Marine

"Heaving oscillators" use wave power to extend shipping range

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Harvesting energy from the motion of the ocean could extend the range of large ships
Harvesting energy from the motion of the ocean could extend the range of large ships
The team calculated the forces placed on the ship's structure by the generator
Shanghai Ship and Shipping Research Institute
The generator would sit below deck
Shanghai Ship and Shipping Research Institute
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Ships can become mobile wave energy converters, say Chinese researchers, using "heaving oscillators" that draw power from heaving, rolling and pitching movements as they move through the sea, while also acting as motion dampers to improve safety.

There are any number of floating wave energy generators under development, goes the thinking here – and yet not many aboard ships, which spend most of their working days in the waves. And where better to generate energy than right there on a ship, where energy storage is shaping up as one of the most difficult hurdles to overcome in the race to decarbonization?

Researchers at the Shanghai Ship and Shipping Institute (go ahead and say that five times fast) proposed a two-body point absorber system that would sit below deck on a freighter, to preserve cargo space, but would also be isolated from the seawater by the hull.

The device would consist of a frame, securely attached to the ship at the top and bottom, with an oscillator body capable of moving up and down the frame rails, a spring to suspend the oscillator, and a hydraulic cylinder attached to the floor and the bottom of the oscillator.

The generator would sit below deck
Shanghai Ship and Shipping Research Institute

The cylinder would pump oil through a hydraulic power take-off device to generate energy as the oscillator slides up and down relative to the ship and the fixed frame. The oscillator, meanwhile, is filled with water, but there's a system for adding and removing water to change its weight. This could be particularly handy under extreme weather, when the oscillator could be de-weighted to reduce stress on the ship's structure.

The design, say the researchers, gives you an oscillator that's "capable of moving along the slide rods when the ship undergoes heaving, rolling, or pitch motion" – thus, generating energy from three different axes of motion, as opposed to previous designs that have managed only one or two.

The team built a model of the system for simulation testing, and ran a bunch of tests to determine how the system would perform at various speeds, wave angles and the like. The study determined the greatest efficiency of energy capture would be in beam seas, where waves are rolling in at 90 degrees, directly hitting the ship's side. Under these conditions, the system could reach "up to 90.71% of theoretical maximum absorbed power by an axisymmetric point absorber under a certain wave period."

The team calculated the forces placed on the ship's structure by the generator
Shanghai Ship and Shipping Research Institute

The team told Recharge News it was planning to prototype its system for wave tank testing as a next step, and that the same system could "easily be extended" to work with other offshore structures.

One thing this study didn't investigate is how much power it could be expected to contribute on an average trip – and that, along with space considerations, will be key to whether systems like this reach widespread deployment.

The study was published in the journal Renewable Energy.

Source: Recharge News

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5 comments
PAV
I was eager to see how much movement this would prevent. Did I miss it? I go on a cruise in 20 days and I certainly would like my cruise ship to have anti roll technology.
Adrian Akau
It will add weight to the vessel so that in ordinary times, the efficiency will be decreased. Why not just design the ship to be more seaworthy?
Nobody
PAV most cruise ships do have anti roll technology(stabilizers). Unless the water is extremely rough, you won't even know the ship is moving.
The biggest problem I see with this oscillator system is the waves from the side are the most undesirable for the crew. You normally try to head directly into the waves in rough water.
Jinpa
This might be interesting to ships that go fishing in rough Arctic waters. They could use catamarans, but don't.
byrneheart
This is the principle behind various wave power generators, allowing the process to be isolated from corrosive saltwater.