UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
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Item 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.Item Towards an Autonomous Algal Turf Scrubber: Development of an Ecologically-Engineered Technoecosystem(2010) Blersch, David Michael; Kangas, Patrick C.; Biological Resources Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The development of an autonomous and internally-controlled technoecological hybrid is explored. The technoecosystem is based on an algal turf scrubber (ATS) system that combines engineered feedback control programming with internal feedback patterns within the ecosystem. An ATS is an engineered, high-turbulent aquatic system to cultivate benthic filamentous algae for the removal of pollutants from an overlying water stream. This research focuses on designing a feedback control system to control the primary production of algae in an ATS through monitoring of the algal turf metabolism and manipulation of the turbulence regime experienced by the algae. The primary production of algae in an ATS, and thus the potential of the waste treatment process, is known to be directly related to the level of turbulence in the flowing water stream resulting from the amplitude and frequency of the wave surge. Experiments are performed to understand the influence of turbulence on the biomass production rate of algae in an ATS. These results show that biomass production is correlated with wave surge amplitude at a constant frequency. Further, the influence of turbulence on the net ecosystem metabolism of an algal turf in an ATS was investigated. Results showed that both net primary production and respiration, measured through the diurnal change of inorganic carbon, follow a subsidy-stress relationship with increasing wave surge frequency, although some of this trend may be explained by the transfer of metabolic gases across the air-water interface. A feedback control algorithm, developed to monitor the net primary production and manipulate a controlling parameter, was found to converge quickly on the state of maximum primary production when the variance of the input data was low, but the convergence rate was slow at only moderate levels of input variance. The elements were assembled into a physical system in which the feedback control algorithm manipulated the turbulence of the flow in an ATS system in response to measured shifts in ecosystem metabolism. Results from this testing show that the system can converge on the maximum algal productivity at the lowest level of turbulence--the most efficient state from an engineering perspective--but in practice the system was often confounded by measurement noise. Investigation into the species composition of the dominant algae showed shifting relative abundance for those units under automated control, suggesting that certain species are more suited for utilizing the technological feedback pathways for manipulating the energy signature of their environment.Item The Use Of Variable Celestial X-ray Sources For Spacecraft Navigation(2005-09-22) Sheikh, Suneel Ismail; Pines, Darryll J.; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Accurate control and guidance of spacecraft require continuous high performance three-dimensional navigation solutions. Celestial sources that produce fixed radiation have demonstrated benefits for determining location near Earth and vehicle attitude. Many interplanetary navigation solutions have also relied on Earth-based radio telescope observations and substantial ground processing. This dissertation investigates the use of variable celestial sources to compute an accurate navigation solution for autonomous spacecraft operation and presents new methodologies for determining time, attitude, position, and velocity. A catalogue of X-ray emitting variable sources has been compiled to identify those that exhibit characteristics conducive to navigation. Many of these sources emit periodic signals that are stable and predictable, and all are located at vast distances such that the signal visibility is available throughout the solar system and beyond. An important subset of these sources is pulsar stars. Pulsars are rapidly rotating neutron stars, which generate pulsed radiation throughout the electromagnetic spectrum with periods ranging from milliseconds to thousands of seconds. A detailed analysis of several X-ray pulsars is presented to quantify expected spacecraft range accuracy based upon the source properties, observation times, and X-ray photon detector parameters. High accuracy time transformation equations are developed, which include important general relativistic corrections. Using methods that compare measured and predicted pulse time of arrival within an inertial frame, approaches are presented to determine absolute and relative position, as well as corrections to estimated solutions. A recursive extended Kalman filter design is developed to incorporate the spacecraft dynamics and pulsar-based range measurements. Simulation results demonstrate that absolute position determination depends on the accuracy of the pulse phase measurements and initial solutions within several tens of kilometers are achievable. The delta-correction method can improve this position solution to within 100 m MRSE and velocity to within 10 mm/s RMS using observations of 500 s and a 1-m2 detector. Comparisons to recorded flight data obtained from Earth-orbiting X-ray astrophysics missions are also presented. Results indicate that the pulsed radiation from variable celestial X-ray sources presents a significant opportunity for developing a new class of navigation system for autonomous spacecraft operation.