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Acoustical Characteristics of Aircraft Panels
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

A deterministic approach based on a modal expansion and modal receptance method has been developed to evaluate the airborne sound insulation of aircraft panels with stringer and ring frame attachments. Furthermore, this method was extended to predict the noise radiation of stiffening panel subjected to TBL excitation. This approach integrates with the fast and accurate methods in evaluating the modal excitation terms and modal radiation efficiency. Based on these advantages, the effects of the curvature, overpressure, stringers, ring frames, hydrodynamic coincidence, composite structures and structural dissipation on the acoustical properties of a typical aircraft panel are able to be investigated efficiently.

Theoretic predictions were compared with laboratory measurements conducted on both model structures and aircraft panels. It was found that a small curvature may result in significant deterioration of the sound transmission loss at frequencies of interest. Unlike a flat uniform panel, the theoretical prediction for curved panels from the infinite model can not provide good agreement with the measurement close to and well below the ring frequency. However, in this frequency range, the finite model has been proved to be applicable

For the large curved airplane panels studied here, it was found that the ring frames have little influence on sound transmission loss in the frequency range of interest. However the stringers may have considerable influence on sound transmission loss. The stringer improves this for a curved panel around the ring frequency, but it may result in a potential deterioration of the sound transmission loss above the ring frequency. In this study it is evident that the sound transmission loss of the composite skin attached with composite stringers is lower than that of the metallic panel attached with metallic stringers.

At frequencies higher than the corresponding ring frequency of the curved panel, both experiment and theoretical prediction reveal that the overpressure at the concave side tends to reduce the sound transmission loss at the rate of about 0.5dB /10000 Pa. While at lower frequencies, say well below the ring frequency, the overpressure may increase or reduce sound transmission loss of a finite panel, depending on the shift of the resonant frequencies resulting from the overpressure.

For TBL excitation, numerical investigation reveals that the panel with the ring frames behaves more like a sub-panel between two frames. Below 500Hz, the ring frames slightly enhance the sound radiation while dramatically increasing it around 1.3kHz. The TBL forcing field excites the same vibration lever for the panel with and without ring frame attachments, but the modes excited for the panel with ring frames radiate more sound. Unlike the ring frames, the stringers increase sound radiation below 1kHz. Above 1kHz, the sub-panels between two bays respond independently and the stringer effects is therefore not obvious.

Place, publisher, year, edition, pages
Stockholm: KTH , 2006. , 23 p.
Series
TRITA-AVE, ISSN 1651-7660 ; 2006:60
Keyword [en]
Acoustics, sound transmission loss, stiffener, stiffening, aircraft panel, cylindrical shell, turbulent boundary layer, TBL, noise, sound radiation
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-4102OAI: oai:DiVA.org:kth-4102DiVA: diva2:10748
Public defence
2006-09-26, Salongen, KTHB, Osquars Backe 31, Stockholm, 13:00
Opponent
Supervisors
Note

QC 20100908

Available from: 2006-09-15 Created: 2006-09-15 Last updated: 2017-02-23Bibliographically approved
List of papers
1. Sound transmission through curved aircraft panels with stringers and ring frames attachments
Open this publication in new window or tab >>Sound transmission through curved aircraft panels with stringers and ring frames attachments
2007 (English)In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Journal of sound and vibration, Vol. 300, no 3-5, 949-973 p.Article in journal (Refereed) Published
Abstract [en]

A numerical approach based on a receptance method has been developed to evaluate the airborne sound insulation of aircraft panels with stringer and ring frame attachments. Theoretical predictions have been compared with laboratory measurements conducted on both model structures and aircraft panels. Certain parameters were varied in this study to gauge stiffener effects on sound transmission through the panel. For large curved aircraft panels studied here, it was found that the ring frames have little influence on sound transmission loss in the frequency range of interest. However, the stringers may have considerable influence on the sound transmission loss. The stringer improves the sound transmission loss for a curved panel in the vicinity of the ring frequency, but may result in a potential deterioration above this frequency. In addition it was found that the sound transmission loss for the composite skin attached with composite stringers was lower than that of the metallic panel attached with metallic stringers. The results suggest that acoustical optimization design for the stringers is necessary to achieve improved airborne sound insulation for aircraft panels

