAT INFLUENCE GRANULAR BEHAVIOR(2024) Pett, Charles Thomas; Hartzell, Christine M; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)On the surfaces of small, airless planetary bodies, forces other than gravity, such as cohesive, magnetic and electrostatic forces, may dominate the behavior of regolith. Yet, the magnitude of these forces remains uncertain, as well as the link between grain-scale and bulk-scale physics. In this work, techniques for measuring and modeling electromagnetic forces that influence granular behavior are developed. We discuss an experimental method for measuring interparticle cohesion by breaking cohesive bonds between grains with electrostatic forces. The centroid positions of the lofted grains at the moment of detachment are imaged in order to numerically calculate initial accelerations to solve for cohesion. We propose the design of a payload that would be deployed on the Moon or an asteroid and use an electrically biased plate to induce electrostatic dust lofting and measure interparticle cohesion in situ. We would call the system \textbf{Small--FORCES} because it would be able to image \textbf{Small} \textbf{F}orces \textbf{O}ptically \textbf{R}esolved for \textbf{C}ohesion \textbf{E}stimation via \textbf{E}lectrostatic \textbf{S}eparation. We numerically integrate Poisson's equation and develop a model for the potential distribution of a photoelectron sheath as a function of distance from surfaces. We use this model to gauge the extent to which the solar wind will perturb the Small-FORCES electric field that is used to loft charged regolith inside the sheath and obtain suitable trajectories for imaging lofted regolith that will be used to measure cohesion. We then derive a formula to quantify the maximum region of our system's electric field that we predict can be shielded from the ambient solar wind, which depends on system dimensions and applied voltage. In another experiment, we investigated the affect of magnetic cohesion on the avalanching behavior of magnetic grains. We will introduce an instrument and novel method for characterizing the bulk magnetic susceptibility of granular mixtures by submerging an inductor coil in a bed of metallic beads. In prior works, the magnetic force on grains was calculated based on the magnetic susceptibility of a single grain, but our coil uniquely quantifies effects from void spaces and demagnetization in the bulk. Compared to both a commercial Terraplus Inc. KT-10 meter and theoretical approximations, we report similar trends in susceptibility values measured as a function of mass of ferromagnetic material per volume. We conclude the talk with a discussion on a conductive model we developed to simulate surfaces other than dielectrics in the solar wind. We use a 2D grid-free treecode to enable complex surface geometries that would be computationally intensive for traditional PIC codes. Instead of using the capacitance matrix method to calculate the induced surface charge magnitudes, we discretized the conductor surface into point charges and allow them to have Coulomb interactions with the external plasma particles. The linear system used to explicitly solve for the induced surface charge magnitudes couples the interaction between surface charges and plasma particles self-consistently via the conductive boundary condition. The model has been validated thus far with image charge theory.Item AEROSOL EFFECTS IN HIGH SUPERSONIC FLOWS(2024) Schoneich, Antonio Giovanni; Laurence, Stuart J; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The understanding of high-speed aerodynamics is becoming evermore pertinent with thegrowth of space tourism, continued interest in space exploration, and pursuit of advanced highspeed aircraft for both military and commercial use. For initial investigations, ground test facilities are preferred to flight tests as they are far cheaper and carry significantly less risk, although wind tunnels can only replicate a subset of the conditions experienced in actual flight. One of these conditions that has not been adequately captured in wind tunnels is the effect of particulates in the atmosphere. Typical wind tunnels use a pure, clean gas (air, nitrogen, etc.) for testing, but this does notcapture the aerosolized nature of the atmosphere, where humidity and condensation can produce a distribution of liquid droplet sizes ranging from the average rain drop of 2mm to sub-micron diameter particles. Similarly, volcanic eruptions and ever-present wildfires result in solid particles exhibiting a variety of species and sizes that are transported to every layer of the atmosphere. At supersonic speeds, encounters with particulates have been shown to lead to detrimental effects, such as material erosion and boundary layer transition. Previous attempts to study this problem in wind tunnels have focused mainly on sub-micronsized solid particles, since aerosol settling time is a major limiting factor. On the other hand, most high-speed experiments involving large liquid droplet impacts have been carried out in gas guns or ballistic ranges due to the difficulty of trying to accelerate a droplet to high speeds without causing it to break up. While these facilities can be used to study impacts, the moving model means that detailed aerodynamic studies are nearly impossible, leading to a large gap in knowledge. To perform high-speed wind tunnel testing with liquid aerosols representative of cloud-likeenvironments (5-20 μm), a Mach-4 facility, referred to as the Multi-phase Investigations Supersonic Tunnel (MIST) has been designed and developed at the University of Maryland (capable of producing supersonic, particle-laden