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Model of Ballast Water Exchange in Great Lakes Bulk-cargo Vessel





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Uploaded on Dec 2, 2009

This animation was prepared by the Naval Surface Warfare Center - Carderock Division as part of the NOAA-Navy CFD ballast tank modeling study. It shows a physical 1/3-scale model of four adjacent sections of a ballast tank from a Great Lakes bulk-cargo vessel constructed with plexiglas. Observations made on the physical scale model during simulated ballast water exchange were used to verify the output of a CFD model of the same structure, which then provided a basis for scaling the CFD model to a full-sized complete ballast tank.

The tank consists of 4 sections, two double-bottom (DB) sections and two side-tank (ST) sections. Physical tank structures are shaded in gray. Transverse data planes through the middle of the front and back tank sections are shaded in red. These are not part of the tank structure, but show the CFD animation flow and salinity changes during water flow. The DB sections are to the left of the viewer and are shaped like rectangular boxes; the ST sections form the right side of the tank and have a curved outer wall; the overflow or exit pipe is seen in the back ST section. Water enters the tank through the funnel-shaped bellmouth visible in the front DB section.

Each animation starts with the tank filled with fresh water (red). The influent seawater (dark blue, salinity = 35) enters at a flow rate of 65 gpm (actual for the physical experiment), which scales-up to a flow rate of 1,012 gpm (230 metric tonnes per hour) at full ballast tank scale.

Features to look for include:

- Initial intense mixing that occurs near the bellmouth.

- Creation of waves caused by influent flow bouncing off structural walls early in the exchange until formation of a stable stratified layer when the density interface reaches about half the tank height.

- Delayed filling of different sections caused by tank partition structures which restrict flow between sections.

- Rapid filling of DB tank sections until the saltwater interface exceeds the height of the manholes, then much slower vertical elevation of the density interface as the ST tanks fill.

- Development of stratification throughout the tank.

- Development of density-driven "waterfalls" at the lightening hole openings between tank sections.

This is an animation of the CFD model for the 1/3-scale experimental tank over a 3-tank-volume exchange, meaning the total volume of influent liquid entering the tank over the course of the experiment is approximately 3x the total volume of the experimental tank. No time indicator was embedded with the animation.

Animation provided by the Great Lakes Environmental Research Laboratory - GLERL


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