Energy Saving Movement Created by the Way Fish Swim

• Researchers at Tohoku University developed a technological simulation model based on the movement of tail fins in fish.
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• They are looking to find out why fish cluster in order to create energy-saving propulsion technology.
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• As a result, they discovered the fact that fish were in schools.
• Fish movement has succeeded in creating an efficient and energy-saving robot.

 

It turns out that the animal world can inspire the presence of new technology such as making robots. Researchers at Tohoku University, Japan, developed a technological simulation model based on the movement of tail fins in fish.

This model reveals the mechanism behind the phenomenon observed in fish, where fish use water eddies formed by their tail fins to conserve energy.

Research entitled Physics of Fluids , published on November 2 2023, reveals how fish swim. For years, researchers have not been able to answer the basic question, do fish swim in groups in an effort to conserve energy?

Lead Researcher Susumu Ito of Tohoku University, explains that the old theory about swimming fish is that they use eddies produced by other fish to conserve energy. They work together to take advantage of the whirlpool's reversing path by adjusting their tail fins.

In the field of fluid physics, the term “vortex” refers to the rotating currents behind an object moving through a fluid. In this case, the vortex shows the opposite direction of rotation.

The researchers developed a theoretical model to better understand these mechanics. Not only does it take into account regular muscle-driven movements and the effects of water forces, but also natural vasuriation, such as physiological factors that can influence how fish move.

As a result, the model created is able to better imitate the natural coordination of swimming fish movements. Ito was also happy because he was able to reproduce the synchronization between the tail and dorsal fins using numerical simulations.

This research suggests that fish may lose energy the distance they move slightly. Because fin movement between fish is not the best way to save energy.

The model also reproduces basic properties, such as the relationship that exists between the speed at which a fish swims and the frequency of its tail beats. This model can also be applied to fish that have carangiform or subcarangiform swimming styles , such as horse mackerel, trout, salmon and goldfish.

Carangiform is usually used by fish that have great strength from their tails which makes it easy to turn when swimming. Meanwhile, subcarangiform is more often carried out by fish that have backbones. Because there is energy that comes from their body movements.

“We have revealed the dynamics of synchronization among biological species. This can be applied to animals, birds, bacteria, and unicellular eukaryotes. This discovery is also useful for robotics; "This could lead to new strategies that save energy for drones even in large numbers," said Ito.

From fish to robot:

According to a research team from the Max Planck Institute of Animal Behavior (MPI-AB), Konstanz University, Germany and Peking University, China, these findings provide answers that have long been suspected but have never been supported by further experiments.

Finally, with the help of a biomimetic fish-like robot, the team demonstrated that fish can apply simple behavioral rules to take advantage of water vortices created by the fish in front of them. This is clearly an interesting finding for robotics science.

Modifying the fish's tail beat in relation to the group shows that the robot gains a hydrodynamic advantage. And what was previously unknown was revealed by robots and is now starting to be solved from free-swimming fish.

“Schools of fish are very dynamic social systems. Our results provide an explanation for how fish can take advantage of the resulting eddies without having to keep their distance from each other.” said Iain Couzin, Senior Study Author and Director of the Max Planck Institute of Animal Behavior

The team investigated robotic fish swimming in pairs with live fish swimming alone. They ran more than 10,000 experiments and tested followers in every possible

position in relation to the leader of a group of fish and then compared energy consumption with fish swimming alone.

The results show a clear difference in energy consumption for robots when swimming in pairs versus robots swimming alone. The researchers found that the reason for this difference in energy consumption was because the fish in front affected the hydrodynamics of the fish behind them.

There are at least two factors determining the energy used by follower fish, namely distance and similarity of time. The secret apparently lies in synchronization. In other words, the follower fish must match the tail flick of the leader fish with a certain time lag based on spatial position.

The approach was dubbed “vortex phase matching” by the researchers. When follower fish are close to the leader fish, the most effective thing for the follower fish to do is to synchronize their tail beats with the leader fish.

However, when follower fish lag, they have to get out of that synchronization with more lag compared to the lead fish's tail beat. So it will expend more energy.

However, do fish actually utilize these techniques to save power? To answer this question, the team developed a hydrodynamic model using AI-assisted analysis of the body postures of fish swimming together.

Then the researchers discovered that the same approach is indeed used in nature. Fish will instinctively always stay close to a group, either to look for food or when avoiding the threat of predators.

“We discovered simple rules for synchronizing with groups that allow followers to continue exploiting the socially generated vortex. But before our robotic experiments, we didn't know what to look for, so these rules were hiding in plain sight," concluded Couzin.