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  • 1
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    Active control of interior noise in a large scale cylinder using piezoelectric actuators (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The noise reduction effectiveness of two types of control force actuator models has been analytically investigated: (1) a point actuator, and (2) an in-plane, piezoelectric actuator. The actuators were attached to the wall of a simply supported, elastic cylinder closed with rigid end caps. Control inputs to the actuators were determined such that the integrated square of the pressure over the interior of the vibrating cylinder was a minimum. Significant interior noise reductions were achieved for all actuator configurations, but especially for the structurally dominated response. Noise reduction of 9 dB to 26 dB were achieved using point force actuators, as well as localized and extended piezoelectric actuators. Control spillover was found to limit overall performance for all cases. However, the use of extended piezoelectric actuators was effective in reducing control spillover, without increasing the number of control degrees of freedom.
    Keywords: ACOUSTICS
    Type: In: AHS and Royal Aeronautical Society, Technical Specialists' Meeting on Rotorcraft Acoustics(Fluid Dynamics, Philadelphia, PA, Oct. 15-17, 1991, Proceedings (A93-29401 10-71); 18 p.
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  • 2
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    Active control of interior noise in a large scale cylinder using piezoelectric actuators (1992)
    In:  CASI
    Details
    Publication Date: 2013-08-29
    Description: The noise reduction effectiveness of two types of control force actuator models has been analytically investigated: (1) a point actuator, and (2) an in-plane, piezoelectric actuator. The actuators were attached to the wall of a simply supported, elastic cylinder closed with rigid end caps. Control inputs to the actuators were determined such that the integrated square of the pressure over the interior of the vibrating cylinder was a minimum. Significant interior noise reductions were achieved for all actuator configurations, but especially for the structurally dominated response. Noise reduction of 9 dB to 26 dB were achieved using point force actuators, as well as localized and extended piezoelectric actuators. Control spillover was found to limit overall performance for all cases. However, the use of extended piezoelectric actuators was effective in reducing control spillover, without increasing the number of control degrees of freedom.
    Keywords: ACOUSTICS
    Type: Fourth Aircraft Interior Noise Workshop; p 173-190
    Format: text
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  • 3
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    Design and flight test of a Kevlar acoustic liner (1984)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: Previously cited in issue 10, p. 1378, Accession no. A83-25963
    Keywords: AIRCRAFT PROPULSION AND POWER
    Type: Journal of Aircraft (ISSN 0021-8669); 21; 491-497
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  • 4
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    A finite difference solution for the propagation of sound in near sonic flows (1984)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: An explicit time/space finite difference procedure is used to model the propagation of sound in a quasi one-dimensional duct containing high Mach number subsonic flow. Nonlinear acoustic equations are derived by perturbing the time-dependent Euler equations about a steady, compressible mean flow. The governing difference relations are based on a fourth-order, two-step (predictor-corrector) MacCormack scheme. The solution algorithm functions by switching on a time harmonic source and allowing the difference equations to iterate to a steady state. The principal effect of the non-linearities was to shift aocustical energy to higher harmonics. With increased source strength, wave steepening was observed. This phenomenon suggests that the acoustical response may approach a shock behavior at higher sound pressure level as the throat Mach number approaches unity. On a peak level basis, good agreement between the nonlinear finite difference and linear finite element solutions was observed, even through a peak sound pressure level of about 150 dB occurred in the throat region. Nonlinear steady state waveform solutions are shown to be in excellent agreement with a nonlinear asymptotic theory. Previously announced in STAR as N83-30167
    Keywords: ACOUSTICS
    Type: Acoustical Society of America, Journal (ISSN 0001-4966); 75; 1052-106
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  • 5
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    An evaluation of active noise control in a cylindrical shell (1989)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The physical mechanisms governing the use of active noise control in an extended volume of a cylindrical shell are discussed. Measured data was compared with computer results from a previously derived analytical model based on an infinite shell theory. For both the analytical model and experiment, the radiation of the external monopoles is coupled to the internal acoustic field through the radial displacement of the thin, elastic cylindrical shell. An active noise control system was implemented in the cylinder using a fixed array of discrete monopole sources, all of which lie in the plane of the exterior noise sources. Good agreement between measurement and prediction was obtained for both internal pressure response and overall noise reduction. Attenuations in the source plane greater than 15 dB were recorded along with a uniformly quieted noise environment over the entire length of the experimental model. Results indicate that for extended axial forcing distributions or very low shell damping, axial arrays of control sources may be required. Finally, the Nyquist criteria for the number of azimuthal control sources is shown to provide for effective control over the full cylinder cross section.
