Robust sparse representation for adaptive sensing of turbulent phenomena

Special Issue on Compressive Sensing and Robust TransformsInternational audienceIn this study, the authors propose a method for turbulence characterisation by using sparse representation of a channel's impulse response. They consider the case of moving vortices created naturally or artificially that do not conserve their physical properties when observed at two distinct positions in space. The existing amplitude-based techniques fail to provide an accurate representation when the physical properties of the dynamic turbulence are altered. A two stages approach is proposed in this study. The first one deals with the design of robust waveforms for sensing of turbulent phenomena. The second stage consists of sparsely representing the decomposition of the turbulence's impulse response, based on a physically driven decomposition basis. The tests conducted in a reduced scale experimental facility show, on real data, the efficiency of the turbulence tracking. They compare several types of signals and show that the wideband signals are best suited for the application, achieving a high resolution combined with excellent results in terms of robustness

Electricité de France's study of the acoustic scintillation flow meter results in expanding its range and sensitivity

International audienceElectricité de France's "Direction Technique Générale" (DTG) branch launched a three-year PhD thesis in order to study the Acoustic Scintillation Flow Meter (ASFM) developed by ASL AQFlow. The study was done in a partnership between EDF DTG (owner of one ASFM system since 2006), Hydro Québec (owner of two ASFM systems) and the manufacturer ASL AQFLow. The partnership aimed at sharing information about the mode of operation and components of the ASFM, as well as sharing the results of the research and development and on-site testing, in order to review the concept of the ASFM and, if feasible, to extend its application beyond its present range. Scientific support was provided by Gipsa-lab, a research laboratory within the Polytechnic Institute of Grenoble (INPG), a major player in the international signal processing community, and the R&D division of EDF located in Chatou, Greater Paris area. In the first two years of the PhD study five major measurement campaigns were performed in France and abroad. In addition, a reduced scale test facility was set up at Gipsa-lab. The main tasks for the PhD candidate were: to review the operational limits for the ASFM, to investigate the impact of various interferences on the discharge measurement, to get a better understanding of the velocity computation algorithm, to develop a method to filter out the scintillation frame vibrations, and to improve the algorithm, if feasible. It is expected that this study may provide the basis for the next generation of acoustic scintillation flow meters

Investigation of the Performance of Acoustic Scintillation Flow Meter when Turbulence Levels are Low

International audienceElectricité de France (EDF) is funding a 3-year PhD work on acoustic scintillation flow metering, in association with Hydro-Québec and ASL AQFlow. The PhD project aims at improving the discharge estimation when hydraulic conditions are not ideal for acoustic scintillation measurements, as well as providing a better understanding of the effects of sources of interference which can be encountered during the measurement process and can cause inaccuracies in the velocity estimation. In order to achieve these objectives, a fast and portable data acquisition system was set up, which relies on high speed acquisition cards. Each four channel acquisition card can be connected in parallel with up to three others, thus forming a high speed multi channel data acquisition (DAQ) system. A first test of this DAQ system was performed at one of Hydro-Québec's hydroelectric plant. As the ASFM replaced the existing trash rack elements, special equipment was designed and built to create turbulence in the flow necessary for the acoustic scintillation to operate. HPP performance tests by Hydro Quebec were duplicated with the EDF measurement system which recorded the acoustic scintillation raw signals. Using the resources available at the time, the acquired time series have a lower resolution than those provided by the Acoustic Scintillation Flow Meter (ASFM). However, valid velocity estimates are possible even at this lower resolution

Using wide band signals for obstacle path correction in acoustic scintillation flow meters

International audienceThis paper deals with the challenges of water flow measurement in hydroelectric plants using acoustic scintillation. One of the drawbacks of ultrasonic signal propagation through water is that measurements require relatively clean water conditions. In water with significant amount of impurities, the level of transmitted signals may not be sufficient for an accurate flow measurement. In terms of signal processing, the effect of impurities is represented by a random loss or fading of received signals. In order to improve the measurement, the wide band signals can be used in order to improve the quality factor of the signals by adaptive filtering using a static mode reference. Results show that, in real configurations, the interference due to the obstacles can be reduced

