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| Registros recuperados: 11 | |
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| Delacroix, Sylvain; Germain, Gregory; Berger, Laurent; Billard, Jean-yves. |
| Bubble sweep-down on oceanographic vessels generates acoustic perturbations. We propose in this work to characterize the sub-surface bubbles occurrence conditions from acoustic data analysis acquired during surveys in relatively shallow water with the IFREMER research vessels Thalassa and Pourquoi Pas?. The methodology of data analysis used in this work allows us to characterize the sailing conditions influence on bubble sweep-down occurrence. The correlation between sailing conditions and acoustic perturbations tends to demonstrate that the presence of bubbles under the hull is clearly related to the wind speed and natural aeration, and that surface bubbles are advected differently in the water column by the two vessels |
| Tipo: Text |
Palavras-chave: Bubble sweep-down; Acoustic perturbation; Ship motion. |
| Ano: 2016 |
URL: http://archimer.ifremer.fr/doc/00294/40557/39632.pdf |
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| Delacroix, Sylvain; Germain, Gregory; Gaurier, Benoit; Billard, Jean-yves. |
| In this second part, images acquired from the specific trials developed in order to study the phenomenon of bubble sweep-down are analysed. A post-processing method has been developed to analyse the two air entrainment mechanisms described in the first part, for several test configurations. Bubble clouds are described in terms of depth, area and velocity for both vortex shedding and breaking wave bubble clouds. A parametric study is also performed to calculate the influence of each test parameter on the frequency of bubble generation. It is demonstrated that the occurrence of bubble clouds is proportional to the wave height, with a considerable influence of the phase shift between waves and motions. The overall results provide new elements for the... |
| Tipo: Text |
Palavras-chave: Bubble sweep-down; Experimental trials; Ship motions; Bow waves. |
| Ano: 2016 |
URL: http://archimer.ifremer.fr/doc/00335/44577/44314.pdf |
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| Dussol, David; Druault, Philippe; Mallat, Bachar; Delacroix, Sylvain; Germain, Gregory. |
| 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... |
| Tipo: Text |
Palavras-chave: Particle image velocimetry; Unsteady free interface; Edge detection method; Morphological analysis. |
| Ano: 2016 |
URL: http://archimer.ifremer.fr/doc/00327/43778/43335.pdf |
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| Delacroix, Sylvain; Germain, Gregory; Gaurier, Benoit; Billard, Jean-yves. |
| Bubble sweep-down is a significant issue for the oceanographic vessels, which affect the acoustic surveys. Experimental trials, carried out in the Ifremer wave and current circulating tank on a 1/30 model of the Pourquoi pas?, are presented. The results demonstrate that this kind of experimental facility is well suited to study the phenomenon of bubble sweep-down encountered around the bow of a ship under specific conditions. From these results, two kinds of bubble clouds formation have been observed and analysed: bubble clouds generated by vortex shedding and breaking waves. The vortex shedding bubble clouds appear randomly in all the configurations tested, even without waves or motions. This phenomenon is due to the interaction between the turbulent flow... |
| Tipo: Text |
Palavras-chave: Bubble sweep-down; Experimental trials; Ship motions; Bow waves. |
| Ano: 2016 |
URL: http://archimer.ifremer.fr/doc/00335/44578/44315.pdf |
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| Delacroix, Sylvain; Germain, Gregory; Billard, Jean-yves; Gaurier, Benoit; Facq, Jean-valery; Bacchetti, Thomas. |
| The bubble sweep-down phenomenon around the hull of scientific vessels leads to a disruption of the acoustic waves emitted by the sonars, and a loss of productivity during the acoustic surveys. Numerical or experimental tools used to study this phenomenon still have limitations, mainly due to scale effects on bubbles generation. An innovative method in a circulating tank, using numerical simulations and a motions generator, has been developed. Two mechanisms of air entrainment have been described, as well as the influence of waves characteristics and turbulence on bubbles generation. |
| Tipo: Text |
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| Ano: 2014 |
URL: http://archimer.ifremer.fr/doc/00247/35807/34321.pdf |
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| Delacroix, Sylvain. |
| One of the main assignments of Ifremer is to study the seabed and the resources undersea, through a large oceanographic fleet used across the globe. For that purpose, ships are equipped with different kinds of SONAR (SOund Navigation And Ranging) to obtain the information sought in the water column. In some sea conditions, waves and ship motions generate significant air entrainment below the surface. Bubble clouds are then carried under the hull by the flow. The interaction between these bubbles and the acoustic waves may result in data loss, and therefore in a considerable reduction of the vessel’s productivity. The tools used to study this phenomenon are currently limited : the numerical models are not efficient enough to simulate at a time air... |
| Tipo: Text |
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| Ano: 2015 |
URL: http://archimer.ifremer.fr/doc/00270/38169/37422.pdf |
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| Registros recuperados: 11 | |
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