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| 10. |
- Beerens, R., et al.
(författare)
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Hybrid PID control for transient performance improvement of motion systems with friction
- 2018
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Ingår i: 2018 Annual American Control Conference (ACC). - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 539-544
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Konferensbidrag (refereegranskat)abstract
- We present a novel reset control approach to improve transient performance of a PID-controlled motion system subject to friction. In particular, a reset integrator is applied to circumvent the depletion and refilling process of a linear integrator when the system overshoots the setpoint, thereby significantly reducing settling times. Moreover, robustness for unknown static friction levels is obtained. A hybrid closed-loop system formulation is derived, and stability follows from a discontinuous Lyapunov-like function and a meagre-limsup invariance argument. The working principle of the controller is illustrated by means of a numerical example.
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| 11. |
- Beerens, R., et al.
(författare)
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Reset integral control for improved settling of PID-based motion systems with friction
- 2019
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Ingår i: Automatica. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0005-1098 .- 1873-2836. ; 107, s. 483-492
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Tidskriftsartikel (refereegranskat)abstract
- We present a reset control approach to improve the transient performance of a PID-controlled motion system subject to Coulomb and viscous friction. A reset integrator is applied to circumvent the depletion and refilling process of a linear integrator when the solution overshoots the setpoint, thereby significantly reducing the settling time. Robustness for unknown static friction levels is obtained. The closed-loop system is formulated through a hybrid systems framework, within which stability is proven using a discontinuous Lyapunov-like function and a meagre-limsup invariance argument. The working principle of the proposed reset controller is analyzed in an experimental benchmark study of an industrial high-precision positioning machine.
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| 12. |
- Besselink, Bart, et al.
(författare)
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A comparison of model reduction techniques from structural dynamics, numerical mathematics and systems and control
- 2013
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 332:19, s. 4403-4422
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Forskningsöversikt (refereegranskat)abstract
- In this paper, popular model reduction techniques from the fields of structural dynamics, numerical mathematics and systems and control are reviewed and compared. The motivation for such a comparison stems from the fact that the model reduction techniques in these fields have been developed fairly independently. In addition, the insight obtained by the comparison allows for making a motivated choice for a particular model reduction technique, on the basis of the desired objectives and properties of the model reduction problem. In particular, a detailed review is given on mode displacement techniques, moment matching methods and balanced truncation, whereas important extensions are outlined briefly. In addition, a qualitative comparison of these methods is presented, hereby focusing both on theoretical and computational aspects. Finally, the differences are illustrated on a quantitative level by means of application of the model reduction techniques to a common example.
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| 13. |
- Bisoffi, Andrea, et al.
(författare)
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Hybrid model formulation and stability analysis of a PID-controlled motion system with Coulomb friction
- 2019
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Ingår i: IFAC PAPERSONLINE. - : ELSEVIER. - 2405-8963. ; , s. 84-89
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Konferensbidrag (refereegranskat)abstract
- For a PID-controlled motion system under Coulomb friction described by a differential inclusion, we present a hybrid model comprising logical states indicating whether the closed loop is in stick or in slip, thereby resembling a hybrid automaton. A key step for this description is the addition of a timer exploiting a peculiar semiglobal dwell time of the original dynamics, which then removes defective and unwanted nonconverging Zeno solutions from the hybrid model. Through it, we then revisit an existing proof of global asymptotic stability, which is significantly simplified by way of a smooth weak Lyapunov function. The relevance of the proposed hybrid representation is also illustrated on a novel control strategy resetting the PID integrator and hinging upon the proposed hybrid model.
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| 18. |
- 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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| 23. |
- Zhou, H., et al.
(författare)
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Broadband planar nearfield acoustic holography based on one-third-octave band analysis
- 2016
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Ingår i: Applied Acoustics. - : Elsevier. - 0003-682X .- 1872-910X. ; 109, s. 18-26
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Tidskriftsartikel (refereegranskat)abstract
- Planar nearfield acoustic holography (PNAH) is usually based on narrow-band, single frequency analysis, which is time consuming when the source behavior over a broad frequency range is of interest, as is the case with many industrial sources. In this paper a method, broadband planar nearfield acoustic holography based on one-third-octave band analysis (BPNAH), is described. Data relating to the complex band pressure on the hologram is obtained by combining the root-mean-square pressure corresponding to a one-third-octave band with the phase of the pressure corresponding to a single frequency line. Numerical simulations and measurements show that the BPNAH method allows a significant reduction in processing time, while keeping a similar accuracy to the conventional reconstruction, which is based on the summation of frequency by frequency in the corresponding band. As a simple, time-saving and robust technique, the BPNAH method is particularly well adapted to industrial studies.
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| 24. |
- Besselink, Bart, et al.
