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  • 1
    Electronic Resource
    Electronic Resource
    Estimation of Nuclear Explosion Energies from Microbarograph Records (1971)
    [s.l.] : Nature Publishing Group
    Nature 232 (1971), S. 253-253 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The various points shown in Fig. 1 correspond to individual microbarograms recorded at Pasadena, California; Berkeley, California; Terceiva, Azores; Fletcher's Ice Island; Whip-pany, New Jersey; Ewa Beach, Hawaii, and Palisades, New York, after the Soviet explosions of (a) September 10 (10 MT), (b) ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/232253a0
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    Paper (German National Licenses)
    Fulltext
  • 2
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    Variation of nuclear explosion generated acoustic-gravity wave forms with burst height and with energy yield (1971)
    American Geophysical Union
    Details
    Publication Date: 1971-07-20
    Print ISSN: 0148-0227
    Electronic ISSN: 2156-2202
    Topics: Geosciences
    Published by American Geophysical Union
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    PAPER CURRENT
  • 3
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    Reply [to “Comments on paper by A. D. Pierce, J. W. Posey, and E. F. Iliff, ‘Variation of nuclear explosion generated acoustic-gravity wave forms with burst height and energy yield’”] (1973)
    American Geophysical Union
    Details
    Publication Date: 1973-11-20
    Print ISSN: 0148-0227
    Electronic ISSN: 2156-2202
    Topics: Geosciences
    Published by American Geophysical Union
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    PAPER CURRENT
  • 4
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    Estimation of Nuclear Explosion Energies from Microbarograph Records (1971)
    Springer Nature
    Details
    Publication Date: 1971-07-01
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Springer Nature
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    PAPER CURRENT
  • 5
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    High Temperature Acoustic Liner Technology (1999)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: This paper describes work currently in progress at Langley on liner concepts that employ structures that may be suitable for broadband exhaust noise attenuation in high speed flow environments and at elevated temperatures characteristic of HSCT applications. Because such liners will need to provide about 10 dB suppression over a 2 to 3 octave frequency range, conventional single-degree-of-freedom resonant structures will not suffice. Bulk absorbers have the needed broadband absorption characteristic; however, at lower frequencies they tend to be inefficient.
    Keywords: Aircraft Propulsion and Power
    Type: First NASA/Industry High Speed Research Program Nozzle Symposium; 34-1 - 34-17; NASA/CP-1999-209423
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 6
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    Quantification of Inlet Impedance Concept and a Study of the Rayleigh Formula for Noise Radiation from Ducted Fan Engines (2004)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: This paper addresses two aspects of duct propagation and radiation which can contribute to more efficient fan noise predictions. First, we assess the effectiveness of Rayleigh's formula as a ducted fan noise prediction tool. This classical result which predicts the sound produced by a piston in a flanged duct is expanded to include the uniform axial inflow case. Radiation patterns using Rayleigh's formula with single radial mode input are compared to those obtained from the more precise ducted fan noise prediction code TBIEM3D. Agreement between the two methods is excellent in the peak noise regions both forward and aft. Next, we use TBIEM3D to calculate generalized radiation impedances and power transmission coefficients. These quantities are computed for a wide range of operating parameters. Results were obtained for higher Mach numbers, frequencies, and circumferential mode orders than have been previously published. Viewed as functions of frequency, calculated trends in lower order inlet impedances and power transmission coefficients are in agreement with known results. The relationships are more oscillatory for higher order modes and higher Mach numbers.
    Keywords: Aircraft Propulsion and Power
    Type: AIAA Paper 98-2248 , 4th AIAA/CEAS Aeroacoustics Conference; Jun 02, 1998 - Jun 04, 1998; Toulouse; France
    Format: application/pdf
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  • 7
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    Turbofan Duct Propagation Model (2001)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    Description: The CDUCT code utilizes a parabolic approximation to the convected Helmholtz equation in order to efficiently model acoustic propagation in acoustically treated, complex shaped ducts. The parabolic approximation solves one-way wave propagation with a marching method which neglects backwards reflected waves. The derivation of the parabolic approximation is presented. Several code validation cases are given. An acoustic lining design process for an example aft fan duct is discussed. It is noted that the method can efficiently model realistic three-dimension effects, acoustic lining, and flow within the computational capabilities of a typical computer workstation.
    Keywords: Acoustics
    Type: NASA/CR-2001-211245 , NAS 1.26:211245
    Format: application/pdf
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  • 8
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    A Fast Method of Deriving the Kirchhoff Formula for Moving Surfaces (2007)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The Kirchhoff formula for a moving surface is very useful in many wave propagation problems, particularly in the prediction of noise from rotating machinery. Several publications in the last two decades have presented derivations of the Kirchhoff formula for moving surfaces in both time and frequency domains. Here we present a method originally developed by Farassat and Myers in time domain that is both simple and direct. It is based on generalized function theory and the useful concept of imbedding the problem in the unbounded three-dimensional space. We derive an inhomogeneous wave equation with the source terms that involve Dirac delta functions with their supports on the moving data surface. This wave equation is then solved using the simple free space Green's function of the wave equation resulting in the Kirchhoff formula. The algebraic manipulations are minimal and simple. We do not need the Green's theorem in four dimensions and there is no ambiguity in the interpretation of any terms in the final formulas. Furthermore, this method also gives the simplest derivation of the classical Kirchhoff formula which has a fairly lengthy derivation in physics and applied mathematics books. The Farassat-Myers method can be used easily in frequency domain.
    Keywords: Acoustics
    Type: 154th Meeting of the Acoustical Society of America; Nov 27, 2007 - Dec 01, 2007; New Orleans, LA; United States
    Format: application/pdf
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  • 9
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    Aeroacoustics Research Program (2005)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Since its inception in January 2003, the program has provided support for 1 faculty and 1 graduate student researcher. One Graduate Research Scholar Assistant was partially supported by this award. One student has completed his M.S. degree program and 1 has nearly completed the D.Sc. degree program (expected completion Fall 2005). The program has generated 1 D.Sc. dissertation. 1 M.S. theses and 2 publications.
    Keywords: Social and Information Sciences (General)
    Format: text
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    NASA TECHNICAL REPORTS
  • 10
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    The Low-Noise Potential of Distributed Propulsion on a Catamaran Aircraft (2006)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The noise shielding potential of an inboard-wing catamaran aircraft when coupled with distributed propulsion is examined. Here, only low-frequency jet noise from mid-wing-mounted engines is considered. Because low frequencies are the most difficult to shield, these calculations put a lower bound on the potential shielding benefit. In this proof-of-concept study, simple physical models are used to describe the 3-D scattering of jet noise by conceptualized catamaran aircraft. The Fast Scattering Code is used to predict noise levels on and about the aircraft. Shielding results are presented for several catamaran type geometries and simple noise source configurations representative of distributed propulsion radiation. Computational analyses are presented that demonstrate the shielding benefits of distributed propulsion and of increasing the width of the inboard wing. Also, sample calculations using the FSC are presented that demonstrate additional noise reduction on the aircraft fuselage by the use of acoustic liners on the inboard wing trailing edge. A full conceptual aircraft design would have to be analyzed over a complete mission to more accurately quantify community noise levels and aircraft performance, but the present shielding calculations show that a large acoustic benefit could be achieved by combining distributed propulsion and liner technology with a twin-fuselage planform.
    Keywords: Acoustics
    Type: AIAA Paper 2006-2622 , 12th AIAA/CEAS Aeroacoustics Conference; May 08, 2006 - May 10, 2006; Cambridge, MA; United States
    Format: application/pdf
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