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  • 1
    Electronic Resource
    Electronic Resource
    A SPACE-TIME FINITE ELEMENT METHOD FOR THE EXTERIOR STRUCTURAL ACOUSTICS PROBLEM: TIME-DEPENDENT RADIATION BOUNDARY CONDITIONS IN TWO SPACE DIMENSIONS (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 1635-1657 
    Details
    ISSN: 0029-5981
    Keywords: finite element method ; radiation boundary conditions ; absorbing boundary conditions ; discontinuous Galerkin method ; structural acoustics ; wave equation ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A time-discontinuous Galerkin space-time finite element method is formulated for the exterior structural acoustics problem in two space dimensions. The problem is posed over a bounded computational domain with local time-dependent radiation (absorbing) boundary conditions applied to the fluid truncation boundary. Absorbing boundary conditions are incorporated as ‘natural’ boundary conditions in the space-time variational equation, i.e. they are enforced weakly in both space and time. Following Bayliss and Turkel, time-dependent radiation boundary conditions for the two-dimensional wave equation are developed from an asymptotic approximation to the exact solution in the frequency domain expressed in negative powers of a non-dimensional wavenumber. In this paper, we undertake a brief development of the time-dependent radiation boundary conditions, establishing their relationship to the exact impedance (Dirichlet-to-Neumann map) for the acoustic fluid, and characterize their accuracy when implemented in our space-time finite element formulation for transient structural acoustics. Stability estimates are reported together with an analysis of the positive form of the matrix problem emanating from the space-time variational equations for the coupled fluid-structure system. Several numerical simulations of transient radiation and scattering in two space dimensions are presented to demonstrate the effectiveness of the space-time method.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 2
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    Increased power to weight ratio of piezoelectric energy harvesters through integration of cellular honeycomb structures (2016)
    Institute of Physics
    Details
    Publication Date: 2016-03-14
    Print ISSN: 0964-1726
    Electronic ISSN: 1361-665X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Published by Institute of Physics
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    PAPER CURRENT
  • 3
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    Noise spectra for monolithic detector arrays (1978)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: Following a brief review of nonstationary processes, the paper deals with mixed stationary processes as they apply to the determination of the power density spectrum for monolithic detector arrays. A rather direct method is developed for realizing the noise power spectrum by transforming the corresponding autocorrelation function. Although the measurements presented pertain to a 96-element photodiode linear array, the method outlined should be applicable to any monolithic device. Theoretical and experimental results are provided.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: IEEE Transactions on Instrumentation and Measurement; IM-27; Sept
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
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    Time-delay-and-integration charge-coupled devices using tin oxide gate technology (1978)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: Doped tin oxide gates are used in a time-delay-and-integration (TDI) CCD scheme in an effort to develop a stable transparent gate technology. Design characteristics of the system are discussed, including 2 sections of 10 by 9 integration stages, four-phase buried channel construction, and 10 input parallel-in/serial-out output shift register at a video rate of 1.25 MHz. A quantum efficiency of 65% with smooth spectral response is attained by front surface imaging. The suitability of the system for the Landsat program is discussed in terms of TDI-CCD operating parameters.
    Keywords: SPACECRAFT INSTRUMENTATION
    Type: IEEE Transactions on Electron Devices; ED-25; Feb. 197
    Format: text
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    NASA TECHNICAL REPORTS
  • 5
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    A design study for an advanced ocean color scanner system (1980)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: Along with a colorimetric data analysis scheme, the instrumental parameters which need to be optimized in future spaceborne ocean color scanner systems are outlined. With regard to assessing atmospheric effects from ocean colorimetry, attention is given to computing size parameters of the aerosols in the atmosphere, total optical depth measurement, and the aerosol optical thickness. It is suggested that sensors based on the use of linear array technology will meet hardware objectives.
