Jack Costello
Providence College
Professor; biology
SURF program mentor

When we last checked in with Jack Costello two years ago, he had just published research findings on propulsion as part of a collaborative team.

Investigating how to incorporate the benefit of flexibility to enhance propulsion, the scientists studied a cross-section of animals moving at their steady state, or regular motion. They found that once moving regularly in fluid, whether through water or air, animal propulsors bended to the same degree.

The puzzling issue that arose was that while there was a similarity in the position of bending, the materials making up the propulsors of the group studied was mixed.

“It makes sense that for something to bend, it has to be flexible,” explains Costello. “What we argue is that material flexibility is necessary, but it is completely insufficient to explain bending.”

Think about it, prompts Costello, noting that he is not saying materials are unimportant to the process. He points out that materials do vary between different groups. Some have backbones, some don’t; some have fins, others feathers. As it turns out, bending is not only a result of material composition (although flexibility is needed), but rather more about how animals move through water or air.

Today, Costello and his collaborators continue to build on their research together, having published several more important papers in 2015 and securing more grant funds to pursue answers and understanding. The group comprises fellow RI EPSCoR researcher and Associate Professor Sean Colin, environmental science, Roger Williams University; Professor John O. Dabiri, engineering, Stanford University; Assistant Professor Brad Gemmell, integrative biology, University of South Florida; and PC and RWU undergraduate students.

“The research very much depends on student involvement and we see the way it influences them. SURF puts them in the environment that scientists are involved in all of the time.”

In comparing jellyfish and lamprey eels, Costello says the researchers looked at how they created pressure gradients around their body, and measured the pressure and force on the body. They found the traditional mechanism of thrust production applied. But there were additional forces used by these animals that help make them such efficient swimmers.

“The high pressure pushes the volume of water away and creates an equal and opposing force on the body, and pushes the body forward,” Costello explains. “By creating this pressure gradient, they create suction in the bends they’re making. That suction pulls the animal through the water at the same time using the pushing force. There is more going on than just pushing.”

For the animals, the pulling or suction part dominates the thrust projection, according to Costello. The bending, which the researchers distinguish from flexibility, creates the pressure gradients, and those gradients create forces on the body.

The intriguing question, he adds, is why do animal propulsors bend, yet manmade ones do not?

“Every design that humans have for propulsion — airplane wings, paddles, oars — is stiff,” Costello says. “With animal propulsors, there is not one that we can think of that is stiff.”

The implications of climate change unpack more questions about propulsion and what warming temperatures may mean. Consider first that temperature affects all fluids, and, consequently, affects any process that involves body-fluid interaction. And since cold water is denser, it changes the mass properties and influences the propulsive properties of motion.

As mentors in the Summer Undergraduate Research Fellowship (SURF) program, Costello and Colin involve students at their respective institutions in their research. The pair received three NSF grants last year — the role of fluid motion on feeding success by jellyfish, the role of bending surfaces on force production and motion by swimming animals, and the building of a piece of equipment that will take underwater the imaging methods used in the lab.

“The research very much depends on student involvement and we see the way it influences them,” Costello says. “SURF puts them in the environment that scientists are involved in all of the time. The program immerses them in the world of research and they can make the decision about whether it is a gateway they want to pass through.”

A big part of the process, he adds, is that the students get the opportunity to experience firsthand the excitement of unanticipated discovery: “Rarely, in my experience, do things work out the way you think they would.”

Story by Amy Dunkle | Photos by Joel Page for Providence College