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Sound transmission through two concentric cylindrical shells connected by ring frames
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
(English)In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568Article in journal (Refereed) Submitted
National Category
Fluid Mechanics and Acoustics
URN: urn:nbn:se:kth:diva-6127OAI: diva2:10747
QS 20120327Available from: 2006-09-15 Created: 2006-09-15 Last updated: 2012-03-27Bibliographically approved
In thesis
1. Acoustical Characteristics of Aircraft Panels
Open this publication in new window or tab >>Acoustical Characteristics of Aircraft Panels
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.
Trita-AVE, ISSN 1651-7660 ; 2006:60
Acoustics, sound transmission loss, stiffener, stiffening, aircraft panel, cylindrical shell, turbulent boundary layer, TBL, noise, sound radiation
National Category
Fluid Mechanics and Acoustics
urn:nbn:se:kth:diva-4102 (URN)1651-7660 (ISBN)
Public defence
2006-09-26, Salongen, KTHB, Osquars Backe 31, Stockholm, 13:00
QC 20100908Available from: 2006-09-15 Created: 2006-09-15 Last updated: 2010-09-08Bibliographically approved

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