After reluctantly taking up the study of jellyfish during a SURF summer at Caltech, John Dabiri is now a professor at the Institute, and he can’t put them down.

By Michael Rogers

Most people think of jellyfish as a nuisance at the beach or, at best, cool–looking translucent blobs that you wouldn’t want to touch. But for John Dabiri, PhD ’05, assistant professor of aeronautics and bioengineering at Caltech, they are elegant and complex creatures whose systems of defense and locomotion may help address engineering problems that range from energy conservation to human health.

Dabiri’s interest in jellyfish didn’t surface until he came to Caltech in 2000 for the Summer Undergraduate Research Fellowships (SURF) program. Then a junior mechanical engineering major at Princeton, he was accepted into SURF by Mory Gharib, PhD ’83, Caltech’s Liepmann Professor of Aeronautics and Bioengineering, who has developed novel approaches to battle human diseases and other problems.

Caltech’s John Dabiri plunged into the study of jellyfish motion after jettisoning an early interest in helicopter design. The Aurelia aurita species of jellyfish—commonly called moon jellyfish—shown in the banner, were photographed in Dabiri’s lab, but make their home off the southern California coast, among other places.

At the time, Dabiri was mostly interested in designing small helicopters that could be used for surveillance and other purposes, and since Gharib is involved in trying to solve small-scale engineering problems, it seemed like a good fit. But Dabiri hadn’t even set foot on campus before Gharib began sending him e-mails outlining his interest in jellyfish. He told Dabiri that he thought the pulsating action of jellyfish might serve as a nifty model for the beating heart, and therefore might be useful in improving heart diagnostics or even in treating heart disease in human patients. “The jellyfish is like a human heart atrium and it’s an amazing platform because it’s so simple,” Gharib says. “There is a convergence of design.”

Dabiri was not impressed. In fact, he immediately began to wonder whether he was making a big mistake. “I thought, ‘What have I gotten myself into?’” recalls Dabiri. “This wasn’t engineering. This was biology, and I hadn’t taken a biology class since the 10th grade. I didn’t know a gene from a protein, and I couldn’t have cared less.”

In the end, Dabiri did come to Caltech, thinking that at least he’d get to see what it was like to live in California. On his very first day, Gharib took him to the Long Beach Aquarium, gave him a video camera, and told him to videotape some jellyfish swimming in tanks. Dabiri had certainly seen jellyfish before on TV nature shows, but this was his first encounter with live ones. As he watched their graceful movements and thought about Gharib’s ideas, he realized that studying jellyfish had as much to do with engineering as with biology. “I immediately thought, ‘This is an interesting problem for fluid dynamics after all.’”

Dabiri spent his SURF summer coming up with a mathematical model for the way jellyfish move, and by the time he went back to Princeton, he wasn’t so interested in helicopters anymore. “Mory became one of the key people in my academic development,” he says.

Before he met Gharib, Dabiri’s primary influences were his parents, who had left their native Nigeria in 1975 to settle in Toledo, Ohio. Dabiri’s dad, a mechanical engineer, got a job teaching math at a community college. His mom, a computer scientist, raised three children and then started a software development company. His dad would occasionally do engineering work on the side, using a drafting table he had set up in the living room. “That’s how I fell in love with engineering—watching him,” says his son.

Educated at a small Baptist high school, where he graduated first in his class in 1997, Dabiri was accepted by Princeton, the only university he had applied to. After struggling a bit with his classwork that first semester, he brought up his grades and spent two summers on the campus doing research that included work on helicopter design. Having grown up in the Rust Belt, home to many auto plants, Dabiri naturally gravitated toward transportation engineering. But he changed gears after his SURF at Caltech, and, after returning to Princeton for his senior year, he applied to the Institute to start graduate work with Gharib’s group. At Caltech, he focused much of his doctoral research on how swirling motions, or vortices, are created by rigid plates compared with flexible plates. “Some questions were biological in nature and some were more pure fluid dynamics,” he says.

