Aerospace Engineering Theses and Dissertations

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    https://aero.umd.edu/graduate/graduate-student-forms
    (2018) Kumar, Rubbel; Oran, Elaine S; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The increased use of explosives in military conflicts has been linked to an increase in the number of traumatic brain injuries (TBIs). Assessing the effectiveness of personal protective equipment to mitigate TBIs requires both the ability to replicate the pressure signatures caused by blast waves and an understanding of the interaction between blast waves and human bodies. Computational Fluid Dynamics (CFD) was used to understand the effect of varying different shock tube design parameters and to propose guidelines for selecting shock tube designs to accurately replicate blast wave pressure signatures representative of free-field explosive events. Additionally, a CFD model was developed to represent a shock tube built to mimic the primary overpressure magnitude and impulse loading on the human head surface as a result of free-field explosive events. This model was used to aid in the understanding of flow within the shock tube, characterize the applied pressure loading to a bare head form, augment experimental findings to fully understand the influence of headborne systems on pressure applied to the human head, and support the design of optimized laboratory test methodologies to represent a broad range of free-field blast events.
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    Disturbance rejection for U.A.S. aircraft using bio-inspired strain sensing
    (2015) Castano Salcedo, Lina Maria; Humbert, Sean J; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    A bio inspired gust rejection mechanism based on structural inputs is proposed. Insect wings possess a wealth of sensor systems which typically consist of fast reflexive neuronal paths. Stretch and strain sensors on insect wings are used for flight control and can be found across many species. These are used for monitoring of bending and torsion during flight. The fast reflexive and proprioceptive mechanisms based on strain sensing found in nature are the inspiration for this work. A strain feedback controller allows for anticipation of the onset of rigid body dynamics due to gust perturbations. This anticipation stems from sensing of higher order states and the possibility of reacting before lower order states are reached. High bandwidth inner loop compensation is therefore enabled. Forces and moments are proportional to wing strain patterns and can be used in fast reaction inner loops. Strain sensors are used for providing an indirect estimation of the differential forces applied to the aircraft wing and therefore to the aircraft rigid body. These sensors can be distributed over the surface of the aircraft wing to encode multiple degree of freedom disturbances. Sensor locations for disturbance rejection are determined based on metrics associated to the observability Grammian. The locations are preselected based on modal energy analyses and are chosen according to wide field integration patterns. A model for wide field integrated strain based on mass participation factors is proposed as well as one which is based on the physics of the forces and moments acting on the wing producing strain patterns which can be used for disturbance rejection. Models of the differential forces via strains on the wings are proposed. Strain feedback was implemented in four platforms under different types of disturbances. The platforms consisted of a glider, a quadrotor, a wing section for wind tunnel testing and an RC airplane with a full span wing. The disturbances included discrete gusts as well as turbulence. The results of using strain feedback showed not only to be faster than IMU estimations but also to be better when compared to a classical attitude controller implementation.
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    INERTIAL MOTION CAPTURE SYSTEM FOR BIOMECHANICAL ANALYSIS IN PRESSURE SUITS
    (2013) Di Capua, Massimiliano; Akin, David L; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    A non-invasive system has been developed at the University of Maryland Space System Laboratory with the goal of providing a new capability for quantifying the motion of the human inside a space suit. Based on an array of six microprocessors and eighteen microelectromechanical (MEMS) inertial measurement units (IMUs), the Body Pose Measurement System (BPMS) allows the monitoring of the kinematics of the suit occupant in an unobtrusive, self-contained, lightweight and compact fashion, without requiring any external equipment such as those necessary with modern optical motion capture systems. BPMS measures and stores the accelerations, angular rates and magnetic fields acting upon each IMU, which are mounted on the head, torso, and each segment of each limb. In order to convert the raw data into a more useful form, such as a set of body segment angles quantifying pose and motion, a series of geometrical models and a non-linear complimentary filter were implemented. The first portion of this works focuses on assessing system performance, which was measured by comparing the BPMS filtered data against rigid body angles measured through an external VICON optical motion capture system. This type of system is the industry standard, and is used here for independent measurement of body pose angles. By comparing the two sets of data, performance metrics such as BPMS system operational conditions, accuracy, and drift were evaluated and correlated against VICON data. After the system and models were verified and their capabilities and limitations assessed, a series of pressure suit evaluations were conducted. Three different pressure suits were used to identify the relationship between usable range of motion and internal suit pressure. In addition to addressing range of motion, a series of exploration tasks were also performed, recorded, and analysed in order to identify different motion patterns and trajectories as suit pressure is increased and overall suit mobility is reduced. The focus of these evaluations was to quantify the reduction in mobility when operating in any of the evaluated pressure suits. This data should be of value in defining new low cost alternatives for pressure suit performance verification and evaluation. This work demonstrates that the BPMS technology is a viable alternative or companion to optical motion capture; while BPMS is the first motion capture system that has been designed specifically to measure the kinematics of a human in a pressure suit, its capabilities are not constrained to just being a measurement tool. The last section of the manuscript is devoted to future possible uses for the system, with a specific focus on pressure suit applications such in the use of BPMS as a master control interface for robot teleoperation, as well as an input interface for future robotically augmented pressure suits.