flows). This range of aerosol sizes makes MIST a unique facility with significant potential for expanding the state of the art in high-speed multi-phase flows. The present work discusses the design and characterization of MIST as well as two major experimental investigations carried out using this new facility. The first investigation examines the force augmentation on a free-flying sphere exposed to supersonic, particle-laden flows. Freeflight measurements are performed with five different particle size and concentration combinations. When comparing the results for particle-free flow in the same facility, the drag coefficient of the sphere was shown to be 1.75-4.5% greater for all multi-phase cases; this is significantly higher than simple estimates based on the increased momentum flux in the freestream would indicate. In addition to force measurements, an experimental investigation into the effect of particle-ladenflows on boundary-layer transition was conducted. It is important to characterize the disturbance environment in wind tunnels since they typically do not represent the levels in atmospheric flight and can lead to earlier onset of boundary-layer transition. In performing such measurements using a single-point Focused Laser Differential Interferometer, it was discovered that the presence of particles in the flow could significantly attenuate the acoustic disturbances generated by the wind tunnel. This finding was further reinforced when investigating the boundary-layer transition on a 5◦ half-angle, sharp cone using high-speed schlieren visualization. For each case presented in this work, the boundary-layer disturbance amplitudes were reduced and transition Reynolds numbers increased in the particle-laden flow cases. This was contrary to expectations, given that prior numerical studies have indicated that particles can induce early transition. These findings potentially open a path to substantially reduce freestream disturbance levels in conventional hypersonic wind tunnels.Item Signal Processing and Forward Modeling of Space Debris Detection via Plasma Solitons(2024) DesJardin, Ian; Hartzell, Christine M; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The nonlinear interaction of objects in low Earth orbit with the space plasma environment has been hypothesized to cause precursor soliton plasma waves. These plasma-object interactions may lead to unique engineering applications, especially the detection of hazardous sub-centimeter orbital debris that is undetectable by conventional methods. This nonlinear perturbation is currently modeled by the forced Korteweg - de Vries (fKdV) equation. This thesis aims to understand and characterize these waves through simulation beyond the fKdV model while progressing space-based and ground detection schemes. Ultimately this technique may play an important role in the problem of detecting small space debris. Three aspects of this detection scheme are developed. This includes two unconventional methods of detecting solitons. First the inverse scattering transform (IST), a mathematical spectral technique for decomposing a time series, is shown to automatically detect solitons from data. A numerical experiment using the fKdV model is performed to demonstrate this ability. The IST is suitable as an in situ detection method. It could be the basis of a debris collision early warning system for spacecraft. Second, the existing technique of ionospheric sensing using Global Navigation Satellite System (GNSS) is extended to detecting spacecraft plasma wakes. Traditionally, it is used for global scale space weather monitoring. An experiment is carried out using a known target, the International Space Station, on existing GNSS receivers that measure the ionospheric irregularity associated with the spacecraft. This experiment shows that there is a modification to the total electron content (TEC) when the ISS flies through the radio line-of-sight. Using models that are compared to the experiment, a multi-point sensor is proposed that would resolve the diffraction pattern from these plasma structures. This work uses multi-fluid plasma simulation to refine the fKdV model of soliton generation from debris. In particular, we find that the range of ion acoustic Mach numbers that are conducive to precursor soliton generation is larger than predicted by the fKdV equation. A new theory that matches the multi-fluid simulation results is derived using pressure balances to predict the supercritical Mach number. This new theoretical understanding of the critical Mach numbers predicts a wider range of orbits that will create precursor solitons than in previous studies. In addition, several new details of precursor solitons are discovered and characterized with multi-fluid simulation. This includes changes in the amplitude scaling of the periodicity of soliton generation (the "intersoliton interval"). Importantly, corrections to the first order results of the fKdV equation which couple fluid velocity, density, and electrostatic potential are identified. A theory that explains this in the small amplitude limit is derived. For debris detection, this effect impacts how the soliton is detected. The same soliton will manifest different amplitudes in each plasma species, contrary to the result of the fKdV equation. Thus, a model error in inferring debris properties from solitons has been discovered.Item Dynamics, Estimation, and Control for Stabilizing the Attitude and Shape of a Flexible Spacecraft(2024) Merrill, Curtis; Paley, Derek A; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Advances in technology have enabled the development of large spacecraft structures