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  • 1
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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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  • 2
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    Active sound attenuation across a double wall structure (1991)
    In:  Other Sources
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    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
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  • 3
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    Forced response sound radiation from acoustically or mechanically excited small plates (1992)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Sound radiation from an acoustically excited, clamped aluminum plate is measured and expressed in terms of noise reduction to take into account the incident acoustic excitation field. Its mode shapes and modal frequencies are measured and show good agreement with the predictions from a finite element MSC/NASTRAN model. Noise reduction is measured at 15 points behind the plate and demonstrate good agreement with predictions employing the SYSNOISE numerical analysis system for acoustic-structure interaction.
    Keywords: ACOUSTICS
    Type: In: DGLR(AIAA Aeroacoustics Conference, 14th, Aachen, Germany, May 11-14, 1992, Proceedings. Vol. 1 (A93-19126 05-71); p. 106-116.
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  • 4
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    Noise reduction of a composite cylinder subjected to random acoustic excitation (1989)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Interior and exterior noise measurements were conducted on a stiffened composite floor-equipped cylinder, with and without an interior trim installed. Noise reduction was obtained for the case of random acoustic excitation in a diffuse field; the frequency range of interest was 100-800-Hz one-third octave bands. The measured data were compared with noise reduction predictions from the Propeller Aircraft Interior Noise (PAIN) program and from a statistical energy analysis. Structural model parameters were not predicted well by the PAIN program for the given input parameters; this resulted in incorrect noise reduction predictions for the lower one-third octave bands where the power flow into the interior of the cylinder was predicted on a mode-per-mode basis.
    Keywords: ACOUSTICS
    Type: AIAA PAPER 89-1049
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  • 5
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    Acoustic transmissibility of advanced turboprop aircraft windows (1987)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Advanced turboprop technology allows propeller aircraft to reach cruise speeds comparable to current jet aircraft yet with considerable fuel savings. Due to the higher blade loading and higher tip speed of these propellers, noise levels of up to 150 dB are expected on the outside of the fuselage in the propeller plane. In this study the transmissibility of triple pane windows, designed to provide 69 dB noise transmission loss at the blade propeller frequency of 164 Hz, was experimentally investigated using insertion loss and three-dimensional intensity techniques. A modal analysis on the outer window panes was conducted to determine pane modal frequencies. Coherence and phase relation of outer panes and window frame were established to obtain double/triple wall and lump mass resonance frequencies. Double/triple wall resonances were found to degrade the transmission loss of the two windows. It was shown that, at the blade passage frequency and the first two overtones, the combinations of window plus scratch shield provide less transmission loss than the average transmission loss of the treated fuselage. Strong disagreement was obtained between the experimental transmission loss of this investigation and the theoretical predictions from another study.
    Keywords: ACOUSTICS
    Type: AIAA PAPER 87-2662
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  • 6
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    Prediction of interior noise due to random acoustic or turbulent boundary layer excitation using statistical energy analysis (1990)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The feasibility of predicting interior noise due to random acoustic or turbulent boundary layer excitation was investigated in experiments in which a statistical energy analysis model (VAPEPS) was used to analyze measurements of the acceleration response and sound transmission of flat aluminum, lucite, and graphite/epoxy plates exposed to random acoustic or turbulent boundary layer excitation. The noise reduction of the plate, when backed by a shallow cavity and excited by a turbulent boundary layer, was predicted using a simplified theory based on the assumption of adiabatic compression of the fluid in the cavity. The predicted plate acceleration response was used as input in the noise reduction prediction. Reasonable agreement was found between the predictions and the measured noise reduction in the frequency range 315-1000 Hz.
