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  • Other Sources  (39)
  • ACOUSTICS  (37)
  • Aircraft Design, Testing and Performance  (2)
  • Cell & Developmental Biology
  • 1
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    Assessment and design of low boom configurations for supersonic transport aircraft (1992)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: A review is presented of presently utilized sonic boom prediction and minimization techniques. The three-pronged approach - acceptability studies, atmospheric propagation studies, and configuration design and operation, to the sonic boom problem as an element of the High Speed Research Program are discussed. Experimental and theoretical results of concepts designed to validate present minimization methods are given.
    Keywords: ACOUSTICS
    Type: In: DGLR(AIAA Aeroacoustics Conference, 14th, Aachen, Germany, May 11-14, 1992, Proceedings. Vol. 1 (A93-19126 05-71); p. 334-341.
    Format: text
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  • 2
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    Aeroacoustics of large wind turbines (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: This paper reviews published information on aerodynamically generated noise from large horizontal axis wind turbines operated for electric power generation. Methods are presented for predicting both the discrete frequency rotational noise components and the broadband noise components, and results are compared with measurements. Refraction effects that result in the formation of high-frequency shadow zones in the upwind direction and channeling effects for the low frequencies in the downwind direction are illustrated. Special topics such as distributed source effects in prediction and the role of building dynamics in perception are also included.
    Keywords: ACOUSTICS
    Type: Acoustical Society of America, Journal (ISSN 0001-4966); 89; 2495-250
    Format: text
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  • 3
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    Sonic boom acceptability studies (1992)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The determination of the magnitude of sonic boom exposure which would be acceptable to the general population requires, as a starting point, a method to assess and compare individual sonic booms. There is no consensus within the scientific and regulatory communities regarding an appropriate sonic boom assessment metric. Loudness, being a fundamental and well-understood attribute of human hearing was chosen as a means of comparing sonic booms of differing shapes and amplitudes. The figure illustrates the basic steps which yield a calculated value of loudness. Based upon the aircraft configuration and its operating conditions, the sonic boom pressure signature which reaches the ground is calculated. This pressure-time history is transformed to the frequency domain and converted into a one-third octave band spectrum. The essence of the loudness method is to account for the frequency response and integration characteristics of the auditory system. The result of the calculation procedure is a numerical description (perceived level, dB) which represents the loudness of the sonic boom waveform.
    Keywords: ACOUSTICS
    Type: First Annual High-Speed Research Workshop, Part 3; p 1295-1311
    Format: application/pdf
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  • 4
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    Measurement and prediction of broadband noise from large horizontal axis wind turbine generators (1995)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: A method is presented for predicting the broadband noise spectra of large wind turbine generators. It includes contributions from such noise sources as the inflow turbulence to the rotor, the interactions between the turbulent boundary layers on the blade surfaces with their trailing edges and the wake due to a blunt trailing edge. The method is partly empirical and is based on acoustic measurements of large wind turbines and airfoil models. Spectra are predicted for several large machines including the proposed MOD-5B. Measured data are presented for the MOD-2, the WTS-4, the MOD-OA, and the U.S. Windpower Inc. machines. Good agreement is shown between the predicted and measured far field noise spectra.
    Keywords: ACOUSTICS
    Type: DASCON Engineering, Collected Papers on Wind Turbine Technology; p 211-220
    Format: application/pdf
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  • 5
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    Wind turbine acoustics (1990)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Available information on the physical characteristics of the noise generated by wind turbines is summarized, with example sound pressure time histories, narrow- and broadband frequency spectra, and noise radiation patterns. Reviewed are noise measurement standards, analysis technology, and a method of characterizing wind turbine noise. Prediction methods are given for both low-frequency rotational harmonics and broadband noise components. Also included are atmospheric propagation data showing the effects of distance and refraction by wind shear. Human perception thresholds, based on laboratory and field tests, are given. Building vibration analysis methods are summarized. The bibliography of this report lists technical publications on all aspects of wind turbine acoustics.
