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  • 1
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    A general low frequency acoustic radiation capability for NASTRAN (1986)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: A new capability called NASHUA is described for calculating the radiated acoustic sound pressure field exterior to a harmonically-excited arbitrary submerged 3-D elastic structure. The surface fluid pressures and velocities are first calculated by coupling a NASTRAN finite element model of the structure with a discretized form of the Helmholtz surface integral equation for the exterior fluid. After the fluid impedance is calculated, most of the required matrix operations are performed using the general matrix manipulation package (DMAP) available in NASTRAN. Far field radiated pressures are then calculated from the surface solution using the Helmholtz exterior integral equation. Other output quantities include the maximum sound pressure levels in each of the three coordinate planes, the rms and average surface pressures and normal velocities, the total radiated power and the radiation efficiency. The overall approach is illustrated and validated using known analytic solutions for submerged spherical shells subjected to both uniform and nonuniform applied loads.
    Keywords: ACOUSTICS
    Type: COSMIC 14th NASTRAN (R) Users' Colloquium; p 293-310
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    The effect of operations on the ground noise footprints associated with a large multibladed, nonbanging helicopter (1978)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: In order to expand the data base of helicopter external noise characteristics, a flyover noise measurement program was conducted utilizing the NASA Civil Helicopter Research Aircraft. The remotely operated multiple array acoustics range (ROMAAR) and a 2560-m linear microphone array were utilized for the purpose of documenting the noise characteristics of the test helicopter during flyby and landing operations. By utilizing both ROMAAR concept and the linear array, the data necessary to plot the ground noise footprints and noise radiation patterns were obtained. Examples of the measured noise signature of the test helicopter, the ground noise footprint or contours, and the directivity patterns measured during level flyby and landing operations of a large, multibladed, nonbanging helicopter, the CH-53, are presented.
    Keywords: ACOUSTICS
    Type: Helicopter Acoustics, Pt. 2; p 519-533
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    On the tones of round choked jets impinging on normal flat plates (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: An experimental investigation of the sound produced by an axisymmetric supersonic jet impinging on plates with variable size and nozzle-to-plate spacings was performed. Spectral analysis and schlieren photography were used to determine the sound characteristics and flow disturbances associated with the production of discrete tones. Two classes of tones, associated with small and large plates, existed for pressure ratios above 2.70. For lower pressure ratios, however, only large plate tones occurred for all plate sizes with choked jet screech appearing at the largest spacings. Reflector tests indicated that both classes of tones were part of a feedback loop to the nozzle. Schlieren photography revealed both symmetric and asymmetric disturbances in the large plate jet flows which corresponded to symmetrical and helical modes of oscillation in the cross-spectrum studies. In addition to this, both symmetric and asymmetric oscillations of the shock waves occurred in the large plate case while symmetric oscillations of the shock wave occurred in the small plate case.
    Keywords: ACOUSTICS
    Type: AIAA PAPER 90-3985
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
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    Correlation of predicted and measured sonic boom characteristics from the reentry of STS-1 orbiter (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Characteristics from sonic boom pressure signatures recorded at 11 locations during reentry of the Space Shuttle Orbiter Columbia are correlated with characteristics of wind tunnel signatures extrapolated from flight altitudes for Mach numbers ranging from 1.23 to 5.87. The flight pressure signature were recorded by microphones positioned at two levels near the descent groundtrack along the California corridor. The wind tunnel signatures used in theoretical predictions were measured using a 0.0041-scale model Orbiter. The mean difference between all measured and predicted overpressures is 12 percent from measured levels. With one exception, the flight signatures are very similar to theoretical n-waves.
    Keywords: ACOUSTICS
    Type: NASA-TP-2475 , S-544 , NAS 1.60:2475
    Format: application/pdf
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  • 5
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    Sonic boom measurement test plan for Space Shuttle STS-1 reentry (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Formal documentation for measurement procedures and system specifications, and general information are relating to the Space Shuttle STS-1 Sonic Boom Measurement Program are supplied. This test plan is designed to provide information, guidance, and assignment of responsibilities for the acquisition of sonic boom and atmospheric measurements, timing correlation, communications and other necessary supporting tasks. Specifically included are details such as mobile data acquisition station locations, measurement systems calibration levels, predicted sonic boom overpressure levels, overpressure level assignment for each data acquisition station, data recording times on and off, universal coordinated time, and measurement system descriptions.
