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- Lopez Arteaga, Ines, et al.
(author)
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Assessment of Linear Predictive Border-padding for PNAH
- 2009
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In: Proceedings of the 16th International Congress on Sound and Vibration.
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Conference paper (other academic/artistic)abstract
- Linear Predictive Border Padding (LPBP) is a recently presented aperture extrapolation technique to extend the applicability of PNAH to small spatial apertures (compared to the source size). Although Planar Near-field Acoustic Holography (PNAH) is recognized as a powerful and extremely fast acoustic imaging method, small measurement apertures over a portion of larger source structures lead to significant and often intolerable errors in the acoustic source images. In this paper an assessment of the accuracy of Linear Predictive Border Padding (LPBP) applied to Planar Near-field Acoustic Holography (PNAH) is presented based onnumerical experiments on two different source types: modal patterns and point sources. These two types of sources represent the two limit situations that one can find in practice: modal patterns have a tonal spectrum in the spatial wave-number domain and are relatively easy to reconstruct accurately, while point sources have a broad-band wave-number spectrum which makes them very challenging to reconstruct. For a given distance to the source, the position and size of the hologram plane apertures is varied. The reconstructed source information is compared to the reference source reconstruction obtained using a large aperture. The same analysis is also carried out with state-of-the-art aperture extrapolation methods. The reconstructed sources are compared both qualitatively (visual comparison) and quantitatively (RMS reconstruction error). The results show that LPBP is a fast, efficient and accurate extrapolation method, which leads to accurate reconstructions even for very small aperture sizes.
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| 2. |
- Lopez Arteaga, Ines, et al.
(author)
-
Frequency loci veering due to deformation in rotating tyres
- 2009
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In: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 324:3-5, s. 622-639
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Journal article (peer-reviewed)abstract
- This paper shows that the eigenfrequencies of a deformed tyre exhibit a mutual repulsion behaviour if the rotation velocity is increased. This phenomenon is known as frequency loci veering and is induced by the a-periodicity resulting from the tyre deformation due to the weight of the car. The corresponding eigenmodes interact in the transition zones and finally interchange. This is not the case for the undeformed tyre, where it is well known that rotation splits the eigenfrequencies around the eigenfrequencies of the non-rotating tyre. The change in eigenfrequencies is linearly related to the rotation velocity and is determined by the circumferential wavenumber and tyre radius only. For the undeformed tyre no modal interaction occurs as a consequence of rotation. Furthermore, modal interaction increases as tyre load increases and decreases as material damping increases. In previous work a methodology to model tyre vibrations has been developed, exploiting a modal base determined in a standard FE package and including rotational effects by a coordinate transformation. Major advantages of this approach are that the complex build-up of a tyre is retained and that the large (nonlinear) deformations and small (linear) vibrations are treated separately. In the present paper, the effects of deformation on the eigenfrequencies of a rotation tyre are examined using this methodology.
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| 3. |
- Lopez Arteaga, Ines, et al.
(author)
-
Linear Predictive Border-padding for PNAH : influence of aperture size and filter order
- 2009
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In: Proceedings of Euronoise 2009.
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Conference paper (other academic/artistic)abstract
- Linear Predictive Border Padding (LPBP) is a recently presented aperture extrapolation technique [1] to extend the applicability of PNAH to small spatial apertures (compared to the source size). Although Planar Near-field Acoustic Holography (PNAH) is recognized as a powerful and extremely fast acoustic imaging method, small measurement apertures over a portion of larger source structures lead to significant and often intolerable errors in the acoustic source images. The strategy presented in [1] to pre-process the spatial acoustic data before applying FFT is robust and minimizes leakage and distortion of the acoustic field. The filter order determines the wave-number content of the extrapolated data and affects the accuracy of the reconstruction. In this paper the influence of the aperture size and filter order on the accuracy of LPBP is studied based on numerical examples and measurements on a hard disk drive and a cooling fan. The reconstructed source information is compared to the reference source reconstruction obtained using a large aperture. The reconstructed sources are compared both qualitatively (visual comparison) and quantitatively (RMS reconstruction error). The results show that LPBP is a fast and efficient extrapolation method, which leads to accurate reconstructions even for very small aperture sizes. The optimal filter order is depends on the SNR and particular source measured, but in practical situations a filter order between 5-10 should lead to adequate reconstructions.
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