| 1. |
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| 2. |
- 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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| 3. |
- Lopez Arteaga, Ines, et al.
(författare)
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Energy dissipation of a friction damper : experimental validation
- 2008
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Ingår i: PROCEEDINGS OF ISMA 2008. - : KATHOLIEKE UNIV LEUVEN. - 9789073802865 ; , s. 881-892
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Friction is frequently seen as an unwanted phenomenon whose influence has to be either minimised or controlled. In this work one of the positive sides of friction is investigated: friction damping. The friction inherently present in a system can be positively used to increase the total damping or alternatively, a friction damper can be designed. Friction dampers can be a cheap and efficient way to reduce the vibration levels of a wide range of mechanical systems. In the present paper the conclusions of previous analytic and numerical results regarding friction damping are validated with results of laboratory experiments, where the energy dissipated through friction is measured. The test set-up consists of a mass sliding on parallel ball-bearings, where additional friction is created by a sledge attached to the mass, which is pre-stressed against a friction plate. No care has been taken to ensure pure dry (Coulomb) friction. Nevertheless, the measured energy dissipation is in good agreement with the theoretical results for Coulomb friction.
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| 4. |
- 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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| 5. |
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| 6. |
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| 7. |
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| 8. |
- 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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| 9. |
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| 10. |
- 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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| 11. |
- Lopez Arteaga, Ines, et al.
(författare)
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Physical modeling of buzzing artificial lips : The effect of acoustical feedback
- 2006
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Ingår i: Acta Acoustica united with Acustica. - 1610-1928 .- 1861-9959. ; 92:6, s. 1047-1059
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Tidskriftsartikel (refereegranskat)abstract
- The influence of the up- and downstream acoustics on the buzzing behavior of artificial lips has been studied. In the presence of a long downstream pipe, the oscillation frequency is well predicted by means of a model assuming a single mechanical degree of freedom for the lips. A minimum of the threshold pressure for buzzing is observed when the lips are just closed at rest. The magnitude of this threshold pressure is underestimated by the model. In order to fit experiments the quality factor of the lip resonance has to be reduced by a factor two compared to the measured quality factor. In the absence of downstream pipe the threshold pressure increases by a factor three and a jump in oscillation frequency from one mechanical lip-mode to another one is observed as the lung pressure is increased. An attempt to describe this behavior by means of a 2-mass-model fails.
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| 12. |
- Lopez Arteaga, Ines, et al.
(författare)
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Prediction and validation of the energy dissipation of a friction damper
- 2009
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 328:4-5, s. 396-410
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Tidskriftsartikel (refereegranskat)abstract
- Friction dampers can be a cheap and efficient way to reduce the vibration levels of a wide range of mechanical systems. In the present work it is shown that the maximum energy dissipation and corresponding optimum friction force of friction dampers with stiff localized contacts and large relative displacements within the contact, can be determined with sufficient accuracy using a dry (Coulomb) friction model. Both the numerical calculations with more complex friction models and the experimental results in a laboratory test set-up show that these two quantities are relatively robust properties of a system with friction. The numerical calculations are performed with several friction models currently used in the literature. For the stick phase smooth approximations like viscous damping or the arctan function are considered but also the non-smooth switch friction model is used. For the slip phase several models of the Stribeck effect are used. The test set-up for the laboratory experiments consists of a mass sliding on parallel ball-bearings, where additional friction is created by a sledge attached to the mass, which is pre-stressed against a friction plate. The measured energy dissipation is in good agreement with the theoretical results for Coulomb friction.
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| 13. |
- Ruty, N., et al.
(författare)
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An in vitro setup to test the relevance and the accuracy of low-order vocal folds models
- 2007
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Ingår i: Journal of the Acoustical Society of America. - : Acoustical Society of America (ASA). - 0001-4966 .- 1520-8524. ; 121:1, s. 479-490
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Tidskriftsartikel (refereegranskat)abstract
- An experimental setup and human vocal folds replica able to produce self-sustained oscillations are presented. The aim of the setup is to assess the relevance and the accuracy of theoretical vocal folds models. The applied reduced mechanical models are a variation of the classical two-mass model, and a simplification inspired on the delayed mass model for which the coupling between the masses is expressed as a fixed time delay. The airflow is described as a laminar flow with flow separation. The influence of a downstream resonator is taken into account. The oscillation pressure threshold and fundamental frequency are predicted by applying a stability analysis to the mechanical models. The measured frequency response of the mechanical replica together with the initial (rest) area allows us to determine the model parameters (spring stiffness, damping, geometry, masses). Validation of theoretical model predictions to experimental data shows the relevance of low-order models in gaining a qualitative understanding of phonation. However, quantitative discrepancies remain large due to an inaccurate estimation of the model parameters and the crudeness in either flow or mechanical model description. As an illustration it is shown that significant improvements can be made by accounting for viscous flow effects.
