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The effects of damping treatment on the sound transmission loss of honeycomb panels
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Structural and vibroacoustics.
2010 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In the industry, all passenger vehicles are treated with damping materials to reduce structure-borne sound. Though these damping materials are effective to attenuate structure-borne sound, they have little or no effect on the air-borne sound transmission.The lack of effective predictive methods for assessing the acoustic effects due to added damping on complex industrial structures leads to excessive use of damping materials.Examples are found in the railway industry where sometimes the damping material applied per carriage is more than one ton. The objective of this thesis is to provide a better understanding of the application of these damping materials in particular when applied to lightweight sandwich panels.

As product development is carried out in a fast pace today, there is a strong need for validated prediction tools to assist in the design process. Sound transmission loss of sandwich plates with isotropic core materials can be accurately predicted by calculating the wave propagation in the structure. A modified wave propagation approach is used to predict the sound transmission loss of sandwich panels with honeycomb cores. The honeycomb panels are treated as being orthotropic and the wave numbers are calculated for the two principle directions. The orthotropic panel theory is used to predict the sound transmission loss of panels. Visco-elastic damping with a constraining layer is applied to these structures and the effect of these damping treatment on the sound transmission loss is studied. Measurements are performed to validate these predictions.

Sound radiated from vibrating structures is of great practical importance.The radiation loss factor represents damping associated with the radiation of sound as a result of the vibrating structure and can be a significant contribution for structures around the critical frequency and for composite structures that are very lightly damped. The influence of the radiation loss factor on the sound reduction index of such structures is also studied.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology , 2010. , vii, 30 p.
Series
Trita-AVE, ISSN 1651-7660 ; 2010:21
Keyword [en]
Sandwich Structures, Honeycomb Panels, Sound Transmission, Loss Factor, Damping, Sound Radiation
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-12514ISBN: 9789174156034 (print)OAI: oai:DiVA.org:kth-12514DiVA: diva2:317219
Presentation
2010-04-25, MWL sal 74, Teknikringen 8, Stockholm, 13:00 (English)
Opponent
Supervisors
Projects
ECO2-Multifunctional body Panels
Note
QC 20100519Available from: 2010-05-19 Created: 2010-05-03 Last updated: 2011-05-03Bibliographically approved
List of papers
1. On application of radiation loss factor in the prediction of sound transmission loss of a honeycomb panel
Open this publication in new window or tab >>On application of radiation loss factor in the prediction of sound transmission loss of a honeycomb panel
2012 (English)In: International Journal of Acoustics and Vibration, ISSN 1027-5851, Vol. 17, no 1, 47-51 p.Article in journal (Refereed) Published
Abstract [en]

The application of the radiation loss factor in the prediction of sound transmission loss of a lightweight, orthotropic sandwich panel is investigated in this paper. Comparisons with measurements show that predictions often underestimate the sound transmission loss of the panel around the corresponding critical frequency when the measured loss factor, which in principle includes the radiation loss factor, is used. This is due to the measurement methods used for the loss factor and the band average. It is thus recommended to use the loss factor measured at low frequencies plus the theoretical radiation loss factor in order to improve the prediction of the sound transmission loss of a honeycomb panel around the critical frequency.

Keyword
radiation loss factor, sound transmission loss, honeycomb panel, orthotropic panel
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-12926 (URN)000301833500005 ()2-s2.0-84860747745 (Scopus ID)
Funder
TrenOp, Transport Research Environment with Novel Perspectives
Note

QC 20120801

Available from: 2010-05-19 Created: 2010-05-19 Last updated: 2017-12-12Bibliographically approved
2. Predicting the sound transmission loss of honeycomb panels using the wave propagation approach
Open this publication in new window or tab >>Predicting the sound transmission loss of honeycomb panels using the wave propagation approach
2011 (English)In: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 97, no 5, 869-876 p.Article in journal (Refereed) Published
Abstract [en]

The sound transmission properties of sandwich panels can be predicted with sufficient degree of accuracy by calculating the wave propagation properties of the structure. This method works well for sandwich panels with isotropic cores but applications to panels with anisotropic cores are hard to find. Honeycomb is an example of anisotropic material which when used as a core, results in a sandwich panel with anisotropic properties. In this paper, honeycomb panels are treated as being orthotropic and the wavenumbers are calculated for the two principle directions. These calculated wavenumbers are validated with the measured wavenumbers estimated from the resonance frequencies of freely hanging honeycomb beams. A combination of wave propagation and standard orthotropic plate theory is used to predict the sound transmission loss of honeycomb panels. These predictions are validated through sound transmission measurements. Passive damping treatment is a common way to reduce structural vibration and sound radiation, but they often have little effect on sound transmission. Visco-elastic damping with a constraining layer is applied to two honeycomb panels with standard and enhanced fluid coupling properties. This enhanced fluid coupling in one of the test panels is due to an extended coincidence range observed from the dispersion curves. The influence of damping treatments on the sound transmission loss of these panels is investigated. Results show that, after the damping treatment, the sound transmission loss of an acoustically bad panel and a normal panel are very similar.

Keyword
Acoustic wave transmission, Anisotropy, Architectural acoustics, Curve fitting, Damping, Honeycomb structures, Orthotropic plates, Resonance, Sandwich structures, Structural dynamics
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-12927 (URN)10.3813/AAA.918466 (DOI)000295114100016 ()2-s2.0-80052447110 (Scopus ID)
Note
QC 20100519 QC 20111017Available from: 2010-05-19 Created: 2010-05-19 Last updated: 2017-12-12Bibliographically approved

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