    Keywords: ACOUSTICS
    Type: NASA-TM-85222 , NAS 1.15:85222
    Format: application/pdf
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  • 6
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    Sonic boom measurement test plan for Space Shuttle STS-4 reentry (1982)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Formal documentation for measurement procedures and system specifications, and general information relating to the Space Shuttle STS-4 Sonic Boom Measurement Program are supplied. This test plan is designed to provide information, guidance, and assignment of responsibilities for the acquisition of sonic boom and atmospheric measurements, timing correlation, communications and other necessary supporting tasks. Specifically included are details such as mobile data acquisition station locations, measurement systems calibration levels, predicted sonic boom overpressure levels, overpressure level assignment for each data acquisition station, data recording times on and off, universal coordinated time, and measurement system descriptions.
    Keywords: ACOUSTICS
    Type: NASA-TM-85224 , NAS 1.15:85224
    Format: application/pdf
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  • 7
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    Sonic boom measurement test plan for Space Shuttle STS-3 reentry (1982)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The lateral area from the reentry ground track affected by sonic boom overpressure levels is determined. Four data acquisition stations are deployed laterally to the STS-3 reentry flight track. These stations provide six intermediate band FM channels of sonic boom data, universal time synchronization, and voice annotation. All measurements are correlated with the vehicle reentry flight track information along with atmospheric and vehicle operation conditions.
    Keywords: ACOUSTICS
    Type: NASA-TM-85223 , NAS 1.15:85223
    Format: application/pdf
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  • 8
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    Preliminary sonic boom correlation of predicted and measured levels for STS-1 entry (1982)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A preliminary analysis correlating peaks from sonic boom pressure signatures recorded during the descent trajectory of the Orbiter Columbia, which landed in the dry lake bed at Edwards Air Force Base (EAFB), California, with measured wind tunnel signatures extrapolated from flight altitudes to the ground has been made for Mach numbers ranging from 1.3 to 6. The flight pressure signatures were recorded by microphones positioned at ground level near the groundtrack, whereas the wind tunnel signatures were measured during a test of a 0.0041-scale model Orbiter. The agreement between overpressure estimates based on wind tunnel data using preliminary flight trajectory data and oscillograph traces from ground measurements appears reasonable at this time for the range of Mach numbers considered. More detailed studies using final flight trajectory data and digitized ground measured data will be performed.
    Keywords: ACOUSTICS
    Type: NASA-TM-58242 , S-511 , NAS 1.15:58242
    Format: application/pdf
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  • 9
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    Sonic boom measurement test plan for Space Shuttle STS-5 launch (1982)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Sonic booms measurements are obtained at key locations within the focus region and the lateral attenuation rate during ascent is determined in order to assess the validity of existing capability to predict the extent of focus boom area, the number of booms within the various zones (focus and nonfocus regions), the overpressures, and focus factors. The sonic boom focus region, consists of a region on the ground (in the form of an inverted 'horseshoe' pattern) in which higher than nominal overpressures can occur.
    Keywords: ACOUSTICS
    Type: NASA-TM-85225 , NAS 1.15:85225
    Format: application/pdf
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  • 10
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    Sonic boom measurement test plan for Space Shuttle STS-2 reentry (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Procedures and system specifications associated with the space shuttle STS-2 sonic boom measurement program are described. Specifically included are details such as mobile data acquisition station locations, measurement systems calibration levels, predicted sonic boom overpressure levels, overpressure level assignment for each data acquisition station, data recording times on and off, universal coordinate time, and measurement system descriptions.
    Keywords: ACOUSTICS
    Type: NASA-TM-84858 , NAS 1.15:84858
    Format: application/pdf
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