Keyword
Acoustic variables measurement, Aircraft parts and equipment, Numerical methods, Optimization, Sound insulation, Structural panels
National Category
Other Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-6123 (URN)10.1016/j.jsv.2006.09.008 (DOI)000243561200030 ()2-s2.0-33845885801 (Scopus ID)
Note
QC 20100908Available from: 2006-09-15 Created: 2006-09-15 Last updated: 2012-03-23Bibliographically approved
2. Influence of overpressure on sound transmission through curved panels
Open this publication in new window or tab >>Influence of overpressure on sound transmission through curved panels
2007 (English)In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Journal of sound and vibration, Vol. 302, no 4-5, 760-776 p.Article in journal (Refereed) Published
Abstract [en]

A great deal of recent research related to the aeronautic industry has been devoted to the theoretical study of sound transmission through fuselage structures. However, the literature records few test data with reference to the influence of overpressure on sound transmission. In this article, the airborne sound transmission through curved panels under the condition of overpressure at the concave side has been investigated experimentally and it is shown that experimental results agree well with a theoretical prediction due to an infinite cylindrical shell model at relatively high frequencies. Discrepancies, which occur at lower frequencies, can be explained, inter alia, by the influence of the finite size and attached stiffeners of the panel.At frequencies higher than the corresponding ring frequency for the curved panel, both experimental and theoretical predictions reveal that the overpressure at the concave side tends to reduce the sound transmission loss at the rate of about 0.5dB/10000Pa. While at lower frequencies, say well below the ring frequency, the overpressure may increase or reduce sound transmission loss of a finite panel depending on the shift of resonant frequencies resulting from the overpressure.

Keyword
thin cylindrical-shell, acoustic behavior, prestress, stringers
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-6124 (URN)10.1016/j.jsv.2006.12.014 (DOI)000245508700009 ()2-s2.0-33947222075 (Scopus ID)
Note
QC 20100908Available from: 2006-09-15 Created: 2006-09-15 Last updated: 2012-03-23Bibliographically approved
3. Noise radiation of aircraft panels subjected to boundary layer pressure fluctuations
Open this publication in new window or tab >>Noise radiation of aircraft panels subjected to boundary layer pressure fluctuations
2008 (English)In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 314, no 3-5, 693-711 p.Article in journal (Refereed) Published
Abstract [en]

In this paper, a method which predicts the sound radiation of aircraft panels subjected to turbulent boundary layer excitation is described. The method is the extension of ail earlier deterministic approach, where the modal expansion and modal receptance methods were used to predict random noise transmission through curved aircraft panels with stringer and ring frame attachments. Here, with implementation of the Corcos and Efimtsov models to characterize the dynamic surface pressure cross-spectra, closed-form solutions for the panel displacements, radiation and transmission pressures are derived. Numerical examples are presented to illustrate the effects of the stringers, ring frames, hydrodynamic coincidence, curvature, in-plane tension, structural dissipation and composite material on the structural and acoustic response of the panel.

Keyword
airplane fuselage structure, randomly excited panel, wave-number approach, flat-plate model, vibration measurements, excitation, turbulence, sound, prediction, element
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-6125 (URN)10.1016/j.jsv.2008.01.045 (DOI)000256501100019 ()2-s2.0-43049089683 (Scopus ID)
Note
QC 20100908Available from: 2006-09-15 Created: 2006-09-15 Last updated: 2010-09-08Bibliographically approved
4. Influence of baffle size and curvature on sound radiated by vibration panels
Open this publication in new window or tab >>Influence of baffle size and curvature on sound radiated by vibration panels
2003 (English)In: The 11th International Congress on Sound and Vibration, 2003, 2003Conference paper, Published paper (Refereed)
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-6126 (URN)
Note
QC 20100908Available from: 2006-09-15 Created: 2006-09-15 Last updated: 2010-09-08Bibliographically approved
5. Sound transmission through two concentric cylindrical shells connected by ring frames
Open this publication in new window or tab >>Sound transmission through two concentric cylindrical shells connected by ring frames
(English)In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568Article in journal (Refereed) Submitted
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-6127 (URN)
Note
QS 20120327Available from: 2006-09-15 Created: 2006-09-15 Last updated: 2012-03-27Bibliographically approved

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