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  • Journals
  • Other Sources  (974)
  • GEOPHYSICS  (762)
  • MECHANICAL ENGINEERING
  • 1990-1994  (974)
  • 1990  (974)
  • 1
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    Accurate GPS measurement of the location and orientation of a floating platform (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: This article describes the design and initial tests of the GPS portion of a system for making seafloor geodesy measurements. In the planned system, GPS antennas on a floating platform will be used to measure the location of an acoustic transducer, attached below the platform, which interrogates an array of transponders on the seafloor. Since the GPS antennas are necessarily some distance above the transducer, a short-baseline GPS interferometer consisting of three antennas is used to measure the platform's orientation. A preliminary test of several crucial elements of the system was performed. The test involved a fixed antenna on the pier and a second antenna floating on a buoy about 80 m away. GPS measurements of the vertical component of this baseline, analyzed independently by two groups using different software, agree with each other and with an independent measurement within a centimeter. The first test of an integrated GPS/acoustic system took place in the Santa Cruz Basin off the coast of southern California in May 1990. In this test a much larger buoy, designed and built at SIO, was equipped with three GPS antennas and an acoustic transducer that interrogated a transponder on the ocean floor. Preliminary analysis indicates that the horizontal position of the transponder can be determined with a precision of about a centimeter.
    Keywords: GEOPHYSICS
    Type: Marine Geodesy (ISSN 0149-0419); p. 255-264.
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  • 2
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    AVHRR imagery reveals Antarctic ice dynamics (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: A portion of AVHRR data taken on December 5, 1987 at 06:15 GMT over a part of Antarctica is used here to show that many of the most significant dynamic features of ice sheets can be identified by a careful examination of AVHRR imagery. The relatively low resolution of this instrument makes it ideal for obtaining a broad view of the ice sheets, while its wide swath allows coverage of areas beyond the reach of high-resolution imagers either currently in orbit or planned. An interpretation is given of the present data, which cover the area of ice streams that drain the interior of the West Antarctic ice sheet into the Ross Ice Shelf.
    Keywords: GEOPHYSICS
    Type: EOS (ISSN 0096-3941); 71; 741
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  • 3
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    Earth Radiation Budget Experiment - Preliminary seasonal results (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Data from the Earth Radiation Budget Satellite (ERBS) and from the operational NOAA-9 satellite being placed in the archive of the earth Radiation Budget Experiment (ERBE) are discussed. The results of the ERBE data validation effort are reviewed along with ERBE solar constant observations and earth-viewing results. The latter include monthly average results for July 1985, annual average clear-sky fluxes, and annual average, zonal, and global results.
    Keywords: GEOPHYSICS
    Type: EOS (ISSN 0096-3941); 71; 297
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  • 4
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    Error analysis for earth orientation recovery from GPS data (1990)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The use of GPS navigation satellites to study earth-orientation parameters in real-time is examined analytically with simulations of network geometries. The Orbit Analysis covariance-analysis program is employed to simulate the block-II constellation of 18 GPS satellites, and attention is given to the budget for tracking errors. Simultaneous solutions are derived for earth orientation given specific satellite orbits, ground clocks, and station positions with tropospheric scaling at each station. Media effects and measurement noise are found to be the main causes of uncertainty in earth-orientation determination. A program similar to the Polaris network using single-difference carrier-phase observations can provide earth-orientation parameters with accuracies similar to those for the VLBI program. The GPS concept offers faster data turnaround and lower costs in addition to more accurate determinations of UT1 and pole position.
    Keywords: GEOPHYSICS
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  • 5
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    Geomagnetic sudden impulses and storm sudden commencements - A note on terminology (1990)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The definitions of and distinctions between storm sudden commencements (SSCs) and geomagnetic sudden impulses (SIs) are examined and present definitions of SIs and SSCs are modernized. Quantitative definitions of the two terms are recommended.
