1. Introduction 2. Scientific rationale for ADCP measurements
Bubble-Sweep down Study and Mitigation for Improved ADCP Data Quality.
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Transcript of Bubble-Sweep down Study and Mitigation for Improved ADCP Data Quality.
![Page 1: Bubble-Sweep down Study and Mitigation for Improved ADCP Data Quality.](https://reader033.fdocuments.us/reader033/viewer/2022051401/56649c8f5503460f9494906f/html5/thumbnails/1.jpg)
Bubble-Sweep down Study and Mitigation for Improved ADCP
Data Quality
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Credits go to:• Mr. Bob Fratantonio - Department of Ocean Engineering
University of Rhode Island
• Dr. Thomas Rossby– Graduate School of Oceanography
University of Rhode Island
• Dr. Charles Flagg– School of Marine and Atmospheric Sciences
Stony Brook University
• Dr. Stephan Grilli– Department of Ocean Engineering
University of Rhode Island
• National Science Foundation (NSF)• Smyril Line
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The M/F Norröna• Build year/Shipyeard: 2003 / Flendern Werft AG, Lübeck • Ship contract price: € 93,4 mill.• Length over all: 165,74m• Breath: 30,00m• Draft: 6,30 m• Dwt: 6.350• GT: 35.966• NT: 15.922• Cabins: 318 (1012 beds)• Passenger capacity: 1482• Crew: 118• Cars: 800 or Trailers: 130• Lane m.: 1830• Cargo capacity: 3.250 tonnes• Service speed: 21 knots• Main engines: 30.000 BHP• Bow Thrusters: 4.755 BHP• Helicopter pad: On top deck at the ferries stern• Stabilizers: 1 pair of stabilizers
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ADCP• 75 kHz RD Instruments Ocean Surveyor• Installed in a 1-week dry dock period in January
2006 in Hamburg, Germany• Cable runs 8 decks to the DAQ system• ADCP is mounted 60 m from bow
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Dry Dock
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The Bubble Fairing
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Previous Results using the Bubble Fairing
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The Problem
• An ADCP system was installed on the M/F Norröna in January 2006 in Hamburg, Germany
• Instrument was functioning properly, but the data was spotty and poor
• Data improved as M/F Norröna passed through fjords towards Bergen, Norway
• As the ferry entered open seas, the acoustic backscatter amplitude became erratic and of poor quality
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Candidates for Source of Problem
• Internal machinery-generated vibration
• Propeller noise• Electronic interference due
to the long length of cable that necessarily ran along-side some of the ship's power cables
• Bubble Sweepdown– Breaching of the bow-thruster
openings?
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CritterCam• Greg Marshall at the
National Geographic Society loaned us the CritterCam
• Features– Autonomous– Records Internally– Diver Deployable
• Records 1 minute of video every 4 hours
• Permanent magnets attach camera to the hull
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CritterCam Results• Best results come from
videos taken during daylight hours
• Bubble clouds are produced in the turbulent bow wave as the ferry pitches up and down– Clouds approach lens at fairly
regular intervals• Using the height of the fairing
(21 cm) as reference, one can estimate the thickness of the clouds seen in the video as roughly 30 cm thick
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CritterCam ResultsIf the video clip does not play automatically, it can be accessed by
clicking the following link: http://www.unols.org/meetings/2009/200903fic/bubblesweep.AVI
Windows users may need to download the free divx codec to view the video clip. The download is available at: http://
www.divx.com/en/products/software/windows/divx
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Cosmos Floworks• Computational Fluid Dynamics were performed to
address the following questions…– Can the shape of the fairing be improved to reduce the
stagnation pressure at the leading edge of the fairing?– Can the addition of rails placed ahead of the fairing produce
significant upwelling to bring bubble-free waters from depth up to the face of the transducer?
• Used Cosmos Floworks CFD package– Fully embedded in Solidworks– Easy to use
• Computations were performed on a Dell Optiplex 755 running Windows XP Professional– 8 GB of RAM– Intel® Core™ 2 Duo CPU E6850 @ 3.00 GHz
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Rails
• The next step was to investigate the influence of rails upstream of the fairing
• Rails were modeled after a hyperbolic tangent functiony = A * tanh(x) + b
• A systematic approach was taken to optimize the parameters of the rails
• Once the rails were optimized, the rail-fairing interaction could be simulated and studied
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Varying Opening Width
• The first parameter to change was the opening between the two rails.
• The slope of the rails remained constant and only the opening was changed
•Equation
y= A*tanh(x)+b
Varying b changes the width of the opening between rails
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Some Results
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Vortices Generated by Rails
Very encouraging!
The rails do appear to generate upwelling
* Note this figure is upside down
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Varying Slope• The next parameter to change was the slope
• The opening between rails remained constant and only the slope was changed
•Equation
y= A*tanh(x)+b
Varying A and offsetting b the same amount changes the width of the opening between rails
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Final Rail Profile• The rails were shortened from their original 4 meters of length (in the x-dir) to 2 meters
• The opening was optimized as the same width as the fairing, ~0.5 meters
• The height of the rails matched that of the fairing, ~20cm
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Rail – Fairing InteractionPlanview of Z-Velocity
Rails are set 10 meters upstream of the fairing
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Chines• Can we simplify the rails even more?
• Straight rails (chines) were of interest due to their simplicity
• Easy and less expensive to manufacture and install
• But do they perform as well as the rails?
• Use approximately same slope as the hyperbolic tangent rails
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Chines vs. Rails
Rails Chines
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Particle Trajectories - Chines
Water particles released downstream 0.5 meters below the hull starting from the centerline and spanning 1 meter starboard
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Particle Trajectories - Rails
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Particle Displacement Profile (Y-Z)
The rails and chines create a similar swath
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Sketch of New Fairing/Rails Position
• The fairing was moved closer to the centerline of the ship with the hyperbolic tangent rails ~10 meters upstream
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The Rails
Photos of the rails just before the ship was refloated, courtesy of Eike Bayer, the Blohm
and Voss project director.
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Plans for the Future
• Still having difficulty collecting good ADCP data– Not entirely sure why– Lack of Zooplankton for acoustic backscatter?
• Would like to use the camera to get visual evidence of whether the rails are successfully creating local upwelling