Current Search: Bubbles (x)
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Title
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Design of an active sonar for measuring bubble clouds under breaking waves.
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Creator
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Quant, Roberta Wendy., Florida Atlantic University, Glegg, Stewart A. L., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
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Abstract/Description
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This thesis describes an active sonar mounted to an Autonomous Underwater Vehicle (AUV) for measuring bubble clouds below breaking waves. A new development is the application of a very broadband sonar signal-processing scheme for the sonar. It is shown that using the active sonar on an Autonomous Underwater Vehicle provides reliable data and that good results are obtained by using a correlation processor. This thesis describes the optimum processing procedure for this application, resolution,...
Show moreThis thesis describes an active sonar mounted to an Autonomous Underwater Vehicle (AUV) for measuring bubble clouds below breaking waves. A new development is the application of a very broadband sonar signal-processing scheme for the sonar. It is shown that using the active sonar on an Autonomous Underwater Vehicle provides reliable data and that good results are obtained by using a correlation processor. This thesis describes the optimum processing procedure for this application, resolution, and signal to noise constraints. Experimental results are given which show that bubbles can be imaged using an active sonar from an AUV platform. It was shown in the experimental results that the additive and the multiplicative processing produced good results for different situations. The multiplicative procedure was more consistent in the identification of bubble clouds than the additive process. One could see from the multiplicative images for the sea experiment where the bubble clouds were located while in the additive images one could only tell that a bubble cloud was identified.
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Date Issued
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2000
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PURL
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http://purl.flvc.org/fcla/dt/15792
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Subject Headings
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Sonar, Bubbles, Ocean waves
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Format
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Document (PDF)
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Title
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Radius distribution of ocean near surface bubbles.
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Creator
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Auffret, Yvan., Florida Atlantic University, Glegg, Stewart A. L.
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Abstract/Description
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This study proposed to determine an ocean surface bubble radius distribution using theoretical noise models, experimental noise spectral data and a theoretical model for the bubble size distribution. The obtained distribution was compared to previous experimental distributions. A good agreement was found for the radius upper cut-off but the shape and the peak radius of the distribution are different from experimental observations. The most probable reasons for these differences were given....
Show moreThis study proposed to determine an ocean surface bubble radius distribution using theoretical noise models, experimental noise spectral data and a theoretical model for the bubble size distribution. The obtained distribution was compared to previous experimental distributions. A good agreement was found for the radius upper cut-off but the shape and the peak radius of the distribution are different from experimental observations. The most probable reasons for these differences were given. Moreover, the validity of recent theoretical bubble noise models was checked. Eventually, the main limitations of the study were pointed out and directions for future works were given.
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Date Issued
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1993
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PURL
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http://purl.flvc.org/fcla/dt/14922
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Subject Headings
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Underwater acoustics, Acoustic surface waves, Bubbles
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Format
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Document (PDF)
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Title
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Computed tomographic measurements of void fraction and modeling of the flow in bubble columns.
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Creator
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Kumar, Sailesh B., Florida Atlantic University, Moslemian, Davood, Dudukovic, M. P., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
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Abstract/Description
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A complete understanding of the gas-liquid two phase flow in bubble columns is required for the development of reliable models for scale-up of these multiphase reactors. Although several models have been proposed to describe the hydrodynamics. lack of adequate experimental data has hindered meaningful evaluation of model parameters and model predictions. The Computer Automated Radioactive Particle Tracking ( CARPT) facility that was implemented earlier has provided interesting results on the...
Show moreA complete understanding of the gas-liquid two phase flow in bubble columns is required for the development of reliable models for scale-up of these multiphase reactors. Although several models have been proposed to describe the hydrodynamics. lack of adequate experimental data has hindered meaningful evaluation of model parameters and model predictions. The Computer Automated Radioactive Particle Tracking ( CARPT) facility that was implemented earlier has provided interesting results on the recirculation patterns of the liquid phase. The technique has provided quantitative information on liquid velocities and turbulence parameters as well. In addition to these hydrodynamic parameters the measurement of void fraction is also important. To complement the capabilities of CARPT a scanner for ;-ray Computed Tomography (CT) was implemented to quantify the local void fraction and its distribution in two phase flow systems. The automated scanner is capable of imaging flows in test sections between 0.02.5 m and 0..15 m in diameter at different elevations above the distributor. The scanner makes use of the same detectors used in the CARPT facility and with the use of a specially designed moving collimator provides a spatial resolution of about 5 mm. A non-conventional algorithm based on maximum likelihood principles called the E-M algorithm was used for imagw reconstruction. Long scanning times are required leading to time averaged density profiles. Although the system is only capable of providing time averaged void fraction distributions. it can provide unique information concerning the structure of two phase flow. The system performance was evaluated by identifying the sources of errors in measurement and their bounds. The capabilities of the scanner for imaging void fraction distribution was demonstrated both qualitatively and quantitatively. Fse of existing radiation detectors and the associated signal processing and data acquisition system helped in reducing the cost of the system. The scanner was utilized to quantify the local void fraction and its distribution in bubble columns of five diameters (0.10. 0.14, 0.19, 0.26. 0.30 m internal diameter) and at four superficial gas velocities. The effect of various operating parameters such as column diameter, superficial gas velocity. the type of distributor. the static liquid height and some changes in the physical properties of the liquid phase were studied. For the first time a comprehensive characterization of the void fraction in an air water bubble column using a non-invasive technique was achieved. The experimental data obtained using CARPT and CT under identical operating conditions was used for developing a methodology for scale-up of bubble columns using a one dimensional model for liquid recirculation. Successful scale-up of liquid hydrodynamics using a one dimensional model requires an adequate closure scheme for the Reynolds shear stress. The existing correlations for the prescription of the eddy viscosity or the mixing length scale are demonstrated to be applicable only for a limited range of conditions. and consequently cannot be used for scale-up predictions. A method for estimating the mixing length scale has been explored and an attempt at unifying a wide range of data available in the literature within the pun·iew of the method has been made. The futility of such an attempt is attributed to the non-reproducibility of the flow in different laboratories and the conasequent lack of data obtained under identical conditions. It is demonstrated, however, that scale-up based on the mixing length distribution is possible when it is obtained from a consistent set of data for liquid velocity and gas void fraction profiles. Using the present method for prescribing the mixing length scale. model predictions for scale-up compare satisfactorily for the data that was obtained as part of this research. The achievement was that the turbulence length scale estimated in one column diameter was successfully used in predicting the liquid velocities in larger diameter columns.
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Date Issued
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1994
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PURL
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http://purl.flvc.org/fcla/dt/12384
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Subject Headings
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Two-phase flow, Hydrodynamics, Bubble chambers, Tomography, Emission
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Format
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Document (PDF)