Fish swim in schools. This research also shows promise for the design and operation of much quieter submarines and autonomous undersea vehicles.fish swimming in schools and found that they produce much less noise compared to when swimming alone. This discovery could have important implications for the development of quieter submarines and autonomous undersea vehicles. Lead researcher Rajat Mittal explained that while it’s well known that fish swim in groups for protection, their study suggests that it also helps reduce the noise they produce. The study has been published in Bioinspiration & Biomimetics. The team used a 3D model to conduct their research.The researchers used a computer model of the common mackerel to experiment with different scenarios of fish swimming in groups. They adjusted the number of fish, their formations, proximity to each other, and the synchronization of their movements. The model, which is relevant to various fish species, simulated the movement of one to nine mackerel propelled by their tail fins.
The study revealed that a school of fish swimming together in a coordinated manner was remarkably effective at reducing noise: A group of seven fish sounded like a single fish.
“A predator, such as a shark, may perceive it as hearing a lone fish instead of a group,” Mittal said. “This could have significant implications for prey fish.”
The research team discovered that the most important factor in reducing sound was the coordination of the school’s tail flapping. When fish moved in unison and flapped their tails at the same time, the sound was not reduced. However, when they alternated tail flaps, the fish were able to cancel out each other’s sound, resulting in a reduction of total sound. According to Mittal, sound behaves like a wave, and it can either add up or cancel out depending on whether the waves are in phase or out of phase. In this case, the alternating tail flaps of the fish resulted in the cancellation of sound waves.
The article mentions that fish produce very faint sounds that are almost inaudible to humans. The movements of a fish’s tail fin not only reduce the sound, but also create a flow interaction that allows the fish to swim faster using less energy. Ji Zhou, a graduate student studying mechanical engineering at Johns Hopkins, stated that these noise reductions do not have to compromise the fish’s performance. In fact, the study found that in some cases, reducing noise also led to an increase in thrust due to hydrodynamic interactions. The team was surprised to discover this.The benefits of noise reduction start as soon as a single swimming fish joins another. The noise reduction increases as more fish join the school, but the researchers believe that the benefits will eventually reach a limit.
“Simply being together and swimming in any manner contributes to reducing the sound signature,” Mittal said. “No coordination between the fish is required.”
Next, the team plans to incorporate ocean turbulence into the models and create simulations that allow the fish to swim more “freely.”
Journal Reference:
- Ji Zhou, Jung-Hee Seo, Rajat Mittal. Effect of schooling on flow generation and noise rnrnThe article titled “The impact of body shape on the hydrodynamics and sounds from carangiform swimmers” was published in the journal Bioinspiration & Biomimetics in 2024. The DOI for the article is 10.1088/1748-3190/ad3a4e.