He resumed his studies of jellyfish in one of his thesis projects, providing a more detailed quantitative analysis of jellyfish movements as a framework for understanding the human heart. “I went from studying the physics of piston-generated flows to an arbitrary geometry like the jellyfish. Under Mory’s supervision, I developed a general mathematical framework and then applied it to the jellyfish and the heart to determine which motions gave optimally efficient performance in each case.

“It’s now a general design paradigm that can be implemented in experiments,” Dabiri says. “So if you want to physically simulate what happens to certain aspects of the mechanics of a diseased heart, you can do that by affecting the health of the jellyfish—for example, by changing the water quality—and monitoring changes in its swimming performance.”

The series of photographs above illustrates how Dabiri and his colleagues are developing techniques to analyze flow currents without touching the jellyfish. The red lines represent the boundary in the water between the currents (in green) that are sensed by the jellyfish and those (in blue) that pass them by unnoticed.

Gharib credits Dabiri with solving some fundamental questions about vortex formation. “For 10 years I had tried to understand how vortex puffs (essentially, the shape created by a sudden burst of air or fluid through a vortex) form like a nuclear mushroom cloud,” Gharib says. “We wanted to see if nature had discovered how to optimize these formations first, and the best candidates for investigating this were squids and jellyfish. John took on the project for his PhD thesis and proved that these creatures do seem to have an optimal way of generating a vortex to get maximum push or force”—in other words, a built-in strategy for efficiently generating the most force.

“I had discovered that at the most fundamental level, all vortices form by pushing fluid out of a nozzle,” says Gharib, “but John discovered that for optimal thrust, the nozzle should not be rigid.” Such a discovery might not be the talk of Toledo, but it could have significant applications in transportation, energy production, and even in medicine, for example, in the design and manufacture of artificial heart valves.

By the time Dabiri was wrapping up his doctoral research, Gharib had concluded that he would make an excellent Caltech professor, although he points out that Caltech thesis advisers don’t usually waste their time trying to get their brand new PhDs an Institute faculty appointment. “Everybody thinks their students are the best,” Gharib says. “But John’s work was so stellar, that other faculty came to me and said, ‘Are you crazy? You can’t let him go.’ Stanford, MIT, and Princeton all tried to recruit him. Caltech needs people like him. He’s smart, energetic, and doing research that other universities envy.” Dabiri skipped the typical postdoctoral route and after graduation joined the Caltech faculty as an assistant professor of aeronautics and bioengineering.

“At the end of the day, I felt that this was a place where I could try out ideas that weren’t conventional engineering,” Dabiri says. “I’d have the resources and be able to get the students I needed. I realized that this would be a place where I could grow.”

Resources have already been coming together for Dabiri, starting with his custom-designed lab in the basement of the Keck Engineering Laboratories. The facility’s centerpiece is a 40-meter-long, 8,000-gallon flume, or water tunnel, that is two floors deep. (The space was previously occupied by a tank used to study sediment motion and problems of fluid dynamics.) In the new tunnel—which will also be used in fluid dynamics courses—Dabiri plans to carefully analyze the movements of jellyfish and squid, which should help him arrive at a more complete understanding of a range of propulsion systems. Biologically inspired, engineered propulsion systems resulting from this research will also be tested in the facility.

In the photos above, Dabiri (left) stands in front of the refurbished 8,000-gallon water tunnel in the basement of the Keck Engineering Laboratories. At right, graduate student Kakani Katija tries to corral a jellyfish under a suction device that she designed to gently hold the creature in place while it’s being studied.

Dabiri is interested in his research’s potential applications to transportation and energy problems. Certain species of jellyfish, he notes, are extremely efficient at gliding through water, while others generate high-force jets when under attack. “A collaboration involving my research group recently discovered this distinction and demonstrated it in terms of the fluid dynamics,” Dabiri says. “It has been hypothesized that certain species might be capable of exhibiting both high efficiency and high thrust—perhaps by using more than one swimming motion. One goal of our upcoming field studies is aimed at testing this hypothesis.” Dabiri was recently awarded a multiyear NSF grant that will enable him and one of his graduate students, Kakani Katija, MS ’05, to apply laser-based measurement techniques—normally used in the lab—during scuba-diving expeditions.