(författare)
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Generalized incremental balanced truncation for nonlinear systems
- 2013
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Ingår i: 2013 IEEE 52nd Annual Conference on Decision and Control (CDC). - : IEEE conference proceedings. - 9781467357173 ; , s. 5552-5557
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Konferensbidrag (refereegranskat)abstract
- The method of generalized incremental balanced truncation is introduced in this paper, providing a technique for model reduction of nonlinear systems in which the autonomous part of the vector field is anti-symmetric. This approach differs from existing balancing-like reduction techniques in the definition of two novel, incremental energy functions, which provides several advantages. First, stability properties of the reduced-order model can be guaranteed, hereby considering the stability of trajectories for both zero and nonzero input. Second, a computable bound on the reduction error is derived. The reduction technique is illustrated by means of application to an example of a nonlinear electronic circuit.
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| 25. |
- Lefeber, E., et al.
(författare)
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Linear Controllers for Exponential Tracking of Systems in Chained Form
- 2000
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Ingår i: International Journal of Robust and Nonlinear Control. - 1099-1239. ; 10:4, s. 243-264
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we address the tracking problem for a class of non-holonomic chained-form control systems. We present a simple solution for both the state feedback and the dynamic output feedback problem. The proposed controllers are linear and render the tracking error dynamics globally ?-exponentially stable. We also deal with both control problems under input saturation. Application of the results to the control of wheeled mobile robots is illustrated by means of simulations of a car pulling a single trailer.
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| 26. |
- 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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| 27. |
- 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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| 28. |
- Lopez Arteaga, Ines, et al.
(författare)
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Energy dissipation of a friction damper
- 2004
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 278:3, s. 539-561
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Tidskriftsartikel (refereegranskat)abstract
- In this paper the energy dissipated through friction is analysed for a type of friction dampers used to reduce squeal noise from railway wheels. A one degree-of-freedom system is analytically studied. First the existence and stability of a periodic solution are demonstrated and then the energy dissipated per cycle is determined as a function of the system parameters. In this way the influence of the mass, natural frequency and internal damping of the friction damper on the energy dissipation is established. It is shown that increasing the mass and reducing the natural frequency and internal damping of the friction damper maximizes the dissipated energy.
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| 29. |
- 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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| 30. |
- Lopez Arteaga, Ines, et al.
(författare)
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Friction dampers, the positive side of friction
- 2004
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Ingår i: Proceedings of the 2004 International Conference on Noise and Vibration Engineering, ISMA. - 9789073802827 ; , s. 589-601
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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. Friction dampers can be a cheap and efficient way to reduce the vibration levels of a wide range of mechanical systems. Here the energy dissipated through friction is analysed for a type of friction dampers used to reduce squeal noise from railway wheels. Three different 1DOF systems of increasing complexity are analytically studied and simple non-dimensional expressions are derived for the optimal friction force and energy dissipation. In this way the influence of the mass, natural frequency and internal damping of the friction damper on the energy dissipation is established. It is shown that increasing the mass and reducing the natural frequency and internal damping of the friction damper maximises the dissipated energy.
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| 33. |
- 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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| 34. |
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| 35. |
- 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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| 36. |
- 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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| 37. |
- Lopez Arteaga, Ines, et al.
(författare)
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Viscoelastic contact model for the prediction of tire/road contact forces and rolling resistance
- 2011
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Ingår i: 18th International Congress on Sound and Vibration 2011, ICSV 2011. - 9781618392596
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A combined Hertz/Maxwell model is presented to approximately describe the interaction between a rigid indenter and a viscoelastic half-space, and therefore the force-indentation relationship including the deformation rate and energy losses. Thismodel is a numerically efficient alternative to the exact viscoelastic half-space formulation, to be implemented in a tyre/road interaction model for the prediction of tyre vibrations, rolling resistance and noise. Here the combined Hertz/Maxwell model is used to assess the influence of road texture on the contact stiffness and damping based on the analysis of 30 road surface types. The parameters of this model are obtained by fitting the load-penetration curves obtained from the exact viscoelastic half-space calculation. It is shown that both the stiffness and damping parameters decrease as the road texture depth increases, since, for a given penetration depth, the effective contact area decreases as the road texture depth increases. Assessing the relevance of these effects for the accurate prediction of tyre/road interaction is subject of ongoing work.
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| 38. |
- Moers, E. M. T., et al.
(författare)
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Detection of plate vibration modes by means of Near-field Acoustic Holography in the presence of reflective surfaces
- 2012
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Ingår i: International Conference on Noise and Vibration Engineering 2012, ISMA 2012, including USD 2012. - : Katholieke Universiteit Leuven. - 9781622768257 ; , s. 3571-3584
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Konferensbidrag (refereegranskat)abstract
- A numerical and experimental study is presented on the influence of reflections on the reconstruction accuracy of the surface velocity of vibrating plates by means of Fourier-based Planar Near-field Acoustic Holography (PNAH) and a single-layer microphone array. At low frequencies (well below coincidence), it is shown that the effect of the presence of the reflective surface on the reconstruction depends on the source. When measuring close to the source, the classical PNAH transformation, based on the free-field radiation assumption, provides a good quantitative reconstruction of the surface vibration velocity. The effectiveness of a modified propagator is investigated which includes the effect of reflections on the inverse propagation from measured pressure at the hologram plane to surface vibration velocity at the source plane. This is done by simulations and measurements for sources that differ in velocity profile and size and that are radiating well below coincidence. Measurements are performed for a free plate in a large baffle in front of a granite block which is less than one acoustic wavelength apart.
