| 1. |
- Lopez Arteaga, Ines, et al.
(författare)
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Assessment of Linear Predictive Border-padding for PNAH
- 2009
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Ingår i: Proceedings of the 16th International Congress on Sound and Vibration.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)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.
(författare)
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Frequency loci veering due to deformation in rotating tyres
- 2009
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 324:3-5, s. 622-639
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Tidskriftsartikel (refereegranskat)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. |
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| 4. |
- Lopez Arteaga, Ines, et al.
(författare)
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Linear Predictive Border-padding for PNAH : influence of aperture size and filter order
- 2009
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Ingår i: Proceedings of Euronoise 2009.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)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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| 5. |
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| 6. |
- Lopez Arteaga, Ines, et al.
(författare)
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Modelling vibrations on deformed rolling tyres - a modal approach
- 2007
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 307:3-5, s. 481-494
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Tidskriftsartikel (refereegranskat)abstract
- This paper examines an approach to model the vibrations of a deformed rolling tyre at low frequencies (below 500 Hz). The starting point for this approach is a finite element (FE) model of the tyre and the aim is to calculate the dynamic response of a rolling tyre including the details of its complex build up. This allows to relate the tyre design parameters to its vibro-acoustic properties. In this context, a modal approximation based on the eigenvalues and eigenvectors extracted from the detailed FE model of the tyre seems a computationally efficient possibility. In the proposed approach the natural frequencies and modeshapes of a deformed tyre are calculated in a standard FE package using the full (nonlinear) FE model. Subsequently, this modal base is transformed to determine the response of the rotating tyre in a fixed (Eulerian) reference frame. Furthermore, this approach makes it possible to define a receptance matrix for the rotating tyre. Results from relatively simple tyre models show that the effects of rotation are modelled correctly and are in accordance with results from literature.
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| 7. |
- Scholte, R., et al.
(författare)
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Applications of Near-field Acoustic Holography on Small Apertures
- 2008
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Ingår i: Proceedings of Acoustics 2008.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Small, finite measurement apertures are a major impediment for accurate and fast application of near-field acoustic holography (NAH). In theory, FFT-based NAH methods are very powerful and acquire extremely fast inverse calculations of the sound field. However, in practice the usually small amount of sensors in a measurement array limit the possibilities of classical implementations of NAH, especially near the edges of the array or measurement grid. An alternative method to, for example, spatial windowing, patch NAH, SONAH, etc. is the recently introduced border-padding technique. This method makes it possible to apply FFT-based NAH with a large increase of accuracy compared to the original methods, specifically at the measurement grid edges, while maintaining the high speed of the inverse process PNAH is known for. This work focuses on the application of border-padding and the practical implementation in a newly developed PNAH system. It illustrates a large variety of extend ed possibilities for PNAH that border-padding enables. Apart from the earlier introduced standard border-padding, experimental results are shown for a highly improved border-padding method. Measurements and calculations on industrial products illustrate the wide applicability of the presented method.
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| 8. |
- Scholte, R., et al.
(författare)
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Experimental application of high precision k-space filters and stopping rules for fully automated near-field acoustical holography
- 2008
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Ingår i: International Journal of Acoustics and Vibration. - 1027-5851 .- 2415-1408. ; 13:4, s. 157-164
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Tidskriftsartikel (refereegranskat)abstract
- In general, inverse acoustics problems are ill-posed. Without proper regularization action taken noisy measurements result in an increasingly disturbed solution of the inverse acoustics wave equation as the distance from the measurement plane to the desired source grows. Two distinctive steps take place in the regularization process for planar near-field acoustical holography (PNAH): first, a low-pass filter function is defined and secondly a stopping rule is applied to determine the parameter settings of the filter. In acoustical imaging practice, it turns out to be very hard to determine the right filter for a certain case, ideally by means of an automatic search for the (near-) optimal parameters. This paper presents the practical application of a novel automated method that combines fitted filters for a broad number of possible experimental sources combined with highly efficient stopping rules by taking advantage of k-space. Also, a number of well-known and newly developed filter functions and stopping rules are discussed and compared with one another. Results based on actual measurements demonstrate the effectiveness, applicability, and precision of the fully implemented and automated regularization process for PNAH. Practical results even show acoustic source visualization below one millimeter primarily by successful application of k-space regularization. Implementations include modifications of Tikhonov, exponential and truncation low-pass filters, L-curve Generalised Cross-Validation (GCV) and the novel Cut-Off and Slope (COS) parameter selection methods for PNAH COS iteration in combination with either a modified exponential or Tikhonov low-pass filter results in an automated selection of the regularization parameters and eventually a fully automated PNAH system.
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| 9. |
- Scholte, R., et al.
(författare)
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Experimental Application of High Precision K-space Filters and Stopping Rules for Fully Automated PNAH
- 2007
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Ingår i: Proceedings of the 14th International Congress on Sound and Vibration.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In general, inverse acoustic problems are ill-posed. Without any proper regularization actiontaken, noisy measurements result in an increasingly useless solution as the distance from themeasurement plane to the desired source grows. Two distinctive steps take place in the regularizationprocess for planar near-field acoustic holography (PNAH); first the low-pass filterfunction is defined and secondly a stopping rule is applied to determine the parameter settingsof said filter. A number of well-known and newly developed filter functions and stopping rulesare discussed and compared to one another, carefully listing the pros and cons. In acousticimaging practice it has proven to be very hard to determine the right filter for a certain casecombined with the automatic search for the near-optimal parameters. This paper presents anovel method that combines fitted filters for a broad number of possible experimental sourcescombined with highly efficient stopping rules, by taking advantage of k-space. Results basedon actual measurements demonstrate the effectiveness, applicability and precision of the fullyimplemented and automated regularization process for PNAH. Implementations include modificationsof Tikhonov, exponential and truncation low-pass filters, L-curve, Generalised Cross-Validation (GCV) and the novel Cut-Off and Slope (COS) parameter selection methods forPNAH.
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| 10. |
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