Showing papers by "Milena Martarelli published in 2004"
TL;DR: In this article, the out-of-plane vibration response mode shape of a vibrating surface was measured by using a scanning laser Doppler vibrometer (LDV).
88 citations
22 Jun 2004
TL;DR: In this article, a procedure for the aero-acoustic characterization of air jets was presented, where the ability of a laser vibrometer to assess the changes in the optical path induced by local fluctuation of air refraction index was used to calculate the pressure oscillations produced by turbulence.
Abstract: In this work a procedure for the aero-acoustic characterization of air jets was presented. The ability of a laser vibrometer to assess the changes in the optical path induced by local fluctuation of air refraction index was used to calculate the pressure oscillations produced by turbulence. The signal from the laser must be treated in order to extract the required information. From the pseudo velocity, which represents the integral of the refraction index distribution along the laser beam, it is possible to calculate, by a tomographic algorithm, the volumetric distribution of the refraction index at each frequency, and then the pressure oscillation. Each pressure voxel represents a sound source, i.e. monopole, that gives contribution to the Sound Pressure Level in each point of the surrounding. The uncertainty of the procedure was also evaluated.
5 citations
22 Jun 2004
TL;DR: In this article, an algorithm has been developed for taking into consideration the fluctuation of the sound wavelength, and the results accuracy has been checked by comparing them to the surface velocity measured in the vibrating source by means of Scanning Laser Doppler Vibrometry (SLDV).
Abstract: Near-field Acoustic Holography (NAH) is one of the most promising and interesting tool for the investigation of vibro-acoustic problems. This hybrid tool is based on array microphones pressure cross-spectra acquisitions from which the acoustic field on the 3D space can be calculated. The reconstruction procedure involves numerical computations where the effect of many uncertainty sources can be propagated. One of these is the temperature factor: if the vibrating object is undergoing a high temperature gradient, the wavelength of sound propagation will change within the surrounding space. The conventional instruments applying NAH do not take into account this effect since they are based on the hypothesis of constant sound speed along the reconstruction path. In order to appreciate the influence of noteworthy temperature gradients on NAH calculations, an algorithm has been developed for taking into consideration the fluctuation of the sound wavelength. Hence, the results accuracy have been checked by comparing them to the surface velocity measured in the vibrating source by means of Scanning Laser Doppler Vibrometry (SLDV). This research work has been performed within the European Growth Project "ACES" (Optimal Acoustic Equivalent Source Descriptors for Automotive Noise Problems) GRD1-1999-11202.