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  • 1994  (7)
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  • 1
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    Parallel, adaptive finite element methods for conservation laws (1994)
    In:  Other Sources
    Details
    Publikationsdatum: 2011-08-24
    Beschreibung: We construct parallel finite element methods for the solution of hyperbolic conservation laws in one and two dimensions. Spatial discretization is performed by a discontinuous Galerkin finite element method using a basis of piecewise Legendre polynomials. Temporal discretization utilizes a Runge-Kutta method. Dissipative fluxes and projection limiting prevent oscillations near solution discontinuities. A posteriori estimates of spatial errors are obtained by a p-refinement technique using superconvergence at Radau points. The resulting method is of high order and may be parallelized efficiently on MIMD computers. We compare results using different limiting schemes and demonstrate parallel efficiency through computations on an NCUBE/2 hypercube. We also present results using adaptive h- and p-refinement to reduce the computational cost of the method.
    Schlagwort(e): COMPUTER PROGRAMMING AND SOFTWARE
    Materialart: Applied Numerical Mathematics (ISSN 0618-9274); p. 255-283
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Optimal disturbance rejecting control of hyperbolic systems (1994)
    In:  CASI
    Details
    Publikationsdatum: 2013-08-31
    Beschreibung: Optimal regulation of hyperbolic systems in the presence of unknown disturbances is considered. Necessary conditions for determining the optimal control that tracks a desired trajectory in the presence of the worst possible perturbations are developed. The results also characterize the worst possible disturbance that the system will be able to tolerate before any degradation of the system performance. Numerical results on the control of a vibrating beam are presented.
    Schlagwort(e): CYBERNETICS
    Materialart: NASA. Langley Research Center, NASA Workshop on Distributed Parameter Modeling and Control of Flexible Aerospace Systems; p 317-322
    Format: application/pdf
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
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    An intelligent control system for failure detection and controller reconfiguration (1994)
    In:  CASI
    Details
    Publikationsdatum: 2013-08-31
    Beschreibung: We present an architecture of an intelligent restructurable control system to automatically detect failure of system components, assess its impact on system performance and safety, and reconfigure the controller for performance recovery. Fault detection is based on neural network associative memories and pattern classifiers, and is implemented using a multilayer feedforward network. Details of the fault detection network along with simulation results on health monitoring of a dc motor have been presented. Conceptual developments for fault assessment using an expert system and controller reconfiguration using a neural network are outlined.
    Schlagwort(e): CYBERNETICS
    Materialart: NASA. Goddard Space Flight Center, The 1994 Goddard Conference on Space Applications of Artificial Intelligence; p 285-291
    Format: application/pdf
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
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    Solidification of Ultrasonically Levitated o-Terphenyl Crystals: A Raman Study (1994)
    In:  Other Sources
    Details
    Publikationsdatum: 2018-06-08
    Beschreibung: Ultrasonic levitation of millimeter size 0-terphenyl crystals was carried out in a variable tempeature enclosure. The trapped crystals were melted (m.p.=331 K), undercooled and then seeded in order to initiate solidification.
    Format: text
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  • 5
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    Mesh quality control for multiply-refined tetrahedral grids (1994)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: A new algorithm for controlling the quality of multiply-refined tetrahedral meshes is presented in this paper. The basic dynamic mesh adaption procedure allows localized grid refinement and coarsening to efficiently capture aerodynamic flow features in computational fluid dynamics problems; however, repeated application of the procedure may significantly deteriorate the quality of the mesh. Results presented show the effectiveness of this mesh quality algorithm and its potential in the area of helicopter aerodynamics and acoustics.
    Schlagwort(e): QUALITY ASSURANCE AND RELIABILITY
    Materialart: NASA-CR-197595 , NAS 1.26:197595 , RIACS-TR-94-19
    Format: application/pdf
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  • 6
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    Computation of helicopter rotor acoustics in forward flight (1994)
    In:  CASI
    Details
    Publikationsdatum: 2019-07-13
    Beschreibung: This paper presents a new method for computing acoustic signals from helicopter rotors in forward flight. The aerodynamic and acoustic solutions in the near field are computed with a finite-difference solver for the Euler equations. A nonrotating cylindrical Kirchhoff surface is then placed around the entire rotor system. This Kirchhoff surface moves subsonically with the rotor in forward flight. The finite-difference solution is interpolated onto this cylindrical surface at each time step and a Kirchhoff integration is used to carry the acoustic signal to the far field. Computed values for high-speed impulsive noise show excellent agreement with model-rotor and flight-test experimental data. Results from the new method offer high accuracy with reasonable computer resource requirements.
    Schlagwort(e): ACOUSTICS
    Materialart: NASA-CR-196132 , NAS 1.26:196132 , RIACS-TR-94-06 , Army Science Conference; Jun 20, 1994 - Jun 24, 1994; Orlando, FL; United States
    Format: application/pdf
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  • 7
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    Observations of enhanced sub-iron (Sc-Cr) to Iron abundance ratios in the low energy galactic cosmic rays in Spacelab-3 and their implications (1994)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-08-28
    Beschreibung: The Anuradha cosmic ray experiment in Spacelab-3, flown in the orbit at 350 km with an inclination of 57 deg for about six days, was used to measure the low energy galactic cosmic ray (GCR) heavy ions using a specially designed CR-39 detector module incorporating the arrival time information of the particles. The abundances of sub-iron (Sc-Cr) and iron particles in the low energy interval of 30-300 MeV/N were determined from the measurements made in four different depths of the Cr-39 detector module of 150 layers. From these studies we obtained sub-iron (Sc-Cr) to iron abundance ratios of 0.8 to 1.2 in 30-300 MeV/N energy range. It is found that these ratios are enhanced by a factor of two as compared to interplanetary ratios of about 0.5. It is shown that the enhancement of the ratio inside the earth's magnetosphere is probably due to the degree of ionization of low energy Sc to Cr and Fe ions in the galactic cosmic rays and to the rigidity filtering effects of the geomagnetic field. Further studies are needed to understand fully the phenomena and their implications.
    Schlagwort(e): SPACE RADIATION
    Materialart: Journal of Astrophysics and Astronomy (ISSN 0250-6335); 15; 1; p. 85-94
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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