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 Dynamics and Control of a Hovering Quadrotor in Wind(2019) Craig, William Stephen; Paley, Derek A; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Quadrotor helicopters show great promise for a variety of missions in commercial, military, and recreational domains. Many of these missions require flight outdoors where quadrotors struggle, partially due to their high susceptibility to wind gusts. This dissertation addresses the problem of quadrotor flight in wind with (1) a physics-based analysis of the interaction between the wind and the quadrotor, (2) the addition of flow sensing onboard the quadrotor to measure external wind, and (3) both linear and nonlinear control development incorporating flow sensing and taking aerodynamic interactions into account. Using flow measurements in addition to traditional IMU sensing enables the quadrotor to react to the wind directly, rather than delaying until the wind affects the rigid-body dynamics as with IMU sensing alone. The aerodynamic response of a quadrotor to wind is modeled using blade flapping, which characterizes the tilt of the rotor plane a result of uneven lift on the blades. The model is validated by mounting a motor and propeller to a spherical pendulum and subjecting it to a wind gust. The blade-flapping model is utilized in a nonlinear geometric feedback-linearization controller that is built in a cascaded framework, first developing the inner-loop attitude controller, then the outer-loop position controller. The controller directly cancels the forces and moments resulting from aerodynamic disturbances using measurements from onboard flow probes, and also includes a variable-gain algorithm to address the inherent thrust limitations on the motors. A linear model and controller is also developed, using frequency-domain system-identification techniques to characterize the model, and handling-qualities-criteria based optimization to select gains. A linear model of the aerodynamic interactions, based on the blade-flapping work, provides flow-feedback capability similar to the nonlinear controller. Experimental testing is performed for each of the developed controllers, all of which show improvement through the use of flow feedback. Attitude is tested independently by mounting the quadrotor on a ball-joint, allowing for both gust and saturation testing. Gust rejection is also tested for both linear and nonlinear controllers in free flight, showing further benefits than considering attitude alone.Item Bioinspired Robust Underwater Behaviors Using Fluid Flow Sensing(2017) Ranganathan, Badri Narayanan; Humbert, Sean; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The lateral line sense organ in fish detects fluid flow around its body, and is used to perform a wide variety of behaviors such as rheotaxis, wall-following, prey detection, and obstacle and predator avoidance. Currently there are no equivalent engineering analogues that can sense fluid flow perturbation to determine location of obstacles and demonstrate closed loop obstacle avoidance. In this dissertation we examine the potential and limitations of this sensor system with respect to obstacle detection, avoidance and rheotaxis. This dissertation presents the development of a novel bioinspired flow-based perception scheme for small and wide-field objects, design and development of a strain sensor system and a robust controller for closed loop demonstration of rheotaxis and small and wide field object detection and avoidance. Potential flow based models are developed for the above mentioned problems of interest. As the modeling technique is approximate, the uncertainties due to modeling and effect of rotation rate are accounted for and used in the synthesis of a robust H$_\infty$ control system. The perturbation signals are spatially decomposed using wide and small-field integration techniques to arrive at information regarding objects in the environment. A high-fidelity, computational fluid dynamic closed-loop simulation is carried out by interfacing control codes with an off-the-shelf software to demonstrate behaviors of rheotaxis, wall-following, tunnel centering and unstructured wide-field obstacle avoidance. A bio-inspired hair array sensor and its corresponding signal conditioning electronics were developed for detecting flow perturbations related to the behaviors of interest. The sensors that were manufactured were strain based and involved the use of micro and macro fabrication approaches. An instrumentation amplifier-based system was developed for signal conditioning. The hair array sensors along with the signal conditioning electronics weighed about 10 gms, which allows it to be easily carried on small scale fish robots. These sensors were integrated onto an airfoil-shaped robot and perturbation signals due to the motion of the robot near a wall and cylindrical objects were obtained and analyzed. The signals that have been measured by the sensor array help in quantifying the magnitude and structure of perturbation that is observed due to interaction with objects, and establishes requirements for sensor design for deployment on autonomous underwater vehicles. Closed loop behavior of rheotaxis was demonstrated in a flow tank.