    Keywords: ACOUSTICS
    Type: NASA-TP-3057 , E-5663 , DOE/NASA/20320-77 , NAS 1.60:3057
    Format: application/pdf
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  • 6
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    Active sound attenuation across a double wall structure (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The possibility of achieving significant local and global sound attenuation across a flat double wall is demonstrated. It is also shown that sound can be prevented from entering the interior of a cabinlike environment. The approach used is unlike established active noise control techniques.
    Keywords: ACOUSTICS
    Type: AIAA PAPER 91-0498
    Format: text
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  • 7
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    Prediction of the far field noise from wind energy farms (1986)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The basic physical factors involved in making predictions of wind turbine noise and an approach which allows for differences in the machines, the wind energy farm configurations and propagation conditions are reviewed. Example calculations to illustrate the sensitivity of the radiated noise to such variables as machine size, spacing and numbers, and such atmosphere variables as absorption and wind direction are presented. It is found that calculated far field distances to particular sound level contours are greater for lower values of atmospheric absorption, for a larger total number of machines, for additional rows of machines and for more powerful machines. At short and intermediate distances, higher sound pressure levels are calculated for closer machine spacings, for more powerful machines, for longer row lengths and for closer row spacings.
    Keywords: ACOUSTICS
    Type: NASA-CR-177956 , NAS 1.26:177956
    Format: application/pdf
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  • 8
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    The Helmholtz resonance behavior of single and multiple rooms (1986)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The results of exploratory measurements of the noise fields inside rooms which are excited to resonance either acoustically or mechanically are presented. The data illustrate the nature and extent of the sound pressure level enhancements in single rooms and also how multiple rooms may resonate by means of either acoustic or mechanical coupling. Sound pressure level enhancements of about 5 dB were measured during resonance of rooms having flexible walls. For such conditions the sound pressure levels in the room were essentially uniform and in phase. Variability of up to 20 dB was measured in a room hallway complex having significant acoustic interactions. Resonant frequency prediction methods which work well at model scale, give only fair results for rooms.
    Keywords: ACOUSTICS
    Type: NASA-CR-178173 , NAS 1.26:178173
    Format: application/pdf
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  • 9
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    Advanced turboprop aircraft noise annoyance - A review of recent NASA research (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Passenger and community response to advanced turboprop aircraft noise are studied. Four experiments were conducted utilizing an aircraft noise synthesis system, an exterior effects room, an anechoic listening room, and a Space Station/aircraft acoustic apparatus; the experimental conditions and procedures for the psychoacoustic studies are described. The community noise studies involved evaluating the effects of various tonal characteristics on annoyance. It was observed that the frequency envelope shape did not effect annoyance; however, the interaction of the fundamental frequency with tone-to-broadband noise ratio did have a large effect on annoyance. The effects of low frequency tones, turbulent boundary layer noise, and tonal beats on passenger annoyance are investigated. The data reveal that passenger annoyance is greater for a given level of boundary layer noise when tones are at levels sufficient to increase the overall sound pressure level within the cabin. The annoyance response of an advanced turboprop and a conventional aircraft are compared. It is determined that the flyover noise level for the turboprop aircraft is not more annoying than that of a conventional aircraft.
    Keywords: ACOUSTICS
    Type: AIAA PAPER 86-1959
    Format: text
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  • 10
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    A new version of the helicopter aural detection program, ICHIN (1986)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: NASA Langley Research Center personnel have conducted an evaluation of the helicopter aural detection program I Can Hear It Now (ICHIN version-5). This was accomplished using flight noise data of five helicopters, obtained from a joint NASA and U.S. Army acoustics measurement program. The evaluation consisted of presenting the noise data to a jury of 20 subjects and to the ICHIN-5 program. A comparative study was then made of the detection distances determined by the jury and predicted by ICHIN-5. This report presents the changes made in the ICHIN-5 program as a result of this comparative study. The changes represent current psychoacoustics and propagation knowledge.
    Keywords: ACOUSTICS
    Type: NASA-TM-87745 , NAS 1.15:87745
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