18 octobre 2014 ( dernière mise à jour : 20 octobre 2014 )
The purpose of this web page is to make acoustic or seismo-acoustic data recorded at the laboratory scale available to the public. The following data sets are unique in the sense that they would be very difficult to acquire with numerical modeling. This is the main purpose of analog experiments at the lab scale.
What makes these data set unique is the fact that they describe the acoustic response of a mechanical system that is evolving in time, thus generating a lot of complexity. For example, think of an acoustic waveguide where two vertical arrays of transducers face each other and record the broadband multipaths waveguide response between each source and each receiver. Now, create surface gravity waves at the air-water interface while you continue to emit and record the impulse response matrix at a rate that is much faster than the characteristic time of the gravity wave. This data set takes a few minutes to be generated at the lab scale. It would take forever, if possible, to create the equivalent data set with numerical simulations.
Each data set proposed below may be quite large. Be aware that the download could last a certain amount of time. The data come in Matlab format with one or a few codes to read / plot the data. There is also a Readme file and some pictures that explains very shortly the acquisition set-up and, sometimes, one scientific paper that was published from this data set.
The idea is to promote collaborative research. Of course, you can download the data and process them the way you want. Whatever the data utilization, for research or for teaching purposes, the only requirement is an acknowledgement to :
Philippe Roux, ISTerre, Université Joseph Fourier, CNRS UMR 5275, Grenoble (France).
Of course, I would be more than happy to describe the data in more details and, why not, participate one way or another to your research investigation. So feel free to interact with me as much as possible….
- Multiply-scattered flexural plate waves interacting with a local and periodic stress load
Picture of the experimental set-up built from a thin duraluminium plate in which 500 holes were drilled to induce multiple scattering and randomness for flexural plate waves propagating in the kHz frequency. Both a piezoelectric pulsed source and 16 mini-accelerometers are attached to the plate. Aligned with the array, a mini-vibrometer (not shown here) applies a load locally (10 N to 45 N) that can be either transient or periodic. The plate deformation is separately monitored with two synchronised cameras and a stereo-correlation algorithm.
- Acoustic transfer matrix in a waveguide interacting with dynamic surface gravity waves
Schematic diagram of the experimental set-up. Vertical 64-element source and receiver arrays face each other in a 1-m-long, 55-mm-deep water waveguide. The waveguide dimensions are large compared to the 1.5 mm wavelength of the ultrasonic wave. The bottom is made of steel, which allows for perfect reflection at this interface. The waveguide transfer matrix, composed of the 64 x 64 source-receiver responses, is fully recorded every 0.1 s. A computer-controlled dynamic shaker is attached to a Plexiglas cylinder placed at the air–water interface on the side of the waveguide. This device generates impulsive gravity waves that travel from the air–water interface and cross the source–receiver axis in a few seconds.
- Acoustic transfer matrix in a waveguide interacting with dynamic thermal plume
Schematic diagram of the experimental set-up. Two coplanar, 64-element, source–receiver ultrasonic arrays centered at 1 MHz face each other in a 1-m-long, 55-mm-deep water waveguide that is delimited by two air–water and water–steel interfaces. At first, the sound speed is uniform in the waveguide. The sound-speed variations are generated by a thermal resistor that is embedded in the bottom of the ultrasonic waveguide (range, 225 mm). During the 40-s-long acoustic acquisition, the heating system is activated at acquisition time = T0 and stopped at time = T0+T (for example, T0=5 s and T=20 s). The waveguide transfer matrix, composed of the 64 x 64 source-receiver responses, is fully recorded every 0.1 s. In a separate experiment, a thermocouple was positioned variously above the resistor to measure the temperature of the thermal plume during the same heating process.
- Ultrafast ultrasonic acquisition for dynamic flow measurement
New insights into the spatio-temporal structure of rough-wall turbulent boundary layers are expected from the development of novel acoustic high-resolution measurement techniques. In particular, the capability to perform two-dimensionnal and two-component (radial + transversal) flow velocity measurements based on Acoustic Particle Image Velocimetry is seen as a promising technology in a variety of fluid mechanics applications.
A first dataset was collected in a fully rough turbulent clear-water open-channel flow. This dataset could be used to test and optimize algorithms applied for acoustic image treatment, 2D image correlation for velocity estimations. The performance of the ultrasonic measurement should be evaluated in terms of turbulence and sediment transport measurements in the studied flow conditions. For example, the capacity to resolve the inertial range of the turbulence spectra, the mean turbulence scales, the fields of turbulence intensities, Reynolds shear stress and turbulent kinetic energy dissipation rate can be investigated.
- Ultrasonic interaction with a vorticity filament before/after vortex burst
This project finds its roots in the two following points. First, acoustics is a tool of choice to study complex flows because it provides a real-time non-invasive signature of the vorticity field. Second, recent works in acoustics have overcome the difficulty to image and detect weak scattering objects. Since two decades, a large amount of work aimed to measure numerically and theoretically the acoustic scattering properties of a single vortex. However, a filamentary vortex is a very weak scatterer whose experimental acoustic signature is often hidden by the phase distortion effect caused by the vortex-induced fluid flow.
The project goal is to combine two newly-developed experimental procedures to (1) generate, control and monitor a single stable fluid vortex of adjustable size and strength, (2) measure the total acoustic cross section of a vorticity filament over a large frequency bandwidth from measurements performed in a highly reverberant acoustic cavity. The combination of these two techniques will result in a data base of scattering cross section of vortices.
The data bank generated will be an important step for (1) the first-ever experimental validation of the acoustic-quantum physics analogy that is classically used to model the scattering cross section of a vortex, (2) the careful study of the long-range interaction – short-scale scattering between an acoustic wave and a vorticity filament and its potential implications in detection/tracking of tornadoes in air acoustics.
- Metamaterial physics observed at the mesoscopic scale
We demonstrate the experimental realization of a multi-resonant metamaterial for Lamb waves, i.e. elastic waves propagating in plates. The metamaterial effect comes from the resonances of long aluminum rods that are attached to an aluminum plate. Using time-dependent measurements, we experimentally prove that such a medium exhibits wide band gaps as well as sub- and supra-wavelength modes for both a periodic and a random arrangement of the resonators. The extraction of the metamaterial dispersion relation allows us to predict this physics through hybridizations between flexural and compressional resonances in the rods and slow and fast Lamb modes in the plate. We finally underline how the various degrees of freedom of such system paves the way to the design of metamaterials for the control of Lamb waves in unprecedented ways.