Automatic dynamic mask extraction for PIV images containing an unsteady interface, bubbles, and a moving structure

Type Article
Date 2016-07
Language English
Author(s) Dussol David1, Druault Philippe1, Mallat Bachar2, Delacroix Sylvain2, Germain GregoryORCID2
Affiliation(s) 1 : Univ Paris 06, Univ Paris 04, Inst Jean Le Rond dAlembert, CNRS,UMR 7190, F-75005 Paris, France.
2 : IFREMER, Marine Struct Lab, 150 Quai Gambetta, F-62321 Boulogne Sur Mer, France.
Source Comptes Rendus Mecanique (1631-0721) (Elsevier France-editions Scientifiques Medicales Elsevier), 2016-07 , Vol. 344 , N. 7 , P. 464-478
DOI 10.1016/j.crme.2016.03.005
WOS© Times Cited 9
Keyword(s) Particle image velocimetry, Unsteady free interface, Edge detection method, Morphological analysis
Abstract When performing Particle Image Velocimetry (PIV) measurements in complex fluid flows with moving interfaces and a two-phase flow, it is necessary to develop a mask to remove non-physical measurements. This is the case when studying, for example, the complex bubble sweep-down phenomenon observed in oceanographic research vessels. Indeed, in such a configuration, the presence of an unsteady free surface, of a solid–liquid interface and of bubbles in the PIV frame, leads to generate numerous laser reflections and therefore spurious velocity vectors. In this note, an image masking process is developed to successively identify the boundaries of the ship and the free surface interface. As the presence of the solid hull surface induces laser reflections, the hull edge contours are simply detected in the first PIV frame and dynamically estimated for consecutive ones. As for the unsteady surface determination, a specific process is implemented like the following: i) the edge detection of the gradient magnitude in the PIV frame, ii) the extraction of the particles by filtering high-intensity large areas related to the bubbles and/or hull reflections, iii) the extraction of the rough region containing these particles and their reflections, iv) the removal of these reflections. The unsteady surface is finally obtained with a fifth-order polynomial interpolation. The resulted free surface is successfully validated from the Fourier analysis and by visualizing selected PIV images containing numerous spurious high intensity areas. This paper demonstrates how this data analysis process leads to PIV images database without reflections and an automatic detection of both the free surface and the rigid body. An application of this new mask is finally detailed, allowing a preliminary analysis of the hydrodynamic flow.
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