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| 14. |
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| 15. |
- Scholte, Rick, et al.
(författare)
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Acoustic holography
- 2008
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Patent (populärvet., debatt m.m.)abstract
- A method of performing near- field acoustic holography comprises the following steps. Establishing (102) acoustic data representing a set of near-field acoustic holography measurements at a first set of positions. Extrapolating (204) acoustic data using a model-based extrapolation to obtain extrapolated acoustic data relating to a plurality of positions outside the aperture. Applying (108) a spatial frequency transform to the padded acoustic data to obtain data in a spatial frequency domain. Propagating (110) the Fourier transformed acoustic data. Applying (112) a regularization in a wavenumber domain. Performing (114) an inverse spatial frequency transform.
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| 16. |
- 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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| 17. |
- 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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| 18. |
- 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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| 19. |
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| 20. |
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| 21. |
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| 22. |
- Scholte, R., et al.
(författare)
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Truncated aperture extrapolation for Fourier-based near-field acoustic holography by means of border-padding
- 2009
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Ingår i: Journal of the Acoustical Society of America. - : Acoustical Society of America (ASA). - 0001-4966 .- 1520-8524. ; 125:6, s. 3844-3854
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Tidskriftsartikel (refereegranskat)abstract
- Although near-field acoustic holography (NAH) is recognized as a powerful and extremely fast acoustic imaging method based on the inverse solution of the wave-equation, its practical implementation has suffered from problems with the use of the discrete Fourier transformation (DFT) in combination with small aperture sizes and windowing. In this paper, a method is presented that extrapolates the finite spatial aperture before the DFT is applied, which is based on the impulse response information of the known aperture data. The developed method called linear predictive border-padding is an aperture extrapolation technique that greatly reduces leakage and spatial truncation errors in planar NAH (PNAH). Numerical simulations and actual measurements on a hard-disk drive and a cooling fan illustrate the low error, high speed, and utilization of border-padding. Border-padding is an aperture extrapolation technique that makes PNAH a practical and accurate inverse near-field acoustic imaging method.
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| 23. |
- Scholte, R., et al.
(författare)
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Wavenumber domain regularization for near-field acoustic holography by means of modified filter functions and cut-off and slope iteration
- 2008
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Ingår i: Acta Acoustica united with Acustica. - 1610-1928 .- 1861-9959. ; 94:3, s. 339-348
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Tidskriftsartikel (refereegranskat)abstract
- Planar Near-field Acoustic Holography (PNAH) is an acoustic imaging method based on the inverse solution of the wave equation. Wavenumber domain low-pass filtering is an essential operation in the PNAH process. An increasingly higher wavenumber filter cut-off results in a "blow-up" of the inverse solution, which is a characteristic of an ill-posed problem. On the other hand, lower cut-off wavenumbers result in spatial acoustic data at very low resolution, where highly detailed information is discarded. Thus, an optimal solution for the cut-off wavenumber somewhere in between is needed. This paper introduces two modified filter functions, namely a modified exponential and a modified Tikhonov filter, that are specifically designed for application in PNAH and compares them with a number of more general applied filter functions. Regularization methods are introduced that exploit the k-space to obtain near-optimal low-pass filter parameter selection at high computational efficiency. These filter functions are discussed and their parameters are selected by k-space application of L-curve, Generalised Cross-Validation and the newly introduced and well-applicable Cut-Off and Slope iteration. Simulations of various sources show that the optimal regularization method is highly dependent on the type of source, the spatial distribution and measurement noise. Finally, a robust regularization strategy is proposed which automatically produces high quality results for a wide range of practical conditions.
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| 24. |
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| 25. |
- van den Boom, J.D.B.J, et al.
(författare)
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Active control of oscillations in a Rijke tube-like flat flame configurations
- 2007
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Ingår i: Proceeding of the European Combustion Meeting.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The use of low NOx premixed surface burners with a large modulation range in modern central heating systemsoften to noise problems. In order to make any further advance in the development of these systems the noise problemhas to be solved. Therefore, the possibility of suppression (and stabilization) of these instabilities is in investigatedusing active model-based control strategies. A model for the condensing gas-fired boiler is derived first. based on anacoustic network approach. Special attention is paid to the flame dynamics. Second, a H1 controller is synthesized,where also modelling uncertainties are taken into account. In the end the performance and the robustness of thecontroller is validated during experiments.
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| 26. |
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| 27. |
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| 28. |
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| 29. |
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| 30. |
- van der Steen, R., et al.
