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Dixia Fan: Flying and Diving into the Future

22, 2022

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On a random day in late spring this year, the staff of the School of Engineering received an unusual message:

"Prof. Weicheng Cui's lab just filled their lab pool. Let's go experience the magic of spotted seals and their water ripples."

The message came from Prof. Dixia Fan, a principal investigator who recently joined the School of Engineering. After receiving the message, everyone scrambled over to Prof. Cui's lab, hoping to see some "magic seals". But actually, the magic was a tool from Fan which accurately depicted the ripples spotted seals generate when moving through the water.

The water ripples created by spotted seals are very unique. Spotted seals use these ripples like sonar to track their prey. But behind this phenomenon lies the fundamental problem of vortex-induced vibration and fluid mechanics.

Graduating from Shanghai Jiao Tong University, Fan studied for his Ph.D. at the Massachusetts Institute of Technology (MIT) and later became an assistant professor at Queen's University. Since his undergraduate studies, Fan has always focused on fluid mechanics in his research. After joining Westlake, he built the Intelligent, Informational, Integrated, Interdisciplinary Fluid-Structure Interaction Laboratory.

Can we swim like a fish or fly like a bird? Can fantasy become reality? These are some of the dreams of Fan, who wrote in his online faculty bio: "At Westlake University, we are all big kids playing with big toys that will change the world."

Rebellion and Curiosity Are Opposite Sides of the Same Coin

In 2010, Fan, who was a third-year undergraduate student at Shanghai Jiao Tong University School of Naval Architecture, Ocean & Civil Engineering, decided to press the "pause button" and take a year off for a change in perspective. That year, Fan left footprints across the whole country. He joined the Wuhan shipyard as an intern for three months, working on the front line. He went to support education in remote areas such as Guizhou and Yunnan. He hitchhiked on trucks, stayed in hostels, and even grew long hair. This experience made a young man who grew up in Shanghai leave his comfort zone and get in touch with reality.

In 2011, Fan returned to Shanghai Jiao Tong University. Shedding the immaturity and anxiety, he finally started a big experiment. At the Shanghai Jiao Tong University State Key Laboratory of Ocean Engineering, Fan followed Prof. Shixiao Fu and began large-scale experiments. Soon he gradually found his interest in flow-induced motion (FIM).

FIM is a type of vibration caused by water flow or wind traveling over an object, and it includes phenomena such as the vortex-induced vibration. When fluid passes through an object at a certain flow rate it will produce alternating vortices on the surface of the object, and these vortices will generate suction and cause vibration. Vortex-induced vibration has a major impact on the stability and safety of the structure of objects. For example, the shaking of the Humen Bridge in Guangdong Province in 2020 was one of these events. FIM is more than just destruction. In fact, the movements of many animals in nature are based on the interaction of fluids and structures, such as fish swimming in the water for food, and birds in the air flapping their wings. It can also be extended to cardiovascular fluid mechanics, vortex fluids, environmental fluids, and other issues closely related to human survival.

The research on convection-induced vibration has been going on for more than 60 years, but the difficulty is that there are too many complex variables. "There is no one absolute formula that can be applied," Fan said.

Fan founded the Intelligent Vehicle Club at Shanghai Jiao Tong University. There he experimented with the "Flying Fish" unmanned underwater vehicle, the "Sunshine" hexapod robot, and the "Dream Chaser” green energy multi-hull sailboat. Before he graduated, the club was selected as a distinguished science and technology organization at the university.

Taking the Leap

In 2013, Fan was accepted to the Department of Mechanical Engineering at MIT with a full scholarship. When applying to MIT, Fan's outstanding hands-on and critical thinking abilities made him stand out among other applicants. His clear and firm goal of looking for "vortex-induced vibration" impressed other professors.

Fan and other members of the research group during his Ph.D. studies

When we were children, parents criticized us for daydreaming. But combining his big dreams and his knowledge of vortex fluids, Fan wishes to develop a multi-task robot capable of flying and diving. "Imagine a drone flying over the sea on a search mission. After spotting the target it has the ability to directly enter the seabed to explore without switching to a submarine robot. When it finds underwater pollution during operations, it can immediately jump into the sky using a pair of wings and judge the extent of pollution," Fan explained, speaking with excitement in his eyes.

One of the main challenges is to design a structure suitable for multiple purposes. The power required for flying in the air and diving in the water is different, and the device must be both waterproof and windproof. So how do you achieve these multiple functions in one object? Fan looked to amphibious birds for inspiration. Another challenge is the nonlinearity of the control system. Such a robot needs a "smart brain”, so Fan aimed to find his answer in artificial intelligence. In addition, he also must find new materials which can adapt to different environments, including the air and water.

While studying at MIT, Fan discovered the limitations of focusing solely on fluid mechanics. In order to find his inspiration, he studied different courses and went off-campus. He even went to Singapore to study for two consecutive winters to explore research hotspots in water, resources, and environments. After graduating with a Ph.D., he went to Brown University and the University of Washington Department of Applied Mathematics to discuss new ideas and methods for solving problems with other professors. Through the Gaussian regression algorithm and reinforcement learning, Fan and his friends shortened the work that would have taken one or two years to two to three weeks. They believe that artificial intelligence and fluid mechanics can be combined to improve the efficiency of studying nonlinear and multi-scale properties in fluid mechanics.

Taking a Step to Change the World

In February, Fan officially joined Westlake University. From the moment he arrived, Westlake became his home. In the two months since he joined Westlake, he has visited lots of laboratories.

Fan visited Prof. Weicheng Cui's laboratory to discuss the design of underwater devices, Prof. Hanqing Jiang's laboratory to understand the relationship between origami and materials, and Prof. Bowen Zhu's laboratory to discuss flexible electronic materials. In fact, for him, drawing inspiration from other disciplines has become a way of life.

Previously, the interdisciplinary reading group he organized has expanded from an internal MIT group meeting to an "Intelligent and Bio-inspired Mechanics Seminar Series" with thousands of registrations and hundreds of people listening online every week. He has partnered with the knowledge-sharing platform Synking to conduct interdisciplinary dialogues and interviews in podcasts. They have brought people together from fields in humanities, arts, technological innovation, and business to gain an in-depth understanding of the differences in our world.

In the future, he hopes to focus on interdisciplinary research with artificial intelligence and fluid mechanics and to explore mechanisms and methodology in depth. He also hopes to develop new methods of artificial intelligence in vortex control, perception of fluid mechanics, and new theories regarding air-sea amphibious robots 

Fan said that, while the power of one person is limited, when all the people come together, they may really change the world.