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  • 1
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    Two-component phase-averaged turbulence statistics downstream of a rotating spoked-wheel wake generator (1989)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Flow-field measurements of unsteady turbulent flow downstream of a rotating spoked-wheel wake generator were performed in a short-duration light-piston tunnel, and the instantaneous-velocity data were phase averaged based on a signal synchronized with the bar-passing frequency. Mean axial velocities were found to agree well with those obtained from measurements behind a stationary cylinder and to be independent of both Reynolds and bar-passing Strouhal numbers. Reynolds stresses were found to be consistent with related cylinder-wake measurements, but were significantly higher than corresponding measurements obtained in large-scale research turbomachines. Phase-averaged triple velocity correlations were calculated from the digital velocity records, revealing the sign and the magnitude of skewness in the velocity probability density distributions for the two components.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: ASME, Transactions, Journal of Turbomachinery (ISSN 0889-504X); 111; 475-482
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  • 2
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    Design and implementation of active members for precision space structures (1992)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: This paper describes the development and implementation of an active member in a precision truss structure. The active member utilizes a piezoelectric actuator motor imbedded in a steel case with built-in displacement sensor. This active member is used in structural quieting. Collocated active damping control loops are designed in order to impedance match piezoelectric active members to the structure. Results from application of these controllers and actuators to the JPL Phase B testbed are given.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: AIAA PAPER 92-1202
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  • 3
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    Control Technology Readiness for Spaceborne Optical Interferometer Missions (1997)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Description: This paper describes the Micro-Precision Interferometer (MPI) testbed and its major achievements to date related to mitigating risk for future spaceborne optical interferometer missions.
    Keywords: Instrumentation and Photography
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  • 4
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    An introduction to wavelet analysis in oceanography and meteorology - With application to the dispersion of Yanai waves (1993)
    In:  Other Sources
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    Publication Date: 2019-08-27
    Description: Wavelet analysis is a relatively new technique that is an important addition to standard signal analysis methods. Unlike Fourier analysis that yields an average amplitude and phase for each harmonic in a dataset, the wavelet transform produces an instantaneous estimate or local value for the amplitude and phase of each harmonic. This allows detailed study of nonstationary spatial or time-dependent signal characteristics. The wavelet transform is discussed, examples are given, and some methods for preprocessing data for wavelet analysis are compared. By studying the dispersion of Yanai waves in a reduced gravity equatorial model, the usefulness of the transform is demonstrated. The group velocity is measured directly over a finite range of wavenumbers by examining the time evolution of the transform. The results agree well with linear theory at higher wavenumber but the measured group velocity is reduced at lower wavenumbers, possibly due to interaction with the basin boundaries.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Monthly Weather Review (ISSN 0027-0644); 121; 10; p. 2858-2866.
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  • 5
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    Numerical simulation of topographically forced mesoscale variability in a well-mixed marine layer (1992)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: A simple nonlinear numerical model of a well-mixed marine layer is employed to examine topographically forced mesoscale variability off coastal California. This model is utilized to simulate a persistent wind maximum observed near Point Conception during northwesterly winds. The model solves for the two horizontal components of the marine-layer height and the marine-layer wind.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Monthly Weather Review (ISSN 0027-0644); 120; 12; p. 2881-2896.
