Bulletin of the American Physical Society
16th APS Topical Conference on Shock Compression of Condensed Matter
Volume 54, Number 8
Sunday–Friday, June 28–July 3 2009; Nashville, Tennessee
Session D3: ED-1a: PDV Fundamentals |
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Chair: Steve Clarke, Los Alamos National Laboratory Room: Hermitage C |
Monday, June 29, 2009 1:30PM - 1:45PM |
D3.00001: Fundamental Experiments in Velocimetry Matthew Briggs, David Holtkamp, Larry Hull, Michael Shinas One can understand what velocimetry does and does not measure by understanding a few fundamental experiments. Photon Doppler Velocimetry (PDV) is an interferometer that will produce fringe shifts when the length of one of the legs changes, so we might expect the fringes to change whenever the distance from the probe to the target changes. However, by making PDV measurements of tilted moving surfaces, we have shown that fringe shifts from diffuse surfaces are actually measured only from the changes caused by the component of velocity along the beam. This is an important simplification in the interpretation of PDV results, arising because surface roughness randomizes the scattered phases. [Preview Abstract] |
Monday, June 29, 2009 1:45PM - 2:00PM |
D3.00002: Heterodyne Velocimetry measurements on solids shock driven by high power lasers Patrick Mercier, Jacky Benier, Pierre-Antoine Frugier, Arnaud Sollier, Emilen Lescoute, Jean-Paul Cuq-Lelandais, Elise Gay, Thibaut De Resseguier, Laurent Berthe, Michel Boustie, Mariette Nivard, Alain Claverie, Marc Rabec le Gloahec A new Heterodyne Velocimeter (PDV) is under development at CEA for high explosive experimentations. Recently, we used it onto metallic target shock driven by high power laser. The aim is to test the ability of this means to reveal the propagation and the effects of shocks into materials, at extremely high strain rate and fast variations into the loading evolution. Spallation and fragmentation experiments carried out on aluminum samples, were performed on the LULI lasers at the Ecole Polytechnique, with both VISAR and HV diagnostics. Comparisons reveal a very good consistency of both experimental results. In addition, HV diagnostic evidence several levels of velocity in the experiment of fragmentation. Interpretation of these measurements is supported by transverse shadowgraphy analysis. [Preview Abstract] |
Monday, June 29, 2009 2:00PM - 2:15PM |
D3.00003: Velocity Extraction from PDV Data Using Advanced Fourier Transform Techniques Michael Furlanetto Photon Doppler Velocimetry (PDV) experiments return surface velocimetry data encoded in the form of time-dependent amplitudes. Typically, these data are analyzed by sliding short-time Fourier transforms (STFTs), which return frequency (velocity) distributions at a number of discrete time windows. The parameters for these STFTs -- sample length, window size and parameters, and overlap -- are often chosen empirically. However, the analysis procedure is usually the largest single source of uncertainty in the returned velocity data, and although the STFT parameters affect the accuracy and precision of the result, their precise impact has not been quantified. Using synthetic PDV data sets, this study has investigated the accuracy with which a single velocity can be extracted by STFT techniques. The impact of the STFT parameters on the resulting accuracy has been measured computationally. Additionally, the increased accuracy gained by the use of multi-resolution and fractional Fourier techniques have been measured, along with the increased computational cost. [Preview Abstract] |
Monday, June 29, 2009 2:15PM - 2:30PM |
D3.00004: High-Resolution Projectile Velocity and Acceleration Measurement using Photonic Doppler Velocimetry Scott Levinson, Sikhanda Satapathy This paper describes the new photonic Doppler velocimetry (PDV) technique for measuring time-resolved projectile velocity and acceleration profiles. This technique is shown to provide excellent temporal and spatial resolution in measurement for full flight of the launch package launched from single- and two-stage guns. The PDV method measures the minute Doppler shift in the monochromatic light reflected from the moving surface, which is directly proportional to its velocity. The Doppler-shifted laser signal is mixed with the unshifted signal to generate a beat signal. Short-time Fourier analysis of the beat signal produces highly resolved and accurate velocity profiles. Off-the-shelf components developed for the telecommunications industry are used, producing a system that is robust and inexpensive. Other examples of PDV measurements are provided in a companion paper on impact response of glass bars. [Preview Abstract] |
Monday, June 29, 2009 2:30PM - 3:00PM |
D3.00005: What does ``velocity'' interferometry really measure? Invited Speaker: Optical interferometers (\textit{e.g.}, VISAR and PDV) are commonly used to measure velocity in dynamic compression experiments. Although the basic function of these interferometers is typically straightforward, there are situations where their operation becomes unclear. Both VISAR and PDV are displacement interferometers because they respond to changes in target position; approximate velocities are determined over a finite time duration of the measured signal(s). However, this distinction becomes muddled in various measurements. Interference fringes can be observed despite the lack of any obvious displacement, while in other situations, no interference fringes are observed even when displacement is seemingly evident. This presentation attempts to reconcile the apparent inconsistencies in optical velocimetry. Many of these inconsistencies stem from intuitive, but incorrect, notions of interferometer operation. Ultimately, ``velocity'' interferometry provides a measure of displacement, though the origin of this displacement may be subtle. [Preview Abstract] |
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