Underwater glider promises silent sea surveys

Researchers in the US are exploring the development of an agile, low-cost autonomous, underwater glider robot that can operate silently.

The team at Purdue University in West Lafayette, Indiana, aimed to create a versatile underwater vehicle with components and sensors easily swapped out or added, according to mission specifications. 

“Our goal is persistent operation of mobile robots in challenging environments,” said Nina Mahmoudian, associate professor of mechanical engineering. “Most underwater robots have limited battery life and must return back after just a few hours. For long-endurance operations, an underwater glider can travel for weeks or months between charges but could benefit from increased deployment opportunities in high-risk areas.”

An underwater glider differs from other marine robots because it has no propeller or active propulsion system. It changes its own buoyancy to sink down and rise up, and to propel itself forward. Although this approach enables very energy-efficient vehicles, the vehicles can be expensive and slow with difficulties moving in shallow water.

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Mahmoudian and her students have now developed ROUGHIE (Research Oriented Underwater Glider for Hands on Investigative Engineering). Around four feet long and shaped like a torpedo, ROUGHIE features no outward propulsion or control surfaces other than a static rear wing. 

According to researchers, ROUGHIE pumps water into its ballast tanks to change its buoyancy and provide initial glide path angle when deployed from shore or boat. To control its pitch, the vehicle’s battery shifts its weight forward and backward, acting as its own control mechanism. To steer, the suite of inner components are mounted on a rail that rotates, controlling the vehicle’s roll. 

Mahmoudian described the approach as ‘totally unique’, explaining that ROUGHIE has a turning radius of only about ten feet compared to an approximately 33-foot turn radius of other gliders. She added that the vehicle can operate in shallow and coastal areas, and won't disturb wildlife or disrupt water currents due to its silent operation. 

The team said the robot was tested in the diving well at Purdue’s Morgan J. Burke Aquatic Center. The vehicle’s movements were tracked by installing a motion capture system of infrared cameras below the water, enabling researchers to characterise its manoeuvring behaviour in three dimensions with millimetre accuracy, researchers confirmed. 

underwater glider
Nina Mahmoudian (center) and her students have developed an underwater glider that can operate silently and in confined spaces. Image: Purdue University/Jared Pike

“We program ROUGHIE with flight patterns ahead of time, and it performs them autonomously,” Mahmoudian said. “It can do standard sawtooth up-and-down movements to travel in a straight line, but it can also travel in circular patterns or S-shaped patterns, which it would use when patrolling at sea.”

ROUGHIE can be fitted with sensors to gather temperature, pressure and connectivity data vital to oceanographers, the team said. It has also been sent into ponds and lakes with a fluorimeter to measure algae bloom, and has been fitted with compact magnetometers to detect anomalies such as shipwrecks and underwater munitions.

The research is detailed in  the journal Sensors.