Adaptive Waveforms for Flow Velocity Estimation Using Acoustic Signals

International audienceIn this paper, we introduce a general framework for waveform design and signal processing, dedicated to the study of turbulent flow phenomena. In a bi-static configuration, by transmitting a specific waveform with a predefined instantaneous frequency law (IFL), within the bounds of the Kolmogorov spectrum, the turbulent media will modify the IFL at the receiving side. We propose a new methodology to estimate this change and to exploit it for velocity estimation using acoustic signals. In this way, the amplitude based velocity estimation techniques can be substituted by non stationary time - frequency signal processing. This technique proves to be more robust in terms of interferences and can provide a more detailed representation of any turbulent environment

Construction et analyse des signaux non-stationnaires adaptés à la caractérisation des phénomènes turbulents

National audienceDans ce papier nous proposons une approche hybride signal-physique pour la détection de la présence de la turbulence dans un fluide. L'idée est de construire une forme d'onde capable de porter, de manière robuste, l'information sur la turbulence et de mettre en place le traitement qui permettra l'extraction des paramètres liés à ce phénomène. Il est donc nécessaire de réaliser une correspondance entre les grandeurs qui caractérisent les écoulements turbulents et les signaux acoustiques. Nous allons montrer que l'utilisation des signaux avec une loi de fréquence instantanée polynomiale est potentiellement porteuse de l'information de turbulence que nous pouvons extraire à partir de l'estimation de la déformation de cette loi

Ultrasound Testing of Metallic Structures using a Dual Symmetric Path Inspection and a Matched Filter-based Method

International audienceIn this paper, we present a new technique for detecting and localising defects in metallic structures, using ultrasound non-destructive inspection. This technique consists in applying a dual path inspection and the matched filter to a stepped frequency-type signal. This new technique is compared with classical non-destructive testing approaches. An experimental setup is presented that allows us to validate the proposed method

Underwater Object Tracking Using Time Frequency Signatures of Acoustic Signals

International audienceDetecting underwater objects is an important ap plication in marine applications. Most of the techniques are based on the amplitude related techniques, whereby the amplitude of the received echo is used to detect objects within specified bounds. Amplitude techniques however are prone to interference and attenuation, thus limiting the capabilities of such systems. Hence, the aim of this paper is to propose a new technique that detect and track underwater moving objects usingthe turbulence generated by the object. Wideband signals have proven to be a very efficient alternative for merging turbulent flow characteristics and waveform design in order to describe and explain the behavior of turbulence, both artificial and natural. Therefore, constructing adapted waveforms to the natural turbulence embedded in the flow, as well as to the artificial turbulence created by an unknown underwater moving object may hold the key for a new technique for underwater object tracking. When acoustic signals with a particular Instantaneous Frequency Law traveling into underwater environment will hit a moving object, their Instantaneous Frequency Law will capture the object's artificial turbulence, as well as the natural turbulence embedded in the flow. Experimental results carried out in our reduced scale facility provide the validation of the technique

Sparse representation of channel's impulse response for underwater inhomogeneities tracking

International audienceIn this paper, we propose a method for underwater inhomogeneities characterization using sparse representation of channel's impulse response. We consider the case of moving vortices created naturally or artificially that do not conserve their physical properties when observed at two distinct positions in space. Existing amplitude-based techniques fail to provide an accurate representation when the physical properties of the dynamic inhomogeneity are altered, but it can be achieved using the decomposition of the inhomogeneity's impulse response, based on a physically driven decomposition basis. Tests carried out in a reduced scale experimental facility show, on real data, the efficiency of the inhomogeneities tracking

Electric Arc Locator in Photovoltaic Power Systems Using Advanced Signal Processing Techniques

International audienceIn this paper, we present two techniques for the localization of electric arcs produced in photovoltaic power systems. High order statistic analysis (HOSA) and recurrence plot analysis (RPA) have already proven successful in detecting the partial discharges associated with the production of an electric arc in a high voltage power system. However, this solves only the first half of the problem, since a localization of the arc also needed. Using a four sensors array detector along with a combination of HOSA and RPA techniques, we estimate the direction of arrival (DOA) of the electric arc, as well as the distance to the detector. An experiment was put in place in order to validate the results