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Science

Swarm-robots for the deep sea

A consortium of German companies, universities and institutes has developed a robot system that can be used for deep sea research. It could also help to find black boxes of aircrafts.

Sven Hoog is a marine engineer at IMPAC Offshore Engineering in Hamburg. He coordinates a consortium of universities, research facilities and industry partners. Together they've been developing an unmanned submarine system that uses swarm intelligence.

SMIS - Subsea Monitoring via Intelligence Swarms - is described as a system because it does not use just one submarine. "At least two submarine vehicles belong to the system," says Hoog. "They perform the mission. A sea bottom station which is used as a charging station also belongs to the system. There's also a watercraft which is used as a relay station to keep contact with the ship and the onshore installation via a satellite."

When the submarines map a larger area or when they are searching for a black box, first the charging station is placed on the sea bottom. Then a vessel on the surface locates its position via satellite navigation. These two benchmarks support the positioning of the submarines by keeping contact with them via acoustic data signals.

Sven Hoog holds a joystick next to a computer screen (Foto: Fabian Schmidt/DW)

Sven Hoog cordinates the development of the remote-controlled deep-sea submarine

"Our aim is to cover an especially large range," says Hoog. "We want dive up to 6,000 meters [20,000 feet] and the horizontal distance should reach eight kilometers [5 miles] from the sea bottom station."

Hoog sees a particularly promising role for the system in the marine extraction of raw materials, especially manganese nodules which contain elements like copper, nickel and cobalt. "Cable routing for offshore wind farms is also an interesting task, as is the search for black boxes. There are many possible tasks which need to be performed at such depths."

The submarines use swarm intelligence for their orientation. That means that each of them knows at any time where the other is, so that they don't get in each others way but support each other. The computer technology used was developed by the Karlsruhe Institute for Technology. Originally it was designed for robots that operate in a two-dimensional space, but the submarines operate three dimensions.

The submarines will be able to operate for three days underwater because they are able to recharge their batteries at the sea bottom station. But they don't have to plug themselves in, since the recharging works via induction, like an electric toothbrush. In this way everything remains sealed and water can't penetrate the electronic systems. The submarines also transfer the collected data to the sea bottom station when they recharge their batteries.

Small dimensions

A remote controlled submarine Foto: Fabian Schmidt/DW

The submarine can be used to exploit marine raw materials

Carl Thiede is an engineer and also the director of ENITECH of Bentwich near Rostock in northern Germany. He assembles the submarines. His specialty is pressure-neutral systems.

That means that the deep sea robots have hardly any pressure receptacles. All hollow spaces have to be completely filled with a suitable elastomer.

"We use industrial silicon," says Thiede. The advantage of this technique is that the material does not deform even under extremely high pressure. And at the same time everything is waterproof.

An underwater vehicle manufactured according to this principle is currently being exhibited at the Hanover trade fair: a remote-controlled robot with a camera and an arm which can be used underwater if something goes wrong.

The most immediately noticeable thing about this submarine is how small it is. "We did not want to build a huge vehicle with five arms," says Thiede. It has only a simple claw-mechanism. But it's also supposed to have everything that defines a ROV - remotely operated vehicle.

It is equipped with several optical cameras, sonar and acoustic communication systems. "If you don't need more than that, you can build it as small as possible," says Thiede. "We don't need five sea containers to transport it to its place of action. We just need two Euro pallets. Then there's a computer and that's it."

A model of a ship with a winch Foto: Fabian Schmidt/DW Seilzugmodell für Untersee-Roboter

A specially developed winch compensates for the effects of the swell

Balancing the swell

The Leibnitz Institute for Baltic Sea Research supports the SMIS project by testing the system on board its research ships on the high seas. Researcher Johann Ruickoldt has come up with a clever solution for a problem which faces all submarines and underwater devices such as probes.

Such devices have to be let into the water using a winch, and they may well have to be fixed at a certain depth for a period of time.

But in practice that's not easy because the ship is moving due to the waves, so that the rope attached to the probe or the submarine moves up and down. That is impractical when you want to take a sample or when you want to measure the ocean current.

"Our solution is this winch that works against the swell," explains Ruickoldt. The winch inversely transfers the oscillatory movement of the ship to the rope. That means the motor driving the winch turns at the same frequency as the swell, back and forth. This is all controlled by a precise sensor in the ship.

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