97 research outputs found

    NASA Workshop on Distributed Parameter Modeling and Control of Flexible Aerospace Systems

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    Although significant advances have been made in modeling and controlling flexible systems, there remains a need for improvements in model accuracy and in control performance. The finite element models of flexible systems are unduly complex and are almost intractable to optimum parameter estimation for refinement using experimental data. Distributed parameter or continuum modeling offers some advantages and some challenges in both modeling and control. Continuum models often result in a significantly reduced number of model parameters, thereby enabling optimum parameter estimation. The dynamic equations of motion of continuum models provide the advantage of allowing the embedding of the control system dynamics, thus forming a complete set of system dynamics. There is also increased insight provided by the continuum model approach

    Control of heat conduction in manufacturing processes : a distributed parameter systems approach

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    Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1997.Includes bibliographical references (leaves 230-241).by Upendra V. Ummenthala.Ph.D

    Orbit Determination Methods for Deep Space Drag-Free Controlled Laser Interferometry Missions

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    The objective of this thesis is to determine if different measurement combinations will improve absolute and relative orbit determination (OD) accuracy for the Laser Interferometer Space Antenna (LISA) mission. LISA, a triangular three-satellite heliocentric constellation, measures the relative length changes between spacecraft. The unique contribution of this work is the incorporation of inter-spacecraft range and range rate observations into the OD process, in addition to Deep Space Network (DSN) range and range rate, and Very Long Baseline Interferometry (VLBI) angle tracking data. MATLAB was used for orbit propagation, simulating measurements, and executing the weighted batch least squares algorithm to obtain the best state estimate. Covariance and Monte Carlo analyses were performed to compare the four test cases. The results concluded that cases with inter-spacecraft data had the least absolute and relative OD errors, VLBI eventually becomes ineffectual, and DSN needs at least 20 days of tracking to become observable

    Aeronautical Engineering: A continuing bibliography with indexes, supplement 185

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    This bibliography lists 462 reports, articles and other documents introduced into the NASA scientific and technical information system in February 1985. Aerodynamics, aeronautical engineering, aircraft design, aircraft stability and control, geophysics, social sciences, and space sciences are some of the areas covered

    Narrow-band passive systems theory with applications to positioning and navigation

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    Prepared under Contract no. DAAB07-75-C-1346, Joint Services Electronics Program. Originally presented as the author's thesis, (Sc.D.), M.I.T. Dept. of Electrical Engineering and Computer Science, 1975.Bibliography: p.197-199.José anuel Fonseca de Moura

    State Space Analysis of Dominant Structures in Dynamic Social Systems

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    Many systems involving human relationships are modeled as dynamic systems, as diverse as urban population growth, diffusion of innovations, spread of viruses, and supply chain management. A fundamental assumption is that these systems contain variables which accumulate and deplete over time (people, innovation adoptions, infections, and orders), and whose dynamics are determined by societal rules and human decision making processes. These assumptions allow the system to be formally expressed by ordinary differential equations which are often nonlinear and contain multiple state variables and feedback loops. Analytical methods have been developed to identify the dominant feedback loops which primarily influence the behavior of the system. However, these dominance methods can produce conflicting results and are often performed in the time-domain under specific initial conditions. This thesis takes a state-space approach to dominance analysis and, in the process, re-examines the definition of dominance. A formal, mathematical definition of dominance is proposed and an analytical procedure is developed and applied to previously studied models. The method produces results consistent with previous analyses and is able explain inconsistencies between other methods. The procedure is then applied in the state-domain and used to identify state-space regions in which certain feedback loops dominate behavior. The procedure is then used to identify the stability properties of equilibria, and a theorem is developed to provide a necessary condition for stability, based on the dominance of balancing (negative) feedback. Lastly, the method is applied to a problem in public health in which a model of the supply and demand of cancer control services is analyzed. The dominant feedback loops are identified for the purpose of revealing potential sources of health disparities between distinct population segments. The analysis revealed the existence of a tipping point condition associated with a single unstable equilibrium point which influences population health outcomes. Furthermore, trajectories near the unstable equilibrium point are dominated by reinforcing (positive) feedback loops which affect the proportion of people seeking cancer control services. These loops result in either virtuous or vicious cycles, depending on which side of the tipping point the system is operating in the state-space. The methods were then used to identify potential leverage points in the system in which small parameter changes cause significant behavior changes. Potential avenues for future dominance research are discussed as well as future transdisciplinary research in public health and implementation science

    Proceedings of the Workshop on Identification and Control of Flexible Space Structures, Volume 2

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    The results of a workshop on identification and control of flexible space structures held in San Diego, CA, July 4 to 6, 1984 are discussed. The main objectives of the workshop were to provide a forum to exchange ideas in exploring the most advanced modeling, estimation, identification and control methodologies to flexible space structures. The workshop responded to the rapidly growing interest within NASA in large space systems (space station, platforms, antennas, flight experiments) currently under design. Dynamic structural analysis, control theory, structural vibration and stability, and distributed parameter systems are discussed
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