These findings could be useful in the fields of transportation and energy. When you look at the sky in early spring, you may notice a flock of birds flying north in perfect harmony. So how do these creatures fly so coordinated and seemingly effortlessly?
Part of the answer lies in precise and previously unknown aerodynamic interactions, a team of mathematicians report in a newly published study. Its discovery expands our understanding of wildlife, including fish farming, and could have applications in transportation and energy.
“This area of research is important because animals are known to use flows such as air or water released by other group members to conserve the energy needed to move or to reduce drag or resistance,” explains Leif. Ristroff is an associate professor at New York University’s Courant Institute of Mathematical Sciences and senior author of the paper in the journal Nature Communication. “Our work may also have applications in transportation (for example, moving air or water more efficiently) and energy (for example, more efficiently harvesting energy from wind, water currents or waves).”
Aerodynamic effect on swarm formation
The team’s results show that the impact of aerodynamics depends on the size of the flying group; While it benefits small groups, it hinders large groups.
“Aerodynamic interactions in small bird flocks help each member occupy a specific position relative to its leading neighbor, but larger groups are disturbed by an effect that pushes members away from these positions, which can lead to collisions,” says École Polytechnique associate professor Sophie Ramananarivu. Paris and co-author of the article.
Ristroff and his colleagues had previously figured out how birds move in groups, but those conclusions had been drawn from experiments simulating interactions. two birds A new study Nature Communication expanded the query to include many postcards.
To recreate the columnar formation of birds lining up one behind the other, researchers created mechanized flaps that move like bird wings. The wings were 3D printed from plastic and powered by motors that flap them through the water, mimicking the airflow around a bird’s wings in flight. This “fake flock” moved through the water and could freely line up in a line or row, as seen in the experiment video.
Flows affected group organization in different ways depending on group size.
Flying in small groups of about four people, the researchers found an effect in which each participant was aided by aerodynamic interactions in maintaining their position relative to their neighbors.
“As the aircraft moves from its position, the eddies or flow eddies left behind by the leading neighbor help push the follower back into place and hold it there,” explains Ristroff, director of the NYU Applied Mathematics Laboratory, where the experiments were conducted. . . “This means that postcards can be placed in a neat row at regular intervals automatically and without extra effort, as physics does all the work.
“However, in large groups, this interaction of flows causes later members to be pushed and thrown out of position, often resulting in the breakup of the group due to collisions between members. This means that very long groups, as seen in some bird species, are not at all easy to form, and later members are probably It means they will have to constantly work to maintain their positions and avoid collisions with their neighbours.’
Mathematical studies of swarm dynamics
The authors then used mathematical modeling to better understand the fundamental forces driving the experimental results. Here they concluded that flow-mediated interactions between neighbors are spring forces that hold each piece in place, just like train cars are connected by springs.
However, these “springs” only work in one direction—the lead bird can apply a force to its follower, but not the other way around—and this non-reciprocal interaction means that the trailing members tend to resonate or oscillate wildly.
“The oscillations are like waves that shake members back and forth, traveling down the group and increasing in intensity, causing subsequent members to crash into each other,” explains Joel Newbolt, who was a graduate student in physics at New York University at the time. study.
The team named these new types of waves “phonons,” based on the similar concept of phonons, which belong to oscillating waves in systems of masses connected by springs and are used to model the motion of atoms or molecules in crystals or other materials. .
“Our findings therefore reveal some interesting connections to materials physics, where birds in an ordered flock are like the atoms in an ordinary crystal,” Newbolt adds.
Source: Port Altele
