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  • 1
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    Structureborne noise measurements on a small twin-engine aircraft (1988)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Structureborne noise measurements performed on a twin-engine aircraft (Beechcraft Baron) are reported. There are two overall objectives of the test program. The first is to obtain data to support the development of analytical models of the wing and fuselage, while the second is to evaluate effects of structural parameters on cabin noise. Measurements performed include structural and acoustic responses to impact excitation, structural and acoustic loss factors, and modal parameters of the wing. Path alterations include added mass to simulate fuel, variations in torque of bolts joining wing and fuselage, and increased acoustic absorption. Conclusions drawn regarding these measurements are presented.
    Keywords: ACOUSTICS
    Type: NASA-CR-4137 , NAS 1.26:4137 , U-1541-349-PT-2
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    Analytical model of the structureborne interior noise induced by a propeller wake (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The structure-borne contribution to the interior noise that is induced by the propeller wake acting on the wing was studied. Analytical models were developed to describe each aspect of this path including the excitation loads, the wing and fuselage structures, and the interior acoustic space. The emphasis is on examining a variety of parameters, and as a result different models were developed to examine specific parameters. The excitation loading on the wing by the propeller wake is modeled by a distribution of rotating potential vortices whose strength is related to the thrust per blade. The response of the wing to this loading is examined using beam models. A model of a beam structurally connected to a cylindrical shell with an internal acoustic fluid was developed to examine the coupling of energy from the wing to the interior space. The model of the acoustic space allows for arbitrary end conditions (e.g., rigid or vibrating end caps). Calculations are presented using these models to compare with a laboratory test configuration as well as for parameters of a prop-fan aircraft.
    Keywords: ACOUSTICS
    Type: NASA-CR-172381 , NAS 1.26:172381
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Analytical modeling of the structureborne noise path on a small twin-engine aircraft (1988)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The structureborne noise path of a six passenger twin-engine aircraft is analyzed. Models of the wing and fuselage structures as well as the interior acoustic space of the cabin are developed and used to evaluate sensitivity to structural and acoustic parameters. Different modeling approaches are used to examine aspects of the structureborne path. These approaches are guided by a number of considerations including the geometry of the structures, the frequency range of interest, and the tractability of the computations. Results of these approaches are compared with experimental data.
    Keywords: ACOUSTICS
    Type: NASA-CR-4136 , NAS 1.26:4136 , U-1541-349-PT-1
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    Acoustic power of a moving point source in a moving medium (1976)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: The acoustic power output of a moving point-mass source in an acoustic medium which is in uniform motion and infinite in extent is examined. The acoustic medium is considered to be a homogeneous fluid having both zero viscosity and zero thermal conductivity. Two expressions for the acoustic power output are obtained based on a different definition cited in the literature for the average energy-flux vector in an acoustic medium in uniform motion. The acoustic power output of the source is found by integrating the component of acoustic intensity vector in the radial direction over the surface of an infinitely long cylinder which is within the medium and encloses the line of motion of the source. One of the power expressions is found to give unreasonable results even though the flow is uniform.
    Keywords: ACOUSTICS
    Type: Acoustical Society of America; vol. 60
    Format: text
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  • 5
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    Investigation of the effects of a moving acoustic medium on jet noise measurements (1976)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Noise from an unheated sonic jet in the presence of an external flow is measured in a free-jet wind tunnel using microphones located both inside and outside the flow. Comparison of the data is made with results of similar studies. The results are also compared with theoretical predictions of the source strength for jet noise in the presence of flow and of the effects of sound propagation through a shear layer.
    Keywords: ACOUSTICS
    Type: NASA-CR-152038
    Format: application/pdf
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  • 6
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    Sound propagation from a simple source in a wind tunnel (1975)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The nature of the acoustic field of a simple source in a wind tunnel under flow conditions was examined theoretically and experimentally. The motivation of the study was to establish aspects of the theoretical framework for interpreting acoustic data taken (in wind) tunnels using in wind microphones. Three distinct investigations were performed and are described in detail.
    Keywords: ACOUSTICS
    Type: NASA-CR-145608
    Format: application/pdf
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    NASA TECHNICAL REPORTS
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