I Ines Lopez

Truncated aperture extrapolation for Fourier-based near-field acoustic holography by means of border-padding

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.

Experimental and numerical study of friction and stiffness characteristics of small rolling tires

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 t ...

Experimental and numerical study of friction and braking characteristics of rolling tires

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.

Transmissibility of a deformed rotating tyre

The major source of environmental noise exposure is road traffic noise. Of all noise sources, tyre rolling noise is dominant for speeds above 30 km/h for passenger cars. Tyre rolling noise can be subdivided into interior and exterior noise. For the interior noise to which the passengers are exposed to, the tyre transmissibility is essential since it relates the contact forces with the axle forces. These axle forces are responsible for the structure borne interior noise. Here, a Finite Element tyre model, including a fully coupled air column, is used to examine the transmissibility in the frequency domain 0‐300 Hz. It is shown that three aspects are essential in modeling the axle forces resulting from tyre‐road interaction: 1) the tyre deformation since it leads to a set of non‐axisymmetric eigenmodes, 2) the relatively low‐damped non‐axisymmetric acoustic resonance, and 3) rotation. A methodology using substructuring techniques is presented to include rotational effects both in the case of an undeformed a...

Applications of Near-field Acoustic Holography on Small Apertures

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 extended possibilities for PNAH that...

Frequency loci veering in deformed rotating tyres

In previous work [1] a methodology to model tyre vibrations has been developed, which exploits a modal base determined in a standard FE package and includes rotational effects by a coordinate transformation. In the present paper, the effect of rotation on the eigenfrequencies of a deformed tyre is examined. It is well‐known that rotation splits the eigenfrequencies of an undeformed tyre symmetrically around the eigenfrequencies of the non‐rotating tyre, where the slope of the eigenfrequency‐lines is determined by the circumferential wave number and tyre radius only. However, the eigenfrequency‐lines of a deformed tyre demonstrate a fascinating mutual repulsion behaviour if the velocity is increased. This phenomenon is known as frequency loci veering and is induced by the a‐periodicity resulting from the tyre deformation. Besides the effect of veering on the eigenfrequencies, the corresponding eigenmodes interact in the transition zones and finally interchange. The effects of veering are extremely intensif...