Squishy critters are inspiring underwater vehicle design at the University of Oregon

(DECEMBER 2, 2022) A gelatinous sea creature could teach engineers a lesson or two.

Nanomia bijuga is a marine animal related to jellyfish. It swims via jet propulsion. A dozen or more squishy structures on its body pump water backwards to push the animal forward. And it can control these jets individually. The animal can use the jets together or separately.

A team of researchers from the University of Oregon studied this animal. They learned that these two different swimming styles let the animal prioritize speed or energy efficiency, depending on its current needs. The discovery could help to design underwater vehicles that perform well under a variety of conditions.

“Most animals can either move quickly or in a way that’s energetically efficient, but not both,” Kelly Sutherland said. Sutherland is a marine biologist and one of the research team members. “Having many, distributed propulsion units allows Nanomia to be both fast and efficient. And, remarkably, they do this without having a centralized nervous system to control the different behaviors.”

Nanomia shares the gelatinous, ethereal form of its jellyfish relatives. But it’s a little more structurally complicated. Each one is technically a colony of individuals. For instance, each of Nanomia’s jets is produced by an individual unit called a nectophore. The nectophores are grouped on a long structure at the front of the animal. Meanwhile, wispy tentacles trail behind, carrying structures specialized for feeding, reproduction and protection.

Many marine creatures move via jet propulsion. However, squid, jellyfish, and others have only one jet. Nanomia often has 10 to 20.

“We're interested in why multijet swimming is useful, and what we were really interested in here was the timing,” Kevin Du Clos said. Du Clos is another member of the research team at the University of Oregon.

Nanomia can use its jets together at the same time, and it can activate them in a sequence. Synchronous pulsing sends Nanomia forward very quickly. This is perfect for a quick escape from a predator. Asynchronous pulsing moves the animal a little more slowly but more steadily. Research experiments suggest that this is more energy efficient.

The intricacies of Nanomia’s movement could be useful for engineers turning to nature for inspiration.

“It gives a framework for developing a robot that has a range of capabilities,” Du Clos said.

For instance, an underwater vehicle could have multiple propulsors, and simple changes in propulsion timing could allow that one vehicle to move either quickly or efficiently as the need arises.