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 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.Item Bio-Inspired Small Field Perception for Navigation and Localization of MAV's in Cluttered Environments(2015) Escobar-Alvarez, Hector Domingo; Humbert, Sean J; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Insects are capable of agile pursuit of small targets while flying in complex cluttered environments. Additionally, insects are able to discern a moving background from smaller targets by combining their lightweight and fast vision system with efficient algorithms occurring in their neurons. On the other hand, engineering systems lack such capabilities since they either require large sensors, complex computations, or both. Bio-inspired small-field perception mechanisms have the potential to enhance the navigation of small unmanned aircraft systems in cluttered unknown environments. In this dissertation, we propose and investigate three methods to extract information about small-field objects from optic flow. The first method, \textit{flow of flow}, is analogous to processes taking place at the medulla level of the fruit-fly visuomotor system. The two other methods proposed are engineering approaches analogous to the figure-detection sensitive neurons at the lobula. All three methods employed demonstrated effective small-field information extraction from optic flow. The methods extract relative distance and azimuth location to the obstacles from an optic flow model. This optic flow model is based on parameterization of an environment containing small and wide-field obstacles. The three methodologies extract the high spatial frequency content of the optic flow by means of an elementary motion detector, Fourier series, and wavelet transforms, respectively. This extracted signal will contain the information about the small-field obstacles. The three methods were implemented on-board both a ground vehicle and an aerial vehicle to demonstrate and validate obstacle avoidance navigation in cluttered environments. Lastly, a localization framework based on wide field integration of nearness information (inverse of depth) is used for estimating vehicle navigation states in an unknown environment. Simulation of the localization framework demonstrates the ability to navigate to a target position using only nearness information.Item The Design, Construction and Testing of a Scour Monitoring System Using Magnetostrictive Materials(2014) Day, Steven Richard; Flatau, Alison B; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A system for the continuous monitoring of scour has been designed, constructed and implemented. The system detects the level of scour by attaching flow to a buried post at known depths, and detecting when individual sensors become unearthed. Two bio-inspired flow sensors were designed and constructed for use on the post. The first, resembling a seal whisker, utilized the magnetostrictive materials Alfenol and Galfenol and was optimized for >0.15m/s flow. The second, resembling seaweed, used a conventional permanent magnet and was optimized for <0.15m/s flow. A small, low powered data acquisition system was designed and constructed to monitor and record the data from the sensors. A total of four scour posts were installed at two different sites; two vertically to monitor conventional scour and two horizontally to monitor lateral riverbed migration. Data from the posts was analyzed and presented and lessons learned were documented.Item Analysis of Factors Affecting the Aerodynamics of Low Reynolds Number Rotating Wings(2013) Schlueter, Kristy Lynn; Jones, Anya R; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A computational analysis was performed to address the effects of walls on wings rotating at a Reynolds number of 120. For rotation angles less than one revolution, a tip clearance of 0.5 chord-lengths is sufficient to approximate a wing rotating in an infinitely large volume of fluid. However, for a maximum rotation of two revolutions, a tip clearance of 5.0 chords is necessary. At the start of the second revolution, the wing encounters its wake, and the wake structure is significantly affected by low tip clearances. Lift and drag forces were measured experimentally for wings rotating at a Reynolds number of 10,000 while parameters including root cutout were varied. Root cutout significantly alters the lift and drag coefficients, including the location of a second local maximum in both lift and drag. The root-relative method of force non-dimensionalization provided the best comparison of force coefficients between cases with different root cutouts.Item Function Based Archival and Retrieval: Developing a Repository of Biologically Inspired Product Concepts(2005-07-20) Golden, Ira Joshua; Gupta, Satyandra K; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Many new product concepts have been developed by using inspiration from the biological world. These bio-inspired concepts offer many advantages in the development of engineered products and devices. However, there exist difficulties in locating promising sources for bio-inspiration. This thesis describes the development of an open repository of biologically inspired product concepts that will provide engineers access to a new resource for design ideas and examples. The current repository contains 89 different biologically inspired products, and new product concepts can be submitted to the repository by their developers. In order to make these design concepts more accessible, a new and easy-to-use method of function based archival and retrieval was developed - the Functional Description Template. This method can be used to archive functions of all classes of products, but is used in this application for bio-inspired products and biological systems. The Functional Description Template uses an extensible functional language to record product functions so that they are more expressive and complete while still being computer interpretable. In order to evaluate this new method, a study was conducted that offers a direct comparison to a Functional Basis, an alternative approach to archiving functions. The evaluation showed that the Functional Description Template method allowed greater expressiveness and completeness in the user's recorded functional statements. Using the Functional Description Template method, the participants in the study recorded more matched terms, averaging an increase of 29 matched terms, and lost less functional information, averaging 7 fewer pieces of information lost. Also, the participants improved their correctness in recording their functions by an average of 23%. Evaluation forms completed by the participants also indicated that the Functional Description Template was easier to use and more accurate in recording the user's functions. In addition to the Functional Description Template, flexible search tools were proposed for the repository, which facilitate a content-based search of the products and concepts. Users can search for products that satisfy functions of similar meaning, but are stated with different terminology. Several different search criteria can also be used to retrieve the concepts available in the repository. This complete system offers a step towards improving the product development process by including bio-inspiration in future product design.