    Keywords: GEOPHYSICS
    Type: EOS (ISSN 0096-3941); 71; 1808
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  • 6
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    Design optimization and probabilistic analysis of a hydrodynamic journal bearing (1990)
    In:  CASI
    Details
    Publication Date: 2004-12-04
    Description: A nonlinear constrained optimization of a hydrodynamic bearing was performed yielding three main variables: radial clearance, bearing length to diameter ratio, and lubricating oil viscosity. As an objective function a combined model of temperature rise and oil supply has been adopted. The optimized model of the bearing has been simulated for population of 1000 cases using Monte Carlo statistical method. It appeared that the so called 'optimal solution' generated more than 50 percent of failed bearings, because their minimum oil film thickness violated stipulated minimum constraint value. As a remedy change of oil viscosity is suggested after several sensitivities of variables have been investigated.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Langley Research Center, The Third Air Force(NASA Symposium on Recent Advances in Multidisciplinary Analysis and Optimization; p 378-386
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  • 7
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    On the maneuvering of a flexible space crane (1990)
    In:  CASI
    Details
    Publication Date: 2004-10-02
    Description: The design of an articulated space crane under NASA's 'Pathfinder' program continues to push forward. However, the large size and extreme flexibility of the crane entail major difficulties in precision positioning. To illustrate this and to gain more insight into its structural dynamic behavior, we have built three-dimensional rigid, flexible, homogenized and non-homogenized finite element models (FEM) of the articulated space crane and simulated its three-dimensional maneuvering. We have also begun to develop control strategies for the flexible system using first a simplified finite element model. The model captures much of the system's low frequency characteristics. From the FEM, a reduced-order model (ROM) based controller is designed based on a specific configuration of the crane. The ROM controller rotates the fixed shape crane about the alpha joint and uses three torque wheels at the tip to actuate its control law. Our analysis of the closed-loop system shows the destabilizing effect of control interaction with unmodeled system dynamics (Controller-Structure-Interaction). Making use of a parallel bank of residual-mode filters (RMF), we are able to compensate for CSI and restore system stability and performance. The implementation of the discrete-time control law on the simplified multi-body model is completed using the SAMCEF code.
    Keywords: MECHANICAL ENGINEERING
    Type: Second Annual Symposium; p 345-361
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  • 8
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    ROM/RMF control of the articulated-truss space crane (1990)
    In:  CASI
    Details
    Publication Date: 2004-10-02
    Description: The design of an articulated space crane under NASA's 'Pathfinder' program continues to push forward. However, the large size and extreme flexibility of the crane entail major difficulties in precision positioning. We have begun to develop control strategies for the flexible system using a simplified finite element model. The model captures much of the system's low frequency characteristics. From the FEM, a reduced-roder model (ROM) based controller is designed based on a specific configuration of the crane. The ROM controller rotates the fixed shape crane about the alpha joint and uses three torque wheels at the tip to actuate its control law. Our analysis of the closed-loop system shows the de-stabilizing effect of control interaction its unmodeled system dynamics (Controller-Structure Interaction). Making use of a parallel bank of residual-mode filters (RMF), we are able to compensate for CSI and restore system stability and performance. Finally, the implementation of the discrete-time control law on the simplified multi-body model is completed using SAMCEF.
    Keywords: MECHANICAL ENGINEERING
    Type: Second Annual Symposium; p 362-373
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  • 9
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    GPS measurements of regional deformation in southern California - Some constraints on performance (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Results from the first major survey of southern California with GPS equipment are presented along with some limited results from late experiments assessing GPS performance by analysis of day-to-day and longer-term repeatability, as well as comparisons with VLBI. GPS performance on longer (50-500 km or longer) baselines, a length range useful for measurement of regional deformation and fault block velocities, is emphasized. The implications of this level of performance for meeting longer-term scientific objectives is addressed. It is concluded that GPS techniques and yield results comparable to those achieved with mobile VLBI techniques in California, assuming that appropriate network design and analysis techniques are used. GPS can thus provide important constraints on regional deformation in California with five yrs or less of measurements.
    Keywords: GEOPHYSICS
    Type: EOS (ISSN 0096-3941); 71; 1051-105
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  • 10
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    Interannual and decade fluctuations in the earth's rotation (1990)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The main findings of a study of earth rotation changes on the longer interannual and decade range of time scales are summarized. The earth rotation data provide important constraints on models of the internal structure and dynamics of the core and lower mantle. Torques at the core-mantle interface are due to time varying fluid motions in the core. A torque of about 0.2 Hadley units is found in the axial component during the 1980 period.
    Keywords: GEOPHYSICS
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