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    Design, Developement, Analysis and Control of a Bio-Inspired Robotic Samara Rotorcraft
    (2012) Ulrich, Evan R.; Pines, Darryll; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    THIS body of work details the development of the first at-scale (>15 cm) robotic samara, or winged seed. The design of prototypes inspired by autorotating plant seed geometries is presented along with a detailed experimental process that elucidates similarities between mechanical and robotic samara flight dynamics. The iterative development process and the implementation of working prototypes are discussed for robotic samara Micro-Air-Vehicles (MAV) that range in size from 7.5 cm to 27 cm. Vehicle design issues are explored as they relate to autorotation efficiency, stability, flight dynamics and control of single winged rotorcraft. In recent years a new paradigm of highly maneuverable aircraft has emerged that are ideally suited for operation in a confined environment. Different from conven- tional aircraft, viscous forces play a large role in the physics of flight at this scale. This results in relatively poor aerodynamic performance of conventional airfoil and rotorcraft configurations. This deficiency has led to the consideration of naturally occurring geometries and configurations, the simplest of which is the samara. To study the influence of geometric variation on autorotation efficiency, a high speed camera system was used to track the flight path and orientation of the mechan- ical samaras. The wing geometry is planar symmetric and resembles a scaled version of Acer diabolicum Blume. The airfoil resembles a scaled version of the maple seed with a blunt leading edge followed by a thin section without camber. Four mechan- ical samara geometries with equal wing loading were designed and fabricated using a high precision rapid prototyping machine that ensured similarity between models. It was found that in order to reduce the descent velocity of an autorotating samara the area centroid or maximum chords should be as far from the center of rotation as possible. Flight data revealed large oscillations in feathering and coning angles, and the resultant flight path was found to be dependent on the mean feathering angle. The different flight modalities provided the basis for the design of a control sys- tem for a powered robotic samara that does not require high frequency sensing and actuation typical of micro-scaled rotorcraft. A prototype mechanical samara with a variable wing pitch (feathering) angle was constructed and it was found that active control of the feathering angle allowed the variation of the radius of the helix carved by the samara upon descent. This knowledge was used to design a hovering robotic samara capable of lateral motion through a series of different size circles specified by precise actuation of the feathering angle. To mathematically characterize the flight dynamics of the aircraft, System identi- fication techniques were used. Using flight data, a linear model describing the heave dynamics of two robotic samara vehicles was verified. A visual positioning system was used to collect flight data while the vehicles were piloted in an indoor laboratory. Closed-loop implementation of the derived PID controller was demonstrated using the visual tracking system for position and velocity feedback. An approach to directional control that does not require the once-per-revolution actuation or high-frequency measurement of vehicle orientation has been demon- strated for the first time. Lateral flight is attained through the vehicles differing responses to impulsive and step inputs that are leveraged to create a control strategy that provides full controllability. Flight testing revealed several linear relationships, including turn rate, turn radius and forward speed. The steady turn discussed here has been observed in scaled versions of the robotic samara, therefore the open-loop control demonstrated and analyzed is considered to be appropriate for similar vehicles of reduced size with limited sensing and actuation capabilities.
