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  • Air Transportation and Safety  (2)
  • Cybernetics  (2)
  • INSTRUMENTATION AND PHOTOGRAPHY  (2)
  • OPTICS  (1)
  • 1
    Publication Date: 2011-08-24
    Description: The paper describes the use of a numerical simulation to predict the dynamic behavior of a photorefractive crystal exposed to interfering light waves at two different frequencies. Unlike static recording media, photorefractive materials allow for the simultaneous diffraction from and generation of refractive index gratings. The grating properties are evaluated in terms of their effect on the performance of a dynamic distributed sensor which uses the crystal as a holographic recording medium. Experimental results are presented which support the behavior predicted by simulation.
    Keywords: OPTICS
    Type: In: European Conference on Smart Structures and Materials, 1st, Glasgow, United Kingdom, May 12-14, 1992, Proceedings (A93-17676 05-31); p. 379-382.
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  • 2
    Publication Date: 2011-08-24
    Description: Design of a distributed holographic interferometric sensor for measuring the surface displacement of a large segmented reflector is proposed. The reflector's surface is illuminated by laser light of two wavelengths and volume holographic gratings are formed in photorefractive crystals of the wavefront returned from the surface. The sensor is based on holographic contouring with a multiple frequency source. It is shown that the most stringent requirement of temporal stability affects both the temporal resolution and the dynamic range. Principal factor which limit the sensor performance include the response time of photorefractive crystal, laser power required to write a hologram, and the size of photorefractive crystal.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: In: Sensors and sensor integration; Proceedings of the Meeting, Orlando, FL, Apr. 4, 1991 (A93-21961 07-35); p. 2-10.
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  • 3
    Publication Date: 2019-07-13
    Description: Toward the goal of reducing the fatal accident rate of large transport airplanes due to loss of control, the NASA Aviation Safety Program has conducted research into flight control technologies that can provide resilient control of airplanes under adverse flight conditions, including damage and failure. As part of the safety program s Integrated Resilient Aircraft Control Project, the NASA Airborne Subscale Transport Aircraft Research system was designed to address the challenges associated with the safe and efficient subscale flight testing of research control laws under adverse flight conditions. This paper presents the results of a series of pilot evaluations of several flight control algorithms used during an offset-to-landing task conducted at altitude. The purpose of this investigation was to assess the ability of various flight control technologies to prevent loss of control as stability and control characteristics were degraded. During the course of 8 research flights, data were recorded while one task was repeatedly executed by a single evaluation pilot. Two generic failures, which degraded stability and control characteristics, were simulated inflight for each of the 9 different flight control laws that were tested. The flight control laws included three different adaptive control methodologies, several linear multivariable designs, a linear robust design, a linear stability augmentation system, and a direct open-loop control mode. Based on pilot Cooper-Harper Ratings obtained for this test, the adaptive flight control laws provided the greatest overall benefit for the stability and control degradation scenarios that were considered. Also, all controllers tested provided a significant improvement in handling qualities over the direct open-loop control mode.
    Keywords: Air Transportation and Safety
    Type: NF1676L-13184 , AIAA Guidance, Navigation, and Control Conference; Aug 08, 2011 - Aug 11, 2011; Portland, OR; United States
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  • 4
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    In:  Other Sources
    Publication Date: 2019-07-12
    Description: A closed-loop control experiment is described in which vibrations of a cantilevered beam are suppressed using measurements from a modal-domain fiber optic sensor. Modal-domain sensors are interference between the modes of a few-mode optical waveguide to detect strain. The fiber is bonded along the length of the beam and provides a measurement related to the strain distribution on the surface of the beam. A model for the fiber optic sensor is derived, and this model is integrated with the dynamic model of the beam. A piezoelectric actuator is also bonded to the beam and used to provide control forces. Control forces are obtained through dynamic compensation of the signal from the fiber optic sensor. The compensator is implemented with a real-time digital controller. Analytical models are verified by comparing simulations to experimental results for both open-loop and closed-loop configurations.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Optical Engineering (ISSN 0091-3286); 31; 8-12
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  • 5
    Publication Date: 2019-07-12
    Description: This paper reviews current and emerging operational experiences, technologies, and human-machine interaction theories to develop an integrated flight system concept designed to increase the safety, reliability, and performance of single-pilot operations in an increasingly accommodating but stringent national airspace system. This concept, know as the Naturalistic Flight Deck (NFD), uses a form of human-centered automation known as complementary-automation (or complemation) to structure the relationship between the human operator and the aircraft as independent, collaborative agents having complimentary capabilities. The human provides commonsense knowledge, general intelligence, and creative thinking, while the machine contributes specialized intelligence and control, extreme vigilance, resistance to fatigue, and encyclopedic memory. To support the development of the NFD, an initial Concept of Operations has been created and selected normal and non-normal scenarios are presented in this document.
    Keywords: Air Transportation and Safety
    Type: NASA/TM-2007-215090 , L-19285
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  • 6
    Publication Date: 2019-07-13
    Description: This paper presents an iterative Linear Quadratic Gaussian (LQG) controller design approach for a linear stochastic system with an uncertain open-loop model and unknown noise statistics. This approach consists of closed-loop identification and controller redesign cycles. In each cycle, the closed-loop identification method is used to identify an open-loop model and a steady-state Kalman filter gain from closed-loop input/output test data obtained by using a feedback LQG controller designed from the previous cycle. Then the identified open-loop model is used to redesign the state feedback. The state feedback and the identified Kalman filter gain are used to form an updated LQC controller for the next cycle. This iterative process continues until the updated controller converges. The proposed controller design is demonstrated by numerical simulations and experiments on a highly unstable large-gap magnetic suspension system.
    Keywords: Cybernetics
    Type: NASA-CR-203238 , NAS 1.26:203238 , Journal of Dynamic Systems, Measurement and Control; 118; 366-372
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  • 7
    Publication Date: 2019-07-13
    Description: An algorithm is presented for identifying a state-space model of linear stochastic systems operating under known feedback controller. In this algorithm, only the reference input and output of closed-loop data are required. No feedback signal needs to be recorded. The overall closed-loop system dynamics is first identified. Then a recursive formulation is derived to compute the open-loop plant dynamics from the identified closed-loop system dynamics and known feedback controller dynamics. The controller can be a dynamic or constant-gain full-state feedback controller. Numerical simulations and test data of a highly unstable large-gap magnetic suspension system are presented to demonstrate the feasibility of this indirect identification method.
    Keywords: Cybernetics
    Type: NASA-CR-203237 , NAS 1.26:203237 , Journal of Guidance, Control, and Dynamics; 19; 4; 836-841
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