The noise generated by pass-by test (ISO 362) was visualized. The moving frame acoustic holography was improved to visualize the pass-by noise and predict its level. The proposed method allowed us to visualize tire and engine noise generated by pass-by test based on the following assumption; the noise can be assumed to be quasistationary. This is first because the speed change during the period of our interest is negligible and second because the frequency change of the noise is also negligible. The proposed method was verified by a controlled loud speaker experiment. Effects of running condition, e.g., accelerating according to ISO 362, cruising at constant speed, and coasting down, on the radiated noise were also visualized. The visualized results show where the tire noise is generated and how it propagates.

Visualization of pass-by noise by means of moving frame acoustic holography.

Numerical validation of shear flow corrections for beamforming acoustic source localisation in open wind-tunnels

The moving frame acoustic holography method, which can increase the aperture size and spatial resolution of a hologram was recently proposed [H.-S. Kwon and Y.-H. Kim, J. Acoust. Soc. Am. 103, 1734–1742 (1998)]. This method continuously sweeps a stationary sound field by using a line array of microphones so that the hologram of a scanned plane can be obtained. This method enables us to visualize the noise generated by moving noise sources based on near-field acoustic holography. However, a drawback is that it can be applied only to sinusoidal components. This limits its practical application. In practice, bandlimited and transient noise, as well as a sinusoidal component, must be dealt with in order to effectively control the noise generated by the moving noise sources. This paper addresses a way to improve the moving frame acoustic holography method so that it can be applied not only to sinusoidal components, but also to a coherent bandlimited noise. The practical applicability of the improved method is ...

An improved moving frame acoustic holography for coherent bandlimited noise

The moving frame acoustic holography (MFAH) method [H.-S. Kwon and Y.-H. Kim, J. Acoust. Soc. Am. 103, 1734–1742 (1998)] enables the visualization of noise generated by moving noise sources, e.g., moving vehicles, by using a line array of microphones affixed to the ground. However, the sound field of a moving noise source has a moving effect, which produces the wavefront distribution different from what would be generated by the source if it were not moving. The moving effect causes errors on the reconstructed hologram by means of MFAH. This paper studies this effect with regard to the speed of noise sources. A formula, which can show the effect, was derived. This enables the analysis of the effect not only on the hologram plane but also on a prediction plane. It was shown that the phase error is more undesirable than that of magnitude. The phase error, which is proportional to the speed of a noise source, shifts the position of noise sources and distorts radiation pattern. A theoretical investigation explicitly showed that the error is negligible for low Mach number (M<0.1). Furthermore, the phase error can be reduced by introducing a correction factor. Several numerical examples illustrate the feasibility of the proposed correction method for low Mach number.

Effects of the speed of moving noise sources on the sound visualization by means of moving frame acoustic holography

In June 2012, fly-over measurements were performed on landing aircraft at P.-E. Trudeau Montreal airport. A custom-made measurement system developed by GAUS (Groupe d’Acoustique de l’Universite de Sherbrooke) including a 95-microphone array with its related audio pre-amplifying and recording system have been used to acquire a comprehensive data set of over 300 flyovers during a five-day period. A particular focus has been made on Bombardier CRJ200 aircraft for which several flight conditions have been measured. Trajectories of aircraft were tracked by a synchronized 2-camera system. Precise localizations of landing gear, flaps and engine have been obtained as preliminary results. The article details source identification results as well as the complete experimental set-up and the algorithms used in de-dopplerization and Beamforming computations.

F. Poisson

Papers

High speed sound sources localization using bilinear time-frequency transformation