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    Automated Kinematic Extraction of Wing and Body Motions of Free Flying Diptera
    (2012) Kostreski, Nicholas Ivan; Humbert, James S; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    In the quest to understand the forces generated by micro aerial systems powered by oscillating appendages, it is necessary to study the kinematics that generate those forces. Automated and manual tracking techniques were developed to extract the complex wing and body motions of dipteran insects, ideal micro aerial systems, in free flight. Video sequences were captured by three high speed cameras (7500 fps) oriented orthogonally around a clear flight test chamber. Synchronization and image-based triggering were made possible by an automated triggering circuit. A multi-camera calibration was implemented using image-based tracking techniques. Three-dimensional reconstructions of the insect were generated from the 2-D images by shape from silhouette (SFS) methods. An intensity based segmentation of the wings and body was performed using a mixture of Gaussians. In addition to geometric and cost based filtering, spectral clustering was also used to refine the reconstruction and Principal Component Analysis (PCA) was performed to find the body roll axis and wing-span axes. The unobservable roll state of the cylindrically shaped body was successfully estimated by combining observations of the wing kinematics with a wing symmetry assumption. Wing pitch was determined by a ray tracing technique to compute and minimize a point-to-line cost function. Linear estimation with assumed motion models was accomplished by discrete Kalman filtering the measured body states. Generative models were developed for different species of diptera for model based tracking, simulation, and extraction of inertial properties. Manual and automated tracking results were analyzed and insect flight simulation videos were developed to quantify ground truth errors for an assumed model. The results demonstrated the automated tracker to have comparable performance to a human digitizer, though manual techniques displayed superiority during aggressive maneuvers and image blur. Both techniques demonstrated non-intrusive methods for establishing reference flight kinematics, which are being used to develop flight dynamics models in future work.
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    Control-Oriented Reduced Order Modeling of Dipteran Flapping Flight
    (2011) Faruque, Imraan A.; Humbert, J Sean; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Flying insects achieve flight stabilization and control in a manner that requires only small, specialized neural structures to perform the essential components of sensing and feedback, achieving unparalleled levels of robust aerobatic flight on limited computational resources. An engineering mechanism to replicate these control strategies could provide a dramatic increase in the mobility of small scale aerial robotics, but a formal investigation has not yet yielded tools that both quantitatively and intuitively explain flapping wing flight as an "input-output" relationship. This work uses experimental and simulated measurements of insect flight to create reduced order flight dynamics models. The framework presented here creates models that are relevant for the study of control properties. The work begins with automated measurement of insect wing motions in free flight, which are then used to calculate flight forces via an empirically-derived aerodynamics model. When paired with rigid body dynamics and experimentally measured state feedback, both the bare airframe and closed loop systems may be analyzed using frequency domain system identification. Flight dynamics models describing maneuvering about hover and cruise conditions are presented for example fruit flies (Drosophila melanogaster) and blowflies (Calliphorids). The results show that biologically measured feedback paths are appropriate for flight stabilization and sexual dimorphism is only a minor factor in flight dynamics. A method of ranking kinematic control inputs to maximize maneuverability is also presented, showing that the volume of reachable configurations in state space can be dramatically increased due to appropriate choice of kinematic inputs.
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    A DYNAMICS-BASED FIDELITY ASSESSMENT OF PARTIAL GRAVITY GAIT SIMULATION USING UNDERWATER BODY SEGMENT BALLASTING
    (2011) Mirvis, Adam Daniel; Akin, David L; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    In-water testing is frequently used to simulate reduced gravity for quasi-static tasks. For dynamic motions, however, the assumption has been that drag effects invalidate any data, and in-water testing has been dismissed in favor of complex and restrictive techniques such as counterweight suspension and parabolic flight. In this study, motion-capture was used to estimate treadmill gait metrics for three environments: underwater and ballasted to 1 g and to 1/6th g, and on dry land at 1 g. Ballast was distributed anthropometrically. Motion-capture results were compared with those for a simulated dynamic walker/runner, and used to assess the effect of the in-water environment on simulation fidelity. For each test case, the model was tuned to the subject's anthropometry, and stride length, pendulum frequency, and hip displacement were computed. In-water environmental effects were found to be sufficiently quantifiable to justify using in-water testing, under certain conditions, to study partial-gravity gait dynamics.
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    Smart Fabric sensors for foot motion monitoring
    (2010) Castano Salcedo, Lina Maria; Flatau, Alison B.; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Smart Fabrics or fabrics that have the characteristics of sensors are a wide and emerging field of study. This thesis summarizes an investigation into the development of fabric sensors for use in sensorized socks that can be used to gather real time information about the foot such as gait features. Conventional technologies usually provide 2D information about the foot. Sensorized socks are able to provide angular data in which foot angles are correlated to the output from the sensor enabling 3D monitoring of foot position. Current angle detection mechanisms are mainly heavy and cumbersome; the sensorized socks are not only portable but also non-invasive to the subject who wears them. The incorporation of wireless features into the sensorized socks enabled a remote monitoring of the foot.