Watercraft Thrusts With Squid Power

Jan. 4, 2007 — Despite the lack of tails or fins, squids and jellyfish maneuver the seas with the greatest of ease.

Now researchers have designed a water thruster inspired by the cephalopods' sleek and efficient propulsion system that could bring new precision to streamlined watercrafts and even lead to tiny diagnostic robots able to navigate the human digestive tract.

The effort, lead by Kamran Mohseni, an assistant professor of aerospace engineering sciences at the University of Colorado at Boulder, is part of a larger plan to develop a fleet of autonomous underwater vehicles that measure and monitor ocean conditions.

The vehicles would stop at docking stations to upload collected data and power up for another trip.

The current state-of-art design of underwater vessels is not adequate for such a network.

Fast, torpedo-shaped vehicles have tail-end propellers that gives them speed but cannot wiggle them side to side or up and down into tight spaces. Boxy vehicles are inefficient by design but their bulky thrusters afford precise movements underwater.

Mohseni wanted to design a vehicle that was both fast and efficient but could maneuver with pinpoint precision.

No stranger to bio-inspired vehicles, Mohseni and his colleagues have a fleet of micro aerial vehicles that sweep their wings like birds to adjust to atmospheric or flight conditions. So the aerospace engineer looked to the oceans for inspiration on this project. He found it in squids and jellyfish.

These animals basically move by jet propulsion. A squid, for example, takes water in through an opening by the head, called a mantle cavity. Once the water is inside, the squid's mantle seals off all other

orifices, except a tube called a siphon. Muscles on the mantle wall squeeze water out of the siphon with great force.

"The jet goes one way and the squid goes the other way," said Mohseni.

To steer, the animal points the siphon in different directions. Squids are the fastest marine invertebrates, able to propel themselves at 25 miles per hour — the speed of a leopard seal.

Mohseni and his team designed a thruster that works in similar way. The thruster has a cavity and cylindrical exit hole. For muscle power,the device employs a kind of plunger. The thruster takes in water at one end and the plunger forces the water out the other end. The result: squid propulsion.

The researchers built a torpedo-shaped submarine 4 and 1/2 feet long and equipped it with four thrusters—two in the front and two in the back. The thrusters are flush with the body of the vehicle, so as not

to compromise the streamlined design. A standard propeller on the tail end gives the vehicle speed.

The thrusters take over when it's time to maneuver the machine into a tight spot. For instance, a burst of water from the right front thruster will make the vehicle's front end move left. A burst from the back left thruster will make the back end move right.

"His stuff is wonderfully creative," said Naomi Ehrich Leonard, professor of mechanical and aerospace engineering at Princeton University.

Leonard, whose research focuses on dynamics and controls of autonomous underwater vehicles, thinks that the next generation of subs will have multiple forms of propulsion to serve all maneuvering needs.

"You could have a glider vehicle with a propeller and pulse jet actuators. When it needs the maneuverabilty, it turns on the jets. When it needs speed, it turns on the propeller. When it needs to be a work horse and collect data, it turns into a glider," she said.

In laboratory tests, the researchers were able to parallel park the 4 1/2 foot sub into a 5-foot space.

Mohseni's grand plan is to one day unite a fleet of the squid-like oceans vessels with his flock of aerial vehicles to gather cross sections of real-time atmospheric and oceanic data.