Theses and Dissertations from UMD
Permanent URI for this communityhttp://hdl.handle.net/1903/2
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item Aeroelastic Stability Analysis of a Wing with a Variable Cant Angle Winglet(2020) Mondragon Gomez, Jose Mauricio; Hubbard, James E; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Currently, multiple air vehicles employ wing shape change to enhance their performance and achieve mission adaptability in different environments inside the Earth's atmosphere. This concept has been around since the dawn of aviation. In 1903, the Wright brothers implemented wing warping to control their aircraft during flight. Subsequently, a variety of techniques and devices have used to achieve wing shape change and make the vehicles more versatile. For example, they include variable wing sweep, folding wing tips, and variable camber. However, aeroelasticity has played in important role in these developments. Thus, this work focuses on the aeroelastic analysis and understanding of the fundamental physics of the flutter mechanism of a wing equipped with a variable cant angle winglet. Two methods are applied to model the wingletted wing system. The Rayleigh Ritz method is the first technique used to model the system. This method involves the implementation of a shape function to represent the entire structure. The second method used in the analysis is the Finite Element Analysis. In this formulation, the wing structure is divided into elements and elemental functions are used for local interpolation. Strip theory is used to model the spanwise aerodynamic loading. In addition, steady, quasi-steady, and unsteady aerodynamic models are used, each with different levels of complexity. Both the structural and aerodynamic models were coupled to generate four dynamic aeroelastic equations that represent the continuous system. Those equations were used to model the system and perform a dynamic aeroelastic analysis. The results indicate that having a vehicle equipped with a variable cant angle winglet can be favorable. It can increase flutter speed and expand its flight envelope. Moreover, when the winglet length is greater than 50% the length of the wing section and the cant angle greater than 50 degrees, the second torsional mode of vibration becomes unstable. Whereas, the first mode remains marginally stable. Thus, the second mode has become the critical mode that leads to structural failure. In this case, that phenomenon is referred as mode switching.Item Photogrammetric Reconstruction of Tandem-Wing Kinematics for Free-Flying Dragonflies Undergoing a Range of Flight Maneuvers(2017) Gabryszuk, Mateusz; Laurence, Stuart J; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Photogrammetric methods are used to reconstruct the body and wing kinematics of free-flying dragonflies. A novel experimental setup was designed and constructed to allow for repeated untethered flights in a constrained flight arena. Kinematic data are presented for twelve individual flights and a total of 23 complete wing strokes, including unaccelerating, accelerating, climbing, and turning flight. High variability is observed in the wing motions employed by individual dragonflies, particularly in terms of stroke amplitude, pitch angle, and wingbeat frequency. Forewing and hindwing flapping is found to be neither in phase nor fully out of phase across all cases, with the forewings lagging the hindwings by an average of 90 degrees. Downstroke durations are observed to be shorter than upstroke durations except in highly accelerating flights. Migratory dragonflies are found to exhibit notably different wing kinematics than non-migratory species.Item Kinematic Determination of an Unmodeled Serial Manipulator by Means of an IMU(2013) Ciarleglio, Constance; Akin, David L; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Kinematic determination for an unmodeled manipulator is usually done through a-priori knowledge of the manipulator physical characteristics or external sensor information. The mathematics of the kinematic estimation, often based on Denavit- Hartenberg convention, are complex and have high computation requirements, in addition to being unique to the manipulator for which the method is developed. Analytical methods that can compute kinematics on-the fly have the potential to be highly beneficial in dynamic environments where different configurations and variable manipulator types are often required. This thesis derives a new screw theory based method of kinematic determination, using a single inertial measurement unit (IMU), for use with any serial, revolute manipulator. The method allows the expansion of reconfigurable manipulator design and simplifies the kinematic process for existing manipulators. A simulation is presented where the theory of the method is verified and characterized with error. The method is then implemented on an existing manipulator as a verification of functionality.Item Decoding of walking kinematics from non-invasively acquired electroencephalographic signals in stroke patients(2012) Nathan, Kevin; Contreras-Vidal, Jose L; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Our group has recently shown the feasibility of decoding kinematics of controlled walking from the lower frequency range of electroencephalographic (EEG) signals during a precision walking task. Here, we turn our attention to stroke survivors who have had lesions resulting in hemiparetic gait. We recorded the EEG of stroke recovery patients during a precision treadmill walking task while tracking bilaterally the kinematics of the hips, knees, and ankles. In offline analyses, we applied a Wiener Filter and two unscented Kalman filters of 1st and 10th orders to predict estimates of the kinematic parameters from scalp EEG. Decoding accuracies from four patients who have had cortical and subcortical strokes were comparable with previous studies in healthy subjects. With improved decoding of EEG signals from damaged brains, we hope we can soon correlate activity to more intentional and normal-form walking that can guide users of a powered lower-body prosthetic or exoskeleton.Item Brain function underlying adaptive sensorimotor control in children with and without Developmental Coordination Disorder(2012) Pangelinan, Melissa Marie; Clark, Jane E; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)One child in every classroom (6% of children) suffers from Developmental Coordination Disorder (DCD). Children with DCD exhibit marked impairments in movement planning and adaptive visuomotor behavior. However, few studies have investigated the brain functions that underlie behavioral difficulties exhibited by children with DCD. The overarching objective of this dissertation was to examine brain function using electroencephalography (EEG) both at rest and during the performance of visuomotor tasks of different levels of complexity (i.e. static vs. dynamic task environments) to determine if deficits in motor behavior are related to disrupted brain function in children with DCD. The first study revealed that the cortical activation patterns exhibited by children with DCD at rest were different than their typically developing (TD) peers, particularly for the left motor cortical region. Moreover, the activation patterns of children with DCD were similar to the patterns previously reported for young TD children, suggesting a "maturational lag" in brain activation specific to motor function. For the remaining studies, children performed line drawing movements on a computer tablet towards visual targets presented on a computer screen. These studies examined whether or not children with DCD exhibit different cortical activation patterns during the execution of goal-directed drawing movements. In Study 2, children performed simple drawing movements to stationary targets. The performance of children with DCD followed the same age-related developmental trajectory as TD children. However, children with DCD engaged motor planning and control brain areas to a greater extent throughout the movement compared to TD children, suggesting greater cortical effort to complete the task. For the last two studies, children performed drawing movements in dynamic environments in which visual stimuli cued participants to either abruptly stop ongoing movements (Study 3.1) or to modify movements online to displaced target locations (Study 3.2). Results from Study 3.1 demonstrated that children with DCD do not have difficulties inhibiting movements, a finding that may be attributed to similar cortical activation patterns as the TD children in response to stop signals. Study 3.2 revealed that children with DCD exhibit difficulties modifying movements online, which may be due to a lack of preparatory cortical activation in this group. Taken together, this dissertation provides evidence that disrupted cortical function both at rest and during movement planning may underlie differences in motor performance in DCD.Item Design and Evaluation of End-Effectors for Autonomous Sampling(2008-09-16) Lewandowski, Craig Michael; Akin, David; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Autonomous underwater vehicles are becoming increasingly prevalent, and their emergence will allow for the execution of previously unfeasible underwater missions. These missions include seeking naval mines, navigation and mapping of ocean features, and sampling on the ocean floor at extreme depths. One method to achieve this latter objective involves the attachment of a robotic manipulator to an underwater vehicle and use of the manipulator to collect specimens and deposit them in containers. This thesis focuses on the design and testing of an end-effector to be used on such a manipulator. End-effectors previously utilized in underwater robotics were evaluated during the conceptualization of the selected tool design. These evaluations in conjunction with manipulator interface requirements were used to produce the end-effector design that was constructed and subsequently tested. In addition, sample containers were designed and fabricated, and kinematics software used to determine sample container position, orientation, and quantity was developed.