While he can’t imagine that this research will lead to the design of a vehicle that looks like a jellyfish, he thinks that certain aspects of the creature’s motion can be applied to vehicles, such as in the design of propellers that are flexible rather than rigid. He’s also interested in using this research to help develop new and better ways of harnessing wave and wind energy as power sources.

“People have been looking at wind and water power for centuries,” he says. “There is currently skepticism about how useful windmill or ocean devices can really be in terms of their relative contribution to the U.S. energy supply. We’re trying to develop a system based on several small-scale devices” that can be combined to generate significant energy. “We’re taking inspiration from energy conversion mechanisms exhibited by fish in order to develop a system that can be effective even in weak currents.

“The starting point for our work is the fact that fish, and the jellyfish studied in my lab, can use vortices in the water to decrease the muscle activity required for locomotion. It’s an energy-saving process that is related to how the animal orients its shape relative to the flow. More specifically, it’s how vortices in the flow are ‘pushed’ around by the animal and how the animal is pushed by the vortices. Exactly how they do this is still a bit of a mystery, and that’s one area of current research interest in my group. Granted, this happens at the scale of individual fish, as opposed to the large-scale engineering devices we’re used to. However, by arranging small-scale devices in an array, the mechanisms used by fish can be scaled up to larger devices.”

Dabiri says that his overall goal “is to describe the animal–fluid interactions in terms of engineering equations that can be used to guide the design of energy technologies. The equations would allow us to predict the dynamics or motions of the energy device in a given air or water flow environment. I don’t want to solve the aerodynamics of just one specific bird or build vehicles that look like animals. I want to come up with a model that can be extrapolated to the physics of other systems and applied to a variety of problems.

“My interest is to give people a blueprint and let them go out and build things. The downside is that we won’t make any money off their inventions, but we can impact a lot more people that way.”

In coming up with mathematical models of jellyfish motion, Dabiri is developing new tools for analyzing different fluid systems. One of the problems with carrying out fluid dynamics experiments on living creatures is that the field’s traditional measuring and sensing devices often interfere with the natural behavior of organisms, making it hard to obtain an accurate picture of what’s going on. So Dabiri, in collaboration with fellow Caltech engineering professor Jerrold Marsden, is trying to develop techniques to analyze highly detailed 3-D images of flow currents, without touching the creatures he’s studying. Although Dabiri doesn’t discount the difficulties involved in gathering crucial fluid–mechanics data solely from photographs, he sounds optimistic about the techniques that he and Marsden are developing. “If you can only see fluid motion, can you measure forces without touching the animal?” Dabiri says. “If you can only take a picture, can you still measure it? We’re developing a theory for noninvasive measurement and are a few months away from a definitive demonstration.”

Dabiri is also continuing his collaboration with Gharib. “We hope we will have a good model for understanding fluid propulsion for movement of blood in the heart,” Gharib says. “We’re very close. We’re getting to a global understanding of how nature uses muscles and biological surfaces to transport objects and fluid.”

In April 2006, Gharib, Dabiri, and several colleagues published a paper in the
Proceedings of the National Academy of Sciences, reporting on their efforts to use ultrasound imaging to diagnose heart disease by creating an extremely detailed picture of the jet of blood as it squirts through the cardiac left ventricle. The jet forms as blood passes from the left atrium to the left ventricle during diastole—the heart-filling phase of the cardiac cycle. Their studies of vortices demonstrated how heart valves should look when they’re performing most efficiently. They are now trying to get funding to carry out a clinical test of their diagnostic technique on a large population of people.

Dabiri says that he finds jellyfish “very inspiring.” But when he studies them in their natural habitats in distant places like Brazil and Croatia—chosen for their clear water and abundance of jellyfish—he lets his graduate students do the diving. Given his interest in fluid dynamics and the fact that, at over six feet tall with broad shoulders, he’s got a swimmer’s physique, it’s easy to assume that Dabiri would love to get in the water and jam with the jellies. But he’s much happier watching them from the shore, or at the very least, from the dry side of the tank. “The running joke is that I don’t swim,” he admits. “I sink like a stone.”