Use of beamforming for detecting an acoustic source inside a cylindrical shell filled with a heavy fluid

Abstract

The acoustic detection of defects or leaks inside a cylindrical shell containing a fluid is of prime importance in the industry, particularly in the nuclear field. This paper examines the beamforming technique which is used to detect and locate the presence of an acoustic monopole inside a cylindrical elastic shell by measuring the external shell vibrations. In order to study the effect of fluid-structure interactions and the distance of the source from the array of sensors, a vibro-acoustic model of the fluid-loaded shell is first considered for numerical experiments. The beamforming technique is then applied to radial velocities of the shell calculated with the model. Different parameters such as the distance between sensors, the radial position of the source, the damping loss factor of the shell, or of the fluid, and modifications of fluid properties can be considered without difficulty. Analysis of these different results highlight how the behaviour of the fluid-loaded shell influences the detection. PFinally, a test in a water-filled steel pipe is achieved for confirming experimentally the interest of the presented approach. -IntroductionThe fast and reliable detection of acoustic sources in complex industrial cylinder systems is of capital interest since such sources can be the consequence of defects or leaks in the installation. In the nuclear field, for example, a leak in a Steam Generator Unit (SGU) of a sodium fast nuclear reactor induces a water-sodium reaction. This reaction can damage the component. The purpose of this paper is to study the possibility of using a passive vibroacoustic method to detect and locate the noise generated by a water-sodium reaction of leak rate inferior to 1 g H2O /s. Different studies focussing on active and passive detection techniques have been published in the past [1][2][3]. The paper written by Kim et al. [4] focusses on characterising the acoustic noise spectra of different water-into-sodium leaks for a small flow rates (<1 g H2O /s). Chikazawa [5] developed a beamforming method to detect a leak at a frequency of 10 kHz assuming that it emits a planar acoustic field. This assumption, which is reasonable in the high frequency domain, necessitates a high number of sensors to cover the whole steam generator. Sing and Rao [6] looked at detecting a water injection into liquid sodium by measuring the acoustic field radiated by the installation with microphones located far from the system. Such a method is very simple but may be easily disturbed by external acoustic sources. Moreover, it may be useful for detecting leaks of flow rate strong enough to come out of the background noise. In the 1980's, Greene et. al developed a beamforming passive vibro-acoustic method called GAAD to detect and locate a sodium-water reaction in a SGU of a sodium-cooled fast nuclear reactor [7][8][9]. In these papers, authors characterized with an experiment the performance of the localization and the detection time against the leak rate and the SGU power level. These papers show that ...

Water experiment for assessing vibroacoustic beamforming gain for acoustic leak detection in a sodium-heated steam generator

“…From the detection on a threshold criterion at the output of beamforming (instead of the reference sensor), this gain allows the improvement of the detection rate while limiting the array sensibility to false alarms. The works of Moriot et al (2015) showed promising results in term of array gain, both numerically and experimentally. However, the numerical results were obtained by using simple academic models (infinite plate in Moriot et al (2012) or infinite cylindrical shell in Moriot et al (2015)) supposing uncorrelated background noise.…”

“…Beamforming over an array of sensors is of main interest due to its ability to increase the signal-to-noise ratio of the acoustic signal induced by the water-sodium reaction, generally masked by the SGU background noise as shown by Kim et al (2010). Moriot et al (2015) had considered the conventional beamforming (called sometimes the Bartlett beamforming) based on a knowledge of the source to be detect and by supposing that the background noise is spatially uncorrelated. In the numerical applications, the source was supposed to be an acoustic monopole (i.e.…”

“…external surface of the SGU). Numerical results (Moriot et al 2012(Moriot et al , 2015 showed that the vibroacoustic beamforming using a linear array of accelerometers fixed on the external surface of the cylindrical shell can be used to localize the acoustic monopole. However, the main interest of the beamforming for the detection remains in the increasing of the SNR.…”

A model-based approach for statistical assessment of detection and localization performance of guided wave–based imaging techniques

“…Structural Health Monitoring (SHM) techniques can reduce maintenance costs significantly by switching from the schedule-based maintenance to a condition-based maintenance, and by allowing the use of lighter materials such as composite or sandwich panel in the case of aerospace structures [1]. SHM has been studied for decades, leading to the development of a large panel of techniques [2,3,4,5,6,7,8,9,10,11,12,13,14,15]. Among them, techniques based on guided wave (GW) propagation with piezoceramic transducers are cost-effective and allow a quick on-demand inspection of large areas over thin metallic and composite structures [16].…”

Acoustic beamforming through a thin plate using vibration measurements

“…More recently, vibration based beamforming has been studied to localize acoustic sources inside a cylindrical shell filled with heavy fluid. 9 The first contribution of the present work is the use of the FAT, usually implemented for the localization of structure borne sources, for the identification of an acoustic pressure field exciting a wall. Recent efforts in that domain might however be cited, concerning the identification of a diffuse field 10 or a turbulent boundary layer.…”