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Two-Port Techniques For Characterisation Of Non-Linear In-Duct Sources
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.ORCID iD: 0000-0002-8474-8563
2008 (English)In: 15th International Congress on Sound and Vibration (ICSV15), 2008Conference paper (Other academic)
Abstract [en]

This paper discusses techniques for obtaining the acoustic properties of in-duct samples with non-linear acoustic characteristics such as perforates and other facing sheets used in aircraft engine liners and automotive mufflers.  It is assumed that the non-linearity occurs locally at constrictions or sharp corners. Non-linear wave propagation and wave steepening are not taken into account. The paper starts with a review of previous impedance tube measurements made for determining the acoustic impedance of non-linear samples. The effect of using different types of excitation and non-linear harmonic interaction mechanisms are discussed. Experiments were previously made using both pure tone and random excitation and the relevant parameters controlling the non-linearity were discussed. A study of harmonic interaction effects using two-tone excitations was made and later extended to multi-tone excitation for different types of perforates. In the linear case the impedance is independent of the sound field but when the sound pressure level is high the perforate impedance will be dependent on the acoustic particle velocity in the holes. For pure tone excitation it is usually assumed that the impedance will be controlled by the acoustic particle velocity at that frequency, even though the non-linearity will in fact cause energy to be transferred to other frequencies. If the acoustic excitation is random or periodic with multiple harmonics the impedance at a certain frequency may depend on the particle velocity at other frequencies. The results show that the total rms-value of the particle velocity in the holes seems to be the relevant parameter controlling the non-linearity. A study was previously made of using non-linear system identification techniques for this purpose. Multi-port techniques using sinusoidal excitation for better characterization of samples with non-linear properties are developed in the present paper. These new techniques take the non-linear energy transfer into account. 

Place, publisher, year, edition, pages
Keyword [en]
Characterisation, Multi-port, Non-linear, Non-linear acoustics, Non-Linearity, Nonlinear properties, Sharp corners, Sinusoidal excitations, Sound fields, Acoustic fields, Acoustic properties, Aircraft engines, Automobile mufflers, Energy transfer, Aeroacoustics
National Category
Engineering and Technology
URN: urn:nbn:se:kth:diva-62222ScopusID: 2-s2.0-84883329212OAI: diva2:479984
15th International Congress on Sound and Vibration. Daejeon, Korea. 6-10 July 2008
QC 20120514Available from: 2012-01-18 Created: 2012-01-18 Last updated: 2012-05-14Bibliographically approved

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