(författare)
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FE modeling of rubber friction on rough roads
- 2008
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Ingår i: Proceedings of the WCCM8, ECCOMAS.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The cornering, braking, traction, rolling resistance and wear performance of tires depend on the generatedfriction forces. These friction forces depend not only on a specific compound, but also on theunderlying road surface. One of the challenges in numerical simulations is a correct prediction of thesefrictional forces. In commercial FEM packages, where usually only the Coulomb friction model ispresent, the surface roughness is not accounted for. It is well-known that for cornering under high slipangles the results with a Coulomb friction model are less accurate. By incorporating surface roughnessa more realistic friction model can be obtained, which should provide a better correlation between FEAand real road experiments.Recently a theory for contact mechanics and sliding friction of rubber has been developed (see Persson[1], [2]). In this work hysteresis friction is assumed, which is caused by the viscoelastic modulus of therubber and the excitation of the road surface. It is possible to calculate a friction coefficient for a set ofsliding velocities considering the mechanical-dynamical material properties and the specific roughnessof the interacting surface.To illustrate this approach an Laboratory Abrasion and skid Tester (LAT 100, [3]) is used, see figure 1.In this setup a small solid tire, with adjustable slip angle, is pressed on an abrasive disk. The appliednormal force on the tire, temperature, speed and surface texture of the disk can be controlled. Thepresent friction between the abrasive disk and tire drives the tire and the resulting forces are measuredwith a tri-axial force sensor.The relevant parts of this setup are modeled in ABAQUS [4], taking into account the non-linear materialbehavior, see figure 2. A 2D cross section of the tire is revolved to create the 3D model. To evaluate thesteady state performance of the wheel under different slip angles, the steady state transport capabilityof ABAQUS is used. Therefore only a dense mesh in the contact area is required, which makes this anefficient approach to calculate the responses.For the contacting surface in the FE model a smooth rigid surface is used. The effect of surfaceroughness is incorporated in the obtained friction model, using the method proposed by Persson, andis implemented into the user-subroutine FRIC. The implementation of the friction law itself is doneanalogous to a plasticity material model by using a return mapping algorithm. Therefore the slidingvelocity is split into a small elastic and an inelastic part [5].Finally the results of this method are compared with the available Coulomb model in ABAQUS andmeasured side-force characteristics on the LAT 100.
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| 31. |
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| 32. |
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| 33. |
- Van Hirtum, A., et al.
(författare)
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Experimental validation of some issues in lip and vocal fold physical models
- 2007
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Ingår i: Acta Acoustica united with Acustica. - 1610-1928 .- 1861-9959. ; 93:2, s. 314-323
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Tidskriftsartikel (refereegranskat)abstract
- Insight into vocal fold and lip oscillation mechanisms is important for the understanding of phonation and the sound generation process in brass musical instruments. In general, a simplified analysis of the physical 3D fluid-structure interaction process between the living tissues and the airflow is favoured by most workers. Several simple models (lumped parameter models) have been proposed and these represent the tissues as a distribution of elastic mass(es). The mass-spring-damper system is acted on by a driving force resulting from the pressure exerted by the airstream. The results from these theoretical models have been validated 'in-vitro' using rigid or deformable replicas mounted in a suitable experimental set-up. Previous research by the authors focused on the prediction of the pressure threshold and oscillation frequency of an 'in-vitro' replica, in the absence and presence of acoustical feedback. In the theoretical model a lip or vocal fold is represented as a simple lumped mass system. The model yielded accurate prediction of the oscillation threshold and frequency. In this paper a new 'in-vitro' set-up is presented, which overcomes some of the limitations of the previous study. By the use of a digital camera synchronised with a light source and of pressure sensors, this set-up allows 1) measurement of the area of the replica opening and 2) imposition of independent initial conditions, such as height of the initial opening and internal pressure in the replica. The impact of these findings on physical modelling is discussed.
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| 34. |
- Viñolas, J., et al.
(författare)
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The effect of damping the wheels and varying wheel/rail friction coefficient on railway noise
- 2007
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Ingår i: 19th International Congress on Acoustics.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The main noise source when a rail vehicle is circulating under approximately 280 km/h is theinteraction between wheel and rail. This paper presents a summary of different solutions thatcould be envisaged to reduce the level of this source. Being the wheel the most criticalcomponent for noise emission, particular attention is being paid to existing solutions to adddamping to the wheel. A wheel including a friction damping solution –a modified ring damper- isanalysed in detail. Ring dampers are steel rings fitted inside grooves cut under the wheel rim,usually one at each side of the tread; in this case it is a heavier ring at one side of the wheel.The paper includes some experimental results obtained in the laboratory aiming at verifying themodal damping for the different modes with this “damped wheel” and some on track test for aglobal evaluation of the solution. Additionally, an analysis of the effectiveness of modifying thefriction coefficient between the rail and the wheel is also reported. A “friction modifier” is addedat the top of the rail and noise and vibration measurements have been carried out on the trackfor an experimental evaluation of its effectiveness.
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