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| 39. |
- 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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| 40. |
- 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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| 41. |
- 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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| 42. |
- 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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| 43. |
- 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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| 44. |
- van Dalen, P. L., et al.
(författare)
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Experimental reconstruction of non-stationary sound and vibration sources by means of Transient Planar Near-field Acoustic Holography
- 2012
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Ingår i: International Conference on Noise and Vibration Engineering 2012, ISMA 2012, including USD 2012. - : Katholieke Universiteit Leuven. - 9781622768257 ; , s. 3631-3643
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Konferensbidrag (refereegranskat)abstract
- A novel algorithm called Transient Planar Near-field Acoustic Holography is presented to analyse nonstationary sound and vibration sources. The method is able to obtain the time-dependent pressure, particle velocity and intensity field at the source plane without any pre-knowledge of the source by inverse propagation of measured pressure fields. This makes it possible to analyse phenomena like transients and run-ups for all kinds of vibrating and sound radiating objects. Transient responses of thin plates are analysed to experimentally validate the performance of the algorithm. The determined velocity at the center of the plate is validated using a laser vibro-meter directed at the center of the plate and the spatial fields are qualitatively compared with theoretical mode shapes. It is shown that the algorithm is able to analyse transient responses of plates with good quantitative as well as qualitative results.
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| 45. |
- Van Der Steen, R., et al.
(författare)
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Experimental and numerical study of friction and braking characteristics of rolling tires
- 2011
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Ingår i: Tire Science and Technology. - : The Tire Society. - 0090-8657 .- 1945-5852. ; 39:2, s. 62-78
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Tidskriftsartikel (refereegranskat)abstract
- Throughout the tire industry, virtual testing has been widely adopted in the design process. Both static deformation and dynamic response of the tire rolling on the road must be accurately predicted to evaluate the handling performance of a tire. Unfortunately, experimental characterization of rubber compound frictional properties is limited, and therefore, the Coulomb friction model is still often used in finite element (FE) simulations. To overcome this limitation, a different strategy is developed to capture observed effects of dry friction. The proposed friction model is decomposed into the product of a contact pressure dependent part and a slip velocity dependent part. The identification of the parameters of the slip velocity dependent part, using measured axle forces, is presented in this paper. The complete phenomenological friction model is coupled to a FE model of the tire under testing. A steady-state transport approach is used to efficiently compute the steady-state longitudinal slip characteristics, which show good quantitative agreement with experiments.
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| 46. |
- Van Der Steen, R., et al.
(författare)
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Experimental and numerical study of friction and stiffness characteristics of small rolling tires
- 2011
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Ingår i: Tire Science and Technology. - : The Tire Society. - 0090-8657 .- 1945-5852. ; 39:1, s. 5-19
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Tidskriftsartikel (refereegranskat)abstract
- Virtual testing is nowadays the standard in the design process of new tires. Besides modeling the static response of the tire itself, the dynamics of a rolling tire in contact with the road needs to be incorporated. Due to the uncontrollable environmental conditions and the complex structure of the tires, it is advantageous to use small-scale testing under more controlled conditions. Experimental characterization of frictional properties of rubber compounds is, however, limited due to the necessity of complex measurement systems. In this paper a commercially available laboratory abrasion and skid tester is used to identify both friction and stiffness characteristics of the same rubber compound. The obtained friction properties are implemented in a finite element model of the setup, and different validation steps are presented. Finally, a steady-state transport approach is used to efficiently compute a steady-state solution, which is compared with the experimental results. The numerical results show a good qualitative agreement with the experimental results.
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| 47. |
- 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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| 48. |
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| 49. |
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| 50. |
- Wang, Yuquan, 1985-, et al.
(författare)
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Filling the gap between low frequency measurements with their estimates
- 2014
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Ingår i: Robotics and Automation (ICRA), 2014 IEEE International Conference on. - : IEEE conference proceedings. ; , s. 175-180
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Konferensbidrag (refereegranskat)abstract
- The use of redundant sensors brings a rich diver-sity of information, nevertheless fusing different sensors thatrun at vastly different frequencies into a proper estimate isstill a challenging sensor fusion problem. Instead of using thesize-varying measurements and thereby the size-varying filtersduring each sampling period, we propose to find a substitute ofthe unavailable low frequency measurements such that we canavoid using different sampling frequencies in one filter. In thegap between the sampling of two low frequency measurements,the use of these substitutes produces smoother estimates. In boththe proof of concept simulation and the localization experimentperformed on an indoor soccer robot, our proposed approachexhibits an improved performance compared to the size-varyingKalman filter methods.
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