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  • 1
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    In:  CASI
    Publication Date: 2013-08-31
    Description: A systematic procedure for the synthesis of fault tolerant control laws to actuator failure has been presented. Two design methods were used to synthesize fault tolerant controllers: the conventional LQ design method and a direct feedback controller design method SANDY. The latter method is used primarily to streamline the full-state Q feedback design into a practical implementable output feedback controller structure. To achieve robustness to control actuator failure, the redundant surfaces are properly balanced according to their control effectiveness. A simple gain schedule based on the landing gear up/down logic involving only three gains was developed to handle three design flight conditions: Mach .25 and Mach .60 at 5000 ft and Mach .90 at 20,000 ft. The fault tolerant control law developed in this study provides good stability augmentation and performance for the relaxed static stability aircraft. The augmented aircraft responses are found to be invariant to the presence of a failure. Furthermore, single-loop stability margins of +6 dB in gain and +30 deg in phase were achieved along with -40 dB/decade rolloff at high frequency.
    Keywords: QUALITY ASSURANCE AND RELIABILITY
    Type: NAS 1.26:178094 , NASA-CR-178094
    Format: application/pdf
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  • 2
    Publication Date: 2013-08-31
    Description: The performance of a 747-200 automatic flight control system (AFCS) subjected to typical Microwave Landing System (MLS) noise is discussed. The performance is then compared with the results from a previous study which had a B747 AFCS subjected to the MLS standards and recommended practices (SARPS) maximum allowable noise. A glide slope control run with Instrument Landing System (ILS) noise is also conducted. Finally, a linear covariance analysis is presented.
    Keywords: AIRCRAFT COMMUNICATIONS AND NAVIGATION
    Type: NAS 1.26:178032 , D6-57212 , NASA-CR-178032
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  • 3
    Publication Date: 2013-08-31
    Description: The bending of flexible body aircraft may degrade the ride coMfort of passengers. This is especially noticeable towards the aft end of the aircraft (due to the relatively large tail surfaces) which may easily be excited when flying through turbulence. In addition, some aircraft may experience a front body bending mode which can be annoying to the cabin crew and first class passengers. Normally, this dominant body bending mode falls between 1 to 5 Hz. This range is easily perceived by the human body. Also, in some situations, the rigid body control law may be out of phase with the mode and aggravate the vibration. Hence, an active modal suppression system is desirable for improving the ride quality of the airplane. The size of the mathematical model, which has both the airplane rigid body and flexible characteristics, could easily exceed 100 states. The computational burden and fidelity of this large structural model is addressed.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: NASA. Langley Research Center, Proceedings of the Workshop on Computational Aspects in the Control of Flexible Systems, Part 2; p 801-823
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  • 4
    Publication Date: 2013-08-31
    Description: A methodology is presented for a modal suppression control law design using flight test data instead of mathematical models to obtain the required gain and phase information about the flexible airplane. This approach is referred to as BODEDIRECT. The purpose of the BODEDIRECT program is to provide a method of analyzing the modal phase relationships measured directly from the airplane. These measurements can be achieved with a frequency sweep at the control surface input while measuring the outputs of interest. The measured Bode-models can be used directly for analysis in the frequency domain, and for control law design. Besides providing a more accurate representation for the system inputs and outputs of interest, this method is quick and relatively inexpensive. To date, the BODEDIRECT program has been tested and verified for computational integrity. Its capabilities include calculation of series, parallel and loop closure connections between Bode-model representations. System PSD, together with gain and phase margins of stability may be calculated for successive loop closures of multi-input/multi-output systems. Current plans include extensive flight testing to obtain a Bode-model representation of a commercial aircraft for design of a structural stability augmentation system.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: NASA. Langley Research Center, Proceedings of the Workshop on Computational Aspects in the Control of Flexible Systems, Part 2; p 825-851
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  • 5
    Publication Date: 2013-08-31
    Description: A soil moisture extraction algorithm is developed using a statistical parameter inversion method. Data sets from two aircraft experiments are utilized for the test. Multifrequency microwave radiometric data surface temperature, and soil moisture information are contained in the data sets. The surface and near surface ( or = 5 cm) soil moisture content can be extracted with accuracy of approximately 5% to 6% for bare fields and fields with grass cover by using L, C, and X band radiometer data. This technique is used for handling large amounts of remote sensing data from space.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: NASA-CR-166719 , P-A826
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  • 6
    Publication Date: 2016-06-07
    Description: A redundant frequency and time distribution system provides a multiplicity of isolated outputs, all of which are derived from three atomic frequency standards. The distribution system monitors input parameters of the signals coming from the Cesium Standards and selects one to be the primary standard, phase locks an internal oscillator which has excellent aging characteristics in the open loop mode and acts as a filter to provide phase noise improvement, and generates 1 megahertz and 100 kHz by direct synthesis. Additionally, the system distributes RF and timing signals consisting of 5 MHz, 1 MHz, 100 kHz, BCD Time-of-Day, 1 pps and 1 ppm.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA. Goddard Space Flight Center Proc. of the 12th Ann. Precise Time and Time Interval. and Planning; p 765-783
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  • 7
    Publication Date: 2016-06-07
    Description: Continuous growth methodology for silicon solar cell ribbons deals with capillary effects, die effects, thermal effects and crystal shape effects. Emphasis centers on the shape of the meniscus at the ribbon edge as a factor contributing to ribbon quality with respect to defect densities. Structural and electrical characteristics of edge defined, film-fed grown silicon ribbons are elaborated. Ribbon crystal solar cells produce AMO efficiencies of 6 to 10%.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: Proc. of the 1st ERDA Semiann. Solar Photovoltaic Conversion Program Conf.; p 104-171
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  • 8
    Publication Date: 2016-06-07
    Description: Introduction of lithium by ion implantation eliminates reproducibility and surface problem deficiencies of other introduction techniques. Implantation has been demonstrated to make possible a degree of control over the cell lithium content which has not previously been available. Front barrier development remains to be completed. Successful development of the barrier will make available the freedom to select optimum lithium concentration throughout the cell, including in the vicinity of the junction.
    Keywords: AUXILIARY SYSTEMS
    Type: JPL Proc. of the Fourth Ann. Conf. on Effects of Lithium Doping on Silicon Solar Cells; p 31-34
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  • 9
    Publication Date: 2017-07-01
    Description: Operational performance of solar cell at low temperatures and under low illumination intensity
    Keywords: AUXILIARY SYSTEMS
    Type: NASA-CR-73465
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  • 10
    Publication Date: 2011-08-24
    Description: The paper describes the superconducting gravity gradiometers (SGGs) and superconducting accelerometers being developed at the University of Maryland, which take advantage of many exotic properties of superconductivity to obtain the required low noise, high stability, and large dynamic range. Results of laboratory demonstrations of some of these instruments are presented together with the design and operating principles. Particular attention is given to the three-axis Model II SGG and a six-axis superconducting accelerometer model (Model I SSA). Model II SGG, after a residual common-mode balance, exhibited a noise level of 0.05/sq rt Hz above 0.1 Hz and a 1/f-squared noise below 0.1 Hz. All six channels of Model I SSA operated simultaneously with linear and angular acceleration noise levels of 3 x 10 exp -10 g(E)/sq rt Hz and 5 x 10 exp -8 rad/sec per sec per sq rt Hz, respectively.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: In: From Mars to Greenland: Charting gravity with space and airborne instruments - Fields, tides, methods, results (A93-55951 24-46); p. 191-201.
    Format: text
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