Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2008. / Source: Dissertation Abstracts International, Volume: 69-05, Section: B, page: 3120. Adviser: Nancy R. Sottos. Includes bibliographical references (leaves 94-99) Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2008. / Source: Dissertation Abstracts International, Volume: 69-05, Section: B, page: 3165. Adviser: Nicholas P. Jones. Includes bibliographical references (leaves 220-227) Available on microfilm from Pro Quest Information and Learning.

Thèse (M.Sc.A.)--Université de Sherbrooke (Canada), 2008. / Titre de l'écran-titre (visionné le 1 février 2007). In ProQuest dissertations and theses. Publié aussi en version papier.

Thesis (Ph. D.)--Drexel University, 2005. / Includes abstract and vita. Includes bibliographical references (leaves 132-137).

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006. / Source: Dissertation Abstracts International, Volume: 67-11, Section: B, page: 6699. Advisers: Lawrence A. Bergman; Alexander F. Vakakis. Includes bibliographical references (leaves 315-327) Available on microfilm from Pro Quest Information and Learning.

Despite the prevalence of insect flight as a form of locomotion in nature, manmade aerial systems have yet to match the aerial prowess of flying insects. Within a tiny body volume, flying insects embody the capabilities to flap seemingly insubstantial wings at very high frequencies and sustain beyond their own body weight in flight. A precise authority over their wing motions enables them to respond to obstacles and threats in flight with unrivaled speed and grace. Motivated by a desire for comparably agile flying machines, research efforts in the last decade have generated crucial developments for realizing an artificial instantiation of insect flight. The need for tiny, high-efficiency mechanical components has produced unconventional solutions for propulsion, actuation, and manufacturing. Early vehicle designs proved to be flightworthy but were critically limited by the inability to produce control torques in flight. In this thesis, we synthesize all existing technologies for insect-scale manufacturing and actuation, and we introduce a new vehicle design, the "dual actuator bee," to address the need for flight control. Our work culminates in the first demonstration of controlled, hovering flight of an insect-scale, flapping-wing robot. As the ultimate goal for this research effort is the creation of fully autonomous flying robots, these vehicles must sustain their own power sources and intelligence. To that end, we explore the challenges of scaling flapping-wing flight to attain greater lift forces. Using a scaling heuristic to determine key vehicle specifications, we develop and successfully demonstrate a hover-capable vehicle design that possesses the requisite payload capacity for the full suite of components required for control autonomy. With this operational vehicle as a point of reference, we introduce an iterative sizing procedure for specifying a vehicle design with payload capacity capable of supporting power autonomy. In the development of these vehicles, the reliability of their construction has been a substantial challenge. We present strategies for systematically addressing issues of vehicle construction. Together, this suite of results demonstrates the feasibility of achieving artificial, insect-like flight. / Engineering and Applied Sciences - Engineering Sciences

A diagnostic method is introduced for helicopter gearboxes that uses the gearbox structure and characteristics of the 'features' of vibration to define the influences of faults on features. The structural influences in this method are defined based on the root mean square value of vibration obtained from a simplified lumped-mass model of the gearbox. Featural influences characterize the frequency-specific information of the vibration features which correspond to the type of gearbox faults the features represent. These influences are defined as fuzzy variables to account for the approximate nature of the simplified model of the gearbox. The fuzzy structural and featural influences are then incorporated as the weights of a connectionist network for diagnosis, so as to avoid supervised training of the network. Diagnosis in this Structure-Based Connectionist Network (SBCN) is performed by propagating the abnormal features through the weights of SBCN to obtain fault possibility values for the components in the gearbox. In the proposed diagnostic method, vibration features obtained from raw vibration are first utilized by an unsupervised Fault Detection Network (FDN) for identifying the presence of faults. Fault diagnosis is then performed by SBCN only if the presence of a fault is prompted by FDN. Since SBCN uses abnormal vibration features as inputs, an unsupervised pattern classifier is designed for abnormality-scaling of features. The abnormality-scaled features are then propagated through the weights of SBCN for isolating faulty components. The proposed diagnostic method is experimentally evaluated in application to two helicopter gearboxes: OH-58A and S-61. Experimental vibration data for the OH-58A gearbox were collected at the NASA Lewis Research Center, and vibration data from three S-61 gearboxes rejected in field operation were collected at Sikorsky Aircraft. The proposed method is evaluated in diagnosis of the OH-58A gearbox faults as well as isolating the faults within the three S-61 gearboxes. The diagnostic results indicate that the SBCN is able to correctly diagnose about 80% of the OH-58A gearbox faults and all the faults in S-61 gearboxes. In addition to evaluation of the structural influences based on diagnostic results, they are validated by comparing them with influences obtained from experimental RMS values as well as the weights of a neural network structurally similar to SBCN, but trained through supervised learning. Moreover a sensitivity analysis is performed to study the effect of variations in structural influences on diagnostic results. The structural influences developed in this method can also be utilized for assessing the importance of various gearbox accelerometers in diagnosis. Three indices are defined based on the structural influences to quantify various aspects of accelerometer significance and are evaluated using the data from the OH-58A gearbox.

Aperture synthesis is applied to passive microwave remote sensing of the earth in an effort to attain high resolution images at low microwave frequencies. An L-band (1.4 GHz) synthetic aperture radiometer, dubbed the Electronically Scanned Thinned Array Radiometer, is tested and calibrated. The instrument is modeled after radio telescopes, and utilizes a thinned array of correlation interferometers to measure the Fourier Transform of the Brightness temperature image. The antenna hardware of such an array is reduced by comparison with real aperture antenna systems, which renders this technique relevant to future spaceborne remote sensing applications that require high resolution. In particular, it is the scientific applications at L-band, including the spaceborne remote sensing of soil moisture and ocean salinity, which have motivated this research. Aperture synthesis concepts are developed and applied to the theoretical ESTAR system in chapter II. Chapter II also includes a description of the prototype which was designed constructed at the University of Massachusetts. Practical calibration algorithms are developed in chapter III, and the synthesis technique is refined in chapter IV to reduce side lobes. Chapter V presents the first known images by this class of remote sensing radiometer, and the concluding chapter suggests avenues for future research.

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