    Keywords: SPACECRAFT INSTRUMENTATION
    Format: text
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    NASA TECHNICAL REPORTS
  • 6
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    Remote sensing using solid-state array technology (1979)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: The paper describes the design features and capabilities of a remote sensor that uses solid-state linear arrays and operates in a 'pushbroom' scan mode to provide the required performance. Pushbroom scanning is a term describing the technique of using the forward motion of a satellite platform to sweep a linear array of detectors oriented perpendicular to the ground track across a scene being imaged. One array is typically used for each spectral channel. Satellite motion provides one direction of scan and electronic sampling of the detectors in the crosstrack dimension provides the orthogonal scan component to form an image. The detector array is sampled at the appropriate rate so that contiguous lines are produced. The performance of a pushbroom system is discussed relative to radiometric sensitivity, detector array geometric fidelity, and radiometric correction. System advantages are precision geometric positioning of the detectors, very high sensitivity and favorable SNR, low power consumption, and no moving optics.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Format: text
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    NASA TECHNICAL REPORTS
  • 7
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    On-board radiometric preprocessing for multispectral linear arrays /MLA/ (1979)
    In:  Other Sources
    Details
    Publication Date: 2019-07-27
    Description: A program that was undertaken to design, fabricate, and test a real-time hardwired data preprocessor is described, which applies a calibration normalization to each detector in a 576-element linear photodiode array. Various calibration problems were uncovered, such as those (1) due to system noise in recording the calibration tables, or (2) due to thermal drift and (3) due to the original quantization process. It was determined that in this experiment, noise and thermal drift led to fixed errors in the normalization of responses on the order of + or - 10 counts, out of 255 counts for many of the detectors.
    Keywords: SPACECRAFT INSTRUMENTATION
    Type: Smart sensors; April 17, 18, 1979; Washington, D. C.
    Format: text
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    NASA TECHNICAL REPORTS
  • 8
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    Frequency-wavelength calculator with table of dielectric properties (1972)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Frequency-wavelength calculator has been developed which rapidly and accurately calculates wavelength of given frequency in specific dielectric material. Unit fits into shirt pocket and includes table of dielectric properties and one-step calculator.
    Keywords: PHYSICAL SCIENCES
    Type: GSC-11200
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 9
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    Multispectral Resource Sampler - An experimental satellite sensor for the mid-1980s (1979)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: An experimental pushbroom scan sensor, the Multispectral Resource Sampler (MRS), being developed by NASA for a future earth orbiting flight is presented. This sensor will provide new earth survey capabilities beyond those of current sensor systems, with a ground resolution of 15 m over a swath width of 15 km in four bands. The four arrays are aligned on a common focal surface requiring no beamsplitters, thus causing a spatial separation on the ground which requires computer processing to register the bands. Along track pointing permits stereo coverage at variable base/height ratios and atmospheric correction experiments, while across track pointing will provide repeat coverage, from a Landsat-type orbit, of every 1 to 3 days. The MRS can be used for experiments in crop discrimination and status, rock discrimination, land use classification, and forestry.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Space optics; May 22, 1979 - May 24, 1979; Huntsville, AL
    Format: text
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    NASA TECHNICAL REPORTS
  • 10
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    Technical issues in focal plane development for terrestrial resource observations (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Performance goals for solid-state detector arrays operating in the pushbroom scan mode for the high-resolution, high-accuracy remote sensing of earth resources from space are discussed and some of the focal plane and system trades involved are identified. Issues in the development of solid-state pushbroom arrays with radiometric calibration to 0.5% precision detector-to-detector over a dynamic range of 1000:1 are considered, with calibration, temporal stability and spectral response conditions noted. Factors influencing the geometric precision of satellite-borne pushbroom scan mode sensors are then examined, including satellite orbit track and attitude errors, and geometric and radiometric correlation between information in the various spectral bands. Approaches to the alignment of linear arrays of thousands of detectors are then discussed that take into account tradeoffs between fabrication and test complexity and ground processing requirements. Continuing science experiments are indicated as necessary to establish tolerances on performance goals.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Technical issues in focal plane development; Apr 21, 1981 - Apr 22, 1981; Washington, DC
    Format: text
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    NASA TECHNICAL REPORTS
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