Georges Elias

The paper summarizes research on the vibroacoustic environment of the Ariane launcher at lift-off carried out to find means to control the vibroacoustic effects. The external acoustic environment is considered first. After a qualitative description of the noise sources associated with rockets and their environment, emphasis is placed on three issues: the use of model experiments, the modeling of the

A new phased-array processing method has been developed to achieve accurate 2D localization of acoustic sources. While conventional processing requires a full 2D array with an excessive number of microphones, the present method is designed for sparse arrays, and uses ...

A flight test campaign with a Dauphin helicopter has been conducted by ONERA, in cooperation with Istres Flight Test Center (CEV). The objective was to investigate the possibility of localizing the noise sources radiated by the helicopter from measurements ...

Résumé/Abstract Array processing is a powerful tool to extract the noise source characteristics from the acoustic signals measured during wind-tunnels tests. For many years, this measurement technology is commonly being used to study airframe noise. ...

Knowledge of the surface field is required for methods of wave extrapolation, with extrapolation performed in the radial direction from data recorded on a single side-line when the wave field is axisymmetric or has lower order azimuthal components. A theoretical basis for radial extrapolation in the spectral domain is provided, describing numerical simulation results, and an experimental application. The application of a spectral method to a cylindrical geometry has permitted the radial extrapolation of an acoustic field measured on a line located within a short distance, using the Fourier transformation. The applicability of wave extrapolation to seismic data, underwater acoustics, SHF antenna radiation, and acoustic fields and laser cavity calculations is noted.

Basic features of focused arrays are discussed. Phased arrays can be processed in frequency-domain. Each channel requires an anti-aliasing filter, an A-D converter, a Fourier transformer in order to obtain the cross-spectral density matrix which is the base of the various images to be plotted. Such images are usually in 3 dimensions (perspective or 2D+color or grey scale). Examples are

In the frame of the VEGA program, a collaboration between AVIO and ONERA has been established in order to characterize the acoustic environment of the VEGA launch vehicle which will lift-off from the exlaunch pad ELA1 of the former Ariane 1 in Kourou. A test ...

To model bidirectional measurements, a numerical method for computing the incoherent light scattered by a diffusing medium is presented. The results are expressed as a function of the incident and the observer angles (theta(i), phi(i)) and (theta(f), phi(f)), in contrast to the N-flux method, which gives no information about the azimuthal-distribution. To solve the multiple-scattering equations, an auxiliary function, expanded on the spherical harmonics, is introduced in the diffusion equation. A set of integral equations on the coefficients are obtained that are well suited for the numerical resolution. The boundary conditions are included in the linear operator of the integral equation, so that each boundary condition is associated with a specific equation. As an illustration, the method is applied to numerical simulations of maps of the light scattered by a thick refractive diffusing layer of refractive index n = 1.5, for two directive phase functions and for several incident collimated-beam angles.

Wave extrapolation methods are commonly used to evaluate the farfield radiation pattern of a complex source from nearfield measurements. The nearfield data are usually collected with transducer arrays or matrices. This standard procedure poses problems of signal ...

Résumé/Abstract Array processing is a powerful tool to extract the noise source characteristics from the acoustic signals measured during wind-tunnels tests. For many years, this measurement technology is commonly being used to study airframe noise. ...