Near-field acoustic holography (NAH) is an effective tool for visualizing acoustic sources from pressure measurements made in the near-field of sources using a microphone array. The method involving the Fourier transform and some processing in the frequency-wavenumber domain is suitable for the study of stationary acoustic sources, providing an image of the spatial acoustic field for one frequency. When the behavior of acoustic sources fluctuates in time, NAH may not be used. Unlike time domain holography or transient method, the method proposed in the paper needs no transformation in the frequency domain or any assumption about local stationary properties. It is based on a time formulation of forward sound prediction or backward sound radiation in the time-wavenumber domain. The propagation is described by an analytic impulse response used to define a digital filter. The implementation of one filter in forward propagation and its inverse to recover the acoustic field on the source plane implies by simulations that real-time NAH is viable. Since a numerical filter is used rather than a Fourier transform of the time-signal, the emission on a point of the source may be rebuilt continuously and used for other post-processing applications.

The aim of this work is to continuously provide the acoustic pressure field radiated from nonstationary sources. From the acquisition in the nearfield of the sources of a planar acoustic field which fluctuates in time, the method gives instantaneous sound field with respect to time by convolving wavenumber spectra with impulse response and then inverse Fourier transforming into space for each time step. The quality of reconstruction depends on the impulse response which is composed of investigated parameters as transition frequency and propagation distance. Sampling frequency also affects errors of the practically discrete impulse response used for calculation. To avoid aliasing, the impulse response is low-pass filtered with Chebyshev or Kaiser-Bessel filter. Another approach to implement the impulse response consists of applying an inverse Fourier transform to the theoretical transfer function for propagation. To estimate the performance of each processing method, a simulation test involving several source monopoles driven by nonstationary signals is executed. Some indicators are proposed to assess the accuracy of the temporal signals predicted in a forward plane. The results show that the use of a Kaiser-Bessel filter numerically implemented or that of the inverse Fourier transform can provide the most accurate instantaneous acoustic signals.

Empirical Mode Decomposition (EMD) is a powerful "timefrequency" tool that is used here in the spatial domain to filter out at each instant, short scale wall pressure fluctuations measured by a linear microphone array beneath a boundary layer. A frequency over streamwise wavenumber representation is used to separate acoustic and turbulent energy: it is obtained by a classical spatial-correlogram which is performed either on original signals or on spatial EMD-filtered signals. It is shown how spatial EMD filtering reduces the spread of the convective energy due to the truncation effects and is tuned to improve the separation of the acoustical energy out of the turbulent energy.

Abstract. This work is about the development of new techniques for the measurement of the three components of the velocity inside a volume. A comparison of two techniques, optical scanning tomography and algebraic reconstruction tomography method, is performed with 3D displacement tests of transparent solid blocks. 3D measurement fieldsThis work is about the development of new techniques to study 3D mechanical problems involved inside a volume, in particular in the framework of fluid mechanics. For that, Tomographic Particle Image Velocimetry (Tomo-PIV) has been developed to measure the three components of the velocity in a whole volume [1]. This technique consists in recording some projections from different orientations and in using an algebraic reconstruction method to generate a volume image of particles. Optical scanning tomography is another method to generate volumes images and is also an alternative to record the volume particles. In this paper, reconstructions of particle volumes by MART algebraic tomography [2][3][4] and by optical scanning tomography [5,6] are compared on rigid body motion tests. For that, resin blocks have been manufactured with different particle diameters and particle rates and are moved in a tank filled with a fluid resin to suppress the effect of refraction index. For the same position, blocks are recorded by four cameras for the multi sensor tomography and by one camera perpendicular to the laser beam for multi-plane tomography. Particle volumes reconstructed by both techniques are compared. Accuracy of the reconstruction, drawbacks and limitations are presented and discussed. For the different positions of the blocks, Digital Volume Correlation (DVC), the 3D extension of Digital Image Correlation (DIC), is used to measure displacement uncertainty and evaluate the influence of each tomography method. Multi-sensor tomographyCurrently the main techniques used in tomography for the volumic reconstruction in fluid mechanics fluids are ART algebraic reconstruction (Algebraic Reconstruction Technic) and MART (Multiplicative ART). Indeed, these methods are well adapted to reconstruct a volume starting from a very limited number of views (2 to 6). The problem of reconstruction can be written like a linear