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New Ship Will Remain Stable By Creating Its Own Inner Waves
Zothecula writes "When offshore oil drilling rigs are being installed, serviced or dismantled, the workers typically stay in cabins located on adjacent floating platforms. These semi-submersible platforms are towed into place (or travel under their own power) and then their hulls are partially filled with water, allowing them to remain somewhat stable in the pitching seas. Now, a ship is being built to serve the same purpose, but that will be a much more mobile alternative. It will keep from rolling with the waves by generating its own waves, inside its hull."
I used to do that in my bathtub. It's nice to see someone finally upscaled it like this.
The system pushes water from side to side using compressed air to counteract rolling from ocean waves. Granted this is for use in drilling rigs (read big money), but I wonder how much power is required to run the air compressors. The compressors have to be high flow to rapidly move a lot of water, albeit at relatively low pressures-- only 4.4 psi required to generate 10ft difference in seawater (this does not take into account viscosity and inertia).
Reminds me of the chapter in Neal Stephenson's The Confusion (part of The Baroque Cycle). Japanese mercury vendors try to disable the Minerva (an armed merchant vessel) by filling its cargo hold with half-filled pots of mercury, rather than filling them to the brim. The idea is that the sloshing in the hull would resonate with the waves at the entrance to the harbour and slow the ship enough to be captured (or something to that effect). There's a discussion of whether Stephenson got the science correct here.
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This has been done for a few years now. Fuel and potable water tanks in the ships sides connected via pipes with computer controlled valves. Some sailboats include pumps to actively move liquid to the windward side tanks to decrease heeling.
Have gnu, will travel.
They had better get it right. When I use to drive a tractor/tanker, if you didn't get your 1st an 2nd gear shifting just right, the chemicals in the tank would shift with such extreme force, that it would almost knock your head off. You can easily hurt your back driving a tanker. I can just see a ship getting the wave out of sink and bursting a hold in the hull.
Small Waterplane Area Twin Hull (SWATH) is a design that minimizes the effect of the waves. Most of the volume that supports the ship is below the level of the waves, making it very stable. The stability comes from the hull design, so it doesn't require any power and the stabilization isn't prone to failure like an active system.
Here's a short video of a SWATH ship in rough seas, with a regular hull ship for comparison. I'm pretty sure this is the one that I saw in a documentary about the design. They showed a glass of water sitting on a table in the SWATH ship, not spilling. I'm pretty sure that the glass would go flying in the other ship.
They certainly are used used today and practical, though the are also somewhat dangerous if not operated with due regard to their ability to increase a ships chance of capsize. In addition to the anti-roll tanks in the Wikipedia article, there are also 'heeling tanks' - large ballast tanks with oversized bilge pumps used primarily in icebreakers to rock them as they transit through ice, though they are not intended to offset a rolling motion. For a vessel where motion control is imperative, such as a research vessel, two controlled tanks might be fitted to react to a larger range of ships self-displacement and wave frequencies. This can be in addition to what you're more like to see on a yacht - active fin control - as fins require forward speed to be effective, anti-roll tanks do not. The basics of this concept were hashed out pretty well by the 1960's ... though today's control systems are more advanced, can be predicted (rather than reactive) by monitoring the oceans surface, and the reaction of the tank can be better modelled through CFD programs as there is inevitably structural elements through the duct which affect the tanks operation.
Having just read the article, no, this is not news. There are commercial outfits who will provide the entire system, turn-key, if the tanks are accounted for in the vessels design.
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This isn't inner waves, but water moving back and forth in a U shaped tank (water is pushed by compressed air on the tops of the U shape, alternatively).
So there's no wave at all in the tank.
I just wonder:
Is the counter-reaction mainly cause by the counter-weight of the water which fills only one side of the U tank, or by the momentum (acceleration) given to the water rolling in the tank ?
In either case, it could be more easily done with some solid weight on rails, with less energy lost (air compression and fluid displacement).