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  • 6
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    The sensitivity to parametric variation in direct minimization techniques (1994)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Solutions of some objective analysis techniques are known to depend upon the subjective values of internal parameters. The change in the solution per change in the parameter is the sensitivity. Parameters with low sensitivity can be varied with large increments during preliminary searches for near-optimal parameter values. Only terms with high sensitivity must be thoroughly investigated once the parameters are determined to be close to optimal. Both absolute and relative sensitivities are discussed and a sensitivity-based definition of the solution uncertainty is proposed. The sensitivity of direct minimization analysis to parametric variation is evaluated using a set of 'response functions' that characterize different aspects of the solution. It is shown that solutions of direct minimization techniques have low absolute sensitivity. Two examples are used to illustrate the usefulness of the technique. Both involved measurements of air-sea quantities (e.g., wind stress and latent heat flux) from a variety of data sources using a direct minimization technique. The examples demonstrate that sensitivity analysis is capable of quantifying regional sensitivities as well as indicating the magnitude and relationship between the various parameters.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Monthly Weather Review (ISSN 0027-0644); 122; 7; p. 1632-1639
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  • 7
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    Development of Advanced Alloys using Fullerenes (1994)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: Development of advanced alloys using fullerenes is currently underway to produce materials for use in the extravehicular mobility unit (EMU). These materials will be directed toward commercial usages as they are continually developed. Fullerenes (of which the most common is C(sub 60)) are lightweight, nanometer size, hollow molecules of carbon which can be dispersed in conventional alloy systems to enhance strength and reduce weight. In this research, fullerene interaction with aluminum is investigated and a fullerene-reinforced aluminum alloy is being developed for possible use on the EMU. The samples were manufactured using standard commercial approaches including powder metallurgy and casting. Alloys have been processed having 1.3, 4.0 and 8.0 volume fractions of fullerenes. It has been observed that fullerene dispersion is related to the processing approach and that they are stable for the processing conditions used in this research. Emphasis will be given to differential thermal analysis and wavelength dispersive analysis of the processed alloys. These two techniques are particularly useful in determining the condition of the fullerenes during and after processing. Some discussion will be given as to electrical properties of fullerene-reinforced materials. Although the aluminum and other advanced alloys with fullerenes are being developed for NASA and the EMU, the properties of these materials will be of interest for commercial applications where specific Dual-Use will be given.
    Keywords: Metallic Materials
    Type: Dual-Use Space Technology Transfer Conference and Exhibition; 1; 335-346; NASA-CP-3263-Vol-1
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  • 8
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    System identification and control of the JPL active structure (1991)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: This paper describes recent advances in structural quieting technology as applied to active truss structures intended for high precision space based optics applications. Collocated active damping control loops are designed in order to impedance match piezoelectric active members to the structure. Noncollocated control loops are also studied in relation to controlling lightly damped structures.
    Keywords: CYBERNETICS
    Type: AIAA PAPER 91-1231 , AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference; Apr 08, 1991 - Apr 10, 1991; Baltimore, MD; United States
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  • 9
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    Heat transfer in gas turbine engines and three-dimensional flows; Proceedings of the Symposium, ASME Winter Annual Meeting, Chicago, IL, Nov. 27-Dec. 2, 1988 (1988)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The present conference on heat transfer characteristics of gas turbines and three-dimensional flows discusses velocity-temperature fluctuation correlations at the flow stagnation flow of a circular cylinder in turbulent flow, heat transfer across turbulent boundary layers with pressure gradients, the effect of jet grid turbulence on boundary layer heat transfer, and heat transfer characteristics predictions for discrete-hole film cooling. Also discussed are local heat transfer in internally cooled turbine airfoil leading edges, secondary flows in vane cascades and curved ducts, three-dimensional numerical modeling in gas turbine coal combustor design, numerical and experimental results for tube-fin heat exchanger airflow and heating characteristics, and the computation of external hypersonic three-dimensional flow field and heat transfer characteristics.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: ASME Winter Annual Meeting; Nov 27, 1988 - Dec 02, 1988; Chicago, IL; United States
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  • 10
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    Some characteristics of bypass transition in a heated boundary layer (1989)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Experimental measurements of both mean and conditionally sampled characteristics of laminar, transitional and low Reynolds number turbulent boundary layers on a heated flat plate are presented. Measurements were obtained in air over a range of freestream turbulence intensities from 0.3 percent to 6 percent with a freestream velocity of 30.5 m/s and zero pressure gradient. Conditional sampling performed in the transitional boundary layers indicate the existence of a near-wall drop in intermittency, especially pronounced at low intermittencies. Nonturbulent intervals were observed to possess large levels of low-frequency unsteadiness, and turbulent intervals had peak intensities as much as 50 percent higher than were measured at fully turbulent stations. Heat transfer results were consistent with results of previous researches and Reynolds analogy factors were found to be well predicted by laminar and turbulent correlations which accounted for unheated starting length. A small dependence of the turbulent Reynolds analogy factors on freestream turbulence level was observed. Laminar boundary layer spectra indicated selective amplification of unstable frequencies. These instabilities appear to play a dominant role in the transition process only for the lowest freestream turbulence level studied, however.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Symposium on Turbulent Shear Flows; Aug 21, 1989 - Aug 23, 1989; Stanford, CA; United States
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