such as solar sails, expansive antennas, and large solar arrays. A critical design constraint for these structures is mass, necessitating lightweight construction which, in turn, increases structural flexibility. This flexibility poses significant challenges resulting from structural deformations and vibrations that complicate attitude control and can degrade the performance and lifespan of the spacecraft. The goal of this research is to develop estimation and control strategies to mitigate the effects of spacecraft flexibility.A flexible spacecraft model is derived using a hub and appendage framework. In this model one or more flexible appendages attach to a central rigid hub. The model represents the appendages as a discretized set of flexibly connected elements called panels. Stiff springs connect the panels, and the dynamic model of the system’s internal forces and moments uses coordinates in the hub’s reference frame. Reaction wheels on the hub perform attitude control, while distributed pairs of magnetic torque rods on the appendage influence its shape. Initially, the model restricts flexibility to one direction, resulting in a planar model. A Lyapunov-based control design provides a feedback law for the reaction wheel and torque rods in the planar model. Numerical simulations demonstrate that the proposed controller meets the control objectives and compares favorably to other controllers. An Extended Kalman Filter is applied to the system to perform state estimation and output feedback control, which performs at nearly the same level as state feedback control. The modeling framework and flexibility are extended to three dimensions. The development of a control law for the magnetic torque rods considers the attitude control of a single panel using two magnetic torque rods. Due to the system being underactuated, the attitude error is defined in terms of the reduced-attitude representation. Lyapunov analysis yields a control law that stabilizes the reduced attitude and angular velocity of a rigid panel using only two magnetic torque rods. Numerical simulations validate the control law’s performance for a single panel. This control law is then applied to the flexible appendage to stabilize its shape. Numerical simulations show that this implementation of shape control significantly reduces structural deformations and dampens structural oscillations compared to scenarios without shape control. To perform state estimation of the high-dimensional flexible spacecraft model, dynamic mode decomposition generates a reduced order model that is linear with respect to the evolution of the resulting modes. A Kalman filter estimates the mode amplitudes of the reduced order model from a limited set of measurements, enabling the reconstruction of the entire system state. The optimization of the number and placement of sensors maximizes the observability of the observer. Numerical simulations demonstrate that this framework yields accurate state estimates with reduced computational cost.Item Applied Aerial Autonomy for Reliable Indoor Flight and 3D Mapping(2024) Shastry, Animesh Kumar; Paley, Derek; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Uncrewed Aerial Systems (UAS) are essential for safely exploring indoor environments damaged by shelling, fire, floods, and structural collapse. These systems can gather critical visual and locational data, aiding in hazard assessment and rescue planning without risking human lives. Reliable UAS deployments requires advanced sensors and robust algorithms for real-time data processing and safe navigation, even in GPS-denied and windy conditions. This dissertation details three research projects to improve UAS performance: (1) in-flight calibration to improve estimation and control, (2) system identification for wind rejection, and (3) indoor aerial 3D mapping. The dissertation begins with introducing a comprehensive nonlinear filtering framework for UAV parameter estimation, which considers factors such as external wind, drag coefficients, IMU bias, and center of pressure. Additionally, it establishes optimized flight trajectories for parameter estimation through empirical observability. Moreover, an estimation and control framework is implemented, utilizing the mean of state and parameter estimates to generate suitable control inputs for vehicle actuators. By employing a square-root unscented Kalman filter (sq-UKF), this framework can derive a 23-dimensional state vector from 9-dimensional sensor data and 4-dimensional control inputs. Numerical results demonstrate enhanced tracking performance through the integration of the estimation framework with a conventional model-based controller. The estimation of unsteady winds results in improved gust rejection capabilities of the onboard controller as well. Closely related to parameter estimation is system identification. Combining with the previous work a comprehensive system identification framework with both linear offline and nonlinear online methods is introduced. Inertial parameters are estimated using frequency-domain linear system identification, incorporating control data from motor-speed sensing and state estimates from automated frequency sweep maneuvers. Additionally, drag-force coefficients and external wind are recursively estimated during flight using a sq-UKF. A custom flight controller is developed to manage the computational demands of online estimation and control. Flight experiments demonstrate the tracking performance of the nonlinear controller and its improved capability in rejecting gust disturbances. Aside from wind rejection, aerial indoor 3D mapping is also required for indoor navigation, and