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  • 1
    Publication Date: 2018-12-01
    Description: The interior noise of aircraft powered by advanced turbo-prop concepts is likely to have nonnegligible contributions from structureborne paths, these paths being those involving propeller loads transmitted to the structures of the lifting surfaces. As a means of examining these paths, structural measurements have been performed on a small twin-engine aircraft, and in addition analytical models of the structure have been developed. In this paper results from both portions of this study are presented.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: AIAA PAPER 86-1905
    Format: text
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  • 2
    Publication Date: 2013-08-31
    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: NAS 1.26:4137 , NASA-CR-4137 , U-1541-349-PT-2
    Format: application/pdf
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  • 3
    Publication Date: 2013-08-31
    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: NAS 1.26:4136 , NASA-CR-4136 , U-1541-349-PT-1
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  • 4
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    In:  CASI
    Publication Date: 2013-08-31
    Description: The acoustic field generated by a circular jet in the presence of a low speed crossflow is calculated. The solution is obtained for a quadrupole source located in a uniformly moving acoustic medium. Ribner's work on straight jets is used to model the flow in the turbulent crossflow jet. The movement of the acoustic medium results in the acoustic intensity being greater upstream of the jet flow than at an equal distance downstream. A summary is also presented of the analysis for the acoustic intensity of a crossflow jet which is in motion through a stationary acoustic medium. The analysis is applicable to the noise generated by the lift jet of a V/STOL aircraft under take-off or landing conditions. The results of these two configurations provide a comparision of the directional distribution of acoustic intensity measured in a wind tunnel test of a crossflow jet and in a corresponding flight test.
    Keywords: AIRCRAFT
    Type: NASA-CR-2169
    Format: application/pdf
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  • 5
    Publication Date: 2013-08-31
    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
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  • 6
    Publication Date: 2018-12-01
    Description: Reported calculations of structure-borne cabin noise for a small twin engine aircraft powered by tractor propellers rely on the following three-stage methodological breakup of the problem: (1) the unsteady-aerodynamic prediction of wing lift harmonics caused by the whipping action of the vortex system trailed from each propeller; (2) the associated wing/fuselage structural response; (3) the cabin noise field for the computed wall vibration. The first part--the estimate of airloads--skirts a full-fledged aeroelastic situation by assuming the wing to be fixed in space while cancelling the downwash field of the cutting vortices. The model is based on an approximate high-frequency lifting-surface theory justified by the blade rate and flight Mach number of application. Its results drive a finite-element representation of the wing accounting for upper and lower skin surfaces, spars, ribs, and the presence of fuel. The fuselage, modeled as a frame-stiffened cylindrical shell, is bolted to the wing.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: AIAA PAPER 87-2681
    Format: text
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  • 7
    Publication Date: 2011-08-16
    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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  • 8
    Publication Date: 2013-08-31
    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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  • 9
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    In:  Other Sources
    Publication Date: 2011-12-21
    Description: The burning behavior of pressed binderless HMX laterally confined in 6.4 mm i.d. steel cases was measured over the pressure range 1.45 to 338 MPa in a constant pressure strand burner. The measured regression rates are compared to those reported previously for unconfined samples. It is shown that lateral confinement results in a several-fold decrease in the regression rate for the coarse particle size HMX above the transition to super fast regression. For class E samples, confinement shifts the transition to super fast regression from low pressure to high pressure. These results are interpreted in terms of the previously proposed progressive deconsolidation mechanism. Preliminary holographic photography and closed bomb tests are also described. Theoretical one dimensional modeling calculations were carried out to predict the expected flame height (particle burn out distance) as a function of particle size and pressure for binderless HMX burning by a progressive deconsolidation mechanism.
    Keywords: PROPELLANTS AND FUELS
    Type: NASA. Langley Res. Center The 17th JANNAF Combust. Meeting, Vol. 2,; p 413-429
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  • 10
    Publication Date: 2017-06-27
    Description: Buoyant Venus station mission study for 1972 - 1973 launch period - backup data including atmospheric models, heat shield requirements, etc.
    Keywords: SPACE VEHICLES
    Type: NASA-CR-66725-4
    Format: application/pdf
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