    Keywords: ACOUSTICS
    Type: AIAA PAPER 90-3964
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  • 7
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    Validation of an interior noise prediction model for a composite cylinder (1987)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: An acoustic modal analysis has been performed in the cavity of a composite cylinder model of an aircraft fuselage. The filament wound, composite shell is 12 feet long and 5.5 feet in diameter. A one-half-in. thick plywood floor is attached to the shell 69 deg from the vertical centerline through the bottom of the shell. The acoustic modal frequencies were obtained from a sound pressure level and phase survey conducted throughout the interior volume bounded by the floor, endcaps and stiffened shell, while being excited by white noise from a loudspeaker source. The measured acoustic resonance frequencies and mode shapes compare well with analytical predictions from the Propeller Aircraft Interior Noise (PAIN) model. Details of the theory and derivation of the acoustic characteristics have been included. Reverberation time measurements, using the integrated impulse technique, have been performed to determine acoustic loss factors. These measured loss factors have been input to the PAIN program in order to more accurately predict the space-averaged interior noise of the composite cylinder.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: AIAA PAPER 87-0529
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  • 8
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    Finite Element Model Development For Aircraft Fuselage Structures (2000)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The ability to extend the valid frequency range for finite element based structural dynamic predictions using detailed models of the structural components and attachment interfaces is examined for several stiffened aircraft fuselage structures. This extended dynamic prediction capability is needed for the integration of mid-frequency noise control technology. Beam, plate and solid element models of the stiffener components are evaluated. Attachment models between the stiffener and panel skin range from a line along the rivets of the physical structure to a constraint over the entire contact surface. The finite element models are validated using experimental modal analysis results.
    Keywords: Aircraft Design, Testing and Performance
    Type: XVIII International Modal Analysis Conference; Feb 01, 2000 - Feb 28, 2000; San Antonio, TX; United States
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  • 9
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    Finite Element Model Development and Validation for Aircraft Fuselage Structures (2000)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The ability to extend the valid frequency range for finite element based structural dynamic predictions using detailed models of the structural components and attachment interfaces is examined for several stiffened aircraft fuselage structures. This extended dynamic prediction capability is needed for the integration of mid-frequency noise control technology. Beam, plate and solid element models of the stiffener components are evaluated. Attachment models between the stiffener and panel skin range from a line along the rivets of the physical structure to a constraint over the entire contact surface. The finite element models are validated using experimental modal analysis results. The increased frequency range results in a corresponding increase in the number of modes, modal density and spatial resolution requirements. In this study, conventional modal tests using accelerometers are complemented with Scanning Laser Doppler Velocimetry and Electro-Optic Holography measurements to further resolve the spatial response characteristics. Whenever possible, component and subassembly modal tests are used to validate the finite element models at lower levels of assembly. Normal mode predictions for different finite element representations of components and assemblies are compared with experimental results to assess the most accurate techniques for modeling aircraft fuselage type structures.
    Keywords: Structural Mechanics
    Type: 18th International Modal Analysis Conference; Feb 07, 2000 - Feb 10, 2000; San Antonio, TX; United States
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  • 10
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    Development of an Efficient Binaural Simulation for the Analysis of Structural Acoustic Data (2003)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Applying binaural simulation techniques to structural acoustic data can be very computationally intensive as the number of discrete noise sources can be very large. Typically, Head Related Transfer Functions (HRTFs) are used to individually filter the signals from each of the sources in the acoustic field. Therefore, creating a binaural simulation implies the use of potentially hundreds of real time filters. This paper details two methods of reducing the number of real-time computations required by: (i) using the singular value decomposition (SVD) to reduce the complexity of the HRTFs by breaking them into dominant singular values and vectors and (ii) by using equivalent source reduction (ESR) to reduce the number of sources to be analyzed in real-time by replacing sources on the scale of a structural wavelength with sources on the scale of an acoustic wavelength. The ESR and SVD reduction methods can be combined to provide an estimated computation time reduction of 99.4% for the structural acoustic data tested. In addition, preliminary tests have shown that there is a 97% correlation between the results of the combined reduction methods and the results found with the current binaural simulation techniques
    Keywords: Acoustics
    Type: Paper 77 , 8th International Conference on Recent Advances in Structural Dynamics; Jul 14, 2003 - Jul 16, 2003; Southampton; United Kingdom
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