therefore, the dissertation introduces a comprehensive pipeline for real-time mapping and target detection in indoor environments with limited network access. Seeking a best-in-class UAS design, it provides detailed analysis and evaluation of both hardware and software components. Experimental testing across various indoor settings demonstrates the system's efficacy in producing high-quality maps and detecting targets.Item Multi-Domain Human-Robot Interfaces(2024) Abdi, Sydrak Solomon; Paley, Derek; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)As autonomous robots become more capable and integrated into daily society, it becomes crucial to consider how a user will interact with them, how a robot will perceive a user, and how a robot will comprehend a user’s intentions. This challenge increases in difficulty when the user is required to interact with and control multiple robots simultaneously. Human intervention is often required during autonomous operations, particularly in scenarios that involve complex decision-making or where safety concerns arise. Thus, the methods by which users interact with multi-agent systems is an important area of research. These interactions should be intuitive, efficient, and effective all while preserving the operator's safety. We present a novel human swarm interface (HSI) that utilizes gesture control and haptic feedback to interact with and control a swarm of quadrotors in a confined space. This human swarm interface prioritizes operator safety while reducing cognitive load during control of an aerial swarm. Human-robot interfaces (HRIs) are mechanisms designed to facilitate communication between humans and robots, enhancing the user's ability to command and collaborate with robots in an intuitive and user-friendly manner. One challenge is providing mobile robotic systems with the capability to localize and interact with a user in their environment. Localization involves estimating the pose (position and orientation) of the user relative to the robot, which is essential for tasks that require close interactions or navigation in shared spaces. We present a novel method for obtaining user pose as well as other anthropometric measurements useful for human-robot interactions. Another challenge is extending these HRI and HSI paradigms to the outdoors. Unlike controlled laboratory conditions, outdoor environments involve a variety of variables such as fluctuating weather conditions as well as a mix of static and dynamic obstacles. In this dissertation, we design a portable human swarm interface that allows an operator to interact with and control a multi-agent system outdoors. The portable HSI takes the form of smart binoculars. The user uses the smart binoculars to select an outdoor location and assign a task for the multi-agent system to complete given the targeted area. This system allows for new methods of multi-agent operation, that will leverage a user's on-the-ground knowledge while utilizing autonomous vehicles for line-of-sight operations, without compromising their situational awareness.Item APPLIED AERIAL ROBOTICS FOR LONG RANGE AUTONOMY AND ADVANCED PERCEPTION(2024) Cui, Wei; Paley, Derek A; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation addresses the challenges of conducting autonomous long-distance operations in settings where communication is restricted or unavailable. It involves the development of aerial autonomy software, ground station user interface, and simulation tools. Field experiments are conducted to assess the real-world performance and scalability of the developed autonomous multi-vehicle systems. A search and revisit framework involving multiple UAS engaged in expansive area exploration has been developed. By employing the ARL MAVericks autonomy stack, we have devised three system designs with improving levels of autonomy. This approach is effective in developing autonomous system capabilities for extended-range missions, enhancing effectiveness in reconnaissance, search, and rescue missions. Furthermore, the dissertation introduces an innovative application of enhanced target detection and localization techniques tailored specifically for small UAS deployment. Neural network fine-tuning and AprilTag detector selection are carefully conducted. Augmented by a meticulously designed workflow for performance evaluation and validation, our approach aims to improve the precision of target detection and localization using a single RGB camera module. Additionally, the dissertation presents the implementation of a specialized ground control user interface. Functioning as a centralized command center, the user interface facilitates real-time monitoring and coordination of heterogeneous aerial and ground robotic platforms engaged in collaborative search missions. By streamlining air-ground coordination and human-robot interaction, the custom user interface optimizes the collective capabilities of diverse aerial and ground robotic platforms, enhancing overall mission effectiveness. The experimental results from multi-vehicle autonomous search missions, evaluating centralized and decentralized control in beyond visual line of sight scenarios, are presented, proving the efficacy of the search and revisit framework operating in real-world scenarios. Finally, the dissertation covers the design and implementation of a resilient network link tailored for robotic platforms operating in environments with limited bandwidth. This essential infrastructure enhancement is devised to overcome communication constraints, ensuring reliable data exchange, and strengthening the resilience of autonomous systems in bandwidth-limited environments.