    Keywords: ACOUSTICS
    Type: ASME, Transactions, Journal of Vibration, Acoustics, Stress, and Reliability in Design (ISSN 0739-3717); 111; 337-342
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  • 6
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    Modal coupling and acoustic intensity measurements (1989)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Acoustic-intensity measurement techniques for highly resonant coupled structural-acoustic systems are discussed. Frequency-averaging effects are shown to cause inaccurate results in such systems, and it is recommended that the analysis bandwidth be selected carefully to account for the response modal density and Q factor. The applicability of these findings to the analysis of reverberation chambers is indicated.
    Keywords: ACOUSTICS
    Type: Journal of Sound and Vibration (ISSN 0022-460X); 130; 171-176
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  • 7
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    A numerical study of active structural acoustic control in a stiffened, double wall cylinder (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-01-25
    Description: It is demonstrated that active structural acoustic control of complex structural/acoustic coupling can be numerically modeled using finite element and boundary element techniques in conjunction with an optimization procedure to calculate control force amplitudes. Appreciable noise reduction is obtained when the structure is excited at a structural resonance of the outer shell or an acoustic resonance of the inner cavity. Adding ring stiffeners as a connection between the inner and outer shells provides an additional structural transmission path to the interior cavity and coupled the modal behavior of the inner and outer shells. For the case of excitation at the structural resonance of the unstiffened outer shell, adding the stiffeners raises the structural resonance frequencies. The effectiveness of the control forces is reduced due to the off resonance structural response. For excitation at an acoustic cavity resonance, the controller effectiveness is enhanced.
    Keywords: ACOUSTICS
    Type: Inst. of Noise Control Engineering, Noise Con 1994: Proceedings of the 1994 National Conference on Noise Control Engineering. Progress in Noise Control for Industry; p 403-408
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  • 8
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    Scout vehicle flight loads. (1965)
    In:  Other Sources
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    Publication Date: 2019-01-25
    Description: Transverse flight loads produced on vertically rising Scout launch vehicle by horizontal winds and gusts
    Keywords: SPACE VEHICLES
    Format: text
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  • 9
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    An evaluation of active noise control in a cylindrical shell (1987)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The physical mechanisms governing the use of active noise control in an extended volume of a cylindrical shell are discussed. Measured data was compared with computer results from a previously derived analytical model based on an infinite shell theory. For both the analytical model and experiment, the radiation of the external monopoles is coupled to the internal acoustic field through the radial displacement of the thin, elastic cylindrical shell. An active noise control system was implemented in the cylinder using a fixed array of discrete monopole sources, all of which lie in the plane of the exterior noise sources. Good agreement between measurement and prediction was obtained for both internal pressure response and overall noise reduction. Attenuations in the source plane greater than 15 dB were recorded along with a uniformly quieted noise environment over the entire length of the experimental model. Results indicate that for extended axial forcing distributions or very low shell damping, axial arrays of control sources may be required. Finally, the Nyquist criteria for the number of azimuthal control sources is shown to provide for effective control over the full cylinder cross section.
    Keywords: ACOUSTICS
    Type: NASA-TM-89090 , NAS 1.15:89090
    Format: application/pdf
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  • 10
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    Active control of propeller induced noise fields inside a flexible cylinder (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: An active noise control model has been evaluated for reducing aircraft interior noise. The structural noise transmission properties of an aircraft fuselage were modelled as a flexible cylinder excited by external acoustic dipoles simulating the noise produced by twin propellers. The amplitudes of an internal distribution of monopole control sources were determined such that the area-weighted mean square acoustic pressure was minimized in the propeller plane. The noise control model was evaluated at low frequencies corresponding to the blade passage frequency and first few harmonics of a typical turbo-prop aircraft. Interior noise reductions of 20 25 dB were achieved, over a substantial region of the cylindrical cross-section, with just a few monopole control sources. The most favorable interior noise reductions were achieved when the active noise control model was used in combination with propeller source phasing